Vol. 94 - No. 11 - November 2020

Journal of
Geodesy
The
Geodesist’s
Handbook
2020

A constituent Association of theInternational Union of Geodesy andGeophysics (IUGG)
Edited by:
IAG Office
Markku Poutanen
Finnish Geospatial Research Institute FGINational Land Survey of Finland
Geodeetinrinne 202430 Masala, Finlande-mail: IAG.office@nls.fi
IAG Communication and Outreach Branch (COB)
Szabolcs Rózsa
Department of Geodesy and Surveying
Budapest University of Technology and Economics
P.O.Box 91
H-1521 Budapest, Hungary
e-mail: szrozsa@iag-aig.org

.
.
.

Journal of Geodesy (2020) 94:1–343
https://doi.org/10.1007/s00190-020-01434-z
Ó 2020 The Author(s)THE GEODESIST’S HANDBOOK 2020
Table of Contents

Foreword ................................................................................................................................................

5

The International Association of Geodesy (IAG)
Historical Overview .......................................................................................................................................
Past Officers of the International Association of Geodesy (2007 – 2019).........................................................
Statutes of the International Association of Geodesy ......................................................................................
Bylaws of the International Association of Geodesy ........................................................................................
Rules for IAG Scientific Meetings ...................................................................................................................
Rules for the IAG Levallois Medal .................................................................................................................
Rules for the IAG Guy Bomford Prize ............................................................................................................
Rules for the IAG Young Authors Award .......................................................................................................
Rules for IAG Travel Awards .........................................................................................................................
IAG Fund .......................................................................................................................................................
IAG Membership ...........................................................................................................................................

7
16
19
23
35
37
38
39
40
41
42

The XXVII IUGG General Assembly
IAG Presidential Address ................................................................................................................................
IAG Levallois Medal Laudation .....................................................................................................................
IAG Guy Bomford Prize Lecture .....................................................................................................................
IAG Young Authors Award Citation ..............................................................................................................
Report of the IAG Secretary General ..............................................................................................................
Minutes of the IAG Council Sessions ..............................................................................................................
Summary of the IAG Executive Committee Sessions .....................................................................................
IUGG Resolutions ...........................................................................................................................................
IAG Resolutions ..............................................................................................................................................

43
46
48
51
57
63
70
76
78

Structures for the Period 2019 – 2023
International Union of Geodesy and Geophysics (IUGG) ................................................................................
International Association of Geodesy (IAG) ...................................................................................................
Commission 1 – Reference Frames .................................................................................................................
Commission 2 – Gravity Field .........................................................................................................................
Commission 3 – Earth Rotation and Geodynamics ..........................................................................................
Commission 4 – Positioning and Applications ................................................................................................
Inter-commission Committee on Theory..........................................................................................................
Inter-Commission Committee for Climate Research ........................................................................................
Inter-Commission Committee for Marine Geodesy ..........................................................................................
Project Novel Sensors and Quantum Technology for Geodesy ........................................................................
Communication and Outreach Branch (COB) ..................................................................................................

81
83
91
110
127
137
160
179
189
191
195

4

The Geodesist’s Handbook 2020

Global Geodetic Observing System (GGOS)
GGOS Terms of Reference and Structure 2019-2023 ...................................................................................... 197
Inventory of Standards and Conventions ......................................................................................................... 221
IAG Scientific Services
International Earth Rotation and Reference Systems Service (IERS) ...............................................................
International DORIS Service (IDS) ..................................................................................................................
International GPS Service (IGS) ......................................................................................................................
International Laser Range Service (ILRS) ........................................................................................................
International VLBI Service for Geodesy and Astrometry (IVS) .......................................................................
International Gravity Field Service (IGFS) .......................................................................................................
International Centre for Global Earth Models (ICGEM) ...................................................................................
International Digital Elevation Models Service (IDEMS) ................................................................................
International Geodynamics and Earth Tide Service (IGETS) ............................................................................
International Gravimetric Bureau – Bureau Gravimetrique International (BGI) ................................................
International Service for the Geoid (ISG) .........................................................................................................
Permanent Service for Mean Sea Level (PSMSL) ............................................................................................

293
295
301
305
308
310
312
317
319
322
328
330

General Information
IAG on the Internet ..........................................................................................................................................
IAG Publications .............................................................................................................................................
IAG Delegates of IUGG Member Countries .....................................................................................................
IAG Representatives to Services, IUGG, and External Scientific Bodies .........................................................

332
334
336
342

Foreword

5

Foreword
Markku Poutanen1 ∙ Szabolcs Rózsa2

The Geodesist’s Handbook is published by the International
Association of Geodesy (IAG) periodically after eachIUGG/IAG General Assembly. The objective is to present
the current IAG structure and its specifications, and to
introduce the terms of reference and the officers of the
Association’s components for the upcoming legislative
period to the broad geodetic community. The scientificprogram and planned activities are described in detail.
The first part of the Handbook 2020 presents thehistorical developments and current regulations of the IAG(Statutes, Bylaws and Rules as reviewed during theIUGG/IAG General Assembly 2019).
The second part summarises the outcome of the IAG
General Assembly held in conjunction with the 27th IUGG
General Assembly in Montreal, Canada, in July 2019. An
overview of the most important IAG results from 2015 to2019 is given in the presidential address. The citations of thescientists decorated in Montreal with the highest IAG
awards (Levallois Medal, Guy Bomford Prize, and Young
Authors Award) are published. Reports of the Secretary
General, the IAG Council and Executive Committee
meetings, and the IUGG and IAG resolutions conclude thissection.

The third part of the Handbook contains the detailed
structures and programs for the period 2019-2023. All IAG
components (Commissions, Inter-commission Committee,
Communication and Outreach Branch, Services, and the
Global Geodetic Observing System) are presented alongwith their sub-components (Sub-commissions, Projects,
Study Groups and Working Groups). This part describes theplaned scientific work of IAG during the coming years.
The fourth part completes the Handbook with some
general information useful for the geodetic community. The
IAG Internet representation and the publication series arehighlighted, and the IAG national delegates andrepresentatives to services and international scientificbodies are listed.
We thank the contributors to the Geodesist’s Handbook
2020. These are in particular all the IAG officers listed in
the structures, but also the uncounted secretaries andtechnicians in the institutions affiliated with IAG or one ofits components and sub-components. The engaged andauthentic cooperation in geodesy is one of the most effectivemeans for the great success of our science. We hope that thiscollaboration will be continued or even extended in thecurrent period 2019-2023.

_
1

Markku Poutanen, IAG Secretary General
iag.office@nls.fi
Finnish Geospatial Research Institute FGI,
National Land Survey of Finland,
Geodeetinrinne 2, 02430 Masala, Finland

2

Szabolcs Rózsa, IAG Communication and Outreach Branchszrozsa@iag-aig.org
Department of Geodesy and Surveying,
Budapest University of Technology and Economics,
P.O. Box 91, 1521 Budapest, Hungary

6

The Geodesist’s Handbook 2020

List of previous Geodesist’s Handbooks

1980: Bulletin Géodesique, Vol. 54, No. 3, http://link.springer.com/journal/190/54/3/page/1
1984: Bulletin Géodesique, Vol. 58, No. 3, http://link.springer.com/journal/190/58/3/page/1
1988: Bulletin Géodesique, Vol. 62, No. 3, http://link.springer.com/journal/190/62/3/page/1
1992: Bulletin Géodesique, Vol. 66, No. 2, http://link.springer.com/journal/190/66/2/page/1
1996: Journal of Geodesy, Vol. 70, No. 12, http://link.springer.com/journal/190/70/12/page/1
2000: Journal of Geodesy, Vol. 74, No. 1, http://link.springer.com/journal/190/74/1/page/1
2004: Journal of Geodesy, Vol. 77, No. 10-11, http://link.springer.com/journal/190/77/10/page/1
2008: Journal of Geodesy, Vol. 82, No. 11, http://link.springer.com/journal/190/82/11/page/1 (open access)2012: Journal of Geodesy, Vol. 86, No. 10, http://link.springer.com/journal/190/86/10/page/1 (open access)2016: Journal of Geodesy, Vol. 90, No. 10, https://link.springer.com/journal/190/90/10/page/1 (open access)Historical Overview

7

The International Association of Geodesy
Historical Overview
H. Drewes1 ∙ J. Adám2 ∙ M. Poutanen3

The history of the International Association of Geodesy
goes back to April 1862 when the Central European Arc
Measurement (“Mitteleuropäische Gradmessung”) was
initiated at a “preliminary consultation” of representativesof the states of Prussia, Austria and Saxony in Berlin. At theend of the year, 16 countries had joined the project. The first
General Conference was held in Berlin, October 1864, withdelegates from 14 countries. In 1867 it was expanded to theEuropean Arc Measurement and in 1886 to the International
Geodetic Association (“Internationale Erdmessung”,“Association Géodésique Internationale”). At theConstitutive Assembly of the International ResearchCouncil (IRC) in Brussels, July 1919, the “Section
Geodesy” was one of the constituents of the International
Union of Geodesy and Geophysics (IUGG) and held its
Constitutive Assembly during the first IUGG General
Assembly in Rome, April-May 1922. The name waschanged to “Association of Geodesy” in Stockholm, August
1930, and to the present name in July 1946. The following
summarises the historic development.

Table 1 General Conferences / General Assemblies of the International Association of Geodesy and predecessors
No

Venue

Year

No

Venue

Year

I. General Conferences
Ia. Mitteleuropäische Gradmessung - Central European
Arc Measurement (1862-1867)

Ic. Internationale Erdmessung - Association GéodésiqueInternationale – Int. Geodetic Association (1886-1922)
9

Paris, France

1889

1

Berlin, Prussia

1864

10

Brussels, Belgium

1892

2

Berlin, Prussia

1867

11

Berlin, German Empire

1895

Arc

12

Stuttgart, German Empire

1898

13

Paris, France

1900

14

Copenhagen, Denmark

1903

15

Budapest, Austria-Hungary

1906

16

Cambridge, United Kingdom

1909

17

Hamburg, German Empire

1912

Ib. Europäische Gradmessung
Measurement (1867-1886)-

European3

Vienna, Austria-Hungary

1871

4

Dresden, German Empire

1874

5

Stuttgart, German Empire

1877

6

Munich, German Empire

1880

7

Rome, Italy

1883

8

Berlin, German Empire

1886

II. General Assemblies of the Section and Association of
Geodesy at the General Assemblies of the IUGG
IIa. IUGG Section of Geodesy (1919-1930)

Technical University Munich, Arcisstr. 21, 80333 München, Germany,h.drewes@tum.de
2
Department of Geodesy and Surveying, Budapest University ofTechnology and Economics, P.O. Box 91, 1521 Budapest, Hungary
3
Finnish Geospatial Research Institute, National Land Survey of Finland
Geodeetinrinne 2, 02430 Masala, Finland, iag.office@nls.fi
1

18

Rome, Italy (Constitutive Assembly)

1922

19

Madrid, Spain

1924

20

Prague, Czechoslovakia

1927

21

Stockholm, Sweden

1930

8

The Geodesist’s Handbook 2020

Table 1 continued
No

Venue

Participants:

Year

IUGG

IAG

IIb. IUGG Association of Geodesy (1930-1946)

No

Venue

33

Participants:

Year

IUGG

IAG

Grenoble, France

1975

2564

398

22

Lisbon, Portugal

1933

200

90

34

Canberra, Australia

1979

1944

278

23

Edinburgh, UK

1936

344

91

35

Hamburg, F.R. Germany

1983

3204

472

24

Washington, USA

1939

805

86

36

Vancouver, Canada

1987

3939

420

IIc. IUGG International Association of Geodesy (1946-…)

37

Vienna, Austria

1991

4331

594

25

Oslo, Norway

1948

368

38

Boulder, USA

1995

4481

567

26

Brussels, Belgium

1951

918

134

39

Birmingham, UK

1999

4052

478

27

Rome, Italy

1954

923

235

40

Sapporo, Japan

2003

4151

407

28

Toronto, Canada

1957

1165

218

41

Perugia, Italy

2007

4351

433

29

Helsinki, Finland

1960

1375

345

42

Melbourne, Australia

2011

3392

370

30

Berkeley, USA

1963

1938

329

43

Prague, Czech Republic

2015

4231

534

31

Zurich/Lucerne, Switzerland

1967

2200

357

44

Montreal, Canada

2019

3715

465

32

Moscow, USSR

1971

2577

449

45

Berlin, Germany

2023

Table 2 Scientific Assemblies of the International Association of Geodesy
No

Venue

Date

Number of Attendees

1

Tokyo, JapanMay 7-15,1982

200

2

Edinburgh, UK

August 3-12,1989

355

3

Beijing, China

August 8-13,1993

340

4

Rio de Janeiro, Brazil

September 3-9,1997

250

5Budapest, Hungary

September 2-7, 2001

461

6

Cairns, Australia

August 22-26, 2005 (joint with IAPSO and IABO)

7

Buenos Aires, Argentina

August 31- Sept. 4, 2009

363

8

Potsdam, Germany

September 1-6, 2013

538

9

Kobe, Japan

July 30 – August 4, 2017 (joint with IASPEI)

10

Beijing, China

June 28 – July 3, 2021

IAG: 145 (in all: 724)

IAG: 361 (in all: 1107)

Table 3 Presidents of the International Association of Geodesy and predecessors
No

PeriodPosition

Name

Residence

Ia. Mitteleuropäische Gradmessung (1862-1867), Europ. Gradmessung (European Arc Measurement) (1867-1886)
11864 – 1868

President of the Permanent Commission

Peter Andreas Hansen

Gotha, Thuringia

2

1869 – 1874

President of the Permanent Commission

August von Fligely

Vienna, Austria-Hungary

31874 – 1886

President of the Permanent Commission

Carlos Ibañez de Ibero

Madrid, Spain

Ib. Internat. Erdmessung - Association Géodésique Internationale (International Geodetic Association) (1886-1917)
3

1887 – 1891

President of the Association

Carlos Ibañez de Ibero

Madrid, Spain

41892 – 1902

President of the Association

Hervé A. E. A. Faye

Paris, France

5

1903 – 1917

President of the Association

Léon J. A. Bassot

Paris, France

Ic. Reduced Geodetic Association among Neutral States (1917-1922)
6

1917 – 1922

President of the Reduced Association

Raul Gautier

Geneva, Switzerland

Historical Overview

9

Table 3 continued
No

PeriodPosition

Name

Residence

IIa. IUGG Section of Geodesy (1919-1930)7

1922 – 1933

President of the Section

William Bowie

Washington, USA

Felix A. Vening-Meinesz

Amersfoort, The Netherlands

IIb. IUGG Association of Geodesy (1930-1946)
8

1933 – 1946

President of the AssociationIIc. International Association of Geodesy (IAG) of the IUGG (1946-…)
9

1946 – 1951

President of the IAG

Walter D. Lambert

Washington, USA

101951 – 1954

President of the IAG

Carl F. Bäschlin

Zurich, Switzerland

11

1954 – 1957

President of the IAG

James de Graaf Hunter

London, United Kingdom

121957 – 1960

President of the IAG

Gino Cassinis

Milan, Italy

13

1960 – 1963

President of the IAG

Charles A. Whitten

Washington, USA

141963 – 1967

President of the IAG

Guy Bomford

London, United Kingdom

151967 – 1971

President of the IAG

Antonio Marussi

Trieste, Italy

16

1971 – 1975

President of the IAG

Youri D. Boulanger

Moscow, USSR

17

1975 – 1979

President of the IAG

Tauno J. Kukkamäki

Helsinki, Finland

18

1979 – 1983

President of the IAG

Helmut Moritz

Graz, Austria

19

1983 – 1987

President of the IAG

Peter V. Angus-Leppan

Kensington, Australia

20

1987 – 1991

President of the IAG

Ivan I. Mueller

Columbus, USA

21

1991 – 1995

President of the IAG

Wolfgang Torge

Hannover, Germany

22

1995 – 1999

President of the IAG

Klaus-Peter Schwarz

Calgary, Canada

23

1999 – 2003

President of the IAG

Fernandó Sansó

Milan, Italy24

2003 – 2007

President of the IAG

Gerhard Beutler

Bern, Switzerland

25

2007 – 2011

President of the IAG

Michael G. Sideris

Calgary, Canada

26

2011 – 2015

President of the IAG

Chris Rizos

Sydney, Australia

27

2015 – 2019

President of the IAG

Harald Schuh

Potsdam, Germany

28

2019 – 2023

President of the IAG

Zuheir Altamimi

Paris, France

Table 4 Permanent Secretaries / Secretaries General of the International Association of Geodesy and predecessors
No
PeriodPosition
Name
Residence
Ia. Internationale Erdmessung - Association Géodésique Internationale (International Geodetic Association) (1886-1917)
1

1886 – 1900

Permanent Secretary

Adolf Hirsch

Neuchatel, Switzerland

2

1900 – 1921

Permanent Secretary

H. G. van de Sande-Bakhuysen

Leiden, The Netherlands

Ib. IUGG Section of Geodesy (1919-1930) and IUGG Association of Geodesy (1930-1946)
3

1922 – 1946

Secretary General

Georges Perrier

Paris, France

Ic. International Association of Geodesy of the IUGG (1946-…)
4

1946 – 1960

Secretary General

Pierre Tardi

Paris, France

5

1960 – 1975

Secretary General

Jean-Jacques Levallois

Paris, France

61975 – 1991

Secretary General

Michel Louis

Paris, France

7

1991 – 1995

Secretary General

Claude Boucher

Paris, France

81995 – 2007

Secretary General

Carl Christian Tscherning

Copenhagen, Denmark

92007 – 2019

Secretary General

Hermann Drewes

Munich, Germany

102019 – 2023

Secretary General

Markku Poutanen

Masala, Finland

10

The Geodesist’s Handbook 2020

Table 5 Central Bureau (since 2007 Office) of the International Association of Geodesy and predecessors
No

Period1231864 – 1885
1886 – 1917
1917 – 1922

Royal Prussian Geodetic Institute

Host InstituteJohann Jacob Baeyer
Friedrich Robert Helmert
J. H. Louis Krüger (p.p.)

Name of Director

Potsdam, Prussia
Potsdam, Germany
Potsdam, Germany

Residence

4

1922 – 1946

Institut Géographique National (IGN)

Georges Perrier

Paris, France

5
6
7
8

1946 – 1960
1960 – 1975
1975 – 1991
1991 – 1995

Pierre Tardi
Jean-Jacques Levallois
Michel LouisClaude Boucher

Paris, France
Paris, France
Paris, France
Paris, France

91995 – 2007

Niels Bohr Institute, Department ofGeophysics, University of Copenhagen

Carl Christian Tscherning

Copenhagen, Denmark

102007 – 2019

Deutsches Geodätisches Forschungsinstitut

Hermann Drewes

Munich, Germany

11

2019 – 2023

Finnish Geospatial Research Institute (FGI)

Markku Poutanen

Masala, Finland

Table 6 Editors in Chief of Official Journals of the International Association of Geodesy and predecessors
No
I.1

JournalName of Editor-in-Chief

Residence

1922 – 1945

Georges Perrier

Paris, France

I.2

1946 – 1951

Pierre Tardi

Paris, France

I.3

1952 – 1964

Jean-Jacques Levallois

Paris, France

I.4

1965 – 1975

Michel Louis

Paris, France

I.5

1975 – 1986

Ivan I. Mueller

Columbus, USA

I.6

1987 – 1995

Carl Christian Tscherning

Copenhagen, Denmark

II.1

Bulletin Géodésique

Period1976 – 1980

Ivan I. Mueller

Columbus, USA

II.2

1980 – 1982

Peter Meissl

Graz, Austria

II.3

1982 – 1988

Erwin Groten

Darmstadt, F.R. Germany

II.4

1989 – 1991

Clyde C. Goad
Erik W. Grafarend

Columbus, USA
Stuttgart, Germany

II.5

1991 – 1995

Petr Vaniček

New Brunswick, Canada

1995 – 2003

Peter J. G. Teunissen

Delft, The Netherlands

III.2

2003 – 2007

William E. Featherstone

Perth, Australia

III.3

2007 – 2015

Roland Klees

Delft, The Netherlands

III:42015 – 2023

Jürgen Kusche

Bonn, Germany

III.1

Manuscripta Geodaetica

Journal of Geodesy

Table 7 Editors of the International Association of Geodesy Symposia Series
No

PeriodName of Editor

Residence

Name of Assistant Editor

Residence1

1991-1995

Wolfgang Torge

Hannover, Germany

2

1995-1999

Klaus-Peter Schwarz

Calgary, Canada

3

1999-2003

Fernandó Sansó

Milan, Italy4

2003-2007

Gerhard Beutler

Bern, Switzerland

5

2007-2011

Michael G. Sideris

Calgary, Canada

6

2011-2015

Chris Rizos

Sydney, Australia

Pascal Willis

Paris, France

7

2015-2023

Jeff Freymueller

Fairbanks, USA

Laura Sánchez

Munich, Germany

Historical Overview

11

Table 8 Editors of The Geodesist’s Handbook
No

Year

EditorResidence

1

1980

Ivan I. Mueller

Columbus, USA

2

1984

Carl Christian Tscherning

Copenhagen, Denmark

3

1988

Carl Christian Tscherning

Copenhagen, Denmark

4

1992

Carl Christian Tscherning

Copenhagen, Denmark

5

1996

Pascal Willis

Paris, France

6

2000

Ole B. Andersen

Copenhagen, Denmark

7

2004

Ole B. Andersen

Copenhagen, Denmark

8

2008

H. Drewes, H. Hornik / J. Ádám, Sz. Rózsa

Munich, Germany / Budapest, Hungary

9

2012

H. Drewes, H. Hornik / J. Ádám, Sz. Rózsa

Munich, Germany / Budapest, Hungary

10

2016

H. Drewes, F. Kuglitsch / J. Ádám, Sz. Rózsa

Munich & Potsdam, Germany / Budapest, Hungary

11

2020

M. Poutanen / Sz. Rózsa

Masala, Finland / Budapest, Hungary
Table 10 Awardees of the IAG Guy Bomford Prize

Table 9 Awardees of the IAG Levallois Medal
No

Year

Name of Awardee

Residence

No

Year

Name of Awardee

Residence1

1979 Charles Whitten

Washington, USA

1

1975 Erik Grafarend

Munich, F.R.Germany

2

1983 Rudolf Sigl

Munich, F.R.Germany

2

1979 Fernandó Sansó

Milan, Italy

3

1987 Arne Bjerhammar

Stockholm, Sweden

3

1983 John Wahr

Boulder, USA

41991 Paul Melchior

Brussels, Belgium

41987 Peter J. Teunissen Delft, The Netherlands

51995 Willem Baarda

Delft, The Netherlands

51991 Shuhei Okubo

Tokyo, Japan

6

1999 Torben Krarup

Copenhagen, Denmark

61995 Thomas Herring

Cambridge, USA

7

2003 George Veis

Athens, Greece

71999 Véronique Dehant

Brussels, Belgium

82007 Carl C. Tscherning Copenhagen, Denmark

82003 Ramon Hanssen

Delft, The Netherlands

92011 Ruth E. Neilan

Pasadena, USA

92007 Masato Furuya

Tokyo, Japan

10

2015 Reiner Rummel

Munich, Germany

102011 Johannes Böhm

Vienna, Austria

11

2019 Christoph Reigber Potsdam, Germany

112015 Yoshiyuki Tanaka

Tokyo, Japan

12

2019 Michal Šprlák

Newcastle, Australia

Table 11 Winners of the IAG Young Authors Award
No

Year

Author’s NameCountry

Title of the Publication

1 1993 Hussein A.
Abd-Elmotaal

Egypt

Vening-Meinesz Moho depths: traditional, exact and approximated.
Manuscripta Geodaetica, 18: 171-181

2 1994 Jean-Pierre Barriot

FranceLine of sight operators in planetary geodesy. Manuscr. Geod., 19: 269-283

3 1995 Srinivas V. Bettadpur India

Hotine’s geopotential formulation revisited. Bull. Géod. 69: 135-142.

4 1996 Giovanna Sona

Italy

Numerical problems in the computation of ellipsoidal harmonics. J. of
Geodesy, 70: 117-126.

5 1998 Cheinway Hwang

TaiwanInverse Vening-Meinesz formula and deflection-geoid formula:applications to the predictions of gravity and geoid over the South China
Sea. J. of Geodesy, 72: 304-312.

6 1999 Peiliang Xu

China

Biases and accuracy of, and an alternative to, discrete nonlinear filters. J.
of Geodesy, 73: 35-46.

7 2000 Christopher Kotsakis

CanadaThe multiresolution character of collocation. J. of Geodesy, 74: 275-290

12The Geodesist’s Handbook 2020

Table 11 continued
No Year

Author’s nameCountry

Title of the Publication

8 2000 Rüdiger Lehmann

Germany

Altimetry-gravimetry problems w. free vertical datum. J.Geod 74:327-334.

9 2001 Susan Skone

CanadaThe impact of magnetic storms on GPS receiver performance. J. of Geodesy,
75: 457-468.

10 2003 Michael Kern

Germany

A study on the combination of satellite, airborne and terrestrial gravity data.
Journal of Geodesy, 77: 217-225.

11 2004 Shfaqat Abbas
Khan

Pakistan

Shallow water loading tides in Japan from superconducting gravity (with
J.L. Hoyer). Journal of Geodesy, 78: 245-250.

12 2005 Roland Pail

Austria

A parametric study on the impact of satellite attitude errors on GOCE
gravity field recovery. Journal of Geodesy, 79: 231-241.

13 2006 Steffen Schön

Germany

Uncertainty in GPS networks due to remaining systematic errors: theinternal approach (with H. Kutterer). Journal of Geodesy, 80: 150-162.

14 2008 Franziska WildPfeiffer

Germany

A comparison of different mass elements for use in gravity gradiometry.
Journal of Geodesy, 82: 637-653.

15 2010 Elizabeth PetriUK

A first look at the effects of ionospheric signal bending on a globallyprocessed GPS network. Journal of Geodesy, 84: 491-499.

16 2011 Thomas Artz

Germany

Assessment of periodic sub-diurnal Earth rotation variations at tidal
frequencies through VLBI normal equations. J. of Geodesy, 85, 565-584.

17 2012 Manuela Seitz

Germany

The 2008 DGFI realization of the ITRS: DTRF2008. Journal of Geodesy,
86: 1097-1123.

18 2013 Krzysztof Sośnica

Switzerland

Impact of loading displacements on SLR-derived parameters and on theconsistency between GNSS and SLR results. J. of Geodesy, 87: 751-769.

19 2014 Alvaro Santamaría France
Gómez

Long-term vertical land motion from double-differenced tide gauge andsatellite altimetry data. Journal of Geodesy, 88: 207-222.

20 2015 Xingxing Li

Germany

Accuracy and reliability of multi-GNSS real-time precise positioning: GPS,GLONASS, BeiDou, and Galileo. J. of Geodesy, 89: 607-635.

21 2016 Olga Didova

Netherlands

An approach for estimating time-variable rates from geodetic time series.
Journal of Geodesy, 90: 1207–1221.

22 2017 Minghui Xu

China

The impacts of source structure on geodetic parameters demonstrated by theradio source 3C371. Journal of Geodesy, 91: 767-781.

23 2018 Athina Peidou

CanadaOn the feasibility of using satellite gravity observations for detecting largescale solid mass transfer events. J. of Geodesy, 92: 517–528.

Table 12 History of IAG Services
No

Acronym

Name of the IAG Service (and Address of the Homepage)

Formation

1 ILS

International Latitude Service (1962 renamed International Polar Motion Service, IPMS)

1899

2 BIH

Bureau International de l’Heure (1987 integrated into IERS)

1912

3 PSMSLPermanent Service for Mean Sea Level / https://www.psmsl.org/

1933

4 BGI

Bureau Gravimetrique International / http://bgi.omp.obs-mip.fr

1951

5 ICETInternational Centre for Earth Tides (2015 integrated into IGETS)

1956

6 IPMSInternational Polar Motion Service (Successor of ILS, 1987 integrated into IERS)

1962

6 IERSInternational Earth Rotation and Reference Systems Service / https://www.iers.org

1987

7 ISG

International Service for the Geoid / http://www.isgeoid.polimi.it

1991

Historical Overview

13

Table 12 continued
No

Acronym

Name of the IAG Service (and Address of the Homepage)

Formation

8 IGS

International GNSS Service / http://www.igs.org

1994

9 ILRSInternational Laser Ranging Service / https://ilrs.cddis.eosdis.nasa.gov/

1998

3 IDEMS

International Digital Elevation Models Service / https://idems.maps.arcgis.com/home/index.html

1999

11 IVSInternational VLBI Service for Geodesy and Astrometry / https://ivscc.gsfc.nasa.gov

1999

4 IDS

International DORIS Service / https://ids-doris.org/

2003

2 ICGEMInternational Centre for Global Earth Models / http://icgem.gfz-potsdam.de/home

2003

7 IGFSInternational Gravity Field Service / http://igfs.topo.auth.gr/

2004

6 IGETSInternational Geodynamics and Earth Tide Service / http://igets.u-strasbg.fr/

2015

Table 13 Fellows of the IAG
1991:
D.A. Adebekun, Nigeria
D.-E. Ajakaiye, USA
V. Ashkenazi, UK
W. Augath, Germany
T.F. Baker, UK
G. Balmino, France
L.W. Baran, Poland
G. Birardi, Italy
A. Bjerhammar, Sweden
D. Blitzkow, Brazil
Y. Bock, USA
G. Boedecker, Germany
J.D. Bossler, USA
C. Boucher, France
P. Brosche, Germany
F.K. Brunner, Austria
M. Burša, Czech Republic
J. Campbell, Germany
G. Carrera, Canada
M. Charfi, Tunisia
J. Y. Chen, China
B. H. Chovitz, USA
O. Coker, Nigeria
O. L. Colombo, USA
A. Comolet-Tirman, France
A.H. Cook, UK
P.A. Cross, UK
K. I. Daugherty, USA
P. de Jonge, USA
A. Dermanis, Greece
J.O. Dickey, USA
A.H. Dodson, UK
B.C. Douglas, USA
A. Drozyner, Poland
H. Dufour, France
D. Eckhardt, USA

O. Fadahunsi, Nigeria
F. Fajemirokun, Nigeria
M. Feissel-Vernier, France
I. Fejes, Hungary
I.K. Fischer, USA
R. Forsberg, Denmark
P. Forsyth, Canada
D. Fritsch, Germany
J. Gaignebet, France
E.M. Gaposchkin, USA
C. Gemael, Brazil
C.C. Goad, USA
E.W. Grafarend, Germany
E. Groten, Germany
E. Gubler, Switzerland
B. Guinot, France
B. Heck, Germany
G. Hein, Germany
H. Henneberg, Venezuela
S. Henriksen, USA
P. Holota, Czech Republic
L. Hora, Czech Republic
H.T. Hsu, China
J.R. Huddle, USA
C. Jekeli, USA
G. Jentzsch, Germany
I. Joó, Hungary
C.S. Joshi, India
H.-G. Kahle, Switzerland
H.P. Kahmen, Austria
J. Kakkuri, Finland
K. Kasahara, Japan
E. Kausel, Chile
H. Kautzleben, Germany
A.H.W. Kearsley, Australia
R.W. King, USA
A. Kiviniemi, Finland

R. Klees, The Netherlands
K.R. Koch, Germany
B. Kolaczek, Poland
K. Konan, Ivory Coast
J. Kovalevsky, France
Y. Kozai, Japan
J. Krynski, Poland
M. Kumar, USA
J.T. Kuo, USA
M.P.M. Lefebvre, France
D. Lelgemann, Germany
G.W. Lennon, Australia
G. Lensen, New ZealandJ-J. Levallois, France
E. Livieratos, Greece
M. Louis, France
G.R. Mader, USA
J. Makris, Germany
A. Mancini, USA
I. Marson, Italy
M. McNutt, USA
D.D. McCarthy, USA
W.G. Melbourne, USA
P. Melchior, Belgium
C. Morelli, Italy
H. Moritz, Austria
I.I. Mueller, USA
I. Nakagawa, Japan
A. Nobili, Italy
J.D. Obel, Kenya
M.Odlanicki-Poczobut,
PolandB.P. Pertsev, Russia
K. Poder, Denmark
C. Poitevin, Belgium
M.T. Prilepin, Russia
J. Rais, Indonesia

R.H. Rapp, USA
C. Reigber, Germany
A.R. Robbins, UK
R.S. Rostom, Kenya
R. Rummel, Germany
F. Sacerdote, Italy
F. Sansó, Italy
N.K. Saxena, USA
B. Schaffrin, USA
G. Schmitt, Germany
B.E. Schutz, USA
K.-P. Schwarz, Canada
G. Seeber, Germany
M.J. Sevilla, Spain
P.J. Shelus, USA
M.G. Sideris, Canada
L.E. Sjöberg, Sweden
R.A. Snay, USA
H. Sünkel, Austria
T. Tanaka, Japan
P. Teunissen, The Netherlands
W. Torge, Germany
C.C. Tscherning, Denmark
P. Vaniček, Canada
C. Veillet, France
P. Vyskočil, Czech Republic
A. Waalewijn, The Netherlands
J. Wahr, USA
D.E. Wells, Canada
W.M. Welsch, Germany
L.A. White, Australia
P. Wilson, Germany
P.L. Woodworth, UK
Y.Y. Yatskiv, Ukraine
K. Yokoyama, Japan
D.B. Zilkoski, USA
J.D. Zund, USA

14

The Geodesist’s Handbook 2020

1995:
J. Ádám, Hungary
R. Barzaghi, Italy
M. Becker, Germany
G. Beutler, Switzerland
W. Bosch, Germany
B.F. Chao, USA
H. Denker, Germany
J. Dow, Germany

G.K. Elgered, Sweden
B. Engen, Norway
A. Geiger, Switzerland
T. Kato, Japan
A. Kleusberg, Germany
J. Kouba, Canada
H. Landau, Germany
R.B. Langley, Canada
K. Linkwitz, Germany

S. Molodensky, Russia
R. Neilan, USA
C. Noll, USA
S. Okubo, Japan
P. Pâquet, Belgium
J.C. Ries, USA
J.M. Rüeger, Australia
E.J.O. Schrama, The
Netherlands

C.-K. Shum, USA
T.A. Spoelstra, The
Netherlands
S. Takemoto, Japan
C. Thomas, France
J.A. Weightman, UK
P. Willis, France
C. Wilson, USA
T. Yunck, USA

1999:
N. Andersen, Denmark
O. Andersen, Denmark
D. Arabelos, Greece
M.G. Arur, India
L. Ballani, Germany
G.B. Benciolini, Italy
M.G. Bevis, USA

G. Blewitt, UK
J.M. Bosworth, USA
A. Cazenave, France
T.A. Clark, USA
J. Degnan, USA
V. Dehant, Belgium
H. Drewes, Germany
B. Ducarme, Belgium

W. Featherstone, Australia
W. Freeden, Germany
T. Herring, USA
K.-H. Ilk, Germany
J. Johanssen, Sweden
P. Knudsen, Denmark
Z.-X. Li, China
J. Manning, Australia

N. Pavlis, USA
C. Rizos, Australia
C. Rocken, USA
I.N. Tziavos, Greece
M. Vermeer, Finland
M. Wei, Canada
D. Wolf, Germany
S. Zerbini, Italy

2003:
E.F. Arias, Argentina
J.-P. Barriot, France
P.A. Berry, UK
C.A. Brunini, Argentina
C. Bruyninx, Belgium
D. Gambis, France
G. Gendt, Germany
R.S. Gross, USA

W. Gurtner, Switzerland
S. Han, Australia
R. Hanssen, The Netherlands
B.G. Harsson, Norway
C. Hwang, Taiwan
W. Keller, Germany
S.C. Kenyon, USA
R. Kursinski, USA
H. Kutterer, Germany

R. Lehman, Germany
A. Marchenko, Ukraine
R. Scharroo, The Netherlands
W. Schlüter, Germany
T. Schöne, Germany
S. Skone, Canada
N. Sneeuw, Canada
M. Stewart, Australia
G. Strykowski, Denmark

C. Tiberius, The Netherlands
H. van der Marel, The
Netherlands
N. Vandenberg, USA
P. Visser, The Netherlands
L. Vitushkin, France
J. Vondrak, Czech Republic
R. Weber, Austria
Y. Yuanxi, China

2007:
Z. Altamimi, France
R. Biancale, France
M. Craymer, Canada
D. Crossley, USA
R. Dietrich, Germany
X. Ding, Hong Kong
L.P.S. Fortes, Brazil
Y. Gao, Hong Kong
D. Grejner-Brzezinska, USA

K. Heki, JapanL. Hothem, USA
J. Huang, China
J. Ihde, Germany
M. Kuhn, Australia
J. Kusche, The Netherlands
U. Marti, Switzerland
C. Merry, South Africa
A.W. Moore, USA
P. Novák, Czech Republic

M.C. Pacino, Argentina
M.R. Pearlman, USA
H.-P. Plag, USA
M. Poutanen, Finland
B. Richter, Germany
M. Rothacher, Germany
Sz. Rózsa, Hungary
M. Scheinert, Germany
H. Schuh, Austria
H.-P. Sun, China

J.A. Torres, Portugal
Gy. Tóth, Hungary
P. Tregoning, Australia
M. Verroneau, Canada
J. Wang, Australia
R. Wonnacott, South Africa
P. Xu, JapanJ. Yu, China
S.Y. Zhu, Germany

2011:
H. Abd-Elmotaal, Egypt
L. Alfonsi, Italy
D. Behrend, USA
S. Bettadpur, USA
S. Bisnath, Canada
A. Brzezinski, Poland
T. van Dam, Luxembourg
J. Davis, USA
Y. Feng, Australia
J. Freymueller, USA

Y. Fukuda, JapanTh. Hobiger, Japan
H. Hornik, Germany
S. Jin, South Korea
M.O. Karslioglu, Turkey
Ch. Kotsakis, Greece
S. Lambert, France
F. Lemoine, USA
C. Ma, USA
Z. Malkin, Russia

S. Matsuzaka, Japan
Gy. Mentes, Hungary
A. Michlenz, Germany
M. Omura, Japan
R. Pail, Germany
J. Ray, USA
A. Reiterer, Germany
G. Retscher, Austria
L.J. Rickards, UK
D. Roman, USA

L. Sanchez, Germany
M. Santos, Canada
M. Schmidt, Germany
F. Seitz, Germany
L. Soudarin, France
G. Tavernier, France
S. Verhagen, The Netherlands
Y.M. Wang, USA
J. Wickert, Germany
H. Wilmes, Germany

Historical Overview

15

2015:
D. Angermann, Germany
D. Avalos, Mexico
F. Barthelmes, Germany
O. Baur, Austria
J. Boehm, Austria
J. Bogusz, Poland
S. Bonvalot, France
C. Braitenberg, Italy

J. Chen, USA
R. Cunderlik, Slovakia
X. Deng, Australia
J. Dawson, Australia
A. Eicker, Germany
J. Ferrandiz, Spain
Ch. Gerlach, Germany
M. Hashimoto, Japan

A. Jäggi, Switzerland
G. Johnston, Australia
A. Kealy, Australia
Sh. Abbas Khan, Denmark
M. King, Australia
W. Kosek, Poland
K. Mikula, Slovakia
H. Ozener, Turkey

S. Pagiatakis, Canada
V. Palinkas, Czech Republic
M. Reguzzoni, Italy
S. Rosat, France
M. Thomas, Germany
M. Weigelt, Germany
B. Wouters, UK/USA
Li Zhenhong, UK

2019:
J. Agren, Sweden
M. Alizadeh, Iran
S. Bergstrand, Sweden
G. Bianco, Italy
S. Claessens, Australia
X. Collilieux, France
L. Combrinck, South Africa
M. Crespi, Italy
J. Dousa, Czech Republic
A. El-Mowafy, Australia
Ch. Eschmann, Germany
F. Flechtner, Germany

J J. Flury, Germany
J. Geng, China
V. Gikas, Greece
R. Heinkelmann, Germany
Ch. Hirt, Germany
M. Hoque, Germany
M. Horwath, Germany
C. Huang, China
U. Hugentobler, Germany
M. Kalantari, Australia
A. Kenyeres, Hungary
A. Khodabandeh, Australia

F. Kuglitsch, Germany
J. LaBrecque, USA
B. Luzum, USA
D. MacMillan, USA
W. Martinez, USA
J. Müller Germany
F. Nievinski, Brazil
A. Nothnagel, Germany
R. Pacione, Italy
J.-A. Paffenholz, Germany
E. Pavlis, USA
U. Schreiber, Germany

M. Seitz, Germany
J. Skaloud, Switzerland
K. Sosnica, Poland)
R. Stanaway, Australia
D. Thaller, Germany
L.-C. Tsai, China-Taipei
D. Tsoulis, Greece
G. Vergos, Greece
P. Wielgosz, Poland
H. Wziontek, Germany
K. Zhang, Australia
X. Zhang, China

16

The Geodesist’s Handbook 2020

Past Officers of the International Association of Geodesy(2007 – 2019)
Compiled by Hermann Drewes
IAG Honorary Secretary General
Technical University Munich, Arcisstr. 21, 80333 München, Germany
h.drewes@tum.de

This Chapter continues the series of articles “History of theInternational Association of Geodesy”. In Geodesist’s
Handbook 2008 article “Past officers of the International
Association of Geodesy (1991-2007)”, Bulletin Géodésique(82) 675-679, 2008, Carl Christian Tscherning summarises
the CVs of the Presidents and Secretaries General during
this period. He refers there to a publication of his Secretary
General (pre-)predecessor, Michel Louis, who wrote asimilar article in 1992, and refers on his part to an article on
the History of IAG, written by the previous Secretary
General J.-J. Levallois in 1980.
Michael Sideris
President 2007 – 2011
Michael George Sideris wasborn on August 16, 1958, in
Pireaus, Greece. He received
his Dipl.-Ing. (honours) degree in surveying engineering from the National Technical University of Athens,
Greece, in 1981. In 1982, hemoved to Canada to continue
his studies in geodesy at the
Department of Surveying of
the University of Calgary (UofC). He obtained his MSc
degree in 1984 and his PhD degree in 1988. After he graduated, he was offered a tenured faculty position at UofC, andhe became full professor of geodesy. He has also served in
major administrative positions, as Associate Dean Researchin the Faculty of Engineering (1999-2005) and Associate
Dean in the Faculty of Graduate Studies (2003-2011).

His research work focuses on physical geodesy, such as
gravity field approximation, precise geoid determination,
vertical datums, satellite altimetry, terrestrial, satellite andairborne gravimetry and gradiometry, geodetic applicationsof wavelets and spectral methods, and geodetic methods forhazards monitoring and resource exploration. His
pioneering research on efficient spectral methods for precise
geoid determination and geodetic boundary value problem(Stokes and Molodensky) solutions earned him an international reputation, and the FFT-based software hedeveloped has been commercialized by UofC’s technology
commercialization office and is being used internationallyby universities, national agencies and geophysical industry.
For his contributions to geodesy, he has been awarded an
Alexander von Humboldt International Research Fellowship (hosted at the University of Stuttgart, Germany, in1998) and a Dr. honoris causa honorary doctorate degree(2004) by the University of Architecture, Civil Engineeringand Geodesy, in Sofia, Bulgaria.
Michael Sideris was first involved with the IAG in 1984
during the International Summer School on Local Gravity
Field Approximation in Beijing, China. Since then, he hasserved the IAG in many leadership positions, including as
Secretary (1995-1999) and President (1999-2003) of IAG’s
Section III “Determination of the Gravity Field”, IAG Vice
President (2003-2007) and IAG President (2007-2011). He
has also organized numerous sessions at IAG, IUGG, EGU
and AGU assemblies. He has taught at nine IAG Schools on
the Determination and Use of the Geoid, as well as at theFirst IAG School on Reference Frames in 2010. At the
IUGG General Assembly 2011, he was elected Vice
President of the IUGG, and at the General Assembly 2015
President of the IUGG.

Past Officers of the IAG

Chris Rizos
President 2011 – 2015
Chris Rizos was born on
October 16, 1952. He received
his BSurv in 1975 and his PhD
in 1980 from the School ofSurveying, University of New
South
Wales
(UNSW),
Sydney, Australia. In 1987, hejoined the academic staff of
UNSW, and was promoted toProfessor in 2001. Chris was
Head of the UNSW School ofSurveying and Geospatial
Engineering (formerly School of Surveying) from 2004
until 2013 when it merged with the School of Civil andEnvironmental Engineering. Chris has been researching thetechnology and high precision applications of GPS since
1985, and has established the Satellite Navigation andPositioning Lab at UNSW in the early 1990s - Australia's
premier academic R&D group for GNSS and wirelesspositioning technology and applications.
The principal research interests of Chris Rizos include thecarrier phase-based kinematic GPS/GNSS positioning on
short, medium and long baselines, the development of
GPS/GNSS-based deformation monitoring systems, andlow-cost GPS systems for survey applications and building
monitoring. He conducted studies on a modern geodetic
datum for upgrade of the Australian Geodetic Datum using
GNSS and ITRF global products and innovative geodetic
techniques. Other topics are the integration of GNSS with
Interferometric SAR techniques, the development of multifunctional CORS networks and “smart” GNSS receivers. He
studied new positioning technologies like indoor
positioning, pseudolites, Locata, WiFi and mobilephone
positioning, GNSS+INS (and other sensors) integration.
Chris Rizos received the following honours and awards:
x University Medal, UNSW, 1975;
x Commonwealth Postgraduate Scholarship, 1975-78;
x Fulbright Fellowship (Postgraduate Category), 1977-78;
x Rothmans Fellowship, 1979;
x Alexander von Humboldt Fellowship, 1981-83, 1991;
x Fellow of the Australian Institute of Navigation, 1999;
x Fellow of the International Association of Geodesy,1999;
x Fellow of the U.S. Institute of Navigation, 2012;x Honorary Professor, Wuhan University, China, 2006.
The first IAG office of Chris Rizos was the membershipin the joint IAG/IHO Advisory Board on the Law of the Sea(ABLOS) from 1995-2011, whose Chair he became in 2009.
In the same year, he joined the Steering Committee of the17

Asia-Pacific Reference Frame (APREF). In 2004, he wasappointed member of the Governing Board of theInternational GNSS Service (IGS), and in 2006 member of
the IGS Executive Committee. After the election as IAG
Vice President in 2007, he was elected IAG President in2011. At the IUGG General Assembly 2015, the IUGG
Council elected him Member of the IUGG Bureau, and in
2019 President Elect of the IUGG.
Harald SchuhPresident 2015 – 2019
Harald Schuh was born on
February 27, 1956, in Heidelberg, Germany. He received
his Dipl.-Ing. (Geodesy) in1979 and his Dr.-Ing. in 1986
from the University Bonn. He
worked there in the scientificstaff of the Geodetic Institutefrom 1980 to 1986 andbecame a Junior Professor in
1987. From 1989 to 1995, he
was a scientist at the German
Aerospace Center (DLR) and changed then to the German
Geodetic Research Institute (DGFI). In 2000, he followed acall as a Professor at the University of Technology, Vienna,
Austria, and 2012 as a Professor at the Technical University
Berlin, Germany, combined with the Head of the Section
Geodesy of the GFZ German Research Centre.
Harald Schuh became internationally known by his
research in Very Long Baseline Interferometry (VLBI). The
research field includes parts of astrophysics andgeodynamics, time series analysis, and monitoring of Earthrotation. His responsibilities in IAG started in 2003 as arepresentative of the Services in the IAG Executive
Committee and the IAG representative to the International
IVS Service (VLBI). In the same year, he became memberof the Directing Board of the International Center for Earth
Tides (ICET). In 2007, he was appointed Chair of the IVS
Directing Board and the Sub-commission Interaction of
Celestial and Terrestrial Reference Frames. He was elected
Vice President of the IAG in 2011 and President in 2015.
From 2007 to 2012, Harald Schuh was the President ofCommission 19 “Rotation of the Earth” of the International
Astronomic Union (IAU), and acted in its Organizing
Committee from 2006 to 2015.
Harald Schuh received the following major awards:
x Descartes Prize of the European Commission for the
Project “Non-rigid Earth nutation model – Pinpoint
positioning in a wobbly world” (team prize);18x Fellow of the International Association of Geodesy,2007;
x Doctor honoris causa (Dr.h.c.), University for
Architecture, Civil Engineering and Geodesy, Sofia,
Bulgaria, 2009;
x Vening Meinesz Medal of the European Union, 2011;
x Adjunct Professor of the University Tehran, Iran, 2016;
x Member of the German National Academy of Scienceand Engineering (acatech), 2017.
Hermann Drewes
Secretary General 2007 – 2019
Hermann Drewes was born on
April 26, 1944, in Lower
Saxony, Germany. He received
his Dipl.-Ing. in 1970 and his
Dr.-Ing. in 1975 from theTechnical University Hannover,Germany. Since 1970, he
worked there in the Institute for
Theoretical Geodesy as scientificassistant, and since 1976 as chiefengineer. From 1977 to 1979, he
was granted a leave as professor
at the University of Zulia, Maracaibo, Venezuela. After his
return, he changed as a senior scientist to the German
Geodetic Research Institute (DGFI), where he became
Director in 1994. In the same year he was awarded Honorary
Professor at the Technical University Munich, Germany.
The key research fields of Hermann Drewes include
gravimetry and geoid determination (since 1970), geodetic

The Geodesist’s Handbook 2020

geodynamics (since 1979), and reference systems andframes (since 1994). Major international positions are:x IAG Representative to the South American Reference
Frame (SIRGAS) since 1994;
x President of the IAG/COSPAR Commission on SpaceTechniques for Geodesy and Geodynamics, 1999-2003;
x Member of the Bureau of the International Lithosphere
Project (ILP), 2001-2008;
x Chair of the International Terrestrial Reference Frame(ITRF) Combination Centre at DGFI, 2001-2010;x President of IAG Commission 1 “Reference Frames”,
2003-2007;
x IUGG Representative to the UN Cartographic Bureau,
2003-2007;
x IUGG Representative to the Pan-American Institute forGeography and History (PAIGH), 2003-2011;x Secretary of IAG’s Global Geodetic Observing System(GGOS), 2003-2005;
x IAG Secretary General, 2007-2019;
x IUGG Representative to the United Nations Geospatial
Information Section, 2015 -2019.
Hermann Drewes received the following major awards:
x Fellow of the International Association of Geodesy(IAG), 1999;
x Cavaleiro do Ordem do Mérito Cartográfico, Brazilian
Society of Cartography, Photogrammetry and Remote
Sensing, 2005;
x Cross of the Order of Merit of the Federal Republic of
Germany, 2007;
x Huesped de Honor Extraordinario, National Universityof La Plata, Argentina, 2010;
x Fellow of the International Union of Geodesy andGeophysics (IUGG), 2019.

IAG Statutes

19

IAG Statutes adopted by the IAG Council
at the XXVII IUGG General Assembly in Montreal, Canada, 2019

1. Definition of Terms

2. International Association of Geodesy

(a)

(a)

Geodesy is the discipline that deals with the measurement and representation (geometry, physics, and temporal variations) of the Earth and other celestial bodies.

(b) IUGG is an acronym for the International Union of Geodesy and Geophysics.
(c)

IAG or Association is an acronym for the International
Association of Geodesy.

(d) Adhering Body and Council have the same meaning as
in the Statutes of the IUGG.
(e)

(f)

IAG General Assembly refers to an assembly for scientific and/or administrative purposes of:(i) scientists from geodesy and other Earth science
disciplines;(ii) the Council Delegates (or Alternative Delegates)
appointed by the Adhering Bodies; and(iii) individual members as defined by Statute 6(b).
IAG Scientific Assembly means an assembly for primarily scientific purposes and therefore it does not normally require the presence of the delegates appointed
by the Adhering Bodies.

(g) Council Delegate means the person appointed by the
Adhering Body to be a member of the Council for one
period (see 1(h)). Adhering Bodies may appoint an Alternative Delegate to an IAG Council meeting if theCouncil Delegate cannot attend the meeting.
(h) Period means the interval of time between the closuresof two successive IAG General Assemblies.

The International Association of Geodesy (IAG):(i) is a constituent Association of the IUGG; and(ii) is subject to the Statutes and Bylaws of the IUGG(b) In the event of the dissolution of the IAG, its assets
shall be ceded to the IUGG.

3. Mission
The Mission of the Association is the advancement of geodesy. The IAG implements its mission by furthering geodetic
theory through research and teaching, by collecting, analyzing, modelling and interpreting observational data, by stimulating technological development and by providing a consistent representation of the figure, rotation, and gravity
field of the Earth and planets, and their temporal variations.

4. Objectives
The IAG shall pursue the following objectives to achieve its
mission:(a)

Study, at the highest possible level of accuracy, all geodetic problems related to Earth observation and globalchange, including:(i) Definition, establishment, and maintenance of
global and regional reference systems for interdisciplinary use.
(ii) Rotation of the Earth and planets.
(iii) Positioning and deformation.
(iv) Gravity field.
(v) Ocean, ice and sea level.
(vi) Atmosphere and hydrosphere.
vii) Time and frequency transfer.

20

The Geodesist’s Handbook 2020(b) Support the maintenance of geodetic reference systems
and frames for continuous, long-term observations andarchival of results.

6. Membership(c)(a) Adhering Bodies; and(b) Individual members in accordance with the Bylaws.

Provide observational and processed data, standards,
methodologies, and models in a form that ensures thebroadest possible range of research and application.

The membership of the IAG shall comprise:(d) Stimulate development and take advantage of emerging space and other technologies to increase the resolution and accuracy of geodetic data and products in orderto advance geodetic and interdisciplinary research.

7. IAG Council(e)

Initiate, coordinate, and promote international cooperation and knowledge exchange through symposia,
workshops, summer schools, training courses, publications, and other means of communication.

(b) The membership of the IAG Council consists of Delegates appointed by the Adhering Bodies.

Foster the development of geodetic activities and infrastructure in all regions of the world, taking into consideration the specific situation of developing countries.

(d) A Delegate may only represent one Adhering Body.

(f)(g) Collaborate with the international science and engineering community in supporting the application ofgeodetic theory and techniques and the interpretationof results.
(h) Cooperate with national and international agencies inestablishing research goals, missions, and projects.

5. Structure and Administration(a)

The Association's structure shall comprise a small
number of components: Commissions, Inter-commission Committees (ICC) (such as the ICC on Theory(ICCT)), the Services, the Global Geodetic Observing
System (GGOS), and the Communication and Outreach Branch (COB).

(b) Subcomponents, such as IAG Projects, Sub-commissions, Commission Projects, and Study and Working
Groups, may be established as provided for in the Bylaws.
(c)

The administration of the IAG is carried out by the IAG
General Assembly, the IAG Council, the IAG Bureau andthe IAG Executive Committee. The COB is the office
responsible for the promotional activities of the IAG
and the communication with its members.

(a)

(c)

(e)

The IAG Council is responsible for governance, strategic policy and direction.

Each Adhering Body may appoint one Delegate subject to the conditions in (d) and (e) below.
The IAG President, Vice President and Secretary General may not serve as Delegates.

8. IAG Bureau(a)

The Bureau of the Association consists of the IAG
President, the Vice President and the Secretary General.

(b) The duties of the IAG Bureau shall be to administer
the affairs of the Association in accordance with these
Statutes and Bylaws and with the decisions of the IAG
Council and the IAG Executive Committee.

9. IAG President(a)

The IAG President shall be elected by the IAG Council.

(b) The IAG President shall provide general leadership for
the Association.
(c)

The IAG President presides over the meetings of the
IAG General Assembly, the IAG Scientific Assembly,
the IAG Council, the IAG Executive Committee, andthe IAG Bureau. In the IAG Council meetings the
President has no vote, except in the case of a tie as provided in 14(g).

(d) The IAG President, on completion of their term of office of one period, shall serve for the next period in theposition of Immediate Past President.

IAG Statutes

21

10. IAG Vice President(a)

The IAG Vice President shall be elected by the IAG
Council.

through effective coordination and through the formulation of general policies.
(e)(b) The IAG Vice President shall perform such tasks as
may be assigned by the IAG President, the IAG Executive Committee or the IAG Council.
(c)

The IAG Vice President assumes the functions, duties
and powers of the President when the latter is absent
or otherwise unable to assume office.

11. IAG Secretary General(a)

The IAG Secretary General shall be elected by the IAG
Council.

(b) The IAG Secretary General shall serve as secretary of
the IAG General Assembly, the IAG Scientific Assembly, the IAG Council, the IAG Executive Committee,
and the IAG Bureau and arrange for meetings of thesebodies in accordance with the Bylaws.
(c)

The IAG Secretary General, on completion of theirterm of office, shall serve for the next period in the position of Immediate Past Secretary General.

13. Council Meetings(a)

The IAG Executive Committee shall consist of the following voting members: each member of the IAG Bureau, the immediate Past President, the immediate Past
Secretary General, the Presidents of the Commissions,the President of the ICCT, the President of GGOS, thePresident of the COB, the three representatives of theServices, and two Members-at-Large.

(b) Presidents of the Inter-commission Committees otherthan the ICCT, Chairs of the IAG Projects, and the Assistant Secretaries shall attend any meeting of the IAG
Executive Committee, with voice but without vote.
The Past Presidents and past Secretaries General may
attend any meeting of the IAG Executive Committee,
with voice but without vote (except for the immediate
Past President and the immediate Past Secretary General, who do have a vote in accordance with Statute12(a) for one 4-year period).
(c)

The election of IAG Executive Committee members
shall be in accordance with the Bylaws.

(d) The responsibilities of the IAG Executive Committee
shall be to further the objectives of the Association

The IAG Council shall meet at the time of an IAG General Assembly.

(b) The IAG Council may hold extraordinary meetings, either in person or electronically, at times other than an
IAG General Assembly. Such meetings must be proposed by the IAG Executive Committee(c) The members of the IAG Executive Committee may
attend meetings of the IAG Council, with voice but
without vote, except for those who are also Delegates.

14. Voting in the Council
Voting in the IAG Council shall follow the following rules:(a)

12. IAG Executive Committee(a)Decisions of the Executive Committee shall be taken
by a simple majority. If a tie should occur in an Executive Committee vote, the IAG President shall cast thedecisive vote.

An Adhering Body which is not represented at an IAG
Council meeting may vote by correspondence on any
specific question, provided that the matter has beenclearly defined on the final agenda distributed in advance, and that the discussion thereon has not produced any significant new considerations or change inits substance, and that the said vote has been received
by the IAG President prior to the voting. In such a casethe vote will be cast in accordance with 14(d)).

(b) Quorum in IAG Council meetings is achieved when
the number of Council Delegates (or Alternative Delegates) in attendance is at least one third of the delegates from countries eligible to vote.
(c)

On questions not involving matters of finance, eachdelegate from an Adhering Body, with its IUGG subscriptions paid up to the end of the calendar year preceding the voting, shall have one vote.

(d) On questions involving finance, each delegate from an
Adhering Body, which has paid its IUGG subscriptions up to the end of the calendar year preceding thevoting, shall have the right to vote. The number ofvotes allotted to each delegate of an Adhering Body
shall then be in accordance with its category of membership, as defined by the IUGG.

22

(e)

(f)

The Geodesist’s Handbook 2020

Prior to any vote in an IAG Council meeting, the IAG
President shall decide whether or not the matter underconsideration is financial in character and whether theprocedure of voting by correspondence applies.
The IAG Council may also deliberate and decide matters at other times by correspondence and/or email ballot, provided that the issues have been communicatedto IAG Council members at least one month in advanceof the voting date.

(g) Decisions of the IAG Council shall be taken by a simple majority, except as otherwise specified in these
Statutes. If a tie should occur in an IAG Council vote,the IAG President shall cast the decisive vote. This
procedure also applies if the vote is taken by email ballot. Simple and two-thirds majorities are determinedby the proportion of affirmative votes to the sum of all
votes (affirmative, negative and abstention). Blank andinvalid ballots and votes not cast by delegates present
are counted as abstentions.
(h) Elections for all for members of the IAG Executive
Committee shall be by electronic ballot. For each post,
the winner must receive an outright majority (numberof votes being greater than the total combined votes ofthe other candidates). If there are three or more candidates for a position and no candidate has an outrightmajority after the first voting round, then the top two
ranked candidates will be retained and a second roundof votes conducted to elect the winner. Ties will be
broken by a coin toss, drawing of lots, or equivalentrandom selection.
(i)

Except as otherwise provided in the Statutes or Bylaws, meetings of the IAG Council, as well as those ofother IAG administrative bodies, shall be conductedaccording to the edition of Robert's Rules of Order currently recommended by the IUGG.

15. Decisions of the Council(a)

Decisions of the IAG Council shall be reported to theindividual membership in a meeting at the IAG General Assembly.

(b) If the majority of those present at this meeting disagrees with the decisions of the IAG Council, the IAG
Council shall reconsider the question, and make a decision, which shall be final.

16. Changes to Statutes and Bylaws
Changes in the Statutes and Bylaws shall be made as follows:(a)

If deemed necessary, the Association may review theStatutes and Bylaws in each period, to ensure an up-todate structure of its scientific and administrative organization. A Review Committee, known as the Cassinis Committee, will be appointed by the IAG Executive Committee to achieve this goal. Proposals for a
substantive change of any article of these Statutes andBylaws must reach the Secretary General at least twomonths before the announced date of the IAG Council
meeting at which it is to be considered. The Secretary
General shall notify all Adhering Bodies of any proposed changes at least one month before the announced date of the IAG Council meeting.

(b) The Statutes may not be modified except a two-thirds
majority of votes cast at an IAG Council meeting, andchanges shall come into force at the close of that meeting.
(c)

The IAG Council shall have the power to adopt Bylaws
within the framework of the Statutes.

(d) The Bylaws may be modified by a simple majority of
votes cast at an IAG Council meeting, and changes
shall come into force at the close of the meeting.

IAG Bylaws

23

IAG Bylaws adopted by the IAG Council
at the XXVII IUGG General Assembly in Montreal, Canada, 2019

1. Definition of Terms(a)

Association component or components refers to theCommissions, the Inter-commission Committee on
Theory (ICCT), other Inter-commission Committees
as they may be established, IAG Projects, the Services,
the Global Geodetic Observing System (GGOS), andthe Communication and Outreach Branch (COB).

(b) Commissions represent major fields of activity in accordance with the IAG Statutes.
(c)Services collect and analyze observations to generate
products relevant to geodesy and other sciences andapplications.

(d) The Global Geodetic Observing System (GGOS)
works with the IAG components in advancing ourunderstanding of the dynamic Earth system by quantifying our planet’s changes in space and time.
(e)

Association subcomponent or subcomponents are
long-term or short-term structures created by the IAG
or one or more of its components.

(f)Long-term subcomponents comprise IAG Projects(broad in scope and of high interest for the entire fieldof geodesy), Sub-commissions and Commission Projects which are expected to operate for several periods.

(g) Short-term subcomponents refer to Study Groups
and Working Groups which are established for a maximum term of one period.
(h) Steering Committee means a group of elected or
appointed IAG officers who oversee the work of Commissions, Inter-commission Committees (see 17), IAG
Projects (see 16), and the Communication and Outreach Branch (see 18).

(i)

Period means the interval of time between the closuresof two successive IAG General Assemblies.

2. Responsibilities of Association Components(a)

The scientific work of the IAG is performed by Commissions, Inter-commission Committees, IAG Projects,
Services and the GGOS.

(b) The responsibilities of the IAG Components are determined by the IAG Council on the recommendation of
the IAG Executive Committee.
(c) Components are expected to interact with each otherwhere their activities are inter-related.
(d) Each Component may set up subcomponents and is
responsible for the activities of those subcomponents.

3. General Responsibilities of Component
Presidents or Chairs, and Steering
Committees(a)Each Component shall have a President or Chair who
will lead a Steering Committee.

(b) The Component President or Chair is responsible forthe scientific development within the Component's
field of interest. The Component’s President or Chair
shall:(i) coordinate the work of the subcomponents;(ii) keep the officers of the Component as well as the
IAG Bureau and IAG Executive Committee
informed of the Component's activities on anannual basis;

24

The Geodesist’s Handbook 2020(iii) collect reports of the subcomponents two months
before each IAG General and Scientific Assembly for publication in the "Travaux de l'Association Internationale de Géodésie";(iv) receive suggestions for new subcomponents, andsuggestions for continuation of existing ones; and(v) recommend changes to subcomponents to the
IAG Executive Committee for approval.
(c)(iv) Up to three representatives of the Services relevant to the work of the Commission.
(v) Up to two Members-at-Large to balance geographical and member country representation.

6. Appointment of Commission Officers(a)

The Component’s Steering Committee is expected tomeet at least once per year and at least once during each
IAG General Assembly.

(d) The Component’s Steering Committee shall review at
one of its meetings (usually the IAG General Assembly, or the IAG Scientific Assembly):(i) the activities of the subcomponents over the past
period;(ii) the structure of the subcomponents; and(iii) the programs for the forthcoming period for thosesubcomponents that will be recommended forcontinuation.
(e)

The Component’s Steering Committee shall inform theSecretary General about all relevant issues.

(f)

The Component’s Steering Committee may organize
scientific and organizational meetings and workshops
provided that they are readily distinguished as being ofa more limited scope than IAG Scientific Symposia or
IAG Sponsored Symposia as described in Bylaws 28
and 29.

The Commission President shall be elected by the IAG
Council for one period without reappointment, except
where exceptional circumstances justify reappointment.

(b) The Commission Vice President shall be appointed by
the IAG Executive Committee for one period without
reappointment, except where exceptional circumstances justify reappointment.
(c)Chairs of the Sub-commissions and Commission Projects shall be nominated by the Commission President
and Vice President within two months following theGeneral Assembly.

(d) The representatives of the Services shall be appointed
by the Commission President and Vice President upon
proposal of the Services.
(e)

The Members-at-Large shall be nominated by theCommission President and Vice President within twomonths following the IAG General Assembly.

(f)

The appointments of Members-at-Large and Chairs ofSub-commissions and Commission Projects takeeffect on approval of the nominations by the IAG
Executive Committee.

4. Commission Responsibilities
Commissions shall promote the advancement of science,technology and international cooperation in their field. They
establish the necessary links with sister disciplines and withthe relevant Services. Commissions shall represent the
Association in all scientific domains related to their field ofgeodesy.

7. Tasks of Commission Steering Committee

5. Commission Steering Committee

(a)

(a)

The Commission Steering Committee shall be set up ateach IAG General Assembly, following the election of
the Association officers.

(b) The Steering Committee shall have the following
voting members:(i) Commission President.
(ii) Commission Vice President.
(iii) Chairs of the Sub-commissions and Commission
Projects.

The Commission Steering Committee is subject to the general responsibilities of component Steering Committees in
Bylaw 3(c), 3(d), 3(e), and 3(f). In particular, its tasks areto:
Review the Commission's field of interests and objectives.

(b) Liaise with the other IAG Commissions, the Inter-commission Committees, and with similar organizations outside the IAG, as appropriate.
(c)

Foster active participation of early career geodesists
and geodesists from under-represented countries.

(d) Coordinate and review the work of its components andreport at the time of the Scientific Assembly to the IAG

IAG Bylaws

Executive Committee on the progress and performance ofthe components.
(e)

Encourage and organize Commission and interdisciplinary symposia and/or sessions at major geodesy related international meetings.

(f)

Maintain a Commission website and email service.

(g) As requested, nominate editors for the Journal of
Geodesy.

8. Current Commissions
On the approval of these Bylaws, there shall be four Commissions with areas of scientific responsibility as outlined
below:

25(4) Commission 4: Positioning and Applications(a)Terrestrial and satellite-based positioning systems
development, including sensor and information fusion.
(b) Navigation and guidance of platforms.
(c) Interferometric laser and radar applications.
(d) Applications of geodetic positioning using geodetic
networks, including monitoring of deformations.
(e) Applications of geodesy to engineering.
(f) Atmospheric investigations using space geodetic
techniques.

9. Commission Subcomponents and Joint
Subcomponents(a)(1) Commission 1: Reference Frames(a)Establishment, maintenance, improvement of the geodetic reference frames.
(b) Advanced terrestrial and space geodetic techniques forthe above purposes.
(c) International collaboration for the definition and deployment of networks of terrestrially-based space geodetic
observatories.
(d) Theory and coordination of astrometric observation forreference frame purposes.
(e) Collaboration with space geodesy/reference frame related international services, agencies and organizations.
(2) Commission 2: Gravity Field
(a)
(b)
(c)
(d)
(e)
(f)

Terrestrial, marine, and airborne gravimetry.
Satellite gravity and altimetry observations.
Gravity field modelling.
Time-variable gravity field.
Geoid determination and height systems.
Satellite orbit modelling and determination.

(3) Commission 3: Earth Rotation and Geodynamics(a)Earth orientation (Earth rotation, polar motion,nutation and precession).
(b) Earth tides.
(c) Tectonics and crustal deformation.
(d) Sea surface topography and sea level changes.
(e) Planetary and lunar dynamics.
(f) Effects of the Earth's fluid layers (e.g., post glacial
rebound, loading).

Commission subcomponents are Sub-commissions,
Commission Projects, Study Groups, and Working
Groups, which all belong to one Commission.

(b) If more than one component is involved in a subcomponent, the term “joint subcomponent” will be used,
e.g. Joint Sub-commission, Joint Commission Project,
Joint Study Group, Joint Working Group.

10. Sub-commissionscommissions
(a)

and

Joint

Sub-

A Sub-commission may be set up for topics where theCommission plays a leading or coordinating role.

(b) Where a topic relates to the scientific responsibilities ofmore than one IAG component, a Joint Sub-commission
shall be established under the lead of one Commission.
(c)

A Sub-commission is expected to be established forseveral periods.

(d) Sub-commissions are established and terminated by
the IAG Executive Committee upon recommendationfrom the Commission President.
(e)

A proposal to the IAG Executive Committee for a Joint
Sub-commission requires the recommendation of the
Presidents of all contributing components.

11. Commission Projects and Joint Projects(a)

A Commission Project may be established when a newscientific method or a new technique is being developed, or when it seems appropriate to apply an existing
technique to a specific geographic area where international collaboration is required.

26

The Geodesist’s Handbook 2020(b) Where a topic for a Commission Project relates to thescientific responsibilities of more than one Commission, or a Commission and a Service, a Joint Commission Project shall be established under the lead of one
Commission.

(i)

The Chair of each Study Group or Working Groupshall issue a brief description of the work to be
performed and a list of members, to be published in the
Geodesist's Handbook after each IAG General
Assembly.

(c)

(j)

The Chair of each Study Group or Working Groupshall report annually to its members and the Commission Steering Committee, on results achieved andoutstanding problems.

A Commission Project is established for one period
and may be extended for another period subject to a
positive review.

(d) Commission Projects are established, extended andterminated by the IAG Executive Committee upon recommendation from the Commission President.
(e)

A proposal to the IAG Executive Committee for a Joint
Commission Project requires the recommendation of
the Presidents of all contributing components.

13. IAG Services(a)12. Study Groups, Working Groups, Joint
Study Groups and Joint Working Groups(a)

A Study Group or Working Group may be establishedat any time to address clearly defined well-focusedscientific topics of limited scope within the field of theComponent. A Study Group is dealing with moretheoretical issues and a Working Group with morepractical realizations.

(b) Where a topic for a Study Group or Working Grouprelates to the scientific responsibilities of more than
one Component, a Joint Study Group or a Joint
Working Group shall be established.
(c)

A Study Group or Working Group is established for a
maximum of one period.

(d) Study Groups and Working Groups, including theposition of the group chair, are established and terminated by the IAG Executive Committee upon recommendation of the Component President.
(e)

A proposal to the IAG Executive Committee for a Joint
Study Group or Joint Working Group requires therecommendation of the Presidents of all contributing
components.

(f) The Chair of a Study Group or Working Group is
responsible for initiating and directing its work andappointing its members.
(g) Study Group and Working Group membership should
be balanced so as to reflect international cooperationin its subject.
(h) A Study Group or Working Group may have at most
20 full members and an unlimited number ofcorrespondent members.

IAG Services (see Bylaw 14) generate products, using
their own observations and/or observations of otherservices, relevant for geodesy and for other sciences
and applications. Accuracy and robustness of products,
quality control, timeliness, and state of the art quality
are the essential aspects of the Services.

(b) Each IAG Service shall define its Terms of Reference
as appropriate to accomplish its mission and shall submit
the Terms of Reference to the IAG Executive Committee
for approval.
(c)Each IAG Service shall have an IAG representative,
appointed by the IAG Executive Committee, as avoting member of its directing or governing board.

(d) IAG Services are linked to at least one of the Commissions and may be also linked to other scientific organizations, such as the World Data System (WDS) or theInternational Astronomical Union (IAU).
(e)

IAG Services should collaborate on a scientific basiswith the Commissions, establish Joint Commission
Projects and Joint Study Groups and help compile theCommissions’ list of themes for Study Groups.

(f)Three representatives shall be elected in accordancewith Bylaw 39 to the IAG Executive Committee toserve the interests of all Services.

(g) On any matter relating to the products of a Service, theService shall represent the IAG.

14. Current IAG Services
There are twelve IAG Services at the time of adoption ofthese Bylaws:(a)International Centre for Global Earth Models(ICGEM)(b) International Digital Elevation Models Service(IDEMS)IAG Bylaws(c)International DORIS Service (IDS)(d) International Earth Rotation and Reference Systems
Service (IERS)(e)(f)

International Geodynamics and Earth Tides Service(IGETS)International GNSS Service (IGS)(g) International Gravimetric Bureau (BGI)(h) International Gravity Field Service (IGFS)(i)

International Laser Ranging Service (ILRS)(j)International Service for the Geoid (ISG)27

16. IAG Projects(a)(b) The establishment of an IAG Project shall be carriedout by a planning group appointed by the IAG Executive Committee.
(c)(k) International VLBI Service for Geodesy and Astrometry (IVS)(l)

Permanent Service for Mean Sea Level (PSMSL)

15. The Global Geodetic Observing System(GGOS)(a)

The GGOS is IAG’s observing system to monitor thegeodetic and the global geodynamic properties of the
Earth as a system.

(b) The Global Geodetic Observing System (GGOS)
works with the IAG Services to facilitate the production of geodetic products (including the geometric reference frames and the gravity field models) that are
fundamental to science and society. In addition GGOS
undertakes activities directed at improving the geodetic
infrastructure that underpins the geodetic products.
Further, GGOS takes advice from the Commissions
and the ICCT concerning new developments, and keeps
the Commissions and ICCT informed of the work of
GGOS.
(c)

GGOS operates under its own Terms of Reference,
defined by the GGOS Coordinating Board andapproved by the IAG Executive Committee. The
GGOS procedures for the nomination and election of
its Officers are specified in its Terms of Reference.

(d) The GGOS President is elected by the IAG Executive
Committee from a slate of nominations submitted by the
GGOS Coordinating Board in consultation with the
Executive Committee. The President is appointed for
one period, which may be renewed once.

IAG Projects are flagship long-term projects of broad
scope and of significant interest for the entire field ofgeodesy.

The Project Steering Committee shall have the following voting members:(i) The Project Chair appointed by the IAG Executive Committee.
(ii) One member from each Commission appointed
by each Commission’s Steering Committee.
(iii) Two Members-at-Large proposed by the members of the Project Steering Committee identified
in clause (i) and (ii) above and approved by the
IAG Executive Committee.
(iv) Chairs of the IAG Project Working Groups (if any).
(v) Representatives of other IAG components, as appropriate.

(d) IAG Project subcomponents are known as Working
Groups.

17. Inter-commission Committees (ICCs)(a)Inter-commission Committees shall be responsible forwell-defined, important and permanent tasks involving
all Commissions.

(b) Each ICC shall have a Steering Committee, whichshall include the following members:(i)

President appointed by the IAG Executive Committee.
(ii) Vice President appointed by the IAG Executive
Committee on the recommendation of the President.
(iii) One representative appointed by each Commission.
(c)

The Terms of Reference for each ICC shall be developed by a planning group appointed by the IAG Executive Committee, for approval by the Executive Committee.

(d) ICCs will be established for at least two periods andshall be reviewed by the IAG Executive Committee
every eight years.
(e)

The ICCs shall report to the IAG Executive Committee.

28

The Geodesist’s Handbook 2020

17.1 The Inter-commission Committee on Theory(ICCT)The mission of the ICCT is to interact and collaborate withother IAG components, in particular the Commissions and
GGOS, in order to further the objectives of ICCT:(i)

to be the international focal point of theoreticalgeodesy;(ii) to encourage and initiate activities to further
geodetic theory in all branches of geodesy; and(iii) to monitor research developments in geodetic
modelling.

18. Communication and Outreach Branch
(COB)
(a)

The function of the Communication and OutreachBranch (COB) is to provide the Association with
communication, educational/public information andoutreach links to the membership, to other scientificorganizations and to the world as a whole.

(b) The responsibilities of the COB shall include thefollowing:(i)

Promote the recognition and usefulness ofgeodesy in general and the IAG in particular.
(ii) Publications (such as newsletters) and social
media platforms.
(iii) Membership development.
(iv) General information service and outreach.
(c)

The COB shall also assist the IAG Secretary Generalin the following tasks as required:(i) Maintenance of the IAG website.
(ii) Setting up Association schools.
(iii) Organizing meetings and conferences.

(d) The IAG Executive Committee establishes the COB ona long-term basis by issuing a Call for Participation. The
responding organization(s) and the IAG Executive
Committee shall then negotiate the Terms of Reference and other conditions.
(e)

The President of the COB shall be elected by the IAG
Council after consideration of a COB proposal.

(f)

Major decisions related to the operations of the COB
shall be made by a Steering Committee consisting of
the following voting members:(i) COB President.
(ii) IAG Secretary General.
(iii) Editor-in-Chief of the Journal of Geodesy.
(iv) Editor-in-Chief of the IAG Symposia Series.

(v) Up to 5 other members appointed by the IAG
Executive Committee on the recommendation of
the President of the COB.

19. IAG Publications(a)

The IAG publications include the Journal of Geodesy,
the IAG Symposia Series, the Geodesist's Handbook,the "Travaux de l'Association Internationale deGéodésie," the IAG Newsletter, and IAG Special
Publications.

(b) The Association's journal is the Journal of Geodesy,hereinafter referred to as the Journal. The Journal ispublished monthly through an agreement between the
Association and a publishing company, or by otherarrangement approved by the IAG Executive Committee. The terms of any agreement for publication of the
Journal shall be negotiated by the President of theCommunications and Outreach Branch and ratified by
the IAG Executive Committee.
(c)

The Journal publishes peer-reviewed papers, covering
the whole range of geodesy, including geodetic applications.

(d) After each IAG General Assembly, a special issue of
the Journal shall be published under the name of "The
Geodesist's Handbook". This issue provides the actual
information on the Association, including the reportsof the IAG President and Secretary General presented
at the previous IAG General Assembly, the resolutions
taken at that assembly, and the Association structure
listing all components and subcomponents for therunning period, rules for the IAG Fund, IAG Awards
and for the conduct of scientific meetings as well as
relevant scientific information.
(e)

The IAG Symposia Series publishes peer-reviewed
papers related to presentations made at IAG Symposia
and/or IAG Sponsored Symposia, provided that sufficient number of papers are submitted and accepted for
publication.

(f)

After each IAG General Assembly, a collection of thereports by the Association components shall be published in the "Travaux de l'Association Internationalede Géodésie". This publication is supplied free ofcharge to the officers of the Association and to the adhering body of each member country.

(g) At every IAG General Assembly each member country
is encouraged to submit a National Report on geodetic
work done since the previous General Assembly to beplaced on the IAG website.

IAG Bylaws(h) The IAG Newsletter is under the editorial responsibility of the Communication and Outreach Branch. It
should be published on the IAG website and distributed to members electronically.

20. Editor-in-Chief and Editorial Board(a)

There shall be one Editor-in-Chief for the Journal of
Geodesy, hereinafter referred to as the Journal Editor.
An Assistant Editor-in-Chief may assist the Journal
Editor. The Journal Editor shall be advised and assisted by an Editorial Board. To ensure broad expertise, each of the Commissions may nominate up to
three members of the Editorial Board.

(b) The Journal Editor shall be responsible for the scientific content of the Journal. The Journal Editor shallmake the final decision on whether a refereed scientificmanuscript is accepted for publication. The Journal
Editor shall keep the IAG Executive Committee
informed of the activities and status of operations of
the Journal.
(c)Three months before each IAG General Assembly, theJournal Editor, in consultation with the IAG Bureau,
shall recommend a preliminary list of candidates forthe new Editorial Board. This list shall be published on
the IAG website at least two months in advance of the
IAG General Assembly to solicit additional nominations for the Editorial Board from the IAG Components, Members, Fellows, Honorary Offices, andCouncil.

(d) At the IAG General Assembly, the current Editorial
Board shall appoint the members of the new Editorial
Board from those recommended. After taking office,the new Editorial Board shall nominate the new Journal Editor and the new Assistant Editor for the next
period. After approval of these nominations by the
IAG Executive Committee, the Journal Editor and theAssistant Editor will be considered as elected.
(e)

(f)

The Journal Editor, the Assistant Editor, and the members of the Editorial Board shall each hold office forone period, but are eligible to be re-elected for one further period.
There shall be one Editor-in-Chief for the IAG Symposia Series, hereinafter referred to as the Series Editor. He/she is appointed by the IAG Executive Committee for one period. An assistant Editor-in-Chief
may also be appointed.

29(g) The Series Editor shall be responsible for the scientificcontent of the IAG Symposia Series. On the recommendation of the volume editor(s), the Series Editor
shall make the final decision on whether a refereed scientific manuscript is accepted for publication. The
Series Editor shall keep the IAG Executive Committee
informed of the activities and status of the IAG Symposia Series.
(h) Each volume of the IAG Symposia Series may haveadditional Volume Editors.

21. IAG Individual Membership(a)

Individuals engaged in geodesy, can become individual members of the IAG on application and paymentof the membership fee.

(b) Applications for individual membership are submitted
to the IAG Secretary General.
(c)

The decision on the membership application shall bemade by the IAG Bureau.

(d) Benefits of membership include:(i)

Reduction in the individual subscription rate to
the Journal of Geodesy.
(ii) The right to participate in the IAG election process both as a nominator and a nominee.
(iii) Upon application, correspondent membership ina Sub-commission or Study Group of choice.
(iv) Reduction in the registration fee for IAG meetings as set under Bylaws 26(d) and 27(b).
(e)

The membership fee per annum is set by the IAG Executive Committee.

(f)

In individual cases, the Secretary General may consider a discount or full remission of membership feeson application by the member.

(g) Where a member provides a donation in excess of themembership fee, the excess shall be assigned to the
IAG Fund.
(h) Membership is terminated if the membership fee is not
paid or if an application for discount or full remission
has not been received one year after the fee was due.

22. Honorary Officers, Fellows(a)

The IAG Executive Committee may appoint a merited
past IAG President as Honorary President or a merited
IAG Secretary General as Honorary Secretary General.

30

The Geodesist’s Handbook 2020(b) The IAG Executive Committee may appoint past officers of the IAG as Fellows.

(f)

23. IAG FundThe IAG Executive Committee may establish an IAG Fundfor supporting specific IAG activities as defined in the IAG
Fund Rules, published in the Geodesist's Handbook. The
Fund is under the direct responsibility of the President. The
Fund's resources are administered by the Secretary General.

26. Scientific Meetings(a)

25. Administration of the IAG General Assemblies(a)the Scientific Symposia held during an IAG General Assembly;(ii) Scientific Assemblies, including IAG ScientificSymposia; and(iii) IAG Sponsored Symposia.

(c)

The IAG Executive Committee shall draw up theagenda for the scientific program. Joint Symposia covering topics of interest to two or more IUGG Associations may be arranged.

(d) The agendas developed according to (b) and (c) above
are sent to the member countries and to all officers of
the Association so as to reach them at least two months
prior to the IAG General Assembly. In principle, only
matters on the agenda may be considered during thesessions, unless a decision to do otherwise is passed bya two-thirds majority of the IAG Council.
(e)(b) The IAG Newsletter shall include a calendar of IAG
Symposia and other scientific meetings organized orsponsored by the IAG or its components.
(c)

The IAG General Assembly will be held at the sametime and at the same place as the International Unionof Geodesy and Geophysics (IUGG) General Assembly.

(b) Before any IAG General Assembly, the IAG Bureau
shall prepare detailed agendas for the IAG Council
meetings, IAG Executive Committee meetings, andthe opening and closing sessions.

At each IAG General Assembly, the IAG President
shall present a report on the scientific work of the Association during their tenure. The IAG Secretary General shall present a report on the administrative workand on the finances of the Association for the same period. The President and Secretary General should include in their reports proposals for work to be undertaken during the coming period, within the limits of
expected resources. These reports shall be published in"The Geodesist's Handbook".

Scientific meetings of the IAG are:(i)

24. IAG Awards
The IAG Executive Committee may establish Awards foroutstanding contributions to geodesy and distinguished service to the IAG. The rules for the awards are to be publishedin “The Geodesist's Handbook”.

At each IAG General Assembly, the work of eachCommission, each Inter-commission Committee, each
Service, the Communication and Outreach Branch,and each IAG Project shall be reported on by its President or Chair. IAG Representatives to other scientificbodies shall report to the IAG Executive Committee.

The IAG Executive Committee shall appoint an IAG
Scientific Meeting Representative for each of the scientific meetings other than the General Assembly andthe Scientific Assembly to be governed by these Bylaws. The representative is obliged to remind the organizers to adhere to the Bylaws for scientific meetings and to report back to the IAG Executive Committee.

(d) A reduced registration fee shall be offered for individual members in accordance with Bylaw 21(d) (iv).

27. IAG Scientific Assemblies(a)

IAG Scientific Assemblies are held mid-way during
the period between two IAG General Assemblies andshall consist of a group of component meetings and/or
a group of scientific symposia, held at the same timeand place.

(b) A reduced registration fee shall be offered for individual members in accordance with Bylaw 21(d)(iv).

28. IAG Scientific Symposia(a)

Scientific symposia take place at the IAG General Assembly and the IAG Scientific Assembly. In general,they shall be organized by IAG components and subcomponents, and be led by their respective Presidents
or Chairs.

(b) The study of some questions may require joint meetingsof several components under a chair, appointed by the
IAG Executive Committee. A committee consisting of

IAG Bylaws

the component chairs shall decide on the agenda andon the inclusion of scientific presentations.
(c)

At each IUGG General Assembly Joint ScientificSymposia covering topics of interest to two or more
Associations within the IUGG and/or other international scientific organizations may be convened.
Though the IAG may be asked to act as convenor or
co-convenor, these symposia shall follow the rules established by the IUGG. The IAG may participate also
in joint symposia at any other time outside of the IAG
General Assembly and governed by the same procedures.

(d) The planning of a scientific symposium shall be subject to the usual approval procedure provided by “The
Geodesist's Handbook”.

29. IAG Sponsored Symposia(a)

The IAG may sponsor a symposium covering broadparts of geodesy and having large attendance at any
suitable time outside the IAG General Assemblies or
IAG Scientific Assemblies, and shall call it an IAG
Sponsored Symposium, provided the following conditions are fulfilled:(i)

One or more IAG component or subcomponent,
or at least two Study Groups, shall sponsor it.
(ii) Host organization of the symposium shall accept
an IAG representative in the Scientific Organizing
Committee (SOC) appointed by the IAG Executive Committee.
(iii) The symposium shall be open to all bona-fide scientists in accordance with the International Science Council (ISC) rules.
(b) The SOC appointed under Bylaw 29(a)(ii) shall be responsible for the quality of science of the symposium
being at a high level. A Local Organizing Committee(LOC) shall be responsible for the organization and logistics.
(c)Applications for approval of an IAG Symposium
should be submitted to the Secretary General at least
one year before the intended date of the meeting.

30. International Cooperation(a)

The IAG may participate in joint bodies of the IUGG
and other scientific organizations, especially those belonging to the ISC.

31(b) The IAG shall initiate international cooperation in scientific work of international and interdisciplinary character. This includes the adequate participation in international programs and projects and the representation
at scientific congresses, symposia, etc., of organizations with related activities.
(c)

Representatives to international programs and projects
shall be appointed by the IAG Executive Committee
and shall inform the IAG Executive Committee on theactivities, on a biannual basis. The representatives
shall also prepare a report for presentation at the IAG
General Assembly.

(d) The IAG Components shall have close cooperation
with inter-governmental organizations responsible forservices and scientific products of particular interest to
the Association (e.g. BIPM, ISO, UNOOSA/ ICG).

31. Responsibilities of the IAG Council(a)

In addition to any other functions, powers and duties
provided in other Statutes and Bylaws, the IAG Council shall:(i)Examine questions of general scientific policy oradministration, and propose actions deemed necessary.
(ii) Elect the voting members of the IAG Executive
Committee, with the exception of the GGOS
Chair (Bylaw 15(d)) and the ICC Presidents, (Bylaw 17(b(i))).
(iii) Receive reports from the Secretary General andconsider for approval the decisions or actions
taken by the IAG Bureau and the IAG Executive
Committee since the last IAG Council meeting.
(iv) Set up and dissolve IAG components.
(v) Appoint the three members of the ad hoc (audit)
committee created for examining the finances of
the IAG, consider its recommendations and adopt
the final budget.
(vi) Consider proposals for changes in the IAG Statutes and Bylaws.
(vii) Decide on the venue of the next IAG Scientific
Assembly.
(viii) Approve the establishment of Inter-commission
Committees and IAG Projects.
(b) IAG Council meetings shall be convened by the IAG
President, and shall meet at least once during each IAG
General Assembly. The IAG Council may be convened at other times, normally coinciding with the
IAG Scientific Assembly according to Statute 13(b).

32

The Geodesist’s Handbook 2020

32. Responsibilities of the IAG Executive
Committee(a)

In addition to any other functions, powers and duties
provided in other Statutes and Bylaws, the IAG Executive Committee shall:(i)

Initiate actions and issue guidelines, as required,to guide the IAG towards the achievement of itsscientific objectives.
(ii) Fill vacancies occurring between IAG General
Assemblies, in accordance with the Statutes andBylaws.
(iii) Approve the internal structure of IAG components.
(iv) Make recommendations to the IAG Council onmatters of general policy of the IAG and on theimplementation of its objectives.
(v) Appoint Honorary Officers and Fellows of theIAG, upon the recommendation of the IAG
Bureau.
(vi) Appoint planning groups for Inter-commission
Committees and IAG Projects.
(vii) Establish Inter-commission Committees and IAG
Projects.
(viii) Appoint a Committee, known as the Cassinis
Committee, for reviewing and updating the IAG
Statutes and Bylaws when deemed necessary.
(ix) Confirm the Assistant Secretaries (if any) of theIAG.
(x) Confirm the links between Commissions andServices.
(xi) Approve the level of the membership fee.
(xii) Appoint the Vice President of each Commission,
the President of GGOS, and the President of each
ICC.
(xiii) Appoint representatives to external bodies.
(b) IAG Executive Committee meetings shall be convenedby the IAG President. It shall meet at IAG General
Assemblies and its members are expected to attend themeetings of the IAG Council, with voice but withoutvote. It shall also meet normally at least once a year,
especially one year before the IAG General Assembly,
in order to prepare the scientific agenda and timetableof the next IAG General Assembly.
(c)

At a meeting of the IAG Executive Committee, no member may be represented by any other person, except by
the corresponding Vice Presidents or Vice Chairs of
the IAG components represented in the Executive
Committee. In order that the deliberations of the IAG
Executive Committee shall be valid, a quorum of atleast half of its members must be present or represented.
(d) The agenda for each meeting of the IAG Executive
Committee shall be prepared by the IAG Bureau andsent to the members at least two months prior to themeeting.

33. Responsibilities of the IAG Bureau(a)

In addition to any other functions, powers and duties
provided in other Statutes and Bylaws, the IAG Bureau
shall:(i)

Draw up the agenda of the meetings of the IAG
Council and IAG Executive Committee and send
these to the members at least two months prior tothe meeting.
(ii) Ensure the adequate administration of the IAG.
(iii) Receive applications for individual memberships
and accept individuals as members of the IAG.
(iv) Recommend Honorary Officers and Fellows to
the IAG Executive Committee.
(b) The IAG Bureau shall normally meet before eachmeeting of the IAG Executive Committee.

34. Responsibilities of the President
In addition to any other functions, powers and duties provided in other IAG Statutes and Bylaws, the IAG President
shall:(a)Provide general leadership for the IAG in all matters.

(b) Convene and preside over the IAG General Assemblyand over all meetings of the IAG Council, IAG Executive Committee and IAG Bureau.
(c)Represent the IAG in IUGG meetings and forums.

(d) Represent the IAG in its dealing with national or international organizations or institutions.
(e)Submit a report to the IAG General Assembly on thescientific work of the IAG during their tenure.

35. Responsibilities of the Vice President
In addition to any other functions, powers and duties provided in other IAG Statutes and Bylaws, the IAG Vice President shall act on behalf of the IAG President whenever the
IAG President is not present or is unable to perform any of
the President’s duties, and shall perform such tasks as may
be assigned by the IAG President, the IAG Executive Committee or the IAG Council.

IAG Bylaws

36. Responsibilities of the Secretary General
In addition to any other functions, powers and duties provided in other IAG Statutes and Bylaws, the IAG Secretary
General shall:(a)(b) The IAG President, after taking advice from the IAG
Executive Committee, shall appoint a Nominating
Committee consisting of a Chair and three other members.
(c)Serve as secretary of the IAG General Assembly, theIAG Scientific Assembly, the IAG Council, the IAG
Executive Committee and the IAG Bureau; and arrange for meetings of these bodies, distribute promptly
the agenda and prepare and distribute the minutes of
all their meetings.

(b) Act as Director of the IAG Office.
(c)

33

Manage the affairs of the IAG, including finances asper Bylaw 42(b), attend to correspondence, and preserve the records.

(d) Circulate all appropriate information related to the
IAG.
(e)

Prepare the reports of the IAG’s activities.

(f)

Coordinate with the COB.

(g) Perform such other duties as may be assigned by the
IAG Bureau.

(d) The Adhering Bodies and the individual membershipshall be informed of these nominations at least fourmonths before the IAG General Assembly.
(e)During the following month further nominations canbe submitted by the Delegates of the Adhering Bodies.
Such additional nominations shall be in writing, shallbe supported by at least two members of the IAG
Council, and shall be submitted with resumes to the
Chair of the Nominating Committee.

(f)Nominations shall be checked against the eligibility
criteria in Bylaw 40 by the Nominating Committee. Ineligible nominations will not be accepted and themembers of the IAG Council who supported the nomination will be advised of the reason for its rejection.

(h) The function of the Secretary General is unpaid andonly expenses incurred in connection with the functions and duties may be reimbursed.

37. Assistant Secretaries(a)

The IAG Secretary General may be assisted by one ormore Assistant Secretaries.

(b) The position(s) of Assistant Secretary is unpaid andonly expenses incurred in connection with the functions and duties may be reimbursed.

38. IAG Office
To assist the IAG Secretary General, the IAG establishes the
IAG Office in the country in which the Secretary General
resides. The IAG Executive Committee negotiates logisticaland financial support with the host country or institution.

39. Procedure for Nomination and Electionof IAG Officers(a)Elections shall take place by electronic voting before
each IAG General Assembly and should be completed
at least two months before the assembly.

The Nominating Committee, after taking advice fromthe Delegates of the Adhering Bodies, the Officers,
Fellows, and Members of the IAG, shall normally propose at least two candidates for each position to be
filled by election of the IAG Council. Candidates shallbe asked to signify their acceptance of nomination andto prepare a short resume, outlining their position, research interests and activities relating to the IAG.

(g) Delegates shall be informed of these further eligible
nominations and resumes and of their supporters.
(h) The Chair of the Nominating Committee shall write to
all Services asking them for nominations from each
Service for the Service representatives on the IAG Executive Committee. The Nominating Committee shallrecommend a minimum of two nominees for each of
the Services’ three positions, considering appropriatescientific and geographic distribution. The procedure
for seeking additional nominations in subclause (e)above does not apply to these positions.
(i)

If candidates have been nominated for more than one
position, they will be asked prior to the election to
make a decision for which position they will allow
their name to stand.

(j)Elections shall be by electronic ballot. The winnermust receive an outright majority (number of votes being greater than the total combined votes of the othercandidates). If there are three or more candidates for aposition and no candidate has an outright majority,then the top two ranked candidates will be retained and

34

The Geodesist’s Handbook 2020a second round of votes conducted to elect the winner.
Ties will be broken by the IAG President’s vote.
(k) The Members-at-Large shall be elected in a subsequent round after the other members of the IAG Executive Committee have been elected, in order to fulfil
the condition of geographical, gender and organizational balance (see Statute 12a).

40. Eligibility & Terms of Office(a)

No person may hold more than one of the following
offices at the same time: IAG President, Vice President, Secretary General, IAG immediate Past President, President of a Commission, President of an Intercommission Committee, Chair of a Service, Presidentof GGOS, President of the COB, Executive Committee
Member-at-Large, or Chair of an IAG Project.

(b) A member of the IUGG Bureau or of the IUGG Finance Committee may not occupy the post of President, Vice President or Secretary General of the IAG.
(c)

The IAG President is elected for one period and may
not be immediately re-elected to the same office.

42. Finances
(a)

(i)

Contributions of IUGG Adhering Bodies ofwhich a portion, determined by the IUGG Council on recommendation of its Finance Committee,
is paid to the IAG by the IUGG Treasurer.
(ii) Sale of publications.
(iii) IAG Fund collected from individual contributions for specific purposes.
(iv) Membership fees.
(v) A portion of the registration fee charged at IAG
symposia.
(vi) Other sources, e.g. grants, interests, and funds remaining after a symposium.
(b) The Secretary General is responsible to the IAG Bureau and to the IAG Council for managing the funds inaccordance with the Statutes and Bylaws. The Secretary General alone shall be responsible for the day-today financial operations of the IAG.
(c)(d) The Vice President is elected for one period and may
not be re-elected to the same office.
(e)

The Secretary General is elected for one period initially. He/she may be re-elected for up to two additional periods.

41. Extraordinary Vacancies(a)Should the position of IAG President become vacantduring the period between two IAG General Assemblies, their duties and responsibilities devolve to theVice President until the closure of the next IAG General Assembly.

(b) Should the post of Secretary General become vacant,the IAG President shall arrange without delay for the
IAG Executive Committee to propose a replacement
and for the IAG Council to appoint a new Secretary
General so as to ensure the continuity of the work of
the IAG Office. This appointment has effect until the
closure of the next IAG General Assembly and shallnot be counted in the restriction of eligibility for reelection of the Secretary General under Bylaw 40(e).

The Finances of the IAG derive from the following
sources:

At each IAG General Assembly the budget proposal
for the next period shall be presented by the Secretary
General and submitted for approval to the IAG Council. The budget as approved by the IAG Council shallbe implemented by the Secretary General.

(d) During each IAG General Assembly, the IAG Council
shall examine all expenditures during the preceding
period to ensure that they were in accordance with theapproved budget. This examination shall be carried out
by an ad hoc (audit) committee appointed by the IAG
Council; see also Bylaw 31(a)(v).
(e)

In addition, the accounts shall be audited and shall thenbe reported to the IUGG Treasurer, as prescribed in
Article 20 of the IUGG Bylaws.

Rules for IAG Scientific Meetings

35

Rules for IAG Scientific Meetings

1. IAG scientific meetings are organized by IAG components (Commissions, Inter-commission Committee on
Theory, Services, and the Global Geodetic Observing
System) or IAG Sub-components (Sub-commissions, other Inter-commission Committees, Projects, Study
Groups, Working Groups). They may take place:a) during IAG General Assemblies, held in conjunction
with the IUGG General Assemblies,b) during IAG Scientific Assemblies, held in-between
successive General Assemblies, orc) at any time and place apart from the General or Scientific Assemblies.
2. During the General or Scientific Assemblies symposia
and other meetings are in general organized by IAG
components or sub-components. For specific topics
there may be joint symposia of several components or
sub-components under a convener appointed by the IAG
Executive Committee. The inclusion of scientific papers
for presentation at a General or Scientific Assembly is
decided by a Scientific Committee established by the
IAG Executive Committee.
3. At General Assemblies joint symposia covering topics
of two or more Associations within the Union and/or
other international scientific organizations may be organized. Though the IAG may act as convener or co-convener, these symposia follow the IUGG rules.
4. The IAG may participate also in joint symposia withother Associations at any other time outside of the General Assemblies, following the same procedures.
5. The IAG may sponsor symposia covering appropriate
topics of Geodesy at any time outside of the General or

Scientific Assemblies. It shall be called IAG sponsored
Symposium if the following conditions are fulfilled:
x The symposium has to be organized by at least one
component or two sub-components of the IAG.
x The host organization of the symposium must accept
a representative in the Scientific Organizing Committee (SOC) appointed by the IAG Executive Committee.
x The symposium must be open to all bonafide scientists in accordance with the ICSU rules.
x The proceedings of the symposium shall be published.
x If there is a registration fee, it must be reduced for
IAG members by at least 10%.
x Immediately after the end of the Symposium the chairperson of the Scientific Committee shall prepare a summary to be published in the IAG Newsletter.
6. Applications for approval to be designated IAG Symposium should be submitted to the Secretary General of the
IAG at least twelve months before the proposed date of
the Symposium. The following information must be provided in the application for approval:a) Title,b) Date and duration,c) Location,d) Sponsoring IAG (Sub-) components,e) Other co-sponsoring scientific organizations with letters enclosed,f) Suggested composition of the Scientific Organizing
Committee,g) Local Organizing Committee, host organization,
name and address of contact, etc.
h) Estimated number of participants,

36

The Geodesist’s Handbook 2020i) Financial support expected from sources other thanthe IAG,j) Names of the proposed editors of proceedings,k) Draft scientific program,l) A detailed account of why the proposed symposium
is useful and necessary at the time proposed, and its
relationship with other meetings.
7. Guidelines for the organization of the symposium:a) The Scientific Organizing Committee is responsible
for ensuring a high standard of scientific value of thesymposium. The chair of the Committee:
x invites participants after the symposium is approved by the IAG Executive Committee,
x invites contributions and sets a deadline for submissions of abstracts, andx informs the IAG Secretary General of all importantmatters pertaining to the symposium.
b) The Local Organizing Committee is responsible forthe smooth running of the symposium. It does not receive financial assistance from the IAG, with all thenecessary expenses being met by local funds or bycontributions from the participants. The requirementsof local organizations are generally as follows:
x providing meeting rooms suitable for the expected
number of participants,
x providing the facilities for oral and visual presentations,x provide adequate space and logistical support for
poster sessions (if any),x reproduction of participants’ document (if necessary), organize publication of proceedings or production of CD version,x sufficient secretarial and technical assistance,x undertake full responsibility for registration of participants, maintaining a web page, printing of brochures and programmes, etc.
x information on accommodation (hostels, hotels,
etc...), sent to the IAG Executive Committee for
acceptance, and to prospective participants,
x organizing receptions and excursions during a free
period within the meeting, or just before or after
the meeting.

8. The IAG Executive Committee shall recognize scientificmeetings other than symposia (workshops, etc.) organized by IAG (Sub-) Components, alone or jointlywith other international and national groups and bodies,at any time outside of the General Assemblies, if they
have been approved by the Executive Committee. The
Meeting may be announced as "International Meeting,organized by the ....... of IAG". It is not permitted to use
the term “IAG Symposium”.
9. The IAG may recognize scientific meetings, organizedby national bodies as important scientific events with benefit for the international geodetic community, andsponsor them if the meeting is open to all scientists according to the ISC Rules, and will be sponsored by atleast one IAG (Sub-) Component, and if the organizer
undertakes to maintain the expected standard for IAGSymposia.
These Meetings may be announced as "International
Meeting, organized by ....., sponsored by IAG". It is not
permitted to use the term “IAG Symposium”. Sponsorship by the IAG means only official recognition anddoes not imply financial support by the IAG. The IAG
may appoint an official representative to that meeting.
The IAG expects that, in the event that proceedings are
published, the Proceedings will be prepared by the localorganizers and published within 6-8 months after the endof the meeting.
Applications for sponsorship should be submitted to
the IAG Secretary General not later than 12 months before the intended date of the meeting.
10. In its decision whether to approve and/or sponsor ascientific meeting, the IAG Executive Committee takes
into account the need for a balanced selection of meetings, a representative coverage of subjects, and a good
geographical distribution. The IAG wishes to avoid duplication of symposia or meetings, and to discourage symposia or meetings with overlapping themes that are heldwith too high a frequency.
The IAG Secretary General shall publish a calendarof IAG Symposia and other scientific meetings organized or sponsored by IAG components or sub-components in the IAG Newsletter, in the Journal of Geodesy, and on the IAG Website.

Rules for IAG Scientific Meetings

37

Rules for the IAG Levallois Medal

PurposeThe Levallois Medal was established by the International
Association of Geodesy in 1979 to honour Jean-Jacques Levallois, and to recognize his outstanding contribution to the
IAG, particularly his long service as Secretary General,
1960-1975.
The award of the Medal will be made in recognition of distinguished service to the Association, and/or to the scienceof geodesy in general.
The Medal is normally awarded at four year intervals, on theoccasion of the General Assemblies of the International

Association of Geodesy and International Union of Geodesy
and Geophysics; but the award may be omitted if it is considered that there is no candidature of sufficient merit, andan additional award may be made at any time if justified by
exceptional circumstances.

Nomination and Election
A nomination for the award shall be made by an ad hoc committee consisting of the Honorary Presidents and must be
confirmed by the IAG Executive Committee. The ad hoc
committee shall prepare a citation, suitable for publication,
setting out the grounds for the proposed award before theGeneral Assembly.

38

The Geodesist’s Handbook 2020

Rules for the IAG Guy Bomford Prize

PurposeThe Guy Bomford Prize is awarded by the International Association of Geodesy for outstanding contribution to Geodesy. It
was established by the British National Committee for Geodesy and Geophysics to mark the contributions to geodesyof Brigadier G. Bomford, formerly of the University of Oxford
and a Past President of the International Association of Geodesy. It has been inaugurated by the IAG in 1975. The
Prize is normally awarded at intervals of four years on theoccasion of the General Assembly of the IAG held concurrently with the General Assembly of the International Union
for Geodesy and Geophysics. The following rules for theaward of the Guy Bomford Prize may be altered by the IAG
Executive Committee if a majority of its voting members
sees a necessity to do so.

Eligibility
The Guy Bomford Prize is awarded to a young scientist or
to a team of young scientists for outstanding theoretical orapplied contributions to geodetic studies particularly in thefour year period preceding the General Assembly at which
the award is made. Scientists who are under 40 years of age
on December, 31, of the year preceding the Assembly at
which the award is made, are eligible for the award.

Nominations
Nominations will be invited by the IAG Bureau from all National Committees of IUGG member countries at least one
year ahead of the General Assembly. Each committee canmake one nomination which has not necessarily to be fromits own country. The deadline for nominations will normallybe six months before the next General Assembly and will be
explicitly started in the letter of invitation.

Nominations must be accompanied by:
x The full name, address, age, academic and/or professional qualifications and position of the candidates andthe name of the National Committee making the nomination.
x An outline of the reasons for the nomination including ageneral summary of the career and scientific achievement of the candidate.
x A review of recent achievements of the candidates which
would merit the award, including references to key papers, published, alone or jointly, during the preceding
four-year period.
x A curriculum vitae, publication list, and copies of up to
two key papers which are considered to justify candidature.
x The name and address of two referees who can be consulted.

Selection procedure
A selection committee will be appointed consisting of thepresidents of the IAG commissions and two other members
to be appointed by the IAG Bureau. Based on the material
submitted by the National committees each member of theselection committee will rank the nominations and select the candidate to be awarded the Guy Bomford prize. The decision (notthe detailed ranking) will be communicated to all National
Committees and to the selected candidate. The prize may be
withheld if, in the opinion of the selection committee, there is no
sufficiently qualified candidate available.

Presentation of award
The Prize shall be presented to the successful candidate at
the opening Plenary Session of the IAG Assembly. He or
she shall be invited to deliver a lecture during the course of
the IAG Assembly.

Rules for IAG Scientific Meetings

39

Rules for the IAG Young Authors Award

PurposeNomination and Selection

The award is to draw attention to important contributions by
young scientists in the Journal of Geodesy and to foster excellence in scientific writing.

For each two-year period the Editor-in-Chief of the Journalof Geodesy will propose a minimum of three candidates forthe award. In addition, proposals made by at least three Fellows or Associates will be considered for the competition.
The voting members of the IAG Executive Committee will
make the final selection. It will be based on the importanceof the scientific contribution, which may be either theoretical or practical, and on the quality of the presentation. The
name and picture of the award winner and a short biography
will be published in Journal of Geodesy.

Eligibility
The applicant must be 35 years of age or younger when submitting the paper for the competition. The paper must present his or her own research, and must have been publishedin the two annual volumes of the Journal of Geodesy preceding either the IAG General Assembly or the Scientific
Assembly. Although multiple author papers will be considered, single author papers will be given more weight in theselection process.

Award
The award consists of a certificate and a cheque of US $ 1000.
Presentation of the awards will be made at each IAG General
Assembly and each Scientific Assembly. Up to two awards
will be presented on each occasion for the two-year period
corresponding to the annual volumes specified above.

Procedure
Each year the conditions for the award will be announced in
the Journal of Geodesy. Nominations should be sent to theSecretary General of the IAG, giving name, address, and ageof the author (at date of submission), the title of the paperon which nomination is based, and a brief justification.
Nominations must be received by March 1 of the year inwhich either an IAG General Assembly or an IAG Scientific
Assembly takes place.

40

The Geodesist’s Handbook 2020

Rules for the IAG Travel Awards

PurposeApplication procedure

The award is established to assist young scientists from IAG
member countries to present results of their research at IAG
meetings (assemblies, symposia, workshops, etc.).

Applicants shall send their application at least threemonths before the meeting to the IAG Secretary General,
iag.office@nls.fi.

Eligibility

The application must contain:
x Full name of the Applicant, address and e-mail address
x Institution and degree/position (e.g. University XX, PhD
Student)
x Date of birthx IAG meeting name, city, country, datex Title, authors, and abstract of the paper to be presentedx A letter of acceptance of the presentation by the organising committee (if available, otherwise it has to be submitted as soon as it is available)
x Travel budget and sources of additional fundingx Name(s) of supporting person(s); the letter(s) of support(either from an IAG Fellow or from two Associates)
should be sent separately by the supporter(s).
By sending the application, the applicant agree that his/herdata are stored internally in the IAG records. Data are used
only for Award-related purposes.

The applicant must present results of his or her research at
the meeting and must be 35 years of age or less at the dateof the application. The application must be supported by atleast one IAG Fellow or two Associates.

Type of awards
There are two awards, one for meetings in the applicant’s
own country, and the other for meetings outside the applicant’s country. The first is called IAG National TravelAward and has a maximum financial value of 750 Euros. It
is available for meetings in developing countries. The second is called IAG International Travel Award and has amaximum financial support of 1500 Euros. The amounts canoccasionally be adjusted by the IAG Executive Committee.
It was adjusted last in 2020.

Additional benefits
The IAG will encourage the organizers of the meetings towaive the registration fees for all IAG Travel award winners.

Selection procedure and criteria
Selection of applicants and the amount granted will be doneby the IAG Bureau. It will be based on the paper to be presented, the letter(s) of support, and the applicant’s ability toactually attend the meeting. Priority will be given to candidates from developing countries. IAG Secretary General
will agree with winners the details of the payment. Normally
it cannot be paid before the meeting.

IAG Membership

41

IAG FundThe IAG Fund aims at supporting specific IAG activities.
Its primary goals are:x to provide travel support for young scientists to attend
IAG Symposia and workshops,
x to assist in the organisation of IAG workshops in developing countries, andx to provide an annual IAG Best Publication Award foryoung scientists.
The fund was established by the IAG Executive Committee
at its meeting in Columbus, Ohio, 1992, see Bulletin Géodésique, Vol. 68, pp. 41-42, 1994.
Contributors are divided in 3 groups:
x Presidents Club (cumulative contributions of US $ 1000and more or equivalent in EUR)x Special contributors (annual contributors of US $ 100 …
US $ 1000 or equivalent in EUR)
x Contributors (annual contributions of less than US$ 100 or equivalent in EUR)
The rules for the IAG Young Authors Award and for the
IAG Travel Award for young scientists are given in a separate section of the Geodesist’s Handbook. The application
forms can be found at the IAG Website.

How to Donate
In connection of the membership fee: In the membership fee
form there is a specific place for donations. The donation
can be of any amount; however, in case of donations US $100 (or equivalent in EUR) or more, please send additionally a notice to the IAG Secretary General.
Donations paid separately: The payment can be made using
the same form as the donations in connection of the membership fee. Please, contact IAG Secretary General in advance.
The membership application / donations form can be foundat the IAG Website https://www.iag-aig.org. Direct link:
https://www.iag-aig.org/doc/IAG_Membership_Application_Form.pdf.

42

The Geodesist’s Handbook 2020

IAG Membership

Individuals engaged in geodesy, can become individual
members of the IAG on application and payment of themembership fee. Applications for individual membershipare submitted to the IAG Secretary General.
Benefits of membership include:
x Reduction in the individual subscription rate to the Journal of Geodesy.
x The right to participate in the IAG election process bothas a nominator and a nominee.
x Upon application, correspondent membership in a Subcommission or Study Group of choice.
x Reduction in the registration fee for IAG meetings
The membership fee per annum is set by the IAG Executive
Committee. In individual cases, the Secretary General may
consider a discount or full remission of membership fees onapplication by the member. There are two specific cases
mentioned on the membership fee form:x Student membership: Students in Universities/Colleges
will have annual free membership of IAG. They must
submit University/College certificate separately every
year to the IAG Secretary General to get the benefit.
x Retired members: Retired people shall send a request to
the Secretary General for getting the exemption.

How to pay
The application form and instructions for the payment canbe found at the IAG web page. The payment can be madeeither by a bank transfer or with a credit card.
The payment can be for one calendar year or four years.
To minimize possible transfer fees, more than one membership fee can be paid at the same time. In that case, the list ofnames/addresses shall be sent separately to the Secretary
General.
After reception of the payment, the certificate and receipt of the payment will be sent by e-mail to the address
given by the member.
In case of any issues or questions, please send the request to the Secretary General.
The membership application form can be found at the
IAG Website https://www.iag-aig.org. Direct link:
https://www.iag-aig.org/doc/IAG_Membership_Application_Form.pdf.

IAG Presidential address

43

The XXVII IUGG General Assembly, Montreal, Canada, 2019
IAG Presidential Address
Harald Schuh
GFZ German Research Centre for Geosciences,
Telegrafenberg, 14473 Potsdam, Germany
schuh@gfz-potsdam.deDear Guests and Colleagues, dear Ladies and Gentlemen,
I welcome you to the IAG General Assembly, taking placein Montreal on the occasion of the 27th General Assemblyof the International Union of Geodesy and Geophysics(IUGG). Chairing this Opening Ceremony is one of my last
responsibilities as outgoing IAG President. For IAG, thequadrennial 2015-2019 was a really dynamic and fruitfulperiod. Together with many individuals of the various IAG
Commissions, Services, and other components, we havepushed quite a number of new developments and IAG is in
a very sound condition today. In Prague four years ago,
Chris Rizos, then the outgoing President, gave a comprehensive overview presentation about the IAG, its internal structure and tasks. It is published in the Geodesist’s Handbook
2016 and I encourage you to look there again. My report
here I will make rather short and will just remind you of themost important highlights and innovations since 2015.
For the year 2016, internally, I would like to mention ourforthcoming in the strategic planning process; in the outer,
political sphere, the establishment of the United Nations
Subcommittee on Geodesy was a real breakthrough for
global geodesy. Both developments will help us to shape future IAG matters much more efficiently.
The IAG Executive Committee met for its third meetingin the term 2015-2019 at the GFZ German Research Centre
for Geosciences in Potsdam, Germany, on April 25, 2016.
At this meeting, the IAG final structure 2015-2019 of Commissions 1 – 4, of the Inter-Commission Committee on Theory, and of GGOS was decided. On the next day, an IAG
Strategic Planning Retreat was conducted. It was mainly
aimed at an IAG SWOT analysis and the following discussion to reveal the current state of the Association. SWOT
stands for strengths, weaknesses, opportunities, and threats,
and a great number of all of them were identified during theretreat. The retreat which was chaired by IAG Past President

Gerhard Beutler took place in a very open-minded and intensive atmosphere.
Based on the retreat material, a guiding document wasformulated that in turn was the basis for the draft strategy
document to be discussed and approved at the next EC meeting in Vienna on April 28, 2017, and to be presented to the
public, in particular to the IAG Council delegates, at the
IAG Scientific Assembly in Kobe in July 2017. This longstrategic planning process shall be completed here in Montreal were the IAG Council delegates will be requested forapproval of the final version of the strategy document thatcan be found on https://office.iag-aig.org/iag-publicationsreports-position-papers o IAG Strategy 2019.
During the first week of August 2016, the United Nations Global Geospatial Information Management (UNGGIM) sixth session took place in New York which I attended representing the IAG. At this UN-GGIM conference,
the UN Committee of Experts on Global Geospatial Information Management endorsed the GGRF (Global Geodetic
Reference Frame) Roadmap and decided to establish a permanent Subcommittee on Geodesy. The suggestion to elevate the Working Group's mandate through the establishment of a UN-GGIM Subcommittee on Geodesy was put
forward by New Zealand and the proposal was supported byseveral member states. The IAG welcomed and unreservedly appreciated the establishment of a United Nations Subcommittee on Geodesy. This advancement will augment the
impacts of geodesy on the political level as well as its visibility in society. IAG and its Global Geodetic Observing
System (GGOS) as promoting geodetic science and coordinating the international geodetic services will strongly support the new Subcommittee whenever necessary and wherever possible.
At the UN-GGIM sixth session in New York, the member states did also endorse the Roadmap for the Global Ge-

44

odetic Reference Frame as a principle based briefing document for national governments. The Roadmap aims to enhance the GGRF and make it more sustainable. Today, the
UN-GGIM Subcommittee on Geodesy consists of about 40
member states and five international and national organizations: besides IAG, they are the International Federation ofSurveyors (FIG), SIRGAS Geocentric Reference System for
the Americas, the World Health Organization (WHO), andNASA.
IAG developed a Position Paper that contains a description of the Global Geodetic Reference Frame and was
adopted by the IAG Executive Committee in April 2016.
The purpose of this document is a brief description of the
GGRF key components as a realization of the Global Geodetic Reference System (GGRS) and it forms the basis for acommon understanding of the GGRF. It thus outlines the
IAG’s perspective of what the GGRF is, and how it is realized through the contributions of the IAG components.
The Position Paper on the UN-GGIM Global Geodetic
Reference Frame (GGRF) adopted by the IAG Executive
Committee can be downloaded from https://office.iagaig.org/iag-publications-reports-position-papers o Description of the Global Geodetic Reference Frame (GGRF)
by the IAG.
In November 2016, at a meeting with the Springer publishing editor responsible for the IAG Series an important
improvement regarding the IAG Symposia Series publishedby Springer was decided: The Series will be published immediately as eBook, i.e. go online. The procedure is a peer
review as before, but each article is being published onlinea few days after the acceptance by the IAG Editor-in-Chief
Jeff Freymueller.
IAG’s top highlight of the year 2017 was the organization and effective running of the IAG/IASPEI Joint Scientific Assembly in Kobe, Japan, from July 30 through August
4, 2017. The business meetings during the IAG Scientific
Assembly in Kobe comprised in particular three IAG Executive Committee Meetings, one IAG Bureau Meeting, andone IAG Council Meeting, and all went very efficiently. The
EC’s decision to establish new sub-components of IAG
Commissions as inter-Association commissions, namely on
Volcano-geodesy, Seismo-geodesy, and Cryosphere geodesy, and to establish the two new inter-Commission projectsof IAG (on New technologies in geodesy and on Marine geodesy) were very timely.
Of the many IAG highlights of the year 2018, I would
like to mention here only a tiny selection, in which I had thehonor to participate: These are the successful launch of theGerman-American satellite mission GRACE-FO (Gravity
Recovery and Climate Experiment Follow-On) aboard aSpaceX Falcon 9 rocket from the Vandenberg Air Force
Base (California) on May 22, 2018, the inauguration of the

The Geodesist’s Handbook 2020

new twin VLBI telescopes at Ny-Ålesund, Svalbard, Norway, on June 6th, 2018, the UN-GGIM conference weekwith several splinter meetings about the GGRF in New Yorkin August 2018, and two very efficient IAG Executive Committee meetings, the first one in Vienna, Austria, during the
EGU General Assembly on April 13, 2018 and the second
one in Washington D.C., USA, during the AGU Fall Meeting on December 10, 2018.
At the Eighth Session of the United Nations Committeeof Experts on Global Geospatial Information Management(UN-GGIM) held at the United Nations Headquarters in
New York from 1 to 3 August 2018, the Roadmap for the
Global Geodetic Reference Frame for Sustainable Development Implementation Plan presented by the UN-GGIM Subcommittee on Geodesy was discussed. IAG is participating
as an observer in all meetings and related activities of UNGGIM. At the session, IAG was represented by myself andMichael Pearlman, Chair of the GGOS Bureau of Networks
and Observations. The IAG delegation made a well-noted
intervention for the GGRF agenda item, comprising the following points:
The International Association of Geodesy commends
the work done by the UN GGIM Subcommittee on Geodesy, and emphasizes that the Roadmap Implementation
Plan is an important building block to determining asustainable Global Geodetic Reference Frame.
Together with its geodetic services, IAG encourages
modernization of geodetic infrastructure, as well as development of Core Observatories, especially in developing regions.
IAG notes that there is a clear need for strengthened
intergovernmental mechanisms in support of global geodesy, and notes with appreciation the Subcommittee on
Geodesy’s efforts to provide this through a Convention
or other possible governance mechanisms mentioned in
the Position Paper on Governance.
IAG encourages the establishment of funding mechanisms for global geodesy, in order to support geodetic
infrastructure and education in developing Member
States. IAG further notes that such funding will provide
a means to strengthen the GGRF overall, as well as help
realize the geodetic contributions to the UN Sustainable
Development Goals and Sendai Framework for Disaster
Risk Reduction.
Four years ago, at our General Assembly in Prague, I
presented to you in my inaugural speech as IAG President
the vision, or call it dream or crazy idea, to establish a World
Geodetic Organization (WGO) to implement geodetic infrastructure all over the world where it is really needed. Thatvision is not a dream anymore: In 2019, a Global Geodetic
Center of Excellence (GGCE) is in planning process underIAG Presidential address

UN-GGIM. The proposal of creating a GGCE under the auspices of the United Nations receives strong support. With
this element, the Subcommittee on Geodesy has reached a
new milestone on the road towards a sustainable GGRF.
Concerning the IAG strategic planning process, the EC
finalized the IAG Strategy Document in 2018 as planned.
Several of the recommendations and action items postulated
in the Strategy Document had already been realized by
2018. The EC decided, for instance, to establish planninggroups of the new bodies within the IAG and also as interassociation entities, all to be established at IUGG2019 here
in Montreal.
In the following, I will summarize some developmentsin IAG since 2015. These new entities in IAG were established (new inter-association joint (Sub-) commissions, IAG
Projects, or IAG Intercommission Committees (ICC):
x with IASPEI (“Seismo-geodesy”), SC 3.5 from IAG
x with IAVCEI (“Volcano-geodesy”), SC 3.2 from IAG
x with IACS (“Cryosphere geodesy”), SC 3.4 from IAG
x new ICC on “Geodesy for climate research”, approved(Chair: A. Eicker)
x new ICC on “Marine geodesy“, approved (Chair: Yangxi
Yang)
x new IAG Project on “Novel sensors and quantum technology in geodesy”, approved (Chair: J. Müller),
the latter dealing with new technologies in geodesy such as
quantum technology, optical clocks, and atom gravimeters.
Regarding IAG Services, the International Geodynamic andEarth Tide Service (IGETS) was established and is in fulloperation since 2017 and the revitalization of the International Altimetry Service is under construction. The International Gravity Field Service (IGFS) has now its own, new
Product Center on “Combination for Time-variable Gravity
field solutions” which will certainly elevate the role and importance of the IGFS. The International Service for the Geoid (ISG) was renamed and had set up a new agreement withIAG.
As the observing system of the IAG, GGOS serves aunique and critically important combination of roles centering upon advocacy, integration, and international relations.
In the last four years, GGOS has also experienced a dynamic
development: In 2016, the new internal structure was confirmed, the new Coordinating Office was established at
BEV, Austria, and the Terms of Reference were updated. In
2017, the new Focus Area 4, Geodetic Space Weather Monitoring, was enacted and Michael Schmidt, TU Munich appointed as Chair, the Bureau of Networks & Observations
and the Bureau of Products & Standards began operations
and Richard Gross took over GGOS chairmanship from
Hansjörg Kutterer.
A few words on IAG publications. The ranking of the
Journal of Geodesy with Jürgen Kusche as editor-in-chief

45

increased significantly (IF 4.633 (2017) and 4.528 (2018)).
The journal receives more than 300 submissions per year;
the acceptance rate is 34%. In 2019, a Continuous Article
Publishing (CAP) was decided.
The latest volumes of the IAG Symposia Series are Vol.
147, International Symposium on Earth and Environmental
Sciences for Future Generations (2018), Vol. 148, International Symposium on Gravity, Geoid and Height Systems(2018), and Vol. 149, Joint IAG/IASPEI Scientific Assembly, Kobe, Japan, 2017 (2019) and another big step forward
is that the IAG Symposia Series will change to open accessstarting with the upcoming 27th General Assembly.
IAG reports, annual and quadrennial reports, monthly
IAG Newsletters, position papers, outreach documents thatcan be found on the IAG homepage at https://www.iagaig.org are a vivid prove about the various activities of IAG
components in the last four years.
The Geodesist’s Handbook https://link.springer.com/ article/10.1007/s00190-016-0948-z provides information on
the IAG history, statutes, bylaws, rules, and membership, a
Report of the General Assembly 2015, and structure andprogram descriptions of the period 2015-2019.
Before coming to the end I have to provide the sad information that during the last quadrennial, the following former IAG officers and outstanding geodesists passed away:
2015: Suriya Tatevian, Russia, Graciela Font, Argentina,
Hermann Seeger, Germany, Camil Gemael, Brazil,
John Wahr, USA
2016: Heinz Henneberg, Venezuela, Alexander Kopaev,
Russia2017: Klaus Linkwitz, Germany, Dieter Lelgemann, Germany, Olumuyiwa Adebekun, Nigeria, Barbara Kolaczek, Poland, Bernard Guinot, France, József Závoti, Hungary
2018: Marcin Barlik, Poland, Michel Louis, France, Hermann Mälzer, Germany, Yoshihide Kozai, Japan,
Jean Dickey, USA, Jean Kovalevsky, France, Mikhail Prilepin, Russia
I am coming now to the end of my talk, and of my termas IAG President. I have truly enjoyed doing this work forthe past four years. I wish to thank all members of the outgoing IAG Executive Committee, and the many other colleagues who make vital contributions to the IAG Commissions, Services, and other components. Your support, yourbrightness, your commitment makes IAG the lively andlearning organization that is counted on and that is listenedto.
I wish the new Executive Committee that was elected byballot prior to this General Assembly lots of success andstamina for the future! Thank you.

46

The Geodesist’s Handbook 2020

Levallois Medal Laudation for Christoph Reigber
Chris Rizos1

The Levallois Medal was established in 1979 to honour
Jean-Jacques Levallois for his long service as General
Secretary of the International Association of Geodesy (IAG)
from 1960 to 1975. It is awarded on the occasion of the IAG
General Assembly to a distinguished geodesist "inrecognition of distinguished service to the Association
and/or to the science of geodesy in general".
An ad hoc committee of past presidents of the IAG has
recommended to award the Medal at the 2019 IAG General
Assembly to Emeritus Professor Christoph Reigber, for hissustained service and leadership over several decades to the
IAG and to geodesy in general.

Professor Harald Schuh handing over the Levallois Medal toProfessor Christoph Reigber at GFZ (Photo: Markus Bradke,
GFZ)
1

University of New South Wales, Sydney, Australia

Christoph Reigber was born in 1939 in Breslau, in today’s Poland. He completed his Diploma in Surveying andGeodesy in 1965 at the Technical University Munich. In
1969 Christoph completed his doctoral thesis at TUM, andobtained his Habilitation in 1974, also from the TUM. His
subsequent university career included Professor in the Department of Astronomical and Physical Geodesy TUM
1982-1992, and Professor at the Institute of Earth and Environmental Sciences, Potsdam University, 1993-2004. He
was made Emeritus Professor upon his retirement in 2004.
Christoph Reigber’s most significant contributions to the
IAG and to geodetic science are best exemplified by his
extraordinary, and far-sighted leadership of numerous
projects and several institutions, over a period spanning four
decades. It is not possible to mention many of these in this
Laudation, hence just a few will be highlighted.
Christoph was appointed Director of the Department“Theoretical Geodesy” at the Deutsches Geodetisches
Forschungs Institut (DGFI – in English, the German
Geodetic Research Institute) in Munich, in 1980, a position
he held until 1992. During this period Christoph had two
major influences on the activities and contributions of DGFI.
The first was an increased focus on the technology and earthscience applications of satellite geodesy. The second was adramatically increased engagement with ESA (and otherspace agencies) in projects, being a co-investigator or
principal investigator, undertaking theoretical studies insupport of new geodetic technologies, as well as direct
participation in satellite missions. These projects included
CI for NASA’s Laser Geodynamics Program, the spaceborne laser study SPALT, several POPSAT system studies,
PRARE tracking technology studies, being an analysis
centre for MERIT and MEDLAS campaigns, several gravity
field mission studies, PI on the ERS-1 mission, to name themost significant. This strong leadership in promoting

Levallois Medalsatellite geodesy, and a focus on developing cutting edge
geodetic technologies and promoting new satellite missions,have been the dominant contributions of Christoph Reigber
to geodesy, from his early days at DGFI, and subsequently
at the GFZ.
Arguably Christoph’s most important contributions to the
IAG, and to geodesy in general, were made during his directorship at the Deutsches GeoForchungsZentrum (GFZ –German Research Centre for Geosciences). The GFZ is Germany’s most significant investment in the geosciences in thelatter half of the 20th century. Christoph was one of thehandful of scientists with the courage and vision to imagine
the total revitalization of the geosciences on Telegrafenberg,
in Potsdam, shortly after the reunification of Germany. This
included a new science-focused geodesy institute, the Department “Geodesy and Remote Sensing”, one of fivefounding departments of the GFZ. This department could
boast a heritage going back to the legendary Central Bureau
established by Johann Jacob Baeyer following the first“General Conference of the Representatives to the Central
European Arc Measurement” held in Berlin in 1864. Thisdate and event is reckoned to be the foundation of the IAG,
and it was fitting that we celebrated the 150th anniversary of
the founding of the IAG in 2013 at the GFZ. This department
was even located in the same building as the original bureau.
Christoph was Director of the department from 1992 until
his retirement at the end of 2004.
While at the GFZ Christoph was able to launch a numberof initiatives, whose significance is still considerable. One
was to establish a GPS Analysis Centre at the GFZ that
became one of the first ACs for the IGS when it was formallylaunched as an IAG service on 1 January 1994. Christoph
was also Project Manager for the GFZ-1 geodynamic
satellite mission. Perhaps his most far-reaching
contributions to geodetic science have been in the field ofsatellite gravity missions. Christoph was Project Manager of
the German CHAMP mission from 1994-2000, and later
Project Director of the CHAMP mission exploitation phase.
He was Co-Principal Investigator for the US-German
GRACE (Gravity Recovery and Climate Experiment)
mission 1997-2007. Today the GFZ continues this vital rolein the GRACE-FO mission.
Christoph Reigber retired from the GFZ in November
2004 not because he’d grown too old to continue playing aleadership role in international geodesy, but due to German
Federal Government regulations on public service retirement at 65 years of age. During his whole career Christophadvocated for, and practiced, international coordination andcollaboration to further the science and applications of modern geodesy. His role in the IAG spanned from being a member of numerous Working Groups, to being President of the
CSTG (International Coordination of Space Techniques for47

Geodesy & Geodynamics), President of the IAG’s Commission 2 (“Advanced Space Technology”), Chair of the Directing Board of the IERS (International Earth Rotation & Reference Systems Service) 1995-2000, Chairman of the Governing Board of the IGS 1999-2002, and Chairman of the
IAG’s GGOS (Global Geodetic Observing System) pilot
project 2003-2005.
Christoph also was a member of many committees, councils and working groups beyond the IAG, all of which reflect
his interest in promoting space technology for the benefit ofscience and society. Several are worthy of mention. Christoph was a Member of the Board of Trustees of the Wernervon Braun Foundation for Space Science Advancement
2002-2008; Member of the Scientific Advisory Board for theSpace Research Institute of the Austrian Academy of
Sciences 2008-2017; and Vice-chair and Member of the Scientific Advisory Board of the Central Asian Institute of Applied Geosciences in Bishkek, Kyrgyzstan 2011-2018.
Christoph’s contributions have won him many honours
and awards, which include the CNES "Médaille de Bronze"(1977), the Alexander von Humboldt Prize for Scientific
Cooperation between Germany and France (1985), theNASA Group Achievement Award (Crustal Dynamics Project) (1986), Fellow of IAG (1991), ERS-1 Award of ESA(1992), AGU Fellow (1994), Honorary Doctorate (Dr.-Ing.
E.h.), University Bonn (1998), the Vening Meinesz Medalof the European Geophysical Society (2002), Honorary Professorship of Wuhan University, China (2003), the DLR
Werner von Braun Medal (2003), the NASA Earth Explorers
Program Office GRACE Mission Award (2006), theWilliam T. Pecora Award for the GRACE Team (2007), theState Award of the Republic of Kyrgyzstan (2008), theGrand Prix of the French Air & Space Academy (2010),
Member of Academia Europaea (2014), and the William
Nordberg Medal of COSPAR (2018), inclusive the renamingof asteroid 6314 to REIGBER.
In summary, Christoph Reigber has made an enormous
contribution to the IAG, and geodesy in general, making him
a most worthy recipient of the Levallois Medal. On a
personal note, I have known Christoph Reigber since 1981,
when I was awarded an Alexander von Humboldt
Fellowship to undertake postdoctoral studies at DGFI. This
was a life-changing experience, and I subsequently took asabbatical at the GFZ in 1995. I am humbled by what he hasachieved in his professional life, but I also treasure mypersonal friendship with Christoph, his wife Nunu, and their
two children Astrid and Andreas. I am honoured to be asked
to prepare this Laudation.

48

The Geodesist’s Handbook 2020

Guy Bomford Prize Lecture
Advancing the theoretical apparatus of physical geodesy
Michal Šprlák1

Mister1President, Mister Secretary General, Ladies andGentlemen, I am very pleased and honoured. The other day,I looked at the list of the Guy Bomford Prize awardees.
Honestly, I feel like a hobbit who has just arrived in the
Rivendell and there are the wise Elves all around him. I will
express my gratitude at the end of this talk. Now, I would
like to tell you a few words about the advancements of thetheoretical apparatus of physical geodesy. This is the topic,
which I have been very passionate about and also quite
productive in terms of research outputs, and brought me hereon this stage tonight. Vast majority of this research has been
performed at the University of West Bohemia in the Czech
Republic together with my colleagues Pavel Novák andMartin Pitoňák. Currently, however, I am employed at the
University of Newcastle in Australia.
You certainly know that gravitational field reveals
important properties of our planet and it definitely deserves
to be one of the main pillars of geodesy. Enormous amountof gravitational data has been collected by various sensors in
the past decades. This has mainly stimulated for various
revolutionary applications in geosciences. But those who are
more theoretically gifted have also been working hard. They
have improved the existing concepts and have even gone
way further than allowed by the available datasets. In my
opinion, we have experienced a renaissance in thetheoretical developments in the past few years. My
colleagues and I have contributed to these advancements bysolving interesting theoretical problems. For simplicity, I
divided our research contributions into three categories andit is now my intention to briefly describe each of them.
The first group is about a more complete picture of thethird-order gravitational tensor. I came with this idea moreor less out of curiosity. No wonder that I encountered strong
School of Engineering, Faculty of Engineering and Built Environment,
University of Newcastle, University Drive, Callaghan, NSW 2308,
Australia;

1

resistance and doubts. Fortunately, I could find papers andpatents reporting actual measurements of the third-order
potential derivatives that saved my initial goal. On the lefthand side (see Fig. 1), you can see the mathematicalexpression of the third-order gravitational tensor in thegradient and component forms. On the right-hand side, you
can observe its visualisation as a cube with 27 components.
Apparently, the third-order gravitational tensor is a complex
mathematical object.

Figure 1: The third-order gravitational tensor
We discovered the secrets of this tensor by looking at its
basic properties, such as symmetries of the components, andby constructing the differential operators (Šprlák and Novák
2015). We then found how the gravitational potential could
be determined from the third-order tensor components bysolving the spherical gravitational curvature boundary-value
problem (Šprlák and Novák 2016). We continued further
with harmonic analysis and even investigated what could beachieved when observing the third-order potential
derivatives by a satellite (Šprlák et al. 2016). Later on, my
younger colleagues dealt with more practical aspects, suchas non-singular harmonic synthesis (Hamáčková et al. 2016)
Currently at: NTIS – New Technologies for the Information Society,
Faculty of Applied Sciences, University of West Bohemia, Technická 8,
306 14 Plzeň, Czech Republic

Guy Bomford Prize Lectureor the integral inversion of these quantities (Pitoňák et al.
2017). In this way, we collected necessary bits and pieces
and built the first systematic methodology for the third-order
gravitational tensor, just like it had been done decades ago,
but for lower-rank gravitational tensors.
The second group of theoretical problems are those on
integral transformations. An excellent example of an integral
transformation is the famous Stokes integral, which every
geodesist and even surveyor knows. It nicely illustrates how
gravity anomalies are converted to geoid undulations. It also
represents analytical solution of the third boundary-value
problem. For real world applications, we directly calculate
this integral or solve its inverse.
There are many quantities that we would like totransform from one to another (see Fig. 2). These are thedisturbing potential on the left, and its first, second, andthird-order derivatives towards right. The quantities that we
integrate over are on the lower level at the reference sphereof radius R. The computed quantities are at the upper levelat the radius r. Imaginary line connecting one box from thelower level with one box at the upper level could define an
existing integral transformation.
Many geodesists have added lines to this schematic andso have we in a collection of seven research papers publishedin Journal of Geodesy. These publications are listed in thebox on the left (see Fig. 2). The different colours help us to
identify individual lines in the diagram and thus the related
quantities. In total, we derived impressive 98 integral
transformations. But we were not obsessed only withequations. We investigated spatial behaviour of the integral
kernels that leads to some practical implications, such as
efficient numerical calculation, the effect of the distantzones, or suitability for inverse problems. Also, almost every
integral formula was implemented in a computer programand validated in a closed-loop simulation.
Finally, our effort culminated in a review paper
published in Earth-Science Reviews (Novák et al. 2017).
Here, we summarised mutual integral formulas among the
disturbing gravitational potential, its first, second, and thirdorder derivatives including eventually all references fromthe geodetic literature. Thus, the diagram in Fig. 2 has been
completed.
So far, we have silently assumed spherical geometry.
Once you solve numerous tasks using this approximation,
you get a little bored and the next challenging step is toconsider its spheroidal equivalent. This is the third part of
my talk. We use a spheroid instead of a sphere, because it
more closely fits the shape and the gravitational field of ourplanet. On the other hand, we lose the comfort of theazimuthal symmetry. In other words, every direction issomewhat different on the spheroidal surface and we cannot
simply introduce the polar coordinates that are so efficient49

on the sphere. In addition, spheroidal counterparts of theaddition theorem and orthogonality relationships either do
not exist or are defined differently from the familiar
spherical case.
With the help of great findings by geodetic forefathers,
we could handle these complications and expand the existingclass of spheroidal integral transformations. Firstly, weformulated a mathematical model for inverting gravimetricand gradiometric measurements to the gravitational potential(Novák and Šprlák 2018). Secondly, we applied two
orthogonalisation approaches to solve the spheroidal verticaland horizontal boundary-value problems (Šprlák andTangamrongsub 2018). There are other interesting tasks to
be solved, thus the spheroidal story is not over yet.
Because we addressed all three parts, it is now time toconclude. You may have seen that we have significantly
extended the theoretical apparatus of physical geodesy.
These advancements are not restricted to geodesy and alsoenhance the more general framework of the potential theory.
The new mathematical formulations represent the basis forthe gravitational field modelling and we have applied someof them in several applied studies. We are confident that the
new complex mathematical models can be implemented anddescribe the reality very well. The presented work has beena part of activities within the Joint Study Group called“Integral equations of potential theory for continuation andtransformation of classical and new gravitational
observables” of the Inter-Commission Committee on Theory
under the umbrella of the International Association of
Geodesy. For the first time, I have acted as a chairman of
this study group that has been a very pleasant experience inaddition to deriving dozens of equations.

Figure 2: Schematic of the derived integral transformations

50

Acknowledgements
I would like to thank the Czech and Italian National
Committees for the nomination and the IAG Guy Bomford
Prize Committee for awarding me this prize. I would like toexpress my sincere gratitude to Pavel Novák, Bjørn
Ragnvald Pettersen, Christian Gerlach, Carla Braitenberg,
Marcel Mojzeš, and Juraj Janák, who have been mysupportive mentors. I thank numerous friends and colleagues
from the Slovak University of Technology in Bratislava,
Slovakia, Research Institute of Geodesy and Cartography in
Bratislava, Slovakia, Norwegian University of Life Sciencesin Ås, Norway, University of West Bohemia in Plzeň, Czech
Republic, University of Newcastle in Callaghan, Australia,
and elsewhere for productive collaboration and uncountablediscussions about geodesy and other subjects. I am sincerely
grateful to my family and my girlfriend Andrea for theirconstant mental support.
References:
Hamáčková E, Šprlák M, Pitoňák M, Novák P (2016) NonSingular expressions for the spherical harmonic
synthesis of gravitational curvatures in a local Northoriented reference frame. Comput Geosci 88: 152-162
Novák P, Šprlák M, Tenzer R, Pitoňák M (2017) Integral
formulas for transformation of potential field parametersin geosciences. Earth-Sci Rev 164: 208-231
Novák P, Šprlák M (2018) Spheroidal integral equations for
geodetic inversion of geopotential gradients. Surv inGeophys 39(2): 245-270Pitoňák M, Šprlák M, Tenzer R (2017) Possibilities of
inversion of satellite third-order gravitational tensor onto
gravity anomalies: a case study for Central Europe.
Geophys J Int 209(2): 799-812
Šprlák M, Novák P (2014a) Integral transformations ofdeflections of the vertical onto satellite-to-satellite
tracking and gradiometric data. J Geod 88(7): 643-657
Šprlák M, Novák P (2014b) Integral transformations ofgradiometric data onto GRACE type of observable. J
Geod 88(4): 377-390
Šprlák M, Sebera J, Vaľko M, Novák P (2014) Sphericalintegral formulas for upward/downward continuation ofgravitational gradients onto gravitational gradients. J
Geod 88(2): 179-197

The Geodesist’s Handbook 2020Šprlák M, Hamáčková E, Novák P (2015) Alternative
validation method of satellite gradiometric data by
integral transform of satellite altimetry data. J Geod
89(8): 757-773
Šprlák M, Novák P (2015) Integral formulas for computing
a third-order gravitational tensor from volumetric massdensity, disturbing gravitational potential, gravity
anomaly and gravity disturbance. J Geod 89(2): 141-157
Šprlák M, Novák P (2016) Spherical gravitational curvatureboundary-value problem. J Geod 90(8): 727-739
Šprlák M, Novák P, Pitoňák M (2016) Spherical harmonic
analysis of gravitational curvatures and its implications
for future satellite missions. Surv Geophys 37(3): 681700
Šprlák M, Novák P (2017) Spherical integral transforms of
second-order gravitational tensor components onto thirdorder gravitational tensor components. J Geod 91(2):167-194Šprlák M, Tangdamrongsub N (2018) Vertical andhorizontal spheroidal boundary-value problems. J Geod
92(7): 811-826

Michal Šprlák

Young Authors Award51

IAG Young Authors Award 2015
Citation for Xingxing Li

The IAG Young Authors Award
2015 is presented to Dr.
Xingxing Li for his paper
Accuracy and reliability ofmulti-GNSS real-time precise
positioning: GPS, GLONASS,
BeiDou, and Galileo. The work
was published in the Journal of
Geodesy, 2015, Volume 89,
Issue 6, pp.607-635.
The lead author, Dr. Xingxing Li, has focused on highprecision GNSS and Geosciences’ applications for morethan ten years. He started his Geodesy studies at Wuhan
University in 2004. In 2010, he was hired by the German
Research Center for Geosciences (GFZ) as a project scientist
for the project “Online-GNSS service with scalable accuracy
for precise positioning and navigation”. In 2015, hedefended his doctoral thesis on “Real-time high rate GNSS
techniques for earthquake monitoring and early warning” at
Technische Universität Berlin.
He has already received several awards. In 2012, he won
the ION paper Award and he won the GFZ “FriedrichRobert-Helmert” Award in 2016. In 2017, he won the EGU
Outstanding Young Scientist Award. Dr. Li has an excellent
publication record with more than 30 papers in leading ISI
journals of his research field during this period and inmajority as first author. Currently, he is the Chair of the IAG
working group “Biases in Multi-GNSS data processing” andthe co-Chair of the EGU session “High-Precision GNSS
Algorithms and Applications in Geosciences”.
The award-winning paper presents a four-system
integrated model with GPS, GLONASS, BeiDou andGalileo for real-time precise orbit determination, clock
estimation and positioning. Meanwhile, an efficient multiGNSS real-time precise positioning service system isdesigned and demonstrated. A rigorous multi-GNSS

analysis is performed to achieve the best possible
consistency by processing the observations from different
GNSS together in one common parameter estimation
procedure. For satellite orbit, the overlap (two adjacent
three-day solutions) RMS values of estimated Galileo orbits
are 2.1, 3.7 and 7.8 cm, respectively in radial, cross andalong components. The corresponding overlap RMS values
for BeiDou IGSO satellites are 2.5, 3.3, and 4.4 cm in thethree components, respectively. The RMS values of BeiDou
MEO satellites are 3.4, 4.3 and 11.3 cm in the radial, cross,and along directions, respectively.
The GEO satellites have comparable performancecompared with IGSO and MEO satellites in the radial andcross directions, but the accuracy in the along component
decreases to about 1 m due to the rather weak geometry. For
satellite clock, the RMS values of clock differences between
the real-time and batch-processed solutions for GPS
satellites are about 0.10 ns, while the RMS values of
BeiDou, Galileo and GLONASS satellites are 0.13, 0.13 and0.14 ns, respectively. Both satellite orbits and clocks canachieve an accuracy of cm level in real time. It is worth
noting that the errors of orbits and clocks can becompensated by each other when they are used together atuser end. For precise point positioning (PPP), it can be used
to validate the capability of real-time precise positioning
service based on the predicted orbits and real-time estimatedclocks.
The multi-GNSS PPP shows faster convergence andhigher accuracy in all three components than single-system
PPP. After adding BeiDou, Galileo and GLONASS systems
to the standard GPS-only processing, the convergence timeis decreased by 70 % and the positioning accuracy isimproved by 25 %. The real-time positioning capabilities of
the combined systems under different elevation cutoffs isdifferent. Its positioning accuracy hardly decreases and an
accuracy of several centimeters is still achievable in52

horizontal components even with a 40° elevation cutoff. At
30° and 40° elevation cutoffs, the availability rates of GPSonly solutions drop dramatically to only around 70 and 40%,
respectively. However, multi-GNSS PPP shows excellent
results.
In a word, the fusion of multiple GNSS significantly
increases the number of observed satellites, optimizes the

The Geodesist’s Handbook 2020

spatial observation geometry at a site and improves
convergence, accuracy, continuity and reliability ofpositioning solutions. Moreover, the performance of multiGNSS integration at high elevation cutoffs will significantly
increase its applications in constrained environments, suchas in urban canyons, open pits and mountainous areas.

Young Authors Award53

IAG Young Authors Award 2016
Citation for Olga Didova

The IAG Young AuthorAward 2016 is given to Olga
Didova for her paper An
approach for estimating timevariable rates from geodetic
time series, which has been
published in the Journal of
Geodesy (2016) 90:12071221. The paper is coauthored by Brian Gunter,
Riccardo Riva, Roland Klees,and Lutz Roese-Koerner representing 3 different scientificinstitutions.
The original article considers the problem of estimating
trends in mass loss over Antarctica from GRACE and GPS
time series in the presence of inter-annual and seasonalvariability. The traditional approach parameterizes the timeseries using a bias, trend, and harmonic constituents, which
are considered as being deterministic. The main weakness of
this approach is that the distinct components of mass loss (asthose of many other geophysical processes) are notdeterministic, but fluctuate in time around some reference
values.
The idea to model them stochastically using a state spacemodel and estimating the state parameters using a Kalmanfilter was introduced to the geodetic community in a paper
by Davis et al (2012), though state space analysis is a wellestablished methodology for treating a wide range ofproblems in the analysis of econometric time series as
documented in the excellent books by Harvey (1989) andDurbin and Koopman (2012). Davis et al (2012) assumed
that the parameters, which determine the stochastic
movements of the state variables (“hyperparameters”), are
known. Moreover, little is known in econometric literature
about the robust estimation of hyperparameters, which is a
non-convex optimization problem.

In her paper, Olga considers the hyperparameters as
unknowns and estimates them using Maximum Likelihood.
The optimization problem is solved using a gradient-based
local solver, which can deal with non-convex problems. To
increase the probability of finding the global minimum, Olgasuggests to define a random set of uniformly distributed
starting values and selects the starting values that provides asolution which has the smallest log likelihood objectivefunction. To improve the chance of finding the global
minimum, Olga suggests several measures to limit theparameter search space. Moreover, she introduces inequality
constraints on some of the hyperparameters, and suggests a
method, involving among others a likelihood ratio test andan algorithm for determining the degrees of freedom for thistest, to verify whether the constraints are supported by thedata.
The suggested methodology is applied to the analysis ofreal GRACE and GPS time series, both representing verticaldeformations due to elastic and visco-elastic responses of thesolid Earth to surface loading. The data analysis reveals thatcompared to the classical deterministic model using leastsquares, the proposed methodology provides more reliable
trend estimates, because it accounts for any long-term
evolution in the time series and avoids any contaminationfrom seasonal variability.
The proposed methodology may become a standard toolin time series analysis of geodetic data, in particular whenlong time series comprising years of data are involved.
Olga Didova studied Geodesy and Geoinformation at the
University of Bonn, Germany. She received her Bachelor of
Science in 2009 and her Master of Science in 2011 under
supervision of Karl Heinz Ilk and Juergen Kusche,respectively. Between 2012 and 2016, she was a PhD
candidate at Delft University of Technology in the
Department of Geoscience and Remote Sensing working on“Separating GIA and ice mass change signals in Antarctica

54

using satellite data”. She will defend her PhD thesis at Delft
University of Technology in fall 2017. Since March 2017,
she is a Postdoctoral Fellow at the University of Bonn andinvolved in the assimilation of remote sensing data in ahydrological model.

The Geodesist’s Handbook 2020

References:
JL Davis, BP Wernicke, ME Tamisiea (2012), On seasonal
signals in geodetic time series. J Geophys Res 117(B01403).
AC Harvey (1989), Forecasting, structural time seriesmodels and the Kalman filter. Cambridge University Press,
Cambridge.
J Durbin, SJ Koopman (2012), Time series analysis by state
space methods. Oxford University Press, Oxford.

Young Authors Award

55

Young Authors Award 2017
Citation for Minghui Xu

The IAG Young Authors Award
2017 is presented to Dr. Minghui Xu for his paper The impactsof source structure on geodetic
parameters demonstrated by theradio source 3C371. The work
was published in the Journal of
Geodesy, 2017, Volume 91,
pp.767-781.
The leading author, Dr.
Minghui Xu, has focused on high-precision very long
baseline interferomery (VLBI) studies for ten years. He
started his Geodesy studies in Shanghai Astronomical
Observatory (SHAO) in 2009. In 2013, he got the German
DAAD scholarship to join the German Research Center for
Geosciences (GFZ) VLBI group for his PhD. He defensed
his doctoral thesis on Determining the acceleration of Solar
System’s Barycenter by VLBI at SHAO in 2015. He wasawarded as a Mercator Fellow in Germany in 2017.
Currently, he is the research fellow in Aalto University
Metsahovi Observtory and is working on mitigating source
structure effects on broadband VLBI (VGOS) observations
in order to achieve the goal of VGOS, the mm accuracy ofstation positions on global scales.
The award-winning paper investigates closure quantities
measured by very-long-baseline interferometry (VLBI)
observations that are independent of instrumental andpropagation instabilities and antenna gain factors, but are
sensitive to source structure. A new method is proposed to
calculate a structure index based on the median values ofclosure quantities rather than the brightness distribution of asource. The results are comparable to structure indices basedon imaging observations at other epochs and demonstrate
the flexibility of deriving structure indices from exactly thesame observations as used for geodetic analysis and without
imaging analysis.
A three-component model for the structure of source
3C371 is developed by model-fitting closure phases. It
provides a real case of tracing how the structure effectidentified by closure phases in the same observations as thedelay observables affects the geodetic analysis, andinvestigating which geodetic parameters are corrupted towhat extent by the structure effect. Using the resulting
structure correction based on the three-component model ofsource 3C371, two solutions, with and without correcting
the structure effect, are made. With corrections, the overallrms of this source is reduced by 1 ps, and the impacts of thestructure effect introduced by this single source are up to 1.4
mm on station positions and up to 4.4 microarcseconds on
Earth orientation parameters. This study is considered as astarting point for handling the source structure effect on
geodetic VLBI from geodetic sessions themselves.

56

The Geodesist’s Handbook 2020

Young Authors Award 2018
Citation for Athina Peidou

Granted for the article: On
the feasibility of using
satellite gravity observations
for detecting large-scalesolid mass transfer events,
Journal of Geodesy, Vol. 92,
pages 517-528 by Athina
Peidou, Georgia Fotopoulos
and Spiros Pagiatakis. The
focus of the paper is to assess
the feasibility of using
dedicated satellite gravity
missions (specifically GRACE) to detect large-scale solid
mass transfer events (e.g. landslides).
Dr. Athina Peidou holds an undergraduate degree fromthe School of Rural and Surveying Engineering at Aristotle
University of Thessaloniki graduating at the top of her class.
She pursued Master’s studies in the Geophysics andGeodesy Lab of the Department of Geological Sciences andGeological Engineering at Queen’s University, Kingston,
Canada. For her PhD studies, Athina joined Prof Spiros
Pagiatakis’s Space Geodesy Lab in the Department of Earthand Space Science and Engineering at York University,
Toronto, Canada. She defended her doctoral thesis in 2020
which was awarded with Canada’s General Governor’s Gold
Medal. Recently, she joined NASA’s Jet Propulsion
Laboratory as a postdoctoral research fellow to work on
GRACE and GRACE-FO missions.
The main objective of the award-winning paper was todetermine the feasibility of detecting landslides andearthquakes using models derived from GRACE mission
measurements. This was assessed through a sensitivity
analysis of GRACE- gravity field solutions in conjunction
with simulated case studies of large-scale solid masstransfers. The simulations focused on determining the effectof various-scale geohazards on the gravity field as measured
by GRACE, and this was achieved by means of 3-D forward
modelling and 2-D wavelet multi-resolution analysis. Realevents studied include catchment-scale events such as theHeart Mountain Landslide (50km x 70km) and the Tohoku
earthquake triggered submarine landslide (40km x 20km) as
well as regional scale events such as the Agulhas slump(750km x 106 km) and the Grand Banks slide (1000km x25km). Results indicate the spatial extent (and volume) of
mass transfer events that can be detected using GRACE
measurements. Additionally, the study proceeds withsensitivity analysis of the impact of the altitude of thesatellite on the resolvability of a mass transfer, assuming an
inherent noise level of approximately 30 microgals (thisincludes satellite noise and aliasing effects). Overall, thisstudy improves our understanding on mass movement
processes and their direct impact on the gravity field as
mapped by the dedicated missions.
Due to limited information on oceanic environments,
most submarine landslides remain unknown while thedetrimental effects of landslides on societies are often
documented in the news. With satellite gravity
measurements being continuously available, detection ofsubmarine events could be feasible; therefore this research
constitutes an important contribution towards detecting the
Earth’s dynamic processes in submarine environments.

Report of the IAG Secretary General

57

Report of the IAG Secretary General
Hermann Drewes

According to the IAG Bylaws, the Secretary General serves
as the secretary of the General Assembly, the Scientific Assembly, the Council, the Executive Committee and the Bureau. He arranges for meetings of these bodies, distributes
promptly the agenda, and prepares and distributes theminutes of all their meetings. He acts as the Director of the
IAG Office and manages the affairs of the Association including the finances. He continuously attends to the IAG
correspondence, preserves the records and circulates all appropriate information related to the Association. He has toprepare the reports of the Association's activities and to perform other duties as may be assigned by the Bureau, theCouncil and the Executive Committee.

1. Administrative work
Administrative works with the greatest efforts in the period
2015-2019 were the preparation and execution of the joint
IAG/IASPEI Scientific Assembly 2017 and the IUGG General Assembly 2019. Other major actions include the editionof the Geodesist’s Handbook 2016 and the IAG Reports
Vol. 40 and Vol. 41 (Travaux de l’AIG 2015–2017 and2015–2019), the organisation of eight meetings of the IAG
Executive Committee, and the sponsoring of 44 IAG scientific meetings. The management of financial affairs applies
to all IAG accountings, including the Journal of Geodesy
and IAG Symposia Series, three IUGG sponsored Projects
and Symposia, and the handling of the individual IAG membership. 61 travel awards were granted to young scientists
for participation in IAG symposia, and 72 awards for assisting the IUGG General Assembly 2019.
1.1 Scientific Assembly
The IAG Scientific Assembly was organised together with
the International Association of Seismology and Physics ofthe Earth’s Interior (IASPEI) in Kobe, Japan, July 30 to August 4, 2017. The full assembly reports are published athttps://www.iag-aig.org/doc/5ceea88fa6e85.pdf and at
http://www.iugg.org/publications/ejournals/IUGGej1712.pdf.
1107 attendees from 65 countries registered and presented
1119 lectures and posters in 43 symposia, 9 of these as joint
IAG-IASPEI Symposia. The symposium proceedings were
published in the IAG Symposia Series, Vol. 149.
1.2 General Assembly
The IAG held its General Assembly, as usual, together with
the IUGG General Assembly in Montreal, Canada, July 8 to18, 2019. The general report is published at
http://www.iugg.org/publications/ejournals/IUGGej1909.pdf
and the IAG part in the present volume. 3952 participants
registered, 437 of them with IAG priority. There were 234
Symposia and 18 Workshops with 4580 presentations, 469
in IAG Symposia. IAG organised one Union Symposium, 7
Joint Symposia with other associations, 6 IAG Symposia,
and 20 business meetings. In addition, IAG co-sponsored 8
Union Symposia and 15 Joint Symposia. Kosuke Heki gavea Union lecture on behalf of the IAG. 72 travel awards for
IAG participants were granted from IUGG and IAG.
1.3 Council
The IAG Council consists of the delegates appointed by the
Adhering Bodies of the IUGG member countries and is responsible for governance, strategic policy and direction of
the IAG. The Secretary General continuously informs themon actual IAG activities and events. The Council meetings
at the Scientific Assembly 2017 in Kobe, Japan, and the
IUGG General Assembly 2019 in Montreal, Canada, wereprepared and minutes were published (the latter in this volume). The national delegates’ list is regularly updated incontact with the IUGG Secretariat.

58

1.4 IAG Executive Committee (EC)The duties of the Executive Committee are to further the objectives of the IAG through effective coordination and theformulation of general policies. Eight EC meetings were organised during the legislative period 2015 to 2019 (Prague,
Czech Republic, July 2015; San Francisco, USA, December
2015; Potsdam, Germany, April 2016; Vienna, Austria,
April 2017 and April 2018; Kobe, Japan, July 2017; Washington, USA, December 2018; and Montreal, Canada, July2019). The minutes were distributed, and meeting summaries were published in the IAG Newsletter, the Journal of Geodesy (the latest in this volume) and on the IAG Websites(https://office.iag-aig.org/meeting-summaries).
1.5 IAG Bureau
The IAG Bureau consists of the IAG President, the Vice
President and the Secretary General. It meets normally before each EC meeting and holds regular teleconferences toadminister the day-to-day affairs. The President and the Secretary General participated in the meetings of the IUGG Executive Committee and represented the IAG at international
meetings of allied scientific bodies.
1.6 IAG Office
The IAG Office was located from 2007 to 2019 at theDeutsches Geodätisches Forschungsinstitut, Technische
Universität München, Germany. A Website for internal IAG
affairs was maintained at https://iag.dgfi.tum.de.
1.7 Publications
The IAG Secretary General manages the financial affairs of
the Journal of Geodesy and IAG Symposia Series. The following volumes of the latter were published 2015-2019:
x 142: VIII Hotine-Marussi Symposium Rome 2013;
x 143: IAG Scientific Assembly, Potsdam 2013;
x 144: 3rd IGFS Symposium, Shanghai 2014;
x 145: GENAH Symposium, Matsushima 2014;
x 146: REFAG Symposium, Luxembourg 2014;
x 147: IAG General Assembly, Prague 2015;
x 148: Gravity, Geoid, Height Systems, Thessaloniki 2016;
x 149: IAG Scientific Assembly, Kobe 2017.
The biannual IAG Reports are published in the Travaux del’AIG 2017 (Vol. 40) and 2019 (Vol. 41) and may be foundat https://iag.dgfi.tum.de. Annual IAG reports are publishedin the IUGG Annual Reports and Yearbooks.
1.8 Individual Membership
The IAG has at present about 180 paying individual members and 40 free student members. The membership fee(USD 50 per year or USD 150 per 4 years) is collected by

The Geodesist’s Handbook 2020

credit cards or bank transfer. The membership list is regularly updated in cooperation with the Communication andOutreach Branch for distributing the IAG Newsletter. The
actual lists are provided to the Organizing Committees of
IAG Symposia in order to reduce the registration fee for
IAG members according to the IAG Bylaws.
1.9 IAG Awards
There are three IAG Awards for meritorious work of IAG
associates, normally presented at the IAG Scientific andGeneral Assemblies (see https://www.iag-aig.org/awards):
x Levallois Medal for distinguished service to the IAG
and/or to the science of geodesy in general. In 2019, it
was granted to Christoph Reigber, Germany.
x Guy Bomford Prize for outstanding contributions of ayoung scientist to geodetic studies. In 2019, it was
granted to Michal Šprlák, Australia.
x Young Authors Awards for the best publications in the
Journal of Geodesy. For 2017 it was granted to Minghui
Xu, China, and for 2018 to Athina Peidou, Canada.

2. IAG Symposia, Workshops and Schools
Important meetings of the IAG components and meetingssponsored by the IAG from July 2015 to June 2019 were:x International DORIS Service (IDS) Analysis Working
Group Meeting, Greenbelt, MD, USA, 15-16 Oct. 2015.
x International Laser Ranging Service (ILRS) Analysis
Working Group Meeting, Matera, Italy, 24 Oct. 2015.
x International Laser Ranging Service (ILRS) Technical
Workshop 2015, Matera, Italy, 26-30 Oct. 2015.
x Latin American Reference System (SIRGAS) Symposium, Santo Domingo, Dominican Republic, 18-20 Nov.
2015.
x 9th International Symposium on Mobile Mapping Technology (MMT2015), Sydney, Australia, 9-11 Dec. 2015.
x IGS Workshop, Sydney, Australia, Feb. 15-19, 2016;
x 9th IVS General Meeting, Ekudeni, Johannesburg,
South Africa, March 13-17, 2016;
x 3rd Joint Symposium on Deformation Monitoring, Vienna, Austria, March 30 – April 1, 2016;
x 4th IAG Symposium “Terrestrial gravimetry: Static andmobile measurements”, Saint Petersburg, Russia, April
12-15, 2016;
x European Reference Frame Symposium (EUREF 2016),
San Sebastian, Spain, May, 25-27, 2016;
x 18th Geodynamics and Earth Tide Symposium 2016,
Trieste, Italy, June 5-9, 2016;
x IAU/IAG/IERS Symposium “Geodesy, Astronomy andGeophysics in Earth Rotation (GAGER2016)”, Wuhan,
Hubei, China, July 18-23, 2016;

Report of the IAG Secretary Generalx International Symposium on Geodesy and Geodynamics(ISGG2016), Tianjin, China, July 22-26, 2016;
x 1st International Conference on GNSS+ (ICG+2016),
Shanghai, China, July 27-30, 2016;x IAG Commission 4 “Positioning and Applications” Symposium, Wroclaw, Poland, Sep. 4-7, 2016;
x 18th General Assembly of WEGENER “Understanding
Earth deformation at plate boundaries”, Ponta Delgada,
Azores, Portugal, Sep. 12-15, 2016;
x 1st Joint Commission 2 and IGFS Meeting, International
Symposium on Gravity, Geoid and Height Systems 2016
(GGHS2016), Thessaloniki, Greece, Sep. 19-23, 2016;
x First International Workshop on VLBI Observations of
Near-field Targets, Bonn, Germany, October 5-6, 2016;
x 20th International Workshop on Laser Ranging, Potsdam, Germany, Oct. 9-14, 2016;
x GGOS Days, Cambridge, MA, USA, Oct. 24-28, 2016;
x IDS Workshop, La Rochelle, France, Oct. 31 – Nov. 1,
2016;
x Reference Frame for South and Central America Symposium (SIRGAS2016), Quito, Ecuador, Nov. 16-18,
2016;
x 1st International Symposium - Applied Geomatics andGeospatial Solutions, Rosario, Argentina, April 3-7,2017;
x 9th IVS Technical Operations Workshop, Westford,
MA, USA, April 30 – May 4, 2017;
x EUREF 2017 Symposium, Wroclaw, Poland, May 1719, 2017;
x DORIS Analysis Working Group Meeting, London, UK,
May 22-24, 2017;x 21st Meeting of the Consultative Committee for Timeand Frequency, Sèvres, France, June 6-9, 2017;
x 1st IUGG Symposium on Planetary Science, Berlin,
Germany, July 3-5, 2017;
x IGS Workshop 2017, University of Paris-Diderot,
France, July 3-7, 2017;
x IAG/GGOS/IERS Unified Analysis Workshop, ParisDiderot, France, July 10-12, 2017;x 2017 GNSS Tsunami Early Warning System Workshop,
Sendai, Japan, July 25-27, 2017;
x IAG and IASPEI Joint Scientific Assembly, Kobe, Japan, July 30 – Aug. 4, 2017.
x Asia-Pacific Space Geodynamics Symposium, Shanghai, China, Aug. 15-18, 2017;x Workshop on Glacial Isostatic Adjustment and Elastic
Deformation, Reykjavik, Iceland, Sep. 5-7, 2017;
x 3rd COSPAR Symposium “Small Satellites for Space
Research”, Jesu, South Korea, Sep. 18-19, 2017;
x IAG Workshop “Satellite Geodesy for Climate Studies”,
Bonn, Germany, Sep. 19-21, 2017;59

x Journées des Systèmes de Référence et de la Rotation Terrestre, Paris, France, Sep. 25-27, 2017;
x International Review Workshop on Satellite Altimetry
Cal/Val Activities and Applications, Chania, Greece,
April 23-26, 2018;
x EUREF Symposium 2018, Amsterdam, Netherlands,
May 30 – June 01, 2018;
x 10th IVS General Meeting, Longyearbyen, Spitsbergen,
Norway, June 3-8, 2018;
x 1st Workshop of the International Geodynamics andEarth Tide Service (IGETS), Potsdam, Germany, June
18-20, 2018;
x IX Hotine-Marussi Symposium on Mathematical Geodesy, Rome, Italy, June 18-22, 2018;
x 42nd COSPAR Scientific Assembly incl. IAG Commission 1 Symposium, July 14-22, 2018;
x IAG Commission 1 Symposium Reference Frames forApplications in Geosciences (REFAG2018), Pasadena,
CA, USA, July 15-21, 2018;
x 8th UN-GGIM Session, New York, USA, Aug. 1-3,
2018;
x XXXth General Assembly of the IAU, Vienna, Austria;
Aug. 20-31, 2018;
x 19th General Assembly of WEGENER, Grenoble,
France, Sep. 10-13, 2018;
x Gravity, Geoid and Height Systems (GGHS 2) Symposium, Copenhagen, Denmark, Sep. 17-21, 2018;
x International DORIS Service (IDS) Workshop, Ponta
Delgada, Azores Portugal, Sep. 24-26, 2018;
x GGOS Days 2018, Tsukuba, Japan, October 2-4, 2018;
x SIRGAS Symposium 2018, Aguascalientes, Mexico,
Oct. 9-12, 2018;
x SIRGAS Workshop on Vertical Reference System,
Mexico, Oct. 15-17, 2018;
x IGS 2018 Workshop, Wuhan, China, Oct. 29 – Nov. 2,
2018;
x International Workshop on GNSS Ionosphere(IWGI2018), Shanghai, China, Nov. 4-6, 2018;x 21st Workshop on Laser Ranging, Canberra, Australia,
Nov. 5-9, 2018.
x 24th Meeting of the European VLBI Group for Geodesy
and Astronomy (EVGA) and 18th IVS Analysis Workshop, Las Palmas, Gran Canaria, Spain, March 14-20,
2019;
x IGS 2019 Analysis Workshop, Potsdam, Germany,
April 15-17, 2019;
x 10th IVS Technical Operations Workshop, Westford,
MA, USA, May 5-9, 2018;
x 4th Joint International Symposium on Deformation
Monitoring, Athens, Greece, May 15-17, 2019;
x EUREF 2019 Symposium, Tallinn, Estonia, May 22-24,
2019.

60

The Geodesist’s Handbook 2020

The following IAG Schools were sponsored:x VII SIRGAS School on Reference Systems, Santo Domingo, Dominican Republic, 16-17 Nov. 2015.
x 2nd IVS Training School on VLBI for Geodesy and Astrometry, Hartebeesthoek, South Africa, March 9 – 12,2016;

x Geoid School, Ulaanbaatar, Mongolia, June 6-10, 2016;
x SIRGAS School on Vertical Reference Systems, Quito,
Ecuador, Nov. 21-25, 2016;
x 3rd IVS Training School on VLBI for Geodesy and Astrometry, Las Palmas, Gran Canaria, Spain, March 1420, 2019.

3. Finances
The financial report includes the result 2015-2018 (Table 1), the budget 2019-2023 (Table 2) and the report of the Audit
Committee (Appendix A).
Table 1: Financial Report 2015-2018
Expenditures

Result 2015 - 2018 in EUR
Receipts

11.2
11.5
11.6
12.2
13.1
14.2
16.2
18.6

Administration Equipment
Administration Travel
Administration Representation
Publications
Assemblies, Organisation
Symposia, Travel Awards
Prizes, Young Authors Awards
Credit Card Service

1.381,71
11.973,25
9.129,02
2.992,50
9.634,20
58.892,35
4.070,00
406,13

15
1
2
3.2
4.1
4.2

IUGG Allocation
Membership Fee
Other Grants
Journal of Geodesy
IAG FundGeoid School

110.326,00
17.619,93
9.202,04
20.000,00
173,0434,33

19

Total Expenditures
SurplusTotal

98.479,16
58.876,18
157.355,34

6

Total Receipts

157.355,34

Total

157.355,34

AssetsBalance 2018 in EUR
Liabilities

Staatoberkasse/TUM 31.12.2014
Deficit 2015
Surplus 2016
Surplus 2017
Surplus 2018
Total

135.726,15-4.941,21
23.344,64
27.731,23
12.741,52
194.602,33

Net Capital 31.12.2018
Surplus / Deficit

194.602,33
0,00

Total

194.602,33

Net Capital 2018 in EUR
Open 1.1.2015
SurplusTotal

135.726,15
58.876,18
194.602,33

Report of the IAG Secretary General

61

Table 2: Budget 2019-2022

11.2
11.5
11.6
12.1
12.2
13.1
13.2
14.2
16.2
18.6
19

Budget for the period 1.1.2019 - 31.12.2022 in EUR
Expenditures
Receipts
Administration, Equipment
3.000
15
IUGG Allocation
Administration, Travel
25.0001
Membership Fee
Administration, Representation
10.0002
Other Grants
Publications, Outreach
7.000
3
Sales of Publications
Publications, IAG Symposia Series
40.000
3.1
IAG Symposia Series
Assemblies, Organization
20.000
3.2
Journal of Geodesy
Assemblies, Travel
10.0004
Miscellaneous
Symposia, Travel Awards
60.000
4.1
IAG FundPrizes, Young Authors Awards
4.000
4.2
Geoid School Lecture Notes
Credit Card Service
1.000
Total Expenditures
180.000
6
Total Receipts
Deficit
Total
180.000
Total

Balance 31.12.2022
Total

Net Capital 2022 in EUR
135.000
Open 1.1.2019
Deficit135.000
Total

Appendix A
IAG Audit Committee Report
Committee members appointed by the IAG Council:
Denizar Blitzkow, Jonas Agren, Matt Amos
1.

The Audit Committee performed the following functions:
1.1 Noted that the accounts had previously been reviewed
by the Financial Department of the Technical University of Munich (TUM). The account is in Euros.
1.2 Examined the receipts and bank statements for the period 2015 – 2018. Checked the balance reports presented by the Secretary General, Hermann Drewes.
1.3 Examined expenditure to ensure conformity with the2015 – 2018 budget as approved by the General Assembly in Melbourne, 2011.
1.4 Examined the budget proposed for the period 2019 –
2023.
2.

The Audit Committee makes the following comments on the IAG accounts:
2.1 The accounts were well presented and the expenditures
supported by receipts and bank statements.
2.2 During this period, the IAG made an unplanned surplusof €58,876.00 in contrast to the €50,000 deficit that was

80.00015.0004.000
020.0001.000
0120.000
60.000180.000

195.000-60.000
135.000

forecast. The variance of €108,876.18 is large considering the total turnover was €255,834.50.
2.3 The 2015-2018 surplus increases the IAG reserve from€135.726,00 to €194.602,00.
2.4 The budget for the next period (2014 – 2023) forecasts
a deficit of €60,000.
3.

The Audit Committee makes the following recommendations:
3.1 The budget is appropriate and the forecast deficit is prudent to reduce the balance of the IAG reserve.
3.2 The Committee recommends that the proposed budget
is approved.
4.

On behalf of the IAG Council the Committee makes
the following acknowledgements:
4.1 Hermann Drewes for his efficient administration andmanagement of IAG Office.
4.2 The Financial Department of TUM for the support andchecking to the accounts.
The audit committee wishes Markku Poutanen, the new Secretary General, a successful administration.
Montreal, July 16, 2019.
Denizar Blitzkow

Jonas Agren

Matt Amos

62

Fig. 1: IAG Executive Committee Meeting, Potsdam, 4 April 2016

Fig. 2: Auditorium at the Joint IAG/IASPEI Scientific Assembly, Kobe 2017

The Geodesist’s Handbook 2020

Minutes of the IAG Council Sessions

63

Minutes of the IAG Council Session at the IAG-IASPEI Scientific
Assembly 2017
Hermann Drewes (Secretary General) ∙ Robert Heinkelmann (minute taker)

Place: Kobe International Conference Center, Room 401
Time: July 31, 18:00-20:00

Agenda18:00 Welcome and adoption of agenda
18:05 Organizational issues of the Scientific Assembly 201718:20 Scientific program breakdown
18:35 Mid-term Report on IAG activities 2015-2017
18:50 IAG Strategy Document and international activities
19:30 Revision of IAG Statutes and Bylaws
19:45 Any other business
20:00 AdjournParticipants
IAG National Delegates (*representatives): Australia(*Chris Rizos), Austria (Johannes Böhm), China (Yamin
Dang, *Shuanggen Yin), Czech Republic (Pavel Novak),Finland (Markku Poutanen), France (*Marie-Francoise
Lalancette), Germany (Jürgen Müller), Greece (*George
Vergos), India (Virendra M. Tiwari), Israel (Gilad EvenTzur), Italy (Mattia Crespi), Japan (Kosuke Heki), New
Zealand (Matt Amos), Poland (Aleksander Brzezinski),Sweden (*Martin Lidberg), Switzerland (*Alain Geiger),
Turkey (Osman Atila Akabali), USA (*Jeffrey Freymueller)
IAG Executive Committee Members and Guests: Harald
Schuh (IAG President), Zuheir Altamimi (IAG Vice
President), Hermann Drewes (IAG Secretary General),Robert Heinkelmann (guest, minute taker)

Minutes
1. Welcome and adoption of agenda
The IAG Council Meeting 2017 took place on 31 July 2017,at the Kobe International Conference Center, in Kobe,
Japan, on the occasion of the IAG-IASPEI Scientific Assembly 2017. The agenda was distributed previously by email
and was unanimously adopted. H. Schuh, the President of
the IAG, welcomed the participants of the IAG Council
Meeting.
2. Organisational issues of the Scientific Assembly 2017
H. Drewes, the IAG Secretary General, welcomed theparticipants and mentioned that most organisational issues
were already presented during the Opening Ceremony. He
explained that the poster sessions are organized in anotherbuilding (Chamber of Commerce and Industry) on the otherside of the street.
3. Scientific programme breakdown
H. Drewes noted that this topic was already covered during
the Opening Ceremony.
4. Mid-term Report on IAG activities 2015-2017
H. Drewes mentioned that the mid-term reports on IAG
Activities 2015-2017 (Travaux) can be found on the IAG
office website under IAG Publications, Reports). Further
comments from the Council Members are very muchappreciated. Printed versions of the final Travaux can bereceived on request.
5. IAG Strategy Document and international activities
H. Schuh gave a presentation about, international activities,IUGG issues, and the IAG Strategy Document. He reported
about a discussion on IUGG membership, the IUGG
governance, news in the IUGG structure and the Statutes andBy-Laws, IUGG within ICSU and other recent IUGG

64

activities. Further, he reported about the IAG Strategy
Document, which was prepared by G. Beutler. The
document says that the basic structure of IAG incl. the fourcommissions, the ICCT and GGOS should remain the same.
In addition, it says that Inter-Commission Committees(ICCs; e.g., under two or more Commissions) and Projects(e.g., under one Commission; also lasting longer than 4
years) could be established. Suggestions for topics shouldcome from the geodetic scientists. H. Schuh further
discussed the visions and ideas for ICCs, which wereidentified. He noted that Planetary Geodesy should becovered by the newly established IUGG Union Commission
on Planetary Sciences (UCPS) and not by IAG.
J. Müller noted that there could be more information andideas about how to implement the Strategy Document (e.g.,
how to attract early-career scientists; ranking the visions).
He suggested incl. an early-career scientist to the IAG EC
who reaches out to interested early-career scientists.
A. Geiger noted the importance of including Marine
Geodesy as an Option (#4) for an ICC, and possibly later for
an IAG-IAPSO Inter-Association Activity, in the Strategy
Document.
H. Drewes asked the IAG Council to give further
comments on the IAG Strategy Document after this meeting.
H. Schuh concluded that the IAG Strategy Document
will be finalized in the next months, endorsed by the EC in
2017, and approved by the Council during the IUGG
General Assembly 2019 in Montreal, Canada, at the latest.
The implementation of the Strategy Document should start
as soon as possible. He noted that one or two Members at
Large could be added to the EC in order to improve the

The Geodesist’s Handbook 2020

geographical balance, however, it would be preferred getting
more nominations for IAG officers from the countries
instead of increasing the number of EC members.
6. Revision of IAG Statutes and Bylaws
C. Rizos, Chair of the Cassinis Committee, presented his
report on the revision of the IAG Statutes and Bylaws. He
reported about the structure and tasks of the committee andexplained the working procedure of the committee fromgetting ideas (e.g., from the Strategy Document) andproposals (e.g., from the Chinese National Committee) for
changes until having the final revisions of the Statutes andBylaws ready.
H. Drewes explained the difference between Statutes(general law) and the Bylaws (explanatory notes). H. Schuhnoted that sometimes it might be better (e.g., when it comesto awards) adding an amendment instead if changing the
Statutes and Bylaws itself.
7. Any other business
H. Drewes explained that the reason for not giving a
reduction of 10% to the IAG individual members on theregistration fee for the IAG-IASPEI Scientific Assembly
was the fact that it is a joint assembly. However, all IAG
members who attended the IAG-IASPEI Scientific
Assembly will get free extension of their IAG membershipby one year.
8. Adjourn
H. Schuh thanked the participants for their contributions andclosed the session at 20:00.

Minutes of the IAG Council Sessions

65

Minutes of the IAG Council Sessions at the General Assembly2019 (session 1)
Hermann Drewes (Secretary General) ∙ Franz Kuglitsch (Assistant Secretary General) ∙ Robert Heinkelmann (minutetaker)

Place: Palais des Congrès, Montreal, Canada, Room 513C
Time: 10 July 2019, 08:30-10:00

Agenda
1. Welcome and adoption of the agenda
2. IUGG2019 organisational issues
3. Agenda of the Opening and Closing Sessions
4. Information on IAG Awards
5. Proposal of the IAG Budget 2019 – 2022
6. Appointment of the Audit Committee
7. Appointment of the Resolutions Committee
8. Review of the 2019 election process and results
9. Review of IAG Statutes and Bylaws
10. IAG Strategy Document
11. Status of Journal of Geodesy and IAG Symposia Series
12. Status of IAG Reports
13. IAG Scientific Assembly 2021
14. Any other business (all)Adjourn

Participants
IAG National Delegates: Austria (Johannes Böhm), Brazil(Gabriel do Nascimento Guimaraes), China-Taipei (MingYang), Czech Republic (Pavel Novak), Denmark (Niels
Andersen), Estonia (Artu Ellmann), Finland (Jyri Näränen),
France (Marie-Francoise Lalancette), Germany (Jürgen
Müller), Greece (Dimitrios Tsoulis), Hungary (Jozsef
Adam), Italy (Mattia Crespi), Rep. of Korea (Jungho Cho),
New Zealand (Matt Amos), Poland (Pawel Wielgosz), Spain(Marcelino Valdez Perez de Vargas), Sweden (Jonas
Agren), Switzerland (Elmar Brockmann), Thailand(Chakorn Boonphakdee), UK (Peter Clarke), USA (Jeffrey
Freymueller)

IAG Executive Committee Members: Harald Schuh (IAG
President), Zuheir Altamimi (IAG Vice President),
Hermann Drewes (IAG Secretary General), Richard Gross(GGOS Chair), Axel Nothnagel (Representative of the IAG
Services), Roland Pail (President of IAG Commission 2),
Chris Rizos (IAG Immediate Past President)
Guests: Denizar Blitzkow, Robert Heinkelmann (minutetaker), Benjamin Männel, Markku Poutanen (IAG Secretary
General 2019-2023)

Minutes
1. Welcome and adoption of agenda
The first session of the IAG Council Meeting 2019 took
place on 10 July 2019, at the Palais des Congrès, Montreal,
Canada, on the occasion of the IUGG General Assembly2019. H. Schuh, the President of the IAG, welcomed theparticipants of the IAG Council Meeting. The agenda wasdistributed previously by e-mail, was unanimously adopted.
2. IUGG2019 organisational issues
H. Drewes, the IAG Secretary General, summarized theorganizational issues of IUGG. He reported about (i) IAG’s
involvement in the science program (IAG Symposia, JointSymposia, poster sessions) compared to previous IUGG
General Assemblies and compared to other Associations,(ii) IAG Business Meetings, (iii) IAG/IUGG ceremonies
and social events, and (iv) IUGG/IAG Travel Grants (IAG
offered grants of around CAD 40,000).
3. Agenda of the Opening and Closing Sessions
H. Drewes presented and discussed the agendas of theOpening and Closing Sessions.

66

4. Information on IAG Awards (Levallois Medal, Guy
Bomford Prize, Young Authors Awards)
H. Drewes presented the IAG awardees 2019. The corresponding rules (https://www.iag-aig.org/statutes-and-bylaws) describe the procedures of nominations and decisionmaking. The Levallois Medal 2019 was awarded to C.
Reigber (Germany), the Guy Bomford Prize 2019 to M.
Sprlak (Australia), and the Young Authors Awards 2017and 2018, respectively, to M. Xu (China; 2017) and A.
Peidou (Canada; 2018). H. Drewes announced that theawards would be presented at the IAG Opening Session.
5. Proposal of the IAG Budget 2019 – 2022
H. Drewes summarized the IAG Financial Report 20152018, and presented the proposed IAG Budget 2019-2022(see IAG Secretary General Report in this Handbook). He
mentioned that there were no major changes, but in future
most of the publication costs would go into open access of
online publications rather than in printed publications.
6. Appointment of the Audit Committee
H. Drewes noted that the Audit Committee should audit andapprove the IAG Financial Report 2015-2018 and the IAG
Budget 2019-2022. He presented the names of the membersof the Audit Committee as proposed by the IAG Executive
Committee incl., D. Blitzkow (Chair), J. Agren, and M.
Amos. The IAG Council Members approved the proposed
members of the Audit Committee unanimously.
7. Appointment of the Resolutions Committee
H. Schuh noted that the Resolution Committee should
prepare future IAG resolutions. He presented the names ofthe members of the Resolutions Committee as proposed by
the IAG Executive Committee incl., G. Blewitt, R. Gross, R.
Pail, L. Sanchez, and A. Kealy. The IAG Council Members
approved the proposed members of the Resolutions
Committee unanimously.
8. Review of the 2019 election process and results
C. Rizos gave the presentation of the results of the IAG
Officers election process 2019. He reported about (i)procedures for nominations and elections, (ii) the
Nominating Committee, (iii) the nomination process, (iv)the election results for IAG Officers (2019-2023), and (v)issues to be considered in future.
9. Review of IAG Statutes and Bylaws (Report of the
Cassinis Committee)
H. Schuh invited C. Rizos, Chair of the Cassinis Committee,
giving his report on the review of the IUGG Statutes andBylaws. C. Rizos gave a presentation. He reported about (i)the tasks of the Cassinis Committee, (ii) the proposed

The Geodesist’s Handbook 2020changes to the IAG Statutes and Bylaws, and (iii) issues tobe considered in future. H. Schuh asked the IAG Council
Members to volunteer for being member on an ad-hoc
committee to work on the final wording of the revised
Statutes and Bylaws. The IAG Council Members appointed
J. Freymueller, P. Clarke, and M. Amos. The final versionsof the revised IAG Statutes and Bylaws are available at the
IAG Office Homepage.
10. IAG Strategy Document
H. Schuh summarized the IAG strategy process, whichstarted in 2015 and ended with a detailed document early in
2019. He highlighted the major challenges, visions andoptions of IAG in the next decade. The IAG Secretary
General, H. Drewes, had sent the IAG Strategy Document
to the Council members well before the meeting, and H.
Schuh asked the Council to adopt it as the official IAG
Strategy Document. It is available at the IAG Office
Homepage.
11. Status of Journal of Geodesy and IAG Symposia
SeriesH. Drewes summarized the status and major changes of the
Journal of Geodesy, and the IAG Symposia Series. He notedthat in future there would be a continuous article publication(CAP) of the Journal of Geodesy. Until now, the articles
were only published as complete volumes. He further noted
that, starting with the proceeding of IUGG2019, the IAG
Symposia Series would change from book publications toopen access online publications. The symposia organizers
will have to pay $50 per participant.
12. Status of IAG Reports (Travaux de l’AIG) andNational Reports 2015-2019
H. Drewes gave a presentation about the status and content
of the IAG Reports Vol. 41 (Travaux de l’AIG 2015-2019),
which are available at the IAG Office Homepage. He notedthat the report of BIPM is still missing, and that only few
countries submitted National Reports. He invited the IAG
Council Members to submit their National Reports still.
13. IAG Scientific Assembly 2021
H. Drewes repeated the notification that the Council
members had elected Beijing, China, by electronic voting inAugust 2018 as the venue of the IAG Scientific Assembly
2021. The Chinese Society of Geodesy, Photogrammetry
and Cartography will organize it together with the Chinese
Academy of Surveying and Mapping from 28 June to 5 July2021.

Minutes of the IAG Council Sessions

14. Any other business
J. Adam invited the IAG Council members to submit
geodesy related news from their countries to the IAG
Communication and Outreach Branch (COB) for
publication in the IAG Newsletter and through the IAG
social media channels.

67

Adjourn
H. Schuh thanked the participants for their contributions andclosed the session at 10:00.

68

The Geodesist’s Handbook 2020

Minutes of the IAG Council Meeting at the IUGG General
Assembly 2019 (session 2)

Place: Palais des Congrès, Montreal, Canada, Room 513C
Time: 16 July 2019, 18:00-20:00

Agenda
15. Report of the Audit Committee and discharge of the
management
16. Approval of the IAG Budget 2019-2022
17. Approval of the revised Statutes and Bylaws
18. Report of the IAG Resolutions Committee
19. Approval of Resolutions
20. Report from IUGG Council and Executive Committee
21. IAG Representatives to external bodies
22. Preparation of the IAG and IUGG Closing Sessions
23. Any other business
Adjourn

Participants
IAG National Delegates: Austria (Johannes Böhm), Brazil(Roberto Luz), China (Yamin Dang), China-Taipei (MingYang), Czech Republic (Pavel Novak), Denmark (Niels
Andersen), Finland (Jyri Näränen), France (MarieFrancoise Lalancette), Germany (Jürgen Müller), Greece(Dimitrios Tsoulis), Hungary (Jozsef Adam), Italy (Mattia
Crespi), Rep. of Korea (Jungho Cho), New Zealand (MattAmos), Poland (Pawel Wielgosz), Slovakia (Juraj Janak),Sweden (Jonas Agren), Switzerland (Elmar Brockmann),
UK (Peter Clarke), USA (Jeffrey Freymueller)
IAG Executive Committee Members: Harald Schuh (IAG
President), Zuheir Altamimi (IAG Vice President),
Hermann Drewes (IAG Secretary General), Richard Gross(GGOS Chair), Axel Nothnagel (Representative of the IAG
Services), Chris Rizos (IAG Immediate Past President)

Guests: Denizar Blitzkow, Franz Kuglitsch (IAG Assistant
Secretary General; minute taker), Markku Poutanen (IAG
Secretary General 2019-2023)

Minutes
15. Report of the Audit Committee and discharge of the
management
D. Blitzkow reported about the work of the Audit
Committee, and mentioned that the committee examined
carefully the IAG Financial Report 2015-2018 including all
the account documents without any objection. He applied
for discharge of the Secretary General w.r.t. his financial
management. The IAG Council Members approved thedischarge of the management unanimously.
16. Approval of the IAG Budget 2019-2022
D. Blitzkow reported that the Audit Committee examinedalso the IAG Budget 2019-2022, which H. Drewes had
proposed in the session on July10 (see agenda item 5) andmoved for the approval. The IAG Council Members
approved the IAG Budget 2019-2022 unanimously.
17. Approval of the revised Statutes and Bylaws
C. Rizos invited the IAG Council Members to submit concerns about the Statutes and Bylaws at any time as they canbe implemented in future. Based on the final comments
made by C. Rizos and J. Freymueller, the IAG Council
Members approved the revised Statutes and Bylaws unanimously.
18. Report of the IAG Resolutions Committee
H. Schuh invited the Chair of the IAG Resolution Committee giving his report on the IAG Resolution Committee. R.
Gross discussed the five proposed resolutions incl.,

Minutes of the IAG Council Sessions- Resolution 1: The International Terrestrial Reference
Frame (ITRF),- Resolution 2: Third Realization of the International
Celestial Reference Frame,- Resolution 3: Establishment of the International Height
Reference Frame (IHRF),- Resolution 4: Establishment of the Infrastructure for
the International Gravity Reference Frame, and- Resolution 5: Improvement of the Earth’s Rotation
Theories and Models,H. Schuh noted that the Resolution 1 on the ITRF was also
submitted to IUGG.
19. Approval of Resolutions
The IAG Council Members approved unanimously the IAG
Resolutions discussed under agenda item 18. Resolutions
are available at the IAG Office Homepage.
20. Report from IUGG Council and Executive
Committee
H. Schuh summarized the major outcome of the IUGG
Council and Executive Committee Meetings and firstnumbers on the 2019 IUGG General Assembly. The size of
this IUGG General Assembly was quite average but slightly
smaller than it was in Prague 2015. The participation ofearly-career scientists was very good. He presented thenames of the newly elected members of the IUGG Bureau
and Finance Committee (2019-2023), incl. C. Rizos as
President-Elect, N. Andersen as Treasurer, and J. Adam as
Finance Committee Member from IAG. He mentioned that
the IUGG General Assembly 2023 will be organized in
Berlin, Germany.

69

21. IAG Representatives to external bodies
H. Drewes reported that the IAG Executive Committee
revised the IAG Representatives to the IAG Services, IUGG
Commissions and Committees, UN-GGIM and UN-OOSA,
other external bodies (ABLOS, IAU, ISO, SIRGAS), andIUGG Liaisons (CCTF, COSPAR, GEO, PAIGH, ISCWDS). The new Executive Committee 2019-2023 may
make further changes and publish it at the IAG Website.
22. Preparation of the IAG and IUGG Closing Sessions
H. Drewes announced the Closing Sessions of IAG andIUGG, which will be held on 17 July 2019, 3:00 pm and4:30 pm, respectively, and invited all assembly participants
to attend. At the IAG Closing Session, all conveners of IAG
related symposia will summarize the highlights.
23. Any other business
J. Freymueller noted that there would be IAG proceedingsof this IUGG General Assembly as an electronic open
access publication by Springer. H. Drewes announced thatthe next Geodesist’s Handbook including the reports of theGeneral Assembly 2019 and the new IAG structure 20192023 would be published as an electronic open accesspublication within the Journal of Geodesy in 2020. H. Schuhnoted that the local organizers of this IUGG General
Assembly would soon send out a questionnaire to allparticipants to improve the quality of IUGG General
Assemblies in future. He invited everyone to participate inthis questionnaire.
Adjourn
H. Schuh thanked the participants for their contributions andclosed the session at 18:30.

70

The Geodesist’s Handbook 2020

Summary of the IAG Executive Committee Sessions
Hermann Drewes (Secretary General) ∙ Franz Kuglitsch (Assistant Secretary)

Place: Palais des Congrès in Montréal, Québec, Canada,
Floor 5, Room 522B
Time: 2019, July 9, 08:30-18:00 (Topics 1-17), July 12,
18:00-20:00 (Topics 18-28) and July 15, 18:0020:00 (Topics 29-40)
Attendees (voting): H. Schuh (IAG President), Z. Altamimi(IAG Vice President), H. Drewes (IAG Secretary General),C. Rizos (Immediate IAG Past President), G. Blewitt(President Commission 1), R. Pail (President Commission2), C. Huang (Vice President Commission 3, temporarily),
M. Santos (President Commission 4, temporarily), P. Novák(President ICC on Theory), R. Gross (Chair of GGOS), J.
Adám (President of the COB), R. Barzaghi and A.
Nothnagel (Representatives of the Services), Y. Dang
(Member-at-Large, temporarily).
Attendees (non-voting): F. Kuglitsch (IAG Assistant
Secretary General, minute taker, temporarily), M. Sideris(IAG Past President).
Guests (temporarily): M. Poutanen (IAG Secretary General
2019-2023), J. Müller (Chair of the Planning Group for a
new IAG Subcomponent on Novel Sensors andTechnologies), C. K. Shum (Chair of the Planning Groupfor the Re-establishment of the International Altimetry
Service), G. Dick (Deputy of the Assistant Secretary
General, minute taker), J. Kusche (Editor-in-Chief of the
Journal of Geodesy), J. Freymueller (Editor-in-Chief of the
IAG Symposia Series), A. Eicker (Chair of the PlanningGroup for the Inter-Commission Committee on Geodesy for
Climate Research).
Regrets: M. Hashimoto (President Commission 3), R.
Neilan (Representative of the Services), M.C. Pacino(Member-at-Large).

Summary of Agenda Items:
1. Welcome and adoption of agenda
The 8th IAG EC Meeting in the term 2015-2019 took placeon the occasion of the IUGG General Assembly 2019 at the
Palais des Congrès, room 522B, in Montréal, Canada, on
July 9, 12 and 15, 2019. The agenda was distributed
previously by e-mail and was unanimously adopted. H.
Schuh, the President of the IAG, welcomed the members of
the IAG Executive Committee in the first session (11 out of
16 voting members, 2 non-voting members and 4 guests).
The EC Members approved the minutes of the 7th IAG EC
Meeting in the term 2015-2019, which took place on 10
December 2018 in Washington DC, USA.
2. IUGG2019 organizational issues
H. Drewes summarized the organizational issues of IUGG.
He reported about (i) IAG’s involvement in the science
program (incl. IAG Symposia, Joint-Symposia, poster
sessions) compared to previous IUGG General Assemblies
and compared to other Associations, (ii) IAG BusinessMeetings, and (iii) IUGG and IAG Travel Grants (IAG paid
nearly CAD 40,000).
3. Agenda of the Council meetings, July 10, 08:30–10:00& July 16, 18:00–20:00
H. Drewes presented and discussed the agenda of theCouncil Meeting. H. Schuh noted that IAG Strategy
Document is now finished and should be approved by theCouncil.
4. Agenda of Opening and Closing Sessions, July 11,
18:00–20:00 & July 17, 15:00–16:30
H. Drewes presented and discussed the draft agenda of theOpening and Closing Sessions.

Summary of the IAG Executive Committee Sessions

5. Proposal for members of the Audit Committee TBD
by the Council
H. Drewes presented and discussed the list of proposed
members of the Audit Committee, which has to beappointed by the IAG Council. H. Schuh noted that themembers of the Audit Committee should be IAG Council
Delegates or National Correspondents, and should preferably represent all continents. M. Sideris suggested asking
some more people before the Council Meeting starts.
6. Nomination of members of the Resolution Committee
for IAG and IUGG
H. Drewes presented and discussed the proposed membersof the Resolutions Committee, which has to be appointed by
the IAG Council. They should represent all IAG
Commissions, GGOS, continents and gender. H. Schuhnoted that IAG has received so far two proposals forresolutions, which should be approved by IAG: (i) on the
3rd realizations of the International Celestial Reference
Frame (ICRF), which was already approved by theInternational Astronomical Union (IAU) in 2018, and (ii) on
the improvement of the Earth Rotation Theories andModels. In addition, a resolution on the International
Terrestrial Reference Frame (ITRF) was proposed, whichshould be approved by IAG and IUGG.
7. Levallois Medal, Guy Bomford Prize, Young Authors
Award, new IAG Fellows
H. Drewes presented the list of proposed IAG awardees andfellows. He noted that C. Reigber (Germany) will beawarded the Levallois Medal 2019, the Guy Bomford Prize
will be given to M. Sprlak (Australia), and the Young
Authors Awards will be given to M. Xu (China; 2017) and
A. Peidou (Canada; 2018). H. Schuh encouraged the EC
Members to nominate more scientists for IAG Awards infuture. H. Drewes said that the deadline for nominating
additional IAG Fellows is before the last EC meeting on
Monday, July 15, when the EC shall appoint the Fellows
officially. They will be presented at the Closing Session on
Wednesday, July 17. M. Sideris proposed giving the Young
Authors Awardees in future a lecture at the General
Assembly and introducing clear criteria on how to become
an IAG Fellow.
8. Results of the 2019 IAG Officers election process
C. Rizos gave the presentation of the results of the 2019 IAG
Officers election process. He reported about (i) procedures
for nominations and elections, (ii) the Nominating
Committee, (iii) the nomination process, (iv) the election
results for IAG Officers (2019-2023), and (v) issues to beconsidered in future. H. Schuh noted that IAG should
definitely go for electronic voting in future, and that the two-71

step procedure in the election process when there are morethan two nominations should be supported to get absolutemajorities. He suggested starting the election process earlier
in future.
9. Report on the review of the IAG Statutes and Bylaws(Cassinis Committee)
C. Rizos reported about (i) the tasks of the so-called Cassinis
Committee, (ii) the proposed (minor) changes to the IAG
Statutes and Bylaws, and (iii) issues to be considered infuture. The EC Members made a few further minor changes
to the IAG Statutes and Bylaws. H. Schuh suggested that
nominations of candidates for the position of the GGOS
President should be made by the GGOS Coordinating Board
in consultation with the EC Members. The EC Members
agreed on adding this change to the Bylaws. The final
version of the revised IAG Statutes and Bylaws will beapproved by the IAG Council. C. Rizos suggested
considering to include the expectations of the National
Correspondents and Adhering Bodies in the Bylaws.
10. Status of IAG Report 2015-2019 (Travaux de l’AIG
2015-2019)
H. Drewes gave a presentation about the status and content
of the IAG Report Vol. 41 (Travaux 2015-2019). The final
version will be available at the IAG Office Homepage. He
further noted that very few countries submitted National
Reports. The EC Members agreed on introducing a DOI for
the Travaux (possibly via the library of the GFZ German
Research Centre for Geosciences). H. Drewes confirmedthat all Springer publications have a DOI.
11. Reports and recommendations of the Commissions
J. Müller gave a presentation about the status of the
Planning Group for a new IAG Project on Novel Concepts
and Quantum Technology in Geodesy and the proposed
Terms of Reference. He reported about (i) new approaches
to observe the Earth gravity fields, and (ii) the preliminary
structure of the new entity incl. possible working groups.
The EC Members approved the progress made by the
Planning Group and asked J. Müller (i) to develop a formal
structure of this new entity, and (ii) prepare final terms ofreference to be approved at the next IAG EC Meeting in
December 2019 in San Francisco CA, USA. G. Blewitt and
H. Schuh suggested considering optical clocks in thisproject, and emphasizing the novel sensors besides thequantum technology in the title. J. Müller agreed on
including these issues. The EC Members agreed on renaming the IAG Project to Novel Sensors and Quantum
Technology for Geodesy.

72

G. Blewitt gave the presentation about Commission 1(Reference Frames). He summarized (i) the activities ofCommission 1 between 2015 and 2019, (ii) the structuralcomponents of Commission 1, and (iii) suggestions for the
future.
R. Pail gave the presentation on Commission 2 (Gravity
Field). He reported about (i) recent activities of Commission
2, and (ii) the proposal to establish an Inter-Commission
Committee on “Geodesy for Climate Research” (ICCC)
incl. objectives, planned activities.
On behalf of M. Hashimoto, R. Gross gave the presentation
about Commission 3 (Earth Rotation and Geodynamics).
He reported about (i) the activities of the five Subcommissions, Joint Study Groups, Joint Working Groups,(ii) the proposal to establish an Inter-Commission
Committee on Marine Geodesy (ICCM). H. Schuh notedthat Sub-commissions 3.2 and 3.5 should be strengthened infuture, as the volcanology and seismology communities arevery active in this field. H. Drewes said that according to thediscussion with IASPEI, Subcommission 3.5 would become
an Inter-Association Sub-Commission (in IAG) or
Commission (in IASPEI) on Seismo Geodesy. A meeting isplanned with IASPEI on July 13, 18:00 (after the Joint
Symposium JS04 Seismo-Geodesy) or on July 14, 18:00.
The EC Members approved the establishment of an InterCommission Committee on Marine Geodesy (ICCM), andasking Yuanxi Yang to develop a formal structure and draft
terms of reference.
On 12 July, A. Eicker reported about her ideas to establish
an Inter-Commission Committee on Geodesy for
Climate Research (ICCC). She reported about (i) the
importance of geodesy for climate research, and (ii) possible
objectives and planned activities of ICCC. Z. Altamimi
asked A. Eicker to contact the Commissions to get more
people involved in ICCC. In addition, he suggested focusing
on a few major topics. H. Schuh noted having 4-5 working
groups is a good start. R. Gross suggested including the
GGOS Chair of the Science Panel in the ICCC activities.
The EC Members established the Inter-Commission
Committee on Geodesy for Climate Research (ICCC) andappointed A. Eicker as ICCC President for the period 20192023. The EC Members asked A. Eicker to finalize a formal
structure and to draft terms of reference of ICCC until the
IAG EC Meeting to be held in December 2019 in San
Francisco CA, USA.
H. Schuh summarized the presentation about Commission
4 (Positioning & Applications; as prepared by M. Santos).
He reported about (i) the activities of Commission 4
between 2015 and 2019, (ii) recommendations for the next

The Geodesist’s Handbook 2020

term, and (iii) the 2nd Commission 4 Symposium to beorganized in September 2020 in Potsdam, Germany.
12. Report and recommendations of the ICCTP. Novák gave a presentation about the ICCT. He reported
about (i) the activities of the ICCT study groups between
2015 and 2019, (ii) the ICCT website, (iii) the HotineMarussi 2018 Symposium and its proceedings, and (iv)
recommendations for the next term. The EC Members
agreed on asking J. Kusche, Editor in Chief of the Journalof Geodesy (JoG), to include a member of ICCT to the JoG
Editorial Board.
13. Appointment of the ICCT President for the period
2019-2023
The EC Members re-appointed P. Novák as ICCT President
for the period 2019-2023.
14. Report and recommendations of the Services’
representatives
C. K. Shum reported about the rationale, objectives, terms ofreference, and future steps to reestablish the International
Altimetry Service (IAS). He confirmed that IAS should
provide a combined product of various analysis centers. H.
Drewes urged to define clearly the products. H. Schuhsuggested including people who already have experience inrunning IAG Services. The EC Members asked C.K. Shumto develop a formal structure and to draft terms of referenceof the new IAS until the IAG EC Meeting in San Francisco
CA, USA, December 2019.
R. Barzaghi gave the first presentation about the Services.
He (i) reported about the activities of the International
Gravity Field Service (IGFS) between 2015 and 2019
including the International Gravimetric Bureau (BGI),International Service for the Geoid (ISG), International
Geodynamics and Earth Tide Service (IGETS),International Center for Global Earth Models (ICGEM),
International DEM Service (IDEMS), and International
Combination Service for Time-variable Gravity Field
Solutions (COST-G), and (ii) gave recommendations for
future topics. Z. Altamimi offered asking T. Otsubo to reporton topics related to gravity in future. The EC Members
agreed. H. Schuh noted that COST-G is a product center ofIGFS. R. Barzaghi agreed on sending an updated slide.
A. Nothnagel gave the second presentation about theServices. He (i) reported about recent activities of theInternational Earth Rotation and Reference Systems Service(IERS), International GNSS Service (IGS), International
Laser Ranging Service (ILRS), InternationalVLBI Service
for Geodesy and Astrometry (IVS), and Permanent ServiceSummary of the IAG Executive Committee Sessions

73

for Mean Sea Level (PSMSL). He further presented therevised terms of reference for the International VLBI
Service for Geodesy and Astrometry (IVS). IVS would liketo introduce a new “Office for Outreach andCommunications”. H. Schuh noted that this outreach teamshould be well linked to the communication and outreachentities of IAG, GGOS etc. H. Schuh also noted that having
17 people in the IVS Directing Board is a lot and might
become inefficient. The EC Members approved the revised
IVS terms of reference unanimously.

with the Commission Presidents from one institution to thenext. In addition, nowadays many institutes have legal
restrictions to host such websites, as they are responsible forthe content. J. Adám agreed on asking S. Rozsa whether it
would be possible to host the Commission websites as partof the IAG website.

15. Report and recommendations of GGOS
R. Gross gave a presentation about the current activities of
the Global Geodetic Observing System (GGOS). He
reported about (i) the GGOS Structure, (ii) the new GGOS
Affiliate “GGOS Japan”, (iii) the GGOS 2018 Days in
Tsukuba, Japan, (iv) the Committee on Essential Geodetic
Variables (EGVs), (v) the Working Group on DOIs forGeodetic Data Sets, (vi) GGOS External Relations, and (vii)the 2019 meetings calendar. He noted that within the last 1.5
years, the visibility of geodesy within the Group on Earth
Observations (GEO) has increased a lot. H. Schuh clarified
that GGOS has the mandate to represent IAG at the GEO
Programme Board. In addition, M. Sideris represents IUGG
within GEO. H. Schuh noted that it would be good for
GGOS to have its own products.

19. Report of the Journal of Geodesy Editor-in-chief
H. Drewes summarized the presentation of the Journal of
Geodesy Editor-in-Chief, Jürgen Kusche. The report
includes (i) proposed changes of the Editorial Board 20202023, (ii) numbers of submitted and accepted manuscripts
and the reviews, the impact factor and top ranking of highest
citing of the Journal of Geodesy, (iii) Special Issues
planned, (iv) editorial practices and new policies. The EC
members congratulated the Editorial Board on the highimpact factor of the Journal of Geodesy.

16. Appointment of the GGOS Chair for the period
2019-2023
R. Gross gave a presentation about the process of finding a
new GGOS Chair for 2019-2023. Only one candidate wasnominated so far. Z. Altamimi and H. Schuh suggested
postponing the election to find at least two additional
candidates. H. Schuh noted that GGOS is IAG’s flagshipcomponent and that the GGOS Chair has to do two businesstrips per year. The EC Members agreed on (i) postponing
the election of the GGOS Chair 2019-2023 to find at least
two additional candidates, (ii) offering IAG travel support
to EC Members from developing countries (if needed), and(iii) clarifying with the Audit Committee if IAG travel
support could be also provided to the GGOS Chair (who has
exceptional responsibilities).
17. Report of the COB
J. Adám reported about current COB activities. He
highlighted (i) the activities of the COB between 2015 and2019, (ii) the IAG website, (iii) the IAG newsletter, (iv)
GIM International, (iv) social media activities, and (v) theUN GGIM WG (focus group on Outreach andCommunication). R. Pail suggested hosting theCommission websites centrally as part of the IAG website.
Then, the Commission websites would not have to move

18. Report of the Members-at-Large
There were no reports available from the Members-atLarge.

20. Proposal of the new Board of Editors of JoG by theold Board
J. Kusche presented the proposed changes of the Editorial
Board 2020-2023. There is no limit in the number of editors.
He noted that next week there will be a meeting of the
Editorial Board to discuss next steps. In addition, theEditorial Board will elect the Editor-in-Chief. The EC
Members discussed the suggested new members of the
Editorial Board and kept the composition as proposed.
21. Report of the Editor of the IAG Symposia Series
J. Freymueller gave the presentation about the IAG
Symposia Series. He reported about (i) the symposia
volumes that have been published since 2013, (ii) the review
process, and (iii) the future outlook incl. open access and theIUGG2019 Montreal Volume.
22. Proposal of the 2019-2023 Editor and Assistant
Editor of the IAG Symposia Series
On 15 July 2019, J. Freymueller mentioned that he would
we willing to continue as the Editor-in-Chief of the IAG
Symposia Series for 2019-2023. Also, L. Sanchez would be
willing to continue as Assistant Editor.
23. Report on the UN-GGIM (Subcommittee on
Geodesy, GGRF, GGIM-GS)
H. Schuh noted that UN-GGIM is in the process ofestablishing a Global Geodetic Center of Excellence basedon a 2015 resolution. IAG is actively contributing throughZ. Altamimi, R. Gross and H. Schuh. The future goal should

74

be to have a UN convention on geodesy. He mentioned thatthe colleagues from the United Nations are often not awareof what kind of geodetic products and services already exist.
24. Report on IUGG activities
F. Kuglitsch reported, that since the last EC Meeting in
December 2018, most of his activities were related to(co)organizing this IUGG General Assembly 2019. He
mentioned that there are four candidate cities to host the
IUGG General Assembly 2023: Athens, Berlin, Geneva,
and Guadalajara. The candidates presented their bids today,
and the IUGG Site Comparison Committee will announce
tomorrow a shortlist of the top two candidates the IUGG
Council can vote on. He invited the EC Members to attend
this IUGG Award Ceremony. H. Schuh noted that the Chairof the IUGG Finance Committee mentioned in his
presentation to the IUGG Council that there is no audit of
the money that goes from IUGG to its Associations, whichcorresponds to around 50% of the total IUGG budget. F.
Kuglitsch mentioned that getting a professional audit of the
IUGG Budget by e.g., PWC, EY, would cost IUGG around
20% of its total budget. For this reason, IUGG will most
likely not hire a professional auditor in future. H. Schuhsuggested IUGG nominating a member in the audit
committees of the Associations.
25. Reports on liaised bodies (ABLOS, IAU Comm. 19,
GEO, ISO, UN)
H. Drewes summarized the reports received from liaisedbodies including ABLOS, GEO, IAU Commission 19, ISO,and UN-GGIM-Geospatial Societies.
26. Appointment of IAG Representatives to IAG
Services, IUGG Commissions & others
H. Drewes discussed the list of IAG Representatives to
Scientific Bodies. The EC Members agreed on the list ofrepresentatives; however, the new EC may revise the list. In
particular, another representative to the International
DORIS Service (IDS) has to be appointed. F. Kuglitschnoted that IUGG Commission Chairs were informed about
the nominated IAG representatives and will invite them totheir business meetings during the IUGG General
Assembly. There, the future membership of a Commission
will be decided. He further noted that the future of the IUGG
Committees and its members will be discussed by the newly
elected IUGG Bureau. If new Committee members areneeded, the Associations will be informed.
27. Status of the IAG Scientific Assembly 2021
Y. Dang gave a presentation about the status of organizing
the IAG Scientific Assembly 2021 to be held in Beijing,
China, from June 28 to July 3, 2021. H. Drewes noted that

The Geodesist’s Handbook 2020

the IAG Secretary General (2019-2023) will be theSecretary of the IAG Assembly. In 2020, he should visit thevenue and make organizational arrangements. All symposia
should be led by IAG. There will not be any joint symposia
with other Associations. He mentioned that there should be
only two (or three at the very maximum) parallel sessions.
In total, having three big (for up to 700 people) and fivesmaller rooms for business meetings should be sufficient.
28. Any other business
H. Schuh noted that there are still candidates available fornomination of GGOS Chair, given that IAG can provide
travel support.
29. Actual status report
H. Schuh summarized the major outcomes of the IUGG
Executive Committee and Council Meetings and presented
first numbers of the General Assembly 2019. In addition, hementioned the three resolutions adopted by IUGG. He
informed that the next IUGG General Assembly will be held
2023 in Berlin, Germany, and that the Associations shouldreport to IUGG about possible improvements. F. Kuglitschnoted that there is an ongoing discussion about further
reducing the number of days of the General Assembly.
30. Approval of the new Board of Editors of the JoG
J. Kusche presented the new Board of Editors of the JoG.
He noted that the old Board of Editors approved the newly
suggested members. He will continue as Editor-in-Chief.
The EC Members approved the new Board of Editors of the
JoG unanimously. H. Drewes noted that the new contracts
between Springer and the IAG w.r.t. the Journal of Geodesy
and the IAG Symposia Series should be signed by the new
IAG President and Secretary General.
31. Approval of the Editor-in-Chief and Assistant
Editor-in-Chief of the IAG Symposia Series
The EC Members approved J. Freymueller and L. Sanchez
as the Editor-in-Chief and Assistant Editor-in-Chief for
2019-2023 unanimously.
32. Summary of the Report of the Audit Committee
H. Drewes noted the report of the Audit Committee will bepresented to the Council tomorrow.
33. Report of the IAG Resolution Committee
R. Gross gave a presentation about the five IAG
Resolutions, and further discussed them with the EC
Members. He noted that the Resolution 1 on the ITRF was
identically submitted to IUGG. The EC Members agreed onchanging the title of resolution 4 to “Establishment of theSummary of the IAG Executive Committee Sessions

Infrastructure for the International Gravity Reference
Frame”.
34. Discussion of proposed resolutions for approval by
the IAG Council
The EC Members proposed the IAG Council to adopt thefive resolutions.
35. Status of reviewed Statutes and Bylaws
J. Freymueller noted that the two steps election procedure
part was rephrased for clarity. The EC Members agreed thatin case of an election tie, only the President should break thetie. J. Freymueller agreed on sending the latest version to
the EC Members.
36. Sponsorship of symposia and workshops
H. Drewes summarized the upcoming IAG Events. He notedthat if a meeting gets sponsored by IAG, early-career
scientists can apply for IAG Travel Awards.
37. Preparation of the IAG Closing Session
H. Drewes summarized the agenda of the IAG Closing
Session (see agenda item 4) and asked all symposia
conveners to prepare a brief report on the highlights.

75

38. Any other business
H. Schuh noted that there is interest of IAGA and IASPEI
for organizing a joint Scientific Assembly together with
IAG in 2025 in Lisbon, Portugal, which should beconsidered in future.
39. Appointment of Honorary Officers (President,
Secretary General, Fellows, Bylaws 22)
The EC Members discussed and approved the final list of
new IAG Fellows (available at IAG web site). The EC
Members appointed H. Schuh as IAG Honorary President
and H. Drewes as IAG Honorary Secretary General.
40. Closing the EC of the legislative period 2015-2019
H. Schuh presented his ideas for the future and concluding
remarks as IAG President, and he thanked especially J.
Adám for being President of the COB for 16 years, and H.
Drewes for being IAG Secretary General for 12 years. He
thanked the EC Members for their contributions over the lastterm and closed the session at 20:00. The EC Members
thanked H. Schuh for his dedication over the last years.

76

The Geodesist’s Handbook 2020

IUGG Resolutions at the XXVII General Assembly 2019

Resolution 1: Reducing the Carbon Foot
Print by the Research Community

Resolution 2: The International Terrestrial
Reference Frame (ITRF)

The International Union of Geodesy and Geophysics

The International Union of Geodesy and Geophysics

Considering
The clearly established impact of human activity on climatechange and biosphere degradation,
Acknowledging
The irreversible consequences of continuing the current
trajectory of greenhouse gas emission for the ecosystems of
the planet and human societies,
NotingThat the Intergovernmental Panel on Climate Change(IPCC), in its recent special report on the impact of global
warming of 1.5°C (IPCC, 2018; https://www.ipcc.ch/sr15/),x Demonstrated the dramatic differences between theconsequences of warming of 1.5°C and 2.0°C above preindustrial levels, andx Showed that limiting the warming to 1.5°C could beobtained only by strongly reducing carbon dioxide
emissions before 2030,
Urges
x IUGG and affiliated Scientific Associations to takecarbon foot print criteria into account when choosing thevenue of future meetings, andx The participants of the 27th IUGG General Assembly,
research institutions and individual researchers tocontribute to an unprecedented effort to evaluate andreduce greenhouse gas emission impact on theenvironment.
Resolves
The research community, which is well aware of the origins
and impact of climate change, should exhibit an exemplary
attitude by modifying its professional practices in order torapidly reduce its carbon footprint.

Consideringx The significant efforts of the International Associationof Geodesy (IAG) in developing and maintaining
fundamental geodetic products, in particular theInternational Terrestrial Reference Frame (ITRF), forscientific and societal benefits, andx The importance of inter-operability of various geospatial
data-sets and geo-referencing applications,Acknowledging
The adoption by the IUGG of Resolution 2 in Perugia 2007of the International Terrestrial Reference System (ITRS) as
the preferred Geocentric Terrestrial Reference System(GTRS) for scientific and technical applications,Notingx That the ITRF is the numerical realization of the ITRS,
developed, maintained and made available to users by
the International Earth Rotation and Reference Systems
Service (IERS), an IAG service, andx That the ITRF is widely used as the standard in various
geo-referencing applications,
Resolves
To recommend to the user community that the ITRF be thestandard terrestrial reference frame for positioning, satellite
navigation and Earth Science applications, as well as for thedefinition and alignment of national and regional reference
frames.

IUGG Resolutions

Resolution 3: Thanks
The International Union of Geodesy and Geophysics
Resolves
To record gratefully its appreciation for the organization,
arrangements, and hospitality at its 27th General Assembly.
On behalf of all participants the Council expresses its warm
thanks to the Local Organizing Committee, the Scientific
Program Committee, the Canadian Geophysical Union(CGU), the Canadian Meteorological and Oceanographic
Society (CMOS) and all others for making the 27th General
Assembly a success in the beautiful city of Montreal.

77

78

The Geodesist’s Handbook 2020

IAG Resolutions at the XXVII IUGG General Assembly 2019

Resolution 1: The International Terrestrial
Reference Frame (ITRF)

Resolution 2: Third Realization of the International Celestial Reference FrameThe International Association of Geodesy,

The International Association of Geodesy,

Considering,x The significant efforts of the International Associationof Geodesy (IAG) in developing and maintaining fundamental geodetic products for scientific and societal benefits, in particular the International Terrestrial Reference
Frame (ITRF);
x The importance of interoperability of various geospatial
data-sets and geo-referencing applications;

Considering,x That the International Union of Geodesy and Geophysics adopted at the 25th General Assembly in Melbourne
2011 Resolution 2 on the second realization of the International Celestial Reference Frame;x That the International Astronomical Union (IAU)
adopted Resolution B2 at its XXXth General Assembly(2018)(https://www.iau.org/static/resolutions/IAU2018_Resol
B2 _English.pdf) that resolves to consider the “Third
Realization of the International Celestial Reference
Frame (ICRF3)” as the fundamental realization of theInternational Celestial Reference System (ICRS) (seenote 1);x That the celestial reference system and the nutation‐
precession model have a large influence on geodetic andgeodynamic observations, analyses and interpretations;x That the ICRF3 was constructed by the International
Astronomical Union (IAU) involving working groupmembers of the International Earth Rotation and Reference Systems Service (IERS) and the International
VLBI Service for Geodesy and Astrometry (IVS)
communities;

Acknowledging,
The adoption by the IUGG Resolution 2 in Perugia 2007 of
the International Terrestrial Reference System (ITRS), as
the preferred Geocentric Terrestrial Reference System(GTRS) for scientific and technical applications;Noting,x That the ITRF is the numerical realization of the ITRS,
developed, maintained and made available to the users
by the International Earth Rotation and Reference Systems Service (IERS), an IAG service;x That the ITRF is widely used as the standard in various
geo-referencing applications;
Resolves,
To recommend to the user community that the ITRF be thestandard terrestrial reference frame for positioning, satellite
navigation and Earth science applications, as well as for thedefinition and alignment of national and regional reference
frames.

Recommends,
x That the ICRF3 should be used as a standard for all
future applications in geodesy and astrometry;x That the organizations responsible for geodetic VLBI
observing programs take appropriate measures tocontinue existing and develop improved VLBI
observing and analysis programs to both maintain andimprove ICRF3;

IAG Resolutions

x That highest consistency between the ICRF, the International Terrestrial Reference Frame (ITRF), and the Earth
Orientation Parameters (EOP) should be a primary goalin all future realizations.
Note 1: The Third Realization of the International Celestial
Reference Frame by Very Long Baseline Interferometry,
Presented on behalf of the IAU Working Group, Patrick
Charlot, Chris Jacobs, David Gordon et al. Astronomy& Astrophysics (in preparation).

Resolution 3: Establishment of the International Height Reference Frame (IHRF)
The International Association of Geodesy,
Considering,x The IAG Resolution for the Definition and Realizationof an International Height Reference System (IHRS) released at the 26th IUGG General Assembly in July 2015;
Acknowledging,
The achievements ofx GGOS Focus Area “Unified Height System” and its
JWG 0.1.2 “Strategy for the Realization of the International Height Reference System (IHRS)”,x IAG JWG 2.2.2 “The 1 cm geoid experiment”,
x IAG SC 2.2 “Methodology for geoid and physical heightsystems”,
x ICCT JSG 0.15 “Regional geoid/quasi-geoid modelling– Theoretical framework for the sub-centimetre
accuracy”;
in realizing this resolution;
Noting,
The need of an operational infrastructure to ensure the determination, maintenance and availability of an International Height Reference Frame (IHRF) in the long-term basis;
Urges,All countries to engage with the IAG and concerned components, in particular the International Gravity Field Service(IGFS), in order to promote and support the implementationof the IHRF by
x Installing IHRF reference stations at national level,x Conducting the necessary gravimetric surveys to guarantee the precise determination of potential values,
x Making data available open access,79

x Contributing to the development of analysis strategies toimprove the estimation of reference coordinates andmodelling of the Earth’s gravity field,
x Describing, archiving and providing geodetic products
associated to the IHRF.

Resolution 4: Establishment of the Infrastructure for the International Gravity Reference FrameThe International Association of Geodesy,
Considering,
The IAG Resolution No. 2 for the establishment of a global
absolute gravity reference system released at the 26th IUGG
General Assembly in July 2015;
Acknowledging,
The achievements ofx JWG 2.1.1 “Establishment of a global absolute gravity
reference system“,x Sub-Commission 2.1 “Gravimetry and Gravity
Networks”,
x International Gravity Field Service (IGFS)
in realizing this resolution;
Noting,That the realization of the International Gravity Reference
System (IGRS), the International Gravity Reference Frame(IGRF), is based on measurements with absolute gravimeters (AG) monitored at reference stations and during international comparisons, which needs the support of national
and international institutions;
Urges,
International and national institutions, agencies and governmental bodies in charge of geodetic infrastructure tox Establish a set of absolute gravity reference stations on
the national level,x Perform regular absolute gravity observations at thesestations,x Participate in comparisons of absolute gravimeters toensure their compatibility,
x Make the results available open access.

80

Resolution 5: Improvement of the Earth’s
Rotation Theories and Models
The International Association of Geodesy,
Recognizing,x That the continuous improvement of the terrestrial andcelestial reference systems and frames pursuing theaccuracy and stability goals set by GGOS is necessary
for determining and investigating the global change of
the Earth;x That the consistent definition and determination of therotation between the two reference frames is tightly
linked to geodynamics and necessary for the accurate
realization of terrestrial frames and the determination of
global geodetic variables;x That the current Earth rotation theories are unable tomodel and predict the Earth orientation parameters(EOP) with an accuracy close to the GGOS requirements, in spite of the improved accuracy and precisionof the individual and combined solutions derived fromsingle or multiple techniques;x That the precession nutation theories IAU2000 and
IAU2006 suffer from internal inconsistencies andsystematics whose correction is available, but also frominconsistencies due to incorporating outdated models
instead of the state-of-art models used in EOP determination;x That the theoretical models of the different EOPs andtheir observations are not always referred to the current
IAG standards, in particular regarding terrestrial reference frames;

The Geodesist’s Handbook 2020

Noting,x The results of the IAG Commission 3 Joint Working
Group on Theory of Earth and validation, joint with theInternational Astronomical Union (IAU) Commission
A2, summarized in its 2015-2019 report (see note 1);x The need of taking advantage of the advances accomplished or yet in progress on different aspects of thetheoretical and empirical modelling and prediction of the
Earth’s rotation to get closer to the GGOS goals;
Resolves,
x To encourage a prompt improvement of the Earth rotation theory regarding its accuracy, consistency, and ability to model and predict the essential EOP,
x That the definition of all the EOP, and related theories,
equations, and ancillary models governing their time
evolution, must be consistent with the reference frames
and the resolutions, conventional models, products, andstandards adopted by the IAG and its components,
x That the new models should be closer to the dynamicallytime-varying, actual Earth, and adaptable as much as
possible to future updating of the reference frames andstandards.
Note 1: Report of Commission 3 Joint Working Group 3.1
Theory of Earth rotation and validation (Joint with theIAU). In: IAG Reports Vol. 41 (Travaux de l’AIG 20152019, IAG Web page)Structures for the Period 2019 – 2023

81

Structures for the Period 2019 – 2023
International Union of Geodesy and Geophysics (IUGG)

Executive Committee

Secretariat of IUGG

BureauThe Secretariat of IUGG is located in Germany:
Helmholtz Centre Potsdam
GFZ German Research Centre for Geosciences
Telegrafenberg, A17
14473 Potsdam, Germany

President:
President-Elect:
Secretary General:
Treasurer:
Members:

Kathryn Whaler
Chris Rizos
Alexander Rudloff
Niels Andersen
Stephen McNutt
Eduard Petrovsky
Jun Xia

UK
Australia
Germany
Denmark
USA
Czech Republic
China

Immediate Past President: Michael Sideris Canada

Presidents of the International Associations
IACS:
IAG:
IAGA:
IAHS:
IAMAS:IAPSO:
IASPEI:
IAVCEI:

Regine HockZuheir Altamimi
Mioara Mandea
Günter Blöschl
Joyce Penner
Trevor McDougall
Kenji Satake
Patrick Allard

USA
FranceFranceAustria
USA
Australia
Japan
FranceFinance Committee
Chair:
Members:

Corina Risso
József ÁdámPriscilla Grew

Argentina
HungaryUSA

Executive Secretary: Franz G. Kuglitsch Germany
Assistant:
Katrin Gundrum
Germany
The Executive Secretary of IUGG is a non-voting Memberof the Bureau of the Union.

International Associations
International Association of Cryospheric Sciences
President:
Regine HockUSA
President-Elect:
Liss M. Andreassen Norway
Secretary General: Richard Essery
New ZealandInternational Association of Geodesy
President:
Zuheir Altamimi
FranceSecretary General: Markku Poutanen Finland
International Association of Geomagnetism and Aeronomy
President:
Mioara Mandea
FranceSecretary General: Monika Korte
Germany
International Association of Hydrological Sciences
President:
Günter Blöschl
Austria
President Elect:
Berit Arheimer
SwedenSecretary General: Christophe Cudennec France

82International Association of Meteorology andAtmospheric Sciences
President:
Joyce Penner
USA
Secretary General: Steven Ackerman
USA
International Association for the Physical Sciences of the Oceans
President:
Trevor McDougall Australia
Secretary General: Stefania Sparnocchia Italy
International Association of Seismology andPhysics of the Earth’s Interior
President:
Kenji Satake
Japan
Secretary General: Johannes Schweitzer Norway
International Association of Volcanology andChemistry of the Earth’s Interior
President:
Patrick Allard
FranceSecretary General: Roberto Sulpizio
Italy

Union Commissions and Working Groups
Union Commission on Climatic and Environmental Changes (CCEC)
Chair:
Jianping Li
China
Secretary:
Tonie Van Dam
Luxembourg

The Geodesist’s Handbook 2020

Union Commission on Mathematical Geophysics(CMG)
Chair:
Alik Ismail-Zadeh Germany/Russia
Secretary:
Ilya Zaliapin
USA
Union Commission on Geophysical Risk and Sustainability (GRC)
Chair:
John LaBrecque
USA
Secretary General: Katia Kontar
USA
Union Commission on Studies of Earth’s Deep Interior (SEDI)
Chair:
Christine Thomas Germany
Secretary:
Michael Bergman USA
Union Commission on Planetary Sciences (UCPS)
Chair:
Shuanggen Jin
China
Secretary:
Scot Rafkin
USA
Union Commission on Data and Information(UCDI)
Chair:
Sateesh Shenoi
India
Secretary:
Anatoly Soloviev
RussiaStructures for the Period 2019 – 2023

83

International Association of Geodesy (IAG)
Markku Poutanen (Secretary General)
iag.office@nls.fi

Overview
The structure of IAG comprises a number of components:
four Commissions, the Inter-Commission Committees on
Theory (ICCT), Climate Research (ICCC), and Marine Geodesy (ICCM), Project Novel Sensors and Quantum Technology for Geodesy (QuGe), twelve International Scientific
Services, the Global Geodetic Observing System (GGOS),
and the Communication and Outreach Branch (COB).
The Commissions are divided into Sub-commissions,
Study Groups and Working Groups. The Inter Commission
Committees (ICCs) and the Project investigate scientificgeodetic-related problems in close cooperation with theCommissions. The Services generate scientific products bymeans of Operation, Data and Analysis Centres.
The Global Geodetic Observing System GGOS is a component of IAG which works with the IAG Services to provide the geodetic infrastructure necessary for monitoring the
Earth system and global change research. GGOS ensures thebasis to maintain a stable, accurate and global reference
frame, which is crucial for all Earth observation.
The COB provides communication, public informationand outreach links, in particular via the IAG Website and themonthly Newsletters.
The IAG General Assembly, the Council, the Executive
Committee, and the Office carry out the administration of
IAG. The Council is composed by the delegates appointed
by the national adhering bodies; the Bureau comprises the
IAG President, Vice-President and Secretary General; theExecutive Committee consists of 17 elected members; andthe Office assists the Secretary General in fulfilling his duties. The COB is responsible for the promotional activitiesof the IAG and the communication with its members. The
detailed programme of the IAG is published in the quadrennial Geodesist’s Handbook, and reports are published in
the bi-annual IAG Reports (Travaux de l’AIG).

Figure 1. Structure of IAG

IAG Executive Committee
IAG Bureau
President:
Vice-President:
Secretary General:

Zuheir Altamimi
Richard Gross
Markku Poutanen

IAG Immediate Past President
President 2015-2019: Harald SchuhFranceUSA
FinlandGermany

IAG Immediate Past Secretary General
S.G. 2007-2019:
Hermann Drewes Germany
IAG Commission Presidents
Commission 1:
Christopher Kotsakis Greece
Commission 2:
Adrian Jäggi
Switzerland
Commission 3:
Janusz Bogusz
PolandCommission 4:
Allison Kealy
Australia

84

The Geodesist’s Handbook 2020

Inter-Commission Committee on Theory (ICCT)ICCT President:
Pavel Novák
Czech Republic
Global Geodetic Observing System (GGOS)
GGOS Chair:
Basara Miyahara Japan
Communication & Outreach Branch (COB)
COB President:
Szabolcs Rózsa
Hungary
Representatives of the Services
Representatives:
Johannes Böhm
Austria
Tom Herring
USA
Toshimichi Otsubo Japan

IAG Symposia Series
Editor in Chief:
Assistant Editor:

Jeff Freymueller
Laura Sánchez

USA
Germany

IAG Commissions
Commission 1: Reference Frames
President:
Christopher Kotsakis Greece
Vice-President
Jean-Paul Boy
FranceCommission 2: Gravity Field
President:
Adrian Jäggi
Vice-President
Mirko Reguzzoni

Switzerland
Italy

Members-at-Large
Members:
Sonia Costa
Yamin Dang

BrazilChina

Non-voting Members
ICCC:
Annette Eicker

Commission 3: Earth Rotation and Geodynamics
President:
Janusz Bogusz
PolandVice-President:
Cheng-Li Huang
China

Germany

ICCM:

Yuanxi Yang

China

QuGe:

Jürgen Müller

Commission 4: Positioning and Applications
President:
Allison Kealy
Australia
Vice-President:
Vassilis Gikas
GreeceIAG Past Presidents: Helmut Moritz
Ivan I. Mueller
Wolfgang Torge
Fernando Sansó
Gerhard Beutler
Michael Sideris
Chris Rizos
IAG Past SGs:
Claude Boucher

Germany
AustriaUSA
Germany
Italy
Switzerland
CanadaAustralia
FranceIAG OfficeFinnish Geospatial Research Institute, National Land Surveyof Finland, Masala, Finland
Director:
Markku Poutanen Finland
Treasurer:
Päivi Koponen
Finland

IAG Communication & Outreach Branch
Budapest University of Technology and Economics
President:
Szabolcs Rózsa
Hungary
Newsletter Editor:
Gyula Tóth
Hungary

Jürgen Kusche

Inter-Commission Committee on Theory (ICCT)ICCT President:
Pavel Novák
Czech Republic
Vice-President:
Mattia Crespi
Italy
Inter-Commission Committee for Climate Research(ICCC)
President:
Annette Eicker
Germany
Vice-President:
Carmen Böning
USA
Inter-Commission Committee on Marine Geodesy(ICCM)
President:
Yuanxi Yang
China
Vice-President:
Heidrun Kopp
Germany
Project Novel Sensors and Quantum Technology for Geodesy (QuGe)
President:
Jürgen Müller
Germany
Vice-President:
Marcelo Santos
CanadaIAG Global Geodetic Observing System

Journal of Geodesy
Editor in Chief:

IAG Inter-Commission Committees

Germany

GGOS Chair:Vice-Chair:

Basara Miyahara
Laura Sanchez

Japan
GermanyStructures for the Period 2019 – 2023

85

IAG Scientific Services

International Service for the Geoid (ISG)
President:
Mirko Reguzzoni
Director:
Daniela Carrion

Italy
Italy

International Gravity Field Service (IGFS)
Chair:
Riccardo Barzaghi
Director of Central Bureau: Georgios Vergos

Italy
GreeceInternational GNSS Service (IGS)
Chair of Governing Board: Gary Johnston
Director of Central Bureau: Allison Craddock

Australia
USA

International Digital Elevation Model Service (IDEMS)
Director:
Kevin M. Kelly USA

International Laser Ranging Service (ILRS)
Chair of Governing Board: Toshimichi Otsubo
Director of Central Bureau: Michael Pearlman

Japan
USA

International DORIS Service (IDS):
Chair Governing Board: Frank Lemoine
Director Central Bureau: Laurent Soudarin

International Service for Geodesy and Astrometry (IVS)
Chair of Directing Board: Axel Nothnagel
Austria
Director of Coord. Centre: Dirk Behrend
USA

Bureau Gravimetrique International (BGI)
Director:
Sylvain Bonvalot

FranceInternational Geodynamics and Earth Tide Service(IGETS)
Chair:
Hartmut Wziontek
Germany
Director Central Bureau: Jean-Paul Boy
FranceInternational Centre for Global Earth Models (ICGEM)
Director:Elmas Sinem Ince
Germany

USA
FranceInternational Earth Rotation and Reference Systems
Service (IERS)
Chair of Directing Board: Brian Luzum
USA
Director of Central Bureau: Daniela Thaller
Germany

Permanent Service for Mean Sea Level (PSMSL)
Director:
Elizabeth Bradshaw UK

Fig. 1. First meeting of the IAG Executive Committee in Montreal 2019

86

The Geodesist’s Handbook 2020

Contact addresses
ALTAMIMI
Dr. Zuheir
President, IAG

Institut National de l'Information
Géographique et Forestière (IGN)
Bâtiment Larmarck A
75013 Paris
FRANCEzuheir.altamimi@ign.fr

BARZAGHI
Prof. Riccardo
Chair, IAG International Gravity Field
Service (IGFS)

Politecnico di Milano
DIIAR
Piazza Leonardo Da Vinci 32
20133 Milan
ITALYriccardo.barzaghi@polimi.it

BEHREND
Dr. Dirk
Director of Coord. Centre, IAG
International VLBI Service for Geodesy &Astrometry (IVS)

NVI, Inc.
NASA Goddard Space Flight Center
Planetary Geodynamics Lab, Code 698
Greenbelt, MD, 20771
USA

dbb@ivscc.gsfc.nasa.gov

BOGUSZ
Prof. dr hab. inż. Janusz
President, IAG Commission 3: Earth
Rotation and Geodynamics

Military University of Technology (MUT) janusz.bogusz@wat.edu.pl
Faculty of Civil Engineering and Geodesy
Gen. S. Kaliskiego, 200-908 Warsaw
PolandBÖHM
Prof. Dr. Johannes
Service Representative, IAG Executive
Committee

Vienna University of Technology
Department of Geodesy andGeoinformation
Gußhausstraße 27-29
1040 Vienna
AUSTRIAjohannes.boehm@geo.tuwien.ac.at

BÖNING
Dr. Carmen
Vice-Pesident ICCC

Jet Propulsion Laboratory
M/S 300-323
4800 Oak Grove Drive
Pasadena, CA 91109
USA

carmen.boening@jpl.nasa.gov

BONVALOT
Dr. Sylvain
Director, IAG Service Bureau
Gravimétrique International (BGI)

Bureau Gravimétrique International
Observatoire Midi-Pyrénées
14-16 avenue Edouard Belin
31401 Toulouse Cedex 4
FRANCE

bonvalot@ird.fr

Ecole et Observatoire des Science de la
BOY
Dr. Jean-Paul
Terre
Director Central Bureau, IAG
5 rue René Descartes
International Geodynamics and Earth Tide 67084 Strasbourg
Service (IGETS)FRANCE

jjpboy@eost.u-strasbg.fr

BRADSHAW
Dr. Elizabeth
Director, IAG Permanent Service for
Mean Sea Level (PSMSL)National Oceanography Centre
Joseph Proudman Building
6 Brownlow Street
Liverpool, L3 5DAUK

psmsl@noc.ac.uk

COSTA
Dr. Sonia
Member-at-Large, IAG Executive
Committee

Instituto Brasileiro de Geografia eEstatística – IBGE
Av. Brasil,
15671 Parada de Lucas
Rio de Janeiro
Brasilsonia.alves@ibge.gov.br

Structures for the Period 2019 – 2023

CRADDOCK
Ms Allison
Director of Central Bureau, IAG
International GNSS Service (IGS)87

IGS Central Bureau
c/o Jet Propulsion Laboratory
Mail Stop 238-600
4800 Oak Grove Drive
PASADENA, CA 91109
USA

Politecnico di Milano
CARRION
IGeS at DIIAR
Prof. Daniela
P.za Leonardo da Vinci, 32
Director, IAG International Service for the 20133 Milano
Geoid (ISG)
ITALY

craddock@jpl.nasa.gov
craddock@igs.org

daniela.carrion@polimi.it

CRESPI
Prof. Mattia
Vice-President, IAG Inter-Commission
Committee on Theory (ICCT)

Università di Roma "La Sapienza"
mattia.crespi@uniroma1.it
Facolta' di Ingegneria Civile e Industriale
Dipartimento di Ingegneria Civile, Edile e
Ambientale
via Eudossiana, 1800184 Roma
ITALY

DANG
Prof. Dr. Yamin
Member at Large, IAG Executive
Committee

Institute of Geodesy and Geodynamics
Chinese Academy of Surveying &Mapping
28 Lianhuachi Xi RD
100830 Beijing
CHINA

dangym2015@163.com

DREWES
Prof. Dr. Hermann
Immedeate Past Secretary General, IAG

German Geodetic Research Institute ,TU München (DGFI-TUM)
Arcisstr. 2180333 Munich
GERMANYh.drewes@tum.de

EICKER
Prof. Dr.-Ing. Annette
President, IAG Inter-Commission
Committee for Climate Research

HafenCity University Hamburg
Geodesy and Geoinformatics
Überseeallee 1620457 Hamburg
GERMANY

annette.eicker@hcu-hamburg.de

FREYMUELLER
Prof. Jeffrey
Editor in Chief, IAG Symposia Series

Thomas A. Vogel Endowed Chair for
Geology of the Solid Earth
Dept. of Earth and Environmental
Sciences
Michigan State University
288 Farm Lane, Rm 207
East Lansing, MI, 48824
USA

freymuel@msu.edu

GIKAS
Prof. Vassilis
Vice-President, Commission 4

National Technical University of Athens
9 I. Polytechniou Str.
15780, Zographos, Athens
GREECEvgikas@central.ntua.gr

GROSS
Dr. Richard S.
Vice-President, IAG

Jet Propulsion Laboratory
Mail Stop 238-600
4800 Oak Grove Drive
Pasadena, CA, 91109
USA

richard.s.gross@jpl.nasa.gov

HERRING
Prof. Thomas
Service Representative, IAG Executive
Committee

Rm 54-322,
Departmant of Earth, Atmospheric andPlanetary Sciences
Massachusetts Institute of Technology
Cambridge, MA, 02139
USA

tah@mit.edu

88

The Geodesist’s Handbook 2020

HUANG
Prof. Cheng-Li
Vice-President, IAG Commission 3: Earth
Rotation and Geodynamics

Shanghai Astronomical Observatory CAS
80 Nandan Rd
Shanghai, 200030
CHINA

clhuang@shao.ac.cn

INCE
Dr. Elmas Sinem
Director, IAG International Centre for
Global Earth Models (ICGEM)GFZ German Research Centre forGeosciences
Telegrafenberg A17
14473 Potsdam
GERMANYelmas.sinem.ince@gfz-potsdam.deJÄGGIProf. Dr. Adrian
President, IAG Commission 2: Gravity
Field

University of Bern
Astronomical Institute
Sidlerstrasse 53012 Bern
Switzerland

adrian.jaeggi@aiub.unibe.ch

JOHNSTON
Dr. Gary
Chair of the Governing Board, IAG
International GNSS Service (IGS)

Geoscience Australia
Minerals and Natural Hazards Division
GPO Box 378
Canberra, ACT, 2601
AUSTRALIA

gary.johnston@ga.gov.au

KEALY
Assoc. Prof. Allison
President, IAG Commission 4: Positioning
and Applications

The University of Melbourne
Department of Infrastructure Engineering
Victoria, 3010
AUSTRALIA

a.kealy@unimelb.edu.au

KELLY
M.A.Sc. Kevin M.
Director, IAG International Digital
Elevation Model Service (IDEMS)

ESRI, Inc.
380 New York Street
Redlands, CA, 92373-8100
USA

kevin_kelly@esri.com

KOPONEN
Ms. Päivi
Assistant Treasurer

National Land Survey of Finland
Box 84 (Opastinsilta 12C)
00521 Helsinki
FINLAND

paivi.koponen@maanmittauslaitos.fi

KOPP
Prof. Heidrun
Vide-President ICCM

Helmholtz Centre for Ocean Research
Kiel
Wischhofstrasse 1-3
Room 8D-227
D-24148 Kiel
GERMANYhkopp@geomar.de

KOTSAKIS
Prof. Dr. Christopher
President, IAG Commission 1: Reference
FramesAUTH - Faculty of Engineering
School of Rural and Surveying
Engineering
Department of Geodesy and Surveying
Univ Box 440, Thessaloniki, 54124,
GREECE

kotsaki@topo.auth.gr

KUSCHE
Prof. Jürgen
Editor in Chief, Journal of Geodesy

University of Bonn
Institute for Geodesy and Geoinformation
Nussallee 1753115 BonnGERMANYjkusche@geod.uni-bonn.de

LEMOINE
PhD Frank
Chair of Governing Board, IAG
International DORIS Service (IDS)

NASA/GSFC
Mail Code: 61A
Greenbelt , MD 20771
USA

frank.g.lemoine@nasa.gov

Structures for the Period 2019 – 2023

89

LUZUM
Dr. Brian
Chair of Directing Board, IAG
International Earth Rotation & Reference
Systems Service (IERS)

U.S. Naval Observatory
Earth Orientation Department
3450 Massachusetts Ave NW
Washington, DC, 20392 5420
USA

brian.luzum@usno.navy.mil

MIYAHARA
Mr. Basara
Chair of the Global Geodetic Observing
System (GGOS)

Geospatial Information Authority of Japan miyahara-b96ip@mlit.go.jp
Ministry of Land, Infrastructure, Transport
and Tourism,
TsukubaJAPANMÜLLER
Prof. Dr.-Ing. habil. Jürgen
President, IAG Project Novel Sensors andQuantum Technology for Geodesy

Leibniz University Hannover
Institute of Geodesy
Schneiderberg 50
30167 Hannover
GERMANYmueller@ife.uni-hannover.de

NOTHNAGEL
Dr. Axel
Chair of Directing Board of IAG
International Service for Geodesy andAstrometry (IVS)

Technische Universität Wien
Forschungsbereich Höhere Geodäsie
Wiedner Hauptstraße 8A-1040 Wien
AUSTRIAaxel.nothnagel@tuwien.ac.at

NOVAKProf. Dr. Pavel
President, IAG Inter-Commission
Committee on Theory (ICCT)

University of West Bohemia
Faculty of Applied Sciences
Univerzitni 22306 14 Pilsen
CZECH REPUBLIC

panovak@kma.zcu.cz

OTSUBO
Prof. Toshimichi
Service Representative, IAG Executive
Committee

Hitotsubashi University
East Bldg, 2-1 Naka,
Kunitachi 186-8601
JAPANt.otsubo@r.hit-u.ac.jp

PEARLMAN
Dr. Michael R.
Director of Central Bureau, IAG
International Laser Ranging Service(ILRS)

Harvard-Smithsonian Center for
Astrophysics
60 Garden Street
Cambridge, MA, 02138
USA

mpearlman@cfa.harvard.edu

POUTANEN
Prof. Markku
Secretary General, IAG

Finnish Geospatial Research Institute FGINational Land Survey of Finland
Geodeetinrinne 202430 Masala
FINLAND

markku.poutanen@nls.fi
iag.office@nls.fi

REGUZZONI
Dr. Mirko
President, IAG International Service for
the Geoid (ISG)

Politecnico di Milano
IGeS at DIIAR
P.za Leonardo da Vinci, 32
20133 Milano
ITALY

mirko.reguzzoni@polimi.it

ROZSA
Dr. Szabolcs
President, IAG Communication &Outreach Branch

University of Technology and Economics
P.O. Box 91
1521 Budapest
HUNGARY

szrozsa@iag-aig.org

SANCHEZ
Dr. Laura
Vice-Chair GGOS
Assistant Editor, IAG Symposia Series

German Geodetic Research Institute
TU München (DGFI-TUM)
Alfons-Goppel-Str. 1180539 Munich
GERMANYlm.sanchez@tum.de

90

The Geodesist’s Handbook 2020

SANTOS
Prof. Marcelo
Vice-President, Project QuGe

University of New Brunswick
Dept. Geodesy and Geomatics Eng.
P.O. Box 4400
Fredericton, NB, E3B 5A3
CANADAmsantos@unb.ca

SCHUH
Prof. Dr. Harald
Immediate Past President, IAG

GFZ German Research Centre forGeosciences
Telegrafenberg A17
14473 Potsdam
GERMANYschuh@gfz-potsdam.de

SOUDARIN
Dr. Laurent
Director, Central Bureau of IAG
International DORIS Service (IDS)

CLS
8-10 rue Hermes
Parc Technologique du Canal
31520 Ramonville Saint-Agne
FRANCE

Laurent.Soudarin@cls.fr

THALLER
Dr. Daniela
Director of Central Bureau, IAG
International Earth Rotation & Reference
Systems Service (IERS)

Federal Agency for Cartography andGeodesy (BKG)
Richard-Strauss-Allee 1160598 Frankfurt
GERMANYdaniela.thaller@bkg.bund.de

VERGOS
Prof. Dr. Georgios
Director of Central Bureau,
IAGInternational Gravity Field Service(IGFS)

Department of Geodesy and Surveying
Aristotle University of Thessaloniki
University Box 440
54124 Thessaloniki
GREECEvergos@topo.auth.gr

WZIONTEK
Dr. Hartmut
Chair, IAG International Geodynamics
and Earth Tide Service (IGETS)BKG Federal Agency for Cartography and hartmut.wziontek@bkg.bund.de
Geodesy
Branch Office Leipzig
Karl-Rothe-Straße 10-1404105 Leipzig
GERMANY

YANG
Prof. Yuanxi
President, IAG Inter-Commission
Committee for Marine Geodesy

Chinese Academy of Sciences
yuanxi_yang@163.com
Xian Research Institute of Surveying and
Mapping, and China National
Administration of GNSS and Applications(CNAGA),
CHINA

Commission 1 – Reference Frames

91

Commission 1 – Reference Frames
President: Christopher Kotsakis (Greece)
Vice President: Jean-Paul Boy (France)
http://www.com1.iag-aig.org

Terms of Reference
Reference systems and frames are of primary importance for
Earth science based research and applications, satellite navigation and orbit determination as well as for practical applications in positioning, mapping and geo-information related fields. A precisely defined reference frame is needed
for an improved understanding of the Earth system, including its rotation and gravity field, sea level change with time,
tectonic plate motion and deformation, glacial isostatic adjustment, geocentre motion, deformation due to earthquakes, local subsidence, and other crustal displacements.
Commission 1 activities and objectives deal with the theoretical and operational aspects of how best to define reference systems and how reference systems can be used forpractical and scientific applications at different spatio-temporal scales on the deformable Earth. Commission 1 willclosely interact with the other IAG Commissions and Services, the ICCT, the newly established ICCC, and the
GGOS components where reference system aspects are ofconcern, to address related problems for the realization ofcelestial and terrestrial reference systems in conformity withpresent and future accuracy needs. Commission 1 is also
linked with the IUGG/COSPAR joint Sub-Commission B2(International Coordination of Space Techniques for Geodesy) under the aim to develop links and coordinate the work
between various groups engaged in the field of space geodesy and geodynamics.

Objectives
The main objectives of Commission 1 are as listed in the
IAG by-laws:
x Definition, establishment, maintenance and improvement of the geodetic reference frames;

x Advanced terrestrial and space observation techniquedevelopment for the above purposes;
x International collaboration for the definition anddeployment of networks of terrestrially-based space
geodetic observatories;
x Theory and coordination of astrometric observation forreference frame purposes;
x Collaboration with space geodesy/reference frame
relatedinternational
services,
agenciesandorganizations;x Promote the definition and establishment of verticalreference systems at global level, considering theadvances in the regional sub-commissions;x Work to maintain a reference frame that is valuable for
global change studies.

Structure
Sub-Commissions
SC 1.1: Coordination of Space Techniques
Chair: Urs Hugentobler (Germany)
SC 1.2: Global Reference Frames
Chair: Xavier Collilieux (France)
SC 1.3: Regional Reference Frames
Chair: Carine Bruyninx (Belgium)
SC 1.3a: Europe
Chair: Martin Lidberg (Sweden)
SC 1.3b: South and Central America
Chair: Sonia Maria Alves Costa (Brazil)
SC 1.3c: North America
Co-Chairs: Michael Craymer (Canada) and
Dan Roman (USA)SC 1.3d: Africa
Chair: Elifuraha Saria (Tanzania)

92

SC 1.3e: Asia-Pacific
Chair: Basara Miyahara (Japan)
SC 1.3f: Antarctica
Chair: Martin Horwath (Germany)
SC 1.4: Interaction of Celestial and Terrestrial Reference
FramesChair: Zinovy Malkin (Russia)
Joint Study Groups
JSG T.32: High-rate GNSS (joint with ICCT, Commissions
3 and 4, GGOS; see description under ICCT)
Chair: Mattia Crespi (Italy)
JSG T.24: Integration and co-location of space geodetic observations (joint with ICCT, Commissions 3 and 4,
GGOS; see description under ICCT)
Chair: Krzysztof Sośnica (Poland)
JSG T.31: Multi-GNSS theory and algorithms (joint with
ICCT, Commission 4, GGOS; see description under ICCT)
Chair: Amir Khodabandeh (Australia)
JSG T.33: Time series analysis in geodesy (joint with ICCT,
Commission 3, GGOS; see description under
ICCT)
Chair: Wieslaw Kosek (Poland)
JSG T.29: Machine learning in geodesy (joint with ICCT,
Commissions 2, 3 and 4, GGOS; see description
under ICCT)
Chair: Benedikt Soja (USA)JSG T.37: Theory and methods related to high-resolution
digital topographic and bathymetric models (joint
with ICCT, Commissions 2 and 3, GGOS; see description under ICCT)
Chair: D.Carrion (Italy)
JSG 3.1: Geodetic, seismic and geodynamic constraints on
GIA (joint with Commissions 2 and 3, IASPEI; see
description under Commission 3)
Chair: Rebekka Steffen (Sweden)
Vice-Chair: Erik R. Ivins (USA)
Joint Working Groups
JWG C.4: Regional sea level and vertical land motion (joint
with ICCC, Commissions 2 and 4, GGOS; see description under ICCC)
Chair: Roelof Rietbroek (Germany)
GGOS Working Group: Towards a consistent set of parameters for a new GRS (joint with Commission 2,
GGOS; see description under GGOS)
Chair: Urs Marti (Switzerland)

The Geodesist’s Handbook 2020

Program of Activities
Commission 1 fosters and encourages research in the areasof its sub-entities by facilitating the exchange of informationand organizing symposia, either independently or at major
conferences in geodesy, geophysics and geodynamics.
Some events will be focused narrowly on the interests of thesub- commissions and other entities listed above, and others
will have a broader commission-wide focus.
More specifically, the program of activities for Commission 1 includes:x Theoretical and applied research activities related toreference frames;
x Research and development activities that impact thereference frame determination and its accuracy, as wellas, the best and optimal usage of reference frames inEarth Science applications;x Interaction with all established IAG Services: IVS, IGS,ILRS, IDS and the IERS, including their Combination
Centres and Working Groups;
x Development in the theory of the transformation
between Celestial and Terrestrial Reference Systems andapplication of the theory to improve the consistency
between ICRF, ITRF and EOPs, in cooperation with IVS
and IERS;x Exploration of advanced methodologies for the
combination of products and raw observations of space
geodetic techniques;x Investigation of systematic error sources and factors
limiting the precision of space geodetic techniques andtheir combination;x Encouraging and assisting regional sub-commission
countries to re-define and modernize their national
geodetic systems so that they are compatible with the
ITRF;
The status of Commission 1, including its structure andmembership, as well as links to the internet sites of its subentities and parent and sister organizations and services, will
be updated regularly and can be viewed on the Commission’s webpage.

Steering Committee
President Commission 1: Christopher Kotsakis (Greece)
Vice President Comm. 1: Jean-Paul Boy (France)
Chair Sub-Comm. 1.1:
Urs Hugentobler (Germany)
Chair Sub-Comm. 1.2:
Xavier Collilieux (France)
Chair Sub-Comm. 1.3:
Carine Bruyninx (Belgium)
Chair Sub-Comm. 1.4:
Zinovy Malkin (Russia)
Representative of IGS: Paul Rebischung (France)
Representative of IERS: Detlef Angermann (Germany)
Member-at-Large:
Guangli Wang (China)

Commission 1 – Reference Frames

93

Sub-Commissions

Working Groups of Sub-Commission 1.1

SC 1.1: Coordination of Space Techniques

JWG 1.1.1: Intra- and Inter-Technique Atmospheric Ties (joint with SC 4.3 and GGOS)

Chair: Urs Hugentobler (Germany)
Terms of Reference
Space techniques play a fundamental role for the realizationand dissemination of highly accurate and long term stableterrestrial and celestial reference frames as well as for accurate monitoring of the Earth orientation parameters linking
the two fundamental frames. The current space geodetic
techniques contributing to ITRF and ICRF, i.e., Very Long
Baseline Interferometry (VLBI), Satellite and Lunar Laser
Ranging (SLR/LLR), Global Navigation Satellite Systems(GNSS) and Doppler Orbitography and Radiopositioning
Integrated by Satellite (DORIS) have particular strengths
and technique-specific weaknesses.
Strengths of the techniques are exploited by combining
them making use of fundamental sites co-locating more than
one technique. Sub-commission 1.1 focusses on the coordination of research related to the geodetic space techniqueswith emphasis on co-location aspects at fundamental geodetic observatories as well as on co- location targets inspace, considering common parameters such as coordinatesof stations and satellites, troposphere parameters, and clockparameters.
Objectives
x Coordinate research on co-location using common parameters in space;x Coordinate research on co-location using common parameters at fundamental geodetic observatories;
x Explore the use of new techniques and technologies;x Interface with IERS WG on Site Survey and Co- location;
x Interface with the GGOS Committee on Performance
Simulations and Architectural Trade-Offs (PLATO);
x Interface with Joint WG on Tropospheric Ties.

Chair: Kyriakos Balidakis (Germany)
Vice-Chair: Daniela Thaller (Germany)
Terms of Reference
The differences between atmospheric parameters (mainly
zenith delays and gradients) at co-located stations that observe nearly simultaneously, and stem from external systems (e.g., meteorological sensors or weather models) are
understood as atmospheric ties. Atmospheric ties mainly exist because of differences in (i) the observing frequency, (ii)the relative position, and (iii) the observing system set-up.
The acquisition of accurate atmospheric delay corrections is of paramount importance for mm-level positioning
employing space geodetic techniques. Atmospheric delay
corrections may stem from dedicated instruments such as
water vapor radiometers, meteorological sensors, numerical
weather models, or from the geodetic data itself. While thelatter is fairly common for modern GNSS and VLBI, observation geometry and accuracy limitations inherent to othersystems such as SLR and DORIS impede the accurate atmospheric parameter estimation, thus hindering among else
positioning. To this end, it might be useful to compare andcombine atmospheric parameters at co-located sites, in amanner similar to the combination of station and satellite
coordinates, as well as Earth rotation parameters (via local,
space, and global ties, respectively). The multi-technique
combination is indispensable to the distinction between real
signals and undesired technique-specific artefacts. Nowadays, the multi-technique combination is facilitated by theincreasing investments in state-of-the-art geodetic infrastructure at co-located sites. However, a host of systematicand random errors render the combination via atmosphericties a difficult task. Moreover, since atmospheric delays are
dependent upon essential climate variables (pressure, temperature, and water vapor), differences in long-term atmospheric delay time derivatives at co-located stations might offer an insight into local climate change.
Objectives
The purpose of this working group is to answer the following questions:x How can one relate atmospheric (electrically neutral)parameter estimates and the time derivatives thereof thatrefer to different place, time, and observing system?
What are the limits in distance, time lag, and observing
system?

94

x What is the optimal way to combine atmosphericparameters?
x What is the benefit from including atmospheric ties in a
multi-techniqueterrestrialreferenceframe
combination?
Proposed activities
x Comparison of atmospheric (electrically neutral) delay
estimates from single-technique geodetic analysis(GNSS, SLR, VLBI, and DORIS).
x Comparison of atmospheric delays from state-of-the-art
meso-β scale weather models (e.g., ERA5 and
MERRA2), and high-resolution runs utilizing theWeather Research and Forecasting (WRF) Model.
x Assessment of spatial and temporal correlation between
atmospheric parameters.
x Assessment of multi-technique combination employing
atmospheric ties on the single site and global TRF level.
List of members
Balidakis, Kyriakos (Germany), Chair
Boisits, Janina (Austria)
Coulot, David (France)Drożdżewski, Mateusz (Poland)
He, Changyong (France)
Heinkelmann, Robert (Germany)
Kitpracha, Chaiyaporn (Germany)
Lemoine, Frank (USA)
Lengert, Lisa (Germany)
Nilsson, Tobias (Sweden)
Pollet, Arnaud (France)
Santos, Marcelo (Canada)
Soja, Benedikt (USA)Sośnica, Krzysztof (Poland)
Thaller, Daniela (Germany), Vice-Chair
Wang, Xiaoya (China)
Wijaya, Dudy (Indonesia)
Zus, Florian (Germany)

SC 1.2: Global Reference Frames
Chair: Xavier Collilieux (France)
Terms of Reference
Sub-commission 1.2 focuses its activity on the definition
and realization of the terrestrial reference system (TRS).
The TRS realization, named Terrestrial Reference Frame(TRF), is fundamental to study and locate global phenomena
or objects at the Earth's surface, in the ocean or in space. It

The Geodesist’s Handbook 2020is used as the basis of several operational observation system processing chains such as sea level determination fromspace and Earth’s rotation monitoring but is also used formost regional and national TRFs. Thus, TRF specificationsin terms of origin, scale and orientation have to be optimallyrealized to satisfy user needs. That’s why sub-commission
1.2 shall study either fundamental questions or more practical aspects that could improve current TRF determinations.
Thanks to the accumulation of space geodesy observations and progress in modeling and analysis, non-stationary
Earth surface displacements are nowadays clearly evidenced. The next generation of TRF should be able to explicitly model them or should be constructed in such a waythat those displacements are accurately modelled. There are
currently two different approaches to represent the TRF:
Long-term linear and nonlinear TRFs. Time series of quasiinstantaneous frames are proposed but practical implementations still need to be investigated so that the implicit reference frame definition reach the required accuracy. Augmented parametric TRF, coupled with enhanced forward
displacement models is an alternative to TRF time series.
This approach is in agreement with past modeling of the International Terrestrial Reference Frame (ITRF) but still require progress in forward models (e.g. loading and postseismic deformations). The dominant non-steady displacement signal is the geocenter motion which is related to theorigin definition of the frame. While its main contribution is
included in non-tidal loading forward models and while it
can be observed by space geodesy, there are still open questions regarding its annual variation.
Technique systematic errors still exist in space geodesy
products, which impact the TRF definition, especially thescale parameter. Dedicated satellite missions with onboard
multi-technique sensors could improve further our understanding of technique systematic errors thanks to solving parameters common to multiple techniques. However, a set of
accurate tie vectors that relate position of various technique
instruments at co-location sites will still be of outmost importance to validate those new space-ties and monitor theirlong-term variations. In parallel, due to the high cost of local
tie surveys, it is worth investigating supplementary ways tomonitor reference point variations with time. Here, the potential of PSInSAR technique to investigate ground/monument deformation is proposed.
A step forward could be established by investigating relativistic reference frames based on a network of clocks inspace linked with time transfer technologies. Such realized
frame would be entirely decoupled from ground fixed stations and could be used to reference any point on the Earth's
surface. The relativistic frequency shift between clocks inspace and on the ground would be a direct measurement of
the Earth gravity potential. This technology can be used toCommission 1 – Reference Frames

realize a world height system based on a network of groundclocks.
While this ultimate goal still requires intensive researchworks, TRF and future World Height Systems need to bestudied in closer partnership in order to connect reference
benchmarks, gravimeters or clocks to the TRF but also toprovide consistent coordinate and height time-variations.
The work of this sub-commission will be done in partnership with the International Earth Rotation and Reference
Systems Service (IERS) as well as IAG Global Geodetic
Observing System (GGOS).
Objectives
The main objectives of sub-commission 1.2 are the following:
x Definition of the global terrestrial reference frame(origin, scale and orientation, time evolution, standards,
conventions, models);
x Methods to determine local tie vectors and to relate
instrument reference points to surveyed ground markers;
x Investigate new methods to determine relative motions
at co-location sites;
x Evaluation of technique systematic errors by focusing onerrors at co-location sites;
x Enhanced forward modeling of the Earth’s surface
deformation;
x Modeling of the reference frame in general relativity;
x Linking global height reference frames with theterrestrial reference frame;x Pursue studies and investigation related to multitechnique satellites (space ties) and concepts of novel
dedicated missions with onboard multi-techniquesensors.
Link to Services
Sub-Commission 1.2 will establish close links to relevant
services for geodetic reference frames, namely the IERS,
GGOS and IAG technique services: International GPS Service (IGS), International Laser Ranging Service (ILRS), International VLBI Service for Geodesy and Astrometry(IVS), and International DORIS Service (IDS). A close linkwith the IERS Conventions Center will be also maintained,
especially for chapter 4 (“Terrestrial Reference Systems andFrames”) updates.

95

Working Groups of Sub-Commission 1.2
WG 1.2.1: Assessing impacts of loading on
Reference Frame realizations
Chair: Anthony Mémin (France)
Terms of Reference
Non-tidal loading (NTL) deforms the Earth's surface adding
variability to the coordinates of geodetic sites. The effectsof NTL are already observed in geodetic time series from
VLBI, SLR, DORIS and GNSS techniques. They occur in awide range of period, from sub-daily to centennial timescale. They also have an impact on crustal velocity estimatesand as a consequence on the realization of the terrestrial reference frame.
It has been shown that unconsidered NTL effects canbias estimates of geodetic vertical velocity by 0.5 mm/yr
over the continent to more than 1 mm/yr in the southern
tropical regions between 1993 and 2014 (SantamaríaGómez and Mémin 2015). It is five to more than ten times
larger than the requirement of the Global Geodetic Observing System on interannual to secular time scales and about
one-third of the current rate of sea level rise.
Geodetic techniques require accurate global circulation
models to allow precise estimation of the Earth's surface displacements to reduce the variability of position time series,
in addition to the corresponding time-variable gravity field
affecting the orbits of artificial satellites. Correcting for
NTL at the observation level reduced for example the variability of GNSS time series by up to 7 mm (Männel et al.
2019).
According to the 2010 IERS conventions, there are currently no recommended surface-mass change models (atmosphere, ocean circulation, ocean response to atmosphericchanges, hydrology, past- and present-day ice-mass, sealevel) nor Earth models (1D vs 3D, elastic, visco-elastic,rheology, coastline definition) to account for NTL deformation in geodetic position time series. Hence, a better understanding of NTL contribution to geodetic time series isrequired. Also, several studies have already shown that aposteriori corrections slightly decrease the variance factor
of a Terrestrial Reference Frame (TRF) multi-technique
combination but the improvement at some sites was alsocounterbalanced by degradation at others. The accuracy andprecision of current space geodetic techniques are such thatseveral scientific studies have already considered atmospheric loading corrections at the observation level. However, there still exist open questions regarding the application of loading corrections for the generation of operational
geodetic products, either a priori or a posteriori.

96

References
Santamaría-Gómez A, Mémin A (2015) Geodetic secularvelocity errors due to interannual surface loading deformation. Geophys J Int Exp Lett 202 (2):763–767,
doi:10.1093/gji/ggv190.
Männel B, Dobslaw H, Dill R, Glaser S, Balidakis K,
Thomas M, Schuh H (2019) Correcting surface loadingat the observation level: impact on global GNSS andVLBI station networks, J Geod,doi.org/10.1007/s00190-019-01298-y.
Objective
The principal objectives of the scientific work are to assess
the effects of load and Earth models and their applications
for TRF utilization and to assemble specific recommendations for users and future IERS conventions.
Program of Activities
x Create and maintain an updated list of loading studies:models and observations.
x Compare and assess differences between existing load
models.
x Assess ice and sea level change loading deformation.
x Assess the propagation of loading model errors anddifferences in using several Earth models into the site
coordinates, TRF parameters and the ITRF.
x Determine whether load models should be applied apriori or a posteriori.
x Organize meetings during international conferences(EGU, AGU…).
x Suggest recommendations for IERS conventions.
List of members
Jean-Paul Boy (France)
Kristel Chanard (France)
Benjamin Maennel (Germany)
Anthony Mémin (France), Chair
Laurent Métivier (France)
Manuela Seitz (Germany)
Giorgio Spada (Italy)
Daniela Thaller (Germany)
Wouter van der Wal (The Netherlands)
Corresponding members
Christopher Kotsakis (Greece)

The Geodesist’s Handbook 2020

JWG 1.2.2: Methodology for surveying geodetic instrument reference points(joint with IERS)

Chair: Ryan Hippenstiel (USA)Vice-Chair: Sten Bergstrand (France)
Terms of Reference
The International Terrestrial Reference System is built upon
multiple geodetic techniques; Satellite Laser Ranging(SLR), Very Long Baseline Interferometry (VLBI), Doppler
Orbitography and Radiopositioning Integrated by satellite(DORIS), and Global Navigation Satellite Systems (GNSS).
At locations where these techniques are co-located, it is vitalto determine and understand the vectors between the reference points of each technique. These vectors are determinedby local tie surveys conducted terrestrially with various procedures and geodetic instruments. The reference points
should be collected and properly aligned to a global reference frame in order to produce relative and absolute coordinates.
As the science of local tie surveys has developed, so has
technology and the expectation of higher precision and improved protocols. It is the desire of this working group to
investigate the current and expected best practices available,
along with documenting past efforts, both in the field andresearched. This working group will share methodology ofexisting tie surveys, continued to develop and document recommended procedures, and also archive surveys completedby all agencies represented.
In addition, efforts will be made to isolate systematic errors of the space geodetic techniques using surveying methods and investigate field procedures that could be completed
during the course of a tie survey in order to provide the operator valuable feedback on potential physical errors foundonsite. One critical example of this is quantifying thermal
and gravitational deformation in VLBI sensors. It is theoverall goal of the working group to encourage consistent
field practice, terminology, and documentation throughout
the community, with a continued eye on the future of tie surveys.
Objective
Enhance and improve knowledge of local tie surveys
through applied field practice, research, and disseminationof materials developed.
Activities
x Investigate thermal and gravitational deformation.
x Consider importance and inclusion of DoV
observations.

Commission 1 – Reference Frames

x Discuss overall error budget and precision(achieved/necessary) considering the above.
x Continue to enhance guidelines on procedures (andsubsequent feedback for improvement).
x Archive reports, tie vectors and raw data of all agencies
conducting tie surveys.
x Gather, distribute, and maintain publications on related
matters.
x Coordinate with and solicit feedback from all geodetic
techniques on developments.
Expectations
x Participation in local tie surveys and/or testing of new
methodologies.
x Attendance of meetings or participation in remote/virtual discussions.
x Reporting of survey results and/or research efforts towards the objectives of the WG.
x Develop and maintain a depository of past and futurereference materials.
List of members
Zuheir Altamimi (France)
Sten Bergstrand (France), Vice-Chair
Steven Breidenbach (USA)
Benjamin Erickson (USA)Kendall Fancher (USA)Charles Geoghegan (USA)
Ryan Hippenstiel (USA), Chair
Kevin Jordan (USA)Jack McCubbine (Australia)
Damien Pesce (France)
Jerome Saunier (France)
Corresponding members
Xavier Collilieux (France)
Mike Pearlman (USA)97

JWG 1.2.3: Toward reconciling Geocenter
Motion estimates(joint with IERS)

Chair: Kristel Chanard (France)
Vice-Chair: Alexandre Couhert (France)
Terms of Reference
The International Terrestrial Reference Frame (ITRF) origin
is realized through Satellite Laser Ranging (SLR) orbit dynamics determining the Center of Mass (CM) of the Earthsystem, e.g. the solid Earth and its fluid envelops. The ITRF
origin is considered, over secular time scales, to be the mean
Earth CM, averaged over the time span of SLR observations(IERS Conventions 2010). Over shorter time scales, the
ITRF origin behaves as an approximated Center of Figure(CF) of the solid Earth surface. The motion of CM with respect to CF is commonly called geocenter motion.
For number of operational and scientific applications,such as improving the ITRF accuracy or refining estimatesof sea level variations, the ITRF origin should coincide with
CM at any time. Thus, accessing true geocentric positions
requires, to this day, to adopt a model for geocenter motion.
However, due to discrepancies in models derived from various techniques and methods, no conventional model for geocenter motion has not been conventionally accepted yet. It
is therefore the focus of this working group to identify scientific and technical obstacles leading to inconsistencies in
geocenter motion estimates obtained from various geodetic
techniques or forward geophysical models. Consequently,
the working group will first gather geocenter motion timeseries derived from geodetic products, along with detailed
information on methods of estimation, compare estimatesand closely investigate discrepancies. We seek to identify
potential sources of geodetic systematic errors and/or inconsistencies in methodologies used to retrieve geocenter motion (network effect, etc.), at both the annual and interannual
time periods. A special attention will then be given to improving and/or developing new methods, less sensitive toerrors in geodetic products and provide refined geocentermotion estimates.
Objectives
x To review all methods to estimate geocenter motion,
both from geodetic data and forward geophysicalmodelling, and systematically compare results.
x To focus on discrepancies in geocenter motion estimatesand investigate potential biases in methods and/or
systematic errors in geodetic products.
x To study the relative merit of geocenter motion datatypes (SLR, DORIS, GNSS, GNSS+LEOs). Special

98emphasis should be placed in evaluating the networkeffect biases.
x To evaluate consistencies in methods used to retrieve
geocenter motion (translational and inverse approaches,
forward modelling).
x To assess the impact of errors in geocenter motion
through variability in estimates for operational andscientific users.
Program of Activities
x Organize a group meeting to discuss the above
objectives.
x Gather estimates of geocenter motion from working
group members and proceed to systematic comparison
highlighting discrepancies.
x Publishing a report on the current status of geocentermotion and associated error budget (and possibly
provide common components to all estimates as a mean
geocenter motion model).
x Contribution to international meetings and conferences(AGU, EGU, IUGG).
x Managing a website with all geocenter motion models
and detailed information on estimates.
x Common publications by working group members.
List of members
Kristel Chanard (France), Chair
Xavier Collilieux (France)
Alexandre Couhert (France), Vice-Chair
Robert Dill (Germany)
Suzanne Glaser (Germany)
Christopher Kotsakis (Greece)
Flavien Mercier (France)
Laurent Métivier (France)
Paul Rebischung (France)
John Ries (USA)
Ricardo Riva (Nehterlands)
Krystof Sosnica (Poland)
Dariusz Strugarek (Poland)
Xiaoping Wu (USA)
Radoslaw Zajdel (Poland)

The Geodesist’s Handbook 2020

Study Groups of Sub-Commission 1.2
SG 1.2.1: Relevance of PSInSAR analyses at
ITRF co-location sites
Chair: Xavier Collilieux (France)
Vice-Chair: Thomas Fuhrmann (Australia)
Terms of Reference
The scientific community has recognized the need for ahighly accurate terrestrial reference frame (TRF) for Earth
Science applications. Current determination of the International Terrestrial Reference System is made by combining
data from space geodetic techniques, namely Satellite Laser
Ranging (SLR), Very Long Baseline Interferometry(VLBI), Doppler Orbitography and Radiopositioning Integrated by satellite (DORIS), Global Navigation Satellite
Systems (GNSS), but also terrestrial measurements from local tie survey at co-location sites. For most of the sites, such
local tie surveys are not performed on a regular basis. Thus,
it is not possible to test the assumption of no relative motion
between instrument reference points which is currently done
almost exclusively by analyzing space geodetic data themselves.
The PSInSAR (Persistent Scatterer Interferometric Synthetic Aperture Radar) technique allows for determining deformation maps over large areas with various spatial resolutions as function of the satellite missions. Due to the availability of freely available SAR data for a significant periodof time at many sites, it is relevant to ask if such data could
supplement local tie measurements for those sites where
sufficiently repeated terrestrial surveys do not exist. There
are however some limitations that need to be addressed suchas the size of a co-location site which is between 100 m and
1 km or the reference points themselves that are not accessible from the SAR satellites. Artificial corner reflectors or
active transponders might however be used to add a PSInSAR measurement point in this context. Studying PSInSAR
results in C- and X-band at some co-location sites is worth
investigating to assess the potential use of this technique inreference frame determination in the future.
Objective
The main objective is to investigate if the PSInSAR technique can be used to supplement local tie surveys at ITRF
multi-technique sites.

Commission 1 – Reference Frames

99

Proposed activities

Objectives

x List strength and weakness of the PSInSAR technique
for this application.
x Collect all studies related to INSAR and moreparticularly PSInSAR at co-location sites.
x If relevant, make an inventory of SAR images (for all
missions) available at ITRF co-location sites.
x If relevant, identify multi-technique co-location sites
where PSInSAR processing should be performed andcompare InSAR results from various software packages.
Compare results of free, but low-resolution, Sentinel-1
data with commercial high-resolution data (e.g.
TerraSAR-X) where available; investigate whether arequest for a supersite could be used to obtain additional
high-resolution data (https://www.earthobservations.org/documents/gsnl/20120918_GSNL_CEOSSelectionPro
cess.pdf).
x Investigate the relevance of installing corner reflectors
or transponders at co-location sites.
x Report conclusions and recommendations in IAG 2021
and/or IUGG2023 proceedings.

In addition to the specific objectives of each regional Subcommission, the main objectives of SC1.3 as a whole are to:x Coordinate the activities of the regional Sub-commissions focusing on exchange of data, competences and results;
x Promote operation of permanent GNSS stations, in connection with IGS whenever appropriate, as the basis forthe long-term maintenance of regional reference frames;
x Promote open access to the GNSS data from permanent
GNSS stations used for the maintenance of regionalreference frames and scientific applications;x Develop specifications for the definition and realizationof regional reference frames, including the vertical component;
x Encourage and stimulate the development of the AFREF
project in close cooperation with IGS and other interested organizations;x Encourage and assist countries, within each regional
Sub-commission, to re-define and modernize their national geodetic systems, compatible with the ITRF;
x Support the efforts of the United Nations Initiative on
Global Geospatial Information Management (UNGGIM) towards a sustainable Global Geodetic Reference Frame (GGRF).

List of members
Xavier Collilieux (France), Chair
Francesco DeZan (Germany)
Stefan Friedländer (Germany)
Thomas Fuhrmann (Australia)
Christoph Gisinger (Germany)
Thomas Gruber (Germany)
Amy Parker (Australia)
Corresponding members
Ann Chen (USA)Clément Courde (France)

SC 1.3: Regional Reference Frames
Chair: Carine Bruyninx (Belgium)
Terms of Reference
Sub-commission 1.3 deals with the definitions and realizations of regional reference frames and their connection to
the global International Terrestrial Reference Frame (ITRF)
and International Height Reference Frame (IHRF). It offersa home for service-like activities addressing theoretical andtechnical key common issues of interest to regional organisations.

Program of Activities
x Provide a forum for addressing activities, results and key
issues of common interest to the regional Sub-commissions;x Develop analysis strategies and compare methods for the
implementation of the regional reference frames andtheir expression in the ITRF, in full interaction with the
IGS;
x Consider developing tectonic deformation models thatwill enable transformation of locations within a definedreference frame between different epochs;

SC 1.3a: Europe (EUREF)
Chair: Martin Lidberg (Sweden)
Secretary: Karin Kollo (Estonia)
Terms of Reference
EUREF, the Regional Reference Frame Sub-commission
for Europe, deals with the definition, realization and maintenance of the European Reference Frames. EUREF is focusing on both the spatial and the vertical components in100

close cooperation with the pertinent IAG components (Services, Commissions, and Inter-commission projects). For
more information, see www.euref.eu.
Objectives
x The definition, realization and maintenance of the European Geodetic Reference Systems;
x The promotion and assistance of the adoption and use ofEuropean Terrestrial Reference System (ETRS89) andEuropean Vertical Reference System (EVRS) in ourpartner countries;
x The development and maintenance of the EUREF GNSS
Permanent Network (EPN) which is the ground based
GNSS infrastructure for scientific and practical applications in positioning and navigation (Global Geodetic
Observing System - GGOS, IGS Real-time Service);x The development of strategies and technologies for therealization of geodetic reference systems.
Structure
EUREF is composed of representatives from European IAG
member countries. The Governing Board (GB) is composedof members elected by the EUREF plenary, members incharge of special tasks and ex-officio members. The current
Chair of GB is Wolfgang Söhne (Germany).
In addition, several Working Groups have been set up:
x Working group on "European Dense Velocities"
Chair: Elmar Brockmann (Switzerland)x Working group on "EPN Densification"
Chair: Ambrus Kenyeres (Hungary)x Working group on "Deformation models"
Chair: Martin Lidberg (Sweden)x Working Group on “Multi GNSS”
Chair: Elmar Brockmann (Switzerland)x Working group on "EPN Reprocessing"
Chair: Christof Völksen (Germany)
Program of Activities
x Continue to develop the EPN in close cooperation with
IGS (International GNSS Service), for the maintenanceof the European Terrestrial Reference Frame (ETRF), asa contribution to the ITRF and as an infrastructure to
support practical applications for precise positioning andreferencing geo-information;
x Extend the Unified European Levelling Network(UELN) in order to include as many countries as possible in the current realization of the European Vertical
Reference System (EVRS), and further continue thelong-term maintenance of the European Vertical Reference Frame (EVRF) applying a kinematic approach;

The Geodesist’s Handbook 2020

x Closely follow and contribute to the developments regarding the International Height Reference System(IHRS) and its realizations in International Height Reference Frames (IHRF), and when appropriate establish
the precise relation between IHRF and EVRF;
x Promote efforts on regional geoid models in Europe as
the link between the ETRF and the EVRF;
x Support new developments in reference frame realization and applications by introducing new technologies
like real-time GNSS data transfer and products, as well
as Galileo for precise positioning;x Realize a dense and homogeneous position and velocity
product for Europe;x Establish a dense velocity field model in Europe for the
long-term maintenance of the European reference frame;x Provide GNSS tropospheric estimates at the EPN stations in support of climate research;x Contribute to the IAG Programme GGOS using the installed infrastructures managed by the EUREF members;
x Promote the adoption of the reference systems definedby EUREF (ETRS89 - European Terrestrial Reference
System 1989 and EVRS - European Vertical Reference
System) in the European countries and European-wide
initiatives related to geo-referencing activities like INSPIRE;x Cooperate with European political and scientific organisations and projects, e.g. EuroGeographics, EUMETNET, CEGRN (Central European GPS Geodynamic
Reference Network), EPOS (European Plate Observing
System), UN-GGIM: Europe, etc.;x Organize annual symposia addressing activities carriedout at national and Europe-wide levels related to theglobal work and objectives of EUREF.
Members of the EUREF Governing Board
The members of the Governing Board in the fall of 2019 are
as follows. However, some new members are foreseen to beelected at the symposium in May 2021. An up to date list isavailable at www.euref.eu.
Carine Bruyninx (Belgium)
Elmar Brockmann (Switzerland)
Rolf Dach (Switzerland)
Ambrus Kenyeres (Hungary)
Karin Kollo (Estonia)
Juliette Legrand (Belgium)
Martin Lidberg (Sweden)
Tomasz Liwosz (Poland)
Rosa Pacione (Italy)
Martina Sacher (Germany)
Wolfgang Söhne (Germany, Chair of GB)
Christof Völksen (Germany)

Commission 1 – Reference Frames

Active honorary members:
Zuheir Altamimi (France)
Alessandro Caporali (Italy)
Markku Poutanen (Finland)João Agria Torres (Portugal)

SC 1.3b: South and Central America (SIRGAS)
Chair: José Antonio Tarrio (SIRGAS WG I Chair)Vice-Chair: Demián Gomez (SIRGAS WG II Chair)Terms of Reference
Sub-commission 1.3b (South and Central America) encompasses the activities developed by the “Geocentric Reference System for the Americas” (SIRGAS). As such, it isconcerned with the definition, realization and maintenanceof a modern geodetic reference infrastructure for South andCentral America and the Caribbean. This includes a geometric reference frame consistent with ITRS/ITRF and a gravity
field-related vertical reference system, defined and realized
globally.
Objectives
x To determine, maintain and make available a geocentricreference frame (a set of stations with high-precise geocentric positions and their variation with time) as a regional densification of the global ITRF;
x To support the SIRGAS countries in the establishment
and maintenance of national geodetic reference networks as local densifications of SIRGAS in order toguarantee accessibility to the global ITRF at national andlocal levels;
x To establish a unified vertical reference system supporting the determination and precise combination of physical and geometric heights as well as their variations withtime;
x To contribute to the GGOS program by developing andimplementing state-of-the-art products based on the
SIRGAS observational infrastructure;x To promote, support, and coordinate the efforts of theLatin American and Caribbean countries to achievethese objectives.
Structure
The structure of the Sub-commission 1.3b is based on thefunctioning SIRGAS Working Group I - Reference System
and Working Group II - National Level. SIRGAS WG I coordinates the functioning and analysis of the SIRGAS Continuously Operating Network (SIRGAS-CON). SIRGAS101

WGI also promotes the installation of the of analysis centres
for SIRGAS, under the responsibility of American institutions and the use of SIRGAS observations for atmospheric(ionosphere and troposphere) studies. SIRGAS WGII is responsible for promoting and supporting the adoption of SIRGAS realization through continuous operating GNSS stations.
x SC1.3b-WG 1: Reference System
Chair: José Antonio Tarrio (Chile)x SC1.3b-WG 2: SIRGAS at National Level
Chair: Demián Gomez (US)The SIRGAS Executive Committee (as it is named in the
SIRGAS statutes) is composed of:x Chair: Sonia María Alves Costa (Brasil).
x Vice-Chair: Diego Alejandro Piñón (Argentina)
x WG1 Chair: José Antonio Tarrio (Chile)x WG2 Chair: Demián Gomez (US)x WG3 Chair: Gabriel do Nascimento Guimarães (Brazil)
Program of Activities
Since the SIRGAS countries are improving their national reference frames by installing an increasing number of continuously operating GNSS stations, it is necessary to outline
the best strategy for the appropriate integration of those frames into the continental frame. This includes:
x Promotion of the IGS and IERS standards within the
SIRGAS countries to ensure the adequate installation,
maintenance, and analysis of continuously operating
GNSS stations;x Establishment of a SIRGAS National Processing Centre
in all the member countries;
x Refinement of the SIRGAS station hierarchy. At present, two classes are considered: core and densification
stations (the establishment of other categories is underconsideration);x Promotion of the adequate usage of SIRGAS as a reference frame by means of capacity building activities. This
comprises SIRGAS schools on reference frames, scientific processing of GNSS data, atmospheric analysis
based on the SIRGAS infrastructure, etc.;
x Promotion and implementation of real-time services
based on the SIRGAS infrastructure to make available
the reference frame to more users;
x The kinematics of the SIRGAS frame, up to now, havebeen represented by linear station movements (i.e. constant velocities). This representation is not sufficiently
precise due to existing seasonal variations in the station
position time series and due to discontinuities caused by
the frequent occurrence of seismic events in the SIRGAS
region.

102

According to this, it is necessary:x To model non-linear station movements within the reference frame computation;
x To implement a methodology aiming at a precise transformation between different epochs and, in general, between pre-seismic and post-seismic reference frame realizations in particular;
x To evaluate the feasibility of computing and using nearreal time reference frames instead of those based on
epoch station positions and constant velocities.
The establishment of a unified vertical reference system
continues to be a big challenge of SIRGAS. The related activities concentrate on:
x Continental adjustment of the national vertical networks
in terms of geo-potential numbers;
x Combined analysis of tide gauge registrations, GNSS
positioning and satellite altimetry observations to determine the dynamic ocean topography at the classical vertical datums;x Determination of potential differences between the reference tide gauges and the global reference surface;x Stronger cooperation with the Sub-Commission 2.4b
(Gravity and Geoid in South and Central America GGSCA) to promote national initiatives regarding themodernization of the gravity reference networks and thecomputation of geoid models of high resolution.
Hourly SIRGAS ionospheric models (vTEC) based on the
GNSS SIRGAS stations have been generated since 2003 to2015. The SIRGAS ionospheric model is being upgraded toinclude a better distribution of the electron density based on
the assimilation of ground- and space-based GNSS observations. In addition, SIRGAS is developing a service for estimate hourly tropospheric Zenith Total Delay (ZTD) basedon the operational SIRGAS processing. The ZTD estimatesallow inferring Integrated Water Vapour (IWV) values withhigh accuracy.
Members
SIRGAS Executive committee
Sonia María Alves Costa, Chair (Brasil)
Diego Alejandro Piñón, Vice-Chair (Argentina)
José Antonio Tarrio SIRGAS-WG1 Chair (Chile)
Demián Gomez SIRGAS-WG2 Chair (US)Gabriel do Nascimento Guimarães SIRGAS-WG3 Chair(Brazil)
SIRGAS Directing council
Hermann Drewes, Representative of IAG
Hector Carlos Rovera Di Landro, Representative of PAIGH
Juan Francisco Moirano (Argentina)
Demian Gómez (Argentina)

The Geodesist’s Handbook 2020

Arturo Echalar Rivera (Bolivia)
Mario Sandoval Nava (Bolivia)
Luiz Paulo Souto Fortes (Brazil)
Sonia Maria Alves Costa (Brazil)
Emilio Aleuy Schwerter (Chile)
Sergio Rozas Bornes (Chile)
Jose Ricardo Guevara Lima (Colombia)
Francisco Javier Mora Torres (Colombia)
Max Lobo Hernández (Costa Rica)Álvaro Álvarez Calderón (Costa Rica)
Bolívar Troncoso Morales (Dominican Republic)
José Leandro Santos (Dominican Republic)
Edgar Fernando Parra Cárdenas (Ecuador)
Jose Luis Carrión (Ecuador)
Carlos Enrique Figueroa (El Salvador)
Wilfredo Amaya Zelaya (El Salvador)Óscar Cruz Ramos (Guatemala)Fernando Oroxan Sandoval (Guatemala)Rene Duesbury (Guyana)
Hilton Cheong (Guyana)
Bruno Garayt (French Guyana)
Alain Harmel (French Guyana)
Luis Alberto Cruz (Honduras)
Enrique Muñoz Goncen (Mexico)
Francisco Medina (Mexico)
Wilmer Medrano Silva (Nicaragua)
Ramón Aviles Aburto (Nicaragua)
Javier Cornejo (Panama)
Melquiades Dominguez (Panama)
Daniel Arias (Paraguay)
Joel Roque Trinidad (Paraguay)
Julio Enrique Llanos Alberca (Peru)
Julio Sáenz Acuña (Peru)
Daniel Piriz (Uruguay)
Gustavo Cauberrere (Uruguay)
Dana J. Caccamise II (USA)
Daniel R. Roman (USA)Jose Napoleón Hernández (Venezuela)
Melvin Jesús Hoyer Romero (Venezuela)
SIRGAS Scientific Council
Hermann Drewes (Germany)
Luiz Paulo Souto Fortes (Brazil)
Laura Sanchez (Germany)
Claudio Brunini (Argentina)
María Virginia Mackern (Argentina)

Commission 1 – Reference Frames

103

SC1.3c: North America (NAREF)

Working Groups of Sub-Commission 1.3c

Co-Chairs: Michael Craymer (Canada)
Dan Roman (USA)WG 1.3c.1: North American Reference
Frame Densification (NAREF)

Terms of Reference
To provide international focus and cooperation for issues involving the horizontal, vertical, and three-dimensional geodetic control networks of North America, including Central
America, the Caribbean and Greenland (Denmark). For
more information, see www.naref.org.
Objectives
In collaboration with the IAG community, its service organisations, and the national geodetic organizations of North
America, the aims and objectives of this regional Sub-commission are to provide international focus and cooperation
for issues involving the horizontal, vertical and three dimensional geodetic control networks of North America. Someof these issues include:x Densification of the ITRF reference frame in North
America and the promotion of its use;
x Definition, maintenance and future evolution of platefixed geometric reference frames for North America, including the North American Datum of 1983 (NAD83)
and the forthcoming North American Terrestrial Reference Frame of 2022 (NATRF2022).
x Effects of crustal motion, including post-glacial reboundand tectonic motions along, e.g., the western coast of
North America and in the Caribbean;x Standards for the accuracy of geodetic positions;x Coordination of efforts with neighbouring SC1.3b SouthAmerica (SIRGAS) to ensure strong ties between eachother’s reference frames;
x Outreach to the general public through focused symposia, articles, workshops and lectures, and technology
transfer to other groups.
Steering committee
Michael Craymer (Canada)
Dan Roman (USA)Finn Bo Madsen (Denmark)Chair: Michael Craymer (Canada)
Programme of Activities
To densify the ITRF reference frame in the North American
region by organizing the computation of weekly coordinate
solutions and associated accuracy information for continuously operating GPS stations that are not part of the current
IGS global network. A cumulative solution of coordinate
and velocities will also be determined on a weekly basis.
The working group will organize, collect, analyse and combine solutions from individual agencies, and archive anddisseminate the weekly and cumulative solutions.
Members
Michael Craymer (Canada), Chair
Mike Piraszewski (Canada)
Remi Ferland (Canada)
Daniel Roman (USA)
Theresa Damiami (USA)Sungpil Yoon (USA)
Jarir Saleh (USA)Finn Bo Madsen (Denmark)

WG 1.3c.2: Plate-Fixed North American Terrestrial
Reference
Frame
of
2022
(NATRF2022)
Chair: Dan Roman (USA)
Programme of Activities
To establish a high-accuracy, geocentric reference frame,
including velocity models, procedures and transformations,tied to the stable part of the North American tectonic plate
which would replace NAD83 and serve the broad scientificand geomatics communities by providing a consistent, mmaccuracy, stable reference with which scientific and geomatics results (e.g., positioning in tectonically active areas) canbe produced and compared.
Members
Daniel Roman (USA), Chair
Michael Craymer (Canada)
Joe Henton (Canada)
Dru Smith (USA)104

Theresa Damiami (USA)Michael Bevis (USA)
Geoff Blewitt (USA)Tom Herring (USA)
Jeff Freymueller (USA)Corné Kreemer (USA)Richard Snay (USA)WG 1.3c.3: Reference Frame Transformations in North America
Chair: Michael Craymer (Canada)
Programme of Activities
To determine consistent relationships between international,
regional and national reference frames in North America, tomaintain (update) these relationships as needed and to provide tools for implementing these relationships.
Members
Michael Craymer (Canada), Chair
Daniel Roman (USA)Dru Smith (USA)SC 1.3d: Africa (AFREF)
Chair: Elifuraha Saria (Tanzania)
Terms of Reference
Sub-commission 1.3d (Africa) is concerned with the definition and realization of a unified continental reference frame(AFREF) for Africa, which will be consistent and homogeneous with the global International Terrestrial Reference
Frame (ITRF).
Objectives
In collaboration with the IAG community and its services,
regional organisations, and the National and Regional Mapping Organizations of Africa, the objectives of Sub-commission 1.3d (Africa) are:x Coordinate the activities of the regional organisations
focusing on exchange of data, competences and results;
x Promote operation of permanent GNSS stations, in connection with IGS whenever appropriate, as the basis forthe long-term maintenance of regional reference frames;
x Promote open access to the GNSS data from permanent
GNSS stations used for the maintenance of regional reference frames and scientific applications;

The Geodesist’s Handbook 2020

x Develop specifications for the definition and realizationof regional reference frames, including the vertical component;
x Encourage and stimulate the development of the AFREF
project in close cooperation with IGS and other interested organizations;x Encourage and assist countries, within each regional organisation, to re-define and modernize their national geodetic systems, compatible with the ITRF;
x Support the efforts of the United Nations Initiative on
Global Geospatial Information Management (UNGGIM) towards a sustainable Global Geodetic Reference Frame (GGRF).
Structure
x Chair: Elifuraha Saria (Tanzania)
x Governing Board (see list of members below)
Programme of Activities
x Provide a forum for addressing activities, results and key
issues of common interest to the regional organisations;x Develop analysis strategies and compare methods for the
implementation of the regional reference frames andtheir expression in the ITRF, in full interaction with the
IGS;
x Consider developing tectonic deformation models thatwill enable transformation of locations within a definedreference frame between different epochs.
Members
Elifuraha Saria (Tanzania), Chair
Emanuel Nkurunziza (Kenya)
Joseph Dodo (Nigeria)
Salah Mahmud (Egypt)
Cesare Mbaria (Kenya)
Prosper Ulotu (Tanzania)
Andre Nonguierma (Burkina Faso)
Akingbade O (Nigeria)
Moha El-Ayachi (Morocco)
Elias Lewi (Ethiopia)
Patrick Vorster (South Africa)
Prof. Kamal Labbassi (Morocco)
Active honorary members:
Richard Wonnacott (South Africa)
Hussein Farah (Kenya)
Olajide Kufoniyi (Nigeria)
Some additional members are foreseen to be elected at the
AFREF meeting in 2020.

Commission 1 – Reference Frames

SC 1.3e: Asia-Pacific (APREF)
Chair: Basara Miyahara (Japan)
Terms of Reference
Sub-commission 1.3e aims to improve regional cooperationthat supports the realization and densification of the ITRF.
This activity will be carried out in close collaboration with
the Geodetic Reference Framework for Sustainable Development Working Group of the United Nations Global Geospatial Information Management for Asia and the Pacific(UN-GGIM-AP). For more details about UN-GGIM-AP
WG1 http://www.un-ggim-ap.org/workinggroups/geodetic.
Objectives
x The densification of the ITRF and promotion of its use
in the Asia Pacific region;x To encourage the sharing of GNSS data from
Continuously Operating Reference Stations (CORS) in
the region;x To develop a better understanding of crustal motion in
the region;x To promote the collocation of different measurement
techniques, such as GNSS, VLBI, SLR, DORIS and tidegauges, and the maintenance of precise local geodetic
ties at these sites; andx To outreach to developing countries through symposia,
workshops, training courses, and technology transfer
activities.
Program of Activities
The activities of Asia-Pacific Sub-commission will principally be those of the Asia-Pacific Reference Frame(APREF) project. The APREF project consists of a Central
Bureau, Network operators, Data centers, and Analysis centers. The Central Bureau, within Geoscience Australia,
functions as the 'day-to-day' APREF coordinating body.
Specifically, the Central Bureau ensures that APREF products are made available to the global geodetic community.
Furthermore, they are the combination center responsible
for analyzing, combining and validating the individual solutions of the contributing Analysis Centers, and for expressing the combined solution in the ITRF. Following APREF
data and products are provided with an open access data policy via the internet following the practice of the IGS. They
consist of daily GNSS RINEX data, station log files, weekly
coordinate estimates in SINEX format, and APREF networkand time-series plots. For more details, see
http://www.ga.gov.au/scientific-topics/positioning-navigation/geodesy/asia-pacific-reference-frame.

105

Members
The members of the Asia-Pacific Sub-commission are national geodetic representatives from the UN-GGIM-AP
member nations and APREF participating organisations.
UN-GGIM-AP WG1 (Geodetic Reference Frame)
Basara Miyahara (Japan), ChairJohn Dawson (Australia), vice-Chair
Yamin Dang (China)
S. K. Singh (India)
Mohd Yunus (Malaysia)
Dalkhaa Munkhtsetseg (Mongolia)
Graeme Blick (New Zealand)
Sangoh Yi (South Korea)
APREF Analysis Group
Guorong Hu (Australia)
Alex Woods (Australia)
Yunbin Yuan (China)
Basara Miyahara (Japan)

SC 1.3f: Antarctica
Chair: Martin Horwath (Germany)
Terms of Reference
Sub-commission 1.3f focuses on the realization and densification of a unified reference frame for Antarctica, which
will be consistent with the global International Terrestrial
Reference Frame (ITRF). The Sub-commission shares objectives and activities of the Scientific Committee on Antarctic Research (SCAR), namely of the SCAR Expert Group
Geodetic Infrastructure of Antarctica (GIANT). The Subcommission closely links IAG and SCAR activities by embedding identical activities, with identical persons where indicated, into the two complementary organisational structures.
Objectives
x Maintenance and densification of the precise geodetic
reference network in Antarctica by permanent observations and GNSS campaigns;
x Realization of a unified vertical datum including GNSS
ties of tide gauges;
x Providing unified reference for further GNSS applications like airborne gravimetry, ground truthing for satellite missions, geodynamics and glaciology;
x Develop technologies for remote geodetic observatories;

106

x Stimulate and coordinate international collaboration on
the above fields, under the unique political conditions of
Antarctic research given by the Antarctic Treaty, in order to make optimum use of logistics and infrastructure.
Program of Activities
x Organization of GNSS campaigns in Antarctica;
x Extend activities for the operation of remote permanent
GNSS stations;x Maintenance of the data archive (SCAR GNSS database) to collect Antarctic GNSS data and provide themto the scientific community;
x Data analysis and determination of the Antarctic GNSS
network as a regional densification of ITRF;
x Provide homogeneous site velocities for e.g. glacial isostatic adjustment determination;
x Support airborne surveys and satellite missions with precise terrestrial reference;x Collaborate with IAG Sub-Commission 3.4 (Cryospheric Deformation) and the SCAR Scientific Research Programme Solid Earth Response and Influence
on Cryosphere Evolution (SERCE) and subsequent programmes, respectively
x Organize special workshop(s) on the consistent analysis
of GNSS data and realization of ITRF
x Organize meetings/sessions at conferences like IAG,IUGG, SCAR Open Science Conference.
Members
Martin Horwath (Germany), Chair
Alessandro Capra (Italy)
Mirko Scheinert (Germany)
Manuel Berrocoso (Spain)
Graeme Blick (New Zealand)
Koishiro Doi (Japan)
Rene Forsberg (Denmark)Thomas James (Canada)
Aspurah Kamburov (Bulgaria)
Matt King (Australia)
Kenichi Matsuoka (Norway)
Alexey Matveev (Russia)
Gennadi Milinevsky (Ukraine)
Elizabeth Petrie (United Kingdom)
Markku Poutanen (Finland)
Goncalo Prates (Portugal)
Lars Sjoberg (Sweden)
Norbertino Suarez (Uruguay)
Terry Wilson (USA)Andres Zakrajsek (Argentina)

The Geodesist’s Handbook 2020

Working Groups of Sub-Commission 1.3
WG 1.3.1: Time-dependent transformations
between reference frames in deforming regions
Chair: Richard Stanaway (Australia)
Terms of ReferenceThis WG will review different approaches used to enabletransformation between reference frames within plateboundary zones and regions affected by glacial isostatic adjustment. These transformations are necessarily time-dependent to account for interseismic strain and also episodic
seismic deformation. In these instances conformal transformations do not adequately model the complexity of the deformation field and other approaches are required to enablehigh precision transformations at different epochs of thesource and target reference frames.
Deformation models and other time-dependent transformation models provide linkages between global reference
frames such as ITRF, regional reference frames and local
reference frames commonly used for positioning, land surveying, mapping and GIS.
The WG will collaborate with other regional reference
frame working groups to develop a global deformation andtransformation model schema. This will require development of a standardized deformation model format that canbe accessed from international registries of geodetic parameters such as those hosted by ISO/TC 211 and IOGP/EPSG.
WG 1.3.1 will work closely with FIG Commission 5 (Positioning and Measurement), specifically FIG Working Group
5.2 (Reference Frames). WG members comprise of a wide
spectrum of researchers from different fields of geophysics,
geodesy, land surveying and GIS.
List of members
Richard Stanaway (Australia), Chair
Wan Anom Wan Aris (Malaysia)
Elmar Brockmann (Switzerland)
Miltiadis Chatzinikos (Greece)
Yingyang Cheng (China)
Michael Craymer (Canada)
Chris Crook (New Zealand)
Nic Donnelly (New Zealand)
Kristian Evers (Denmark)Jeff Freymueller (USA)Pasi Häkli (Finland)
Muzaffer Kahveci (Turkey)
Kevin Kelly (USA)Martin Lidberg (Sweden)

Commission 1 – Reference Frames

Niraj Manandhar (Nepal)
Basara Miyahara (Japan)
José Antonio Tarrío Mosquera (Chile)
Chris Pearson (New Zealand)
Susilo Sarimun (Indonesia)
Corresponding members:
Graeme Blick (New Zealand)
Carine Bruyninx (Belgium)
Xavier Collileux (France)
Paul Denys (New Zealand)
Craig Roberts (Australia)
Yoshiyuki Tanaka (Japan)
Norman Teferle (G.-D. Luxembourg)

SC 1.4: Interaction of Celestial and Terrestrial Reference Frames
Chair: Zinovy Malkin (Russia)
Terms of Reference
International terrestrial and celestial reference frames, ITRF
and ICRF, respectively, as well as the tie between them expressed by the Earth Orientation parameters (EOP) are key
products of geodesy and astrometry. The requirements to all
the components of this triad grow steadily and the mm/μas
level of accuracy is the current goal of the astronomic andgeodetic community.
The current computation procedures for ITRF and ICRF
are based on multi-stage processing of observations madewith several space geodetic techniques: VLBI, SLR, GNSS,
and DORIS. Not all of them provide equal contributions to
the final products. The latest ITRF realizations have been
derived from combination of normal equations obtained
from all four techniques, whereas the ICRF is a result of asingle global VLBI solution. The latter is tied to the ITRF
using an arbitrary set of reference stations. But VLBI relieson the ITRF origin provided by satellite techniques andshares responsibility with SLR for the ITRF scale. And all
the techniques contribute to positions and velocities of ITRF
stations.
This situation causes complicated mutual impact of
ITRF and ICRF, which should be carefully investigated inorder to improve the accuracy of both reference systems andthe consistency between each other and EOP. The subject
becomes more and more complicated when moving to millimeter accuracy in all components of this fundamental
triad. As a consequence, we face systematic errors involving
the connection between the ICRF and ITRF realizations,which cannot be fixed by datum correction during the current solution.

107

Objectives
Several issues are currently preventing the realization of theterrestrial and celestial reference systems (TRF and CRF,
respectively) at the mm/μas level of accuracy, such as: (a)insufficient number and non-optimal distribution of active
and stable (systematically and physically) stations (VLBI
and SLR in the first place) and radio sources, (b) technological (precision) limitations of existing techniques, (c) incompleteness of the theory and models, and (d) not fully understood and agreed-upon details of the processing strategy.
These issues are the subject of research of the IAG SubCommission 1.4.

Working Groups of Sub-Commission 1.4
WG 1.4.1: Improving and unification of geophysical and astronomical modeling for better consistency of reference frames
Chair: Daniel MacMillan (USA)Terms of Reference
WG 1.4.1 is aimed to promote and coordinate investigationsof the impact of geophysical and astronomical modeling on
the terrestrial and celestial reference frames (TRF and CRF)
and the consistency between CRF, TRF, and Earth orientation parameters (EOP), the latter serving as the transformation parameters between TRF and CRF. The primary attention will be given to VLBI as the only technique nowadays that can provide highly consistent global solutions for
TRF, CRF, and EOP.
Objectives
x Encourage and develop cooperation and collaboration intheoretical studies, simulations, and processing of real
data aimed at a better understanding of the impact ofgeophysical and astronomical modeling on TRF, CRF,
and EOP derived from VLBI observations.
x Advance means of comparing models as well as TRF,
CRF, and EOP realizations.
x Compare different theoretical models and theirrealizations used by VLBI analysis centers. Study the
propagation of differences in those models to differencesin geodetic and astrometric products.
x Develop practical recommendations for VLBI analysis
centers and the IERS Conventions Center on the optimalmodels to be used during processing of VLBI
observations.

108

List of members
Robert Heinkelmann (Germany)
Hana Krasna (Austria, Czech Republic)
Sebastien Lambert (France)
Daniel MacMillan (USA), Chair
Zinovy Malkin (Russia)
David Mayer (Austria)
Lucia McCallum (Australia)
Tobias Nilsson (Sweden)
Stanislav Shabala (Australia)

WG 1.4.2: Improving VLBI-based ICRF andcomparison with Gaia-CRF
Chair: Sébastien Lambert (France)
Terms of Reference
WG 1.4.2 is aimed to review the current CRF status, to identify deficiencies and to make proposals for improvements.
The WG will pay a particular attention to the next ICRF
VLBI realization, ICRF3 extension or ICRF4, which should
be a significant improvement over ICRF3 in respect of number of core and supplement radio sources, uncertainty andaccuracy of the source position, and uniform distribution
over the sky. Moreover, the Gaia mission is expected to improve an optical realization of the CRF with precision similar to the ICRF and with 1–2 order of magnitude more objects. However, as the set of extragalactic objects suitablefor both optical and radio observation is limited, one goal of
the WG is to identify such objects, oversee the relevant observations, and to analyze the data to permit the best possible connection between the radio and optical CRF realizations.
Objectives
x Analyze the ICRS/ICRF definition in view of the latest
developments in astrometry and space geodesy.
x Study systematic errors in the current individual CRF
and ICRF realizations.
x Review systematic differences between CRF
realizations at different wavelengths due to, e.g., coreshift or host galaxies.
x Analyze different modeling options and analysis
strategies of computation of the next ICRF realization.
x Develop optimal procedures to align GCRF to ICRF.
List of members
Christopher Jacobs (USA)Maria Karbon (Germany)

The Geodesist’s Handbook 2020

Sebastien Lambert (France), Chair
Daniel MacMillan (USA)Zinovy Malkin (Russia)
Francois Mignard (France)
Jacques Roland (France)
Manuela Seitz (Germany)

JWG 1.4.3: Consistent realization of TRF,
CRF, and EOP (joint with IAU Commission A2 and
IERS)

Chair: Robert Heinkelmann (Germany)
Vice-Chair: Manuela Seitz (Germany)
Terms of Reference
Many applications, e.g. in geodesy, astronomy, or navigation, rely on the consistency between terrestrial (TRF) andcelestial (CRF) reference frames and Earth Orientation Parameters (EOP). The EOP connect the CRF and TRF in
terms of their orientation and rotation differences. The EOP
can only be considered as physically meaningful when determined consistently with the reference frames. The quality
requirements for the applications including societal contributions were quantified through the IAG GGOS as 1 mm
accuracy and 0.1 mm/yr stability, i.e. about 33 μas and 3.3
μas/yr in terms of EOP. For Earth system science based on
EOP the consistency is a crucial characteristic. Today, thequality requirements for reference frames and EOP are notmet.
Data and model inconsistency. Currently, TRF and CRF
are determined independently of each other. Individual
Working Groups (CRF) or Combination Centers (TRF)
compute the frames through reprocessing/combination efforts every five to ten years. The releases of the terrestrial
and celestial frames do not happen at the same time. In thisway, the frames are computed based on different input dataand on different analysis models in case of updates of theconventional models. Following independent approaches,
the consistency of a new release of one of the frames canonly be quantified and thus ensured to the last release of therespective other frame. If the frames are not fully consistent,
the EOP based on these frames cannot be consistent.
Multi-technique vs. single technique analysis. DORIS,
GNSS, SLR and VLBI observations are combined with local tie vectors at co-location sites for the TRF computation,
whereas the CRF is directly connected to the TRF through
VLBI alone. This situation does not change when applying
alternative data analysis procedures. Nevertheless, as VLBI
networks are sparse in comparison to multi-technique networks, it has been shown that the terrestrial part of the Earthorientation significantly improves through the combination

Commission 1 – Reference Frameswith satellite-based data. The celestial parts of Earth orientation, dUT1 (UT1 ~ ERA) and CPO, determined by VLBI
observations only – and possibly by LLR data –, can in turnimprove due to correlations between the EOP within the
VLBI data analysis. CRF realizations in other wavelengths
are aligned to the X/S VLBI CRF and thus, do not contributeto the CRF orientation for ICRF3. Nevertheless, they allow
for an independent validation. Apart from the rotation andspin, catalogues based on Gaia (optical) data releases canprovide independent insight into deformations and othertechnique-dependent systematic errors and thus present another independent validation for the VLBI-based CRF.
Prediction problem. The reference frames and the EOP
are customarily applied in prediction mode, e.g. for geodetic
and astrometric data analyses. Accordingly, values have to
be given beyond the data time span considered for the reference frame realization. As long as no significant non-linearity occurs, the global coordinates can be used very well for
predicting the position into the future. For most of the applications, predicted EOP have to be available as well. The predicted EOP require consistency to the frames and to the reprocessed EOP at the same time. It is impossible to fulfill
both requirements when new reference frame releases become available.
Objectives
Addressing the abovementioned issues, the working groupwill:
x compute multi-technique CRF-TRF solutions together
with EOP in one step, which will serve as a basis toquantify the consistency of the current conventionalreference frames and EOP as well as the consistency of
reprocessed and predicted EOP;x investigate the impact of different analysis options,model choices and combination strategies on theconsistency between TRF, CRF, and EOP;x study the differences between multi-technique and
VLBI-only solutions;x study the differences between VLBI solutions at
different radio wavelengths;
x study the differences between Gaia (optical) and VLBI
(radio) reference frames;
x study the effects on the results, when different data timespans are considered;x compare the practically achievable consistency with thequality requirements theoretically addressed by IAG
GGOS; andx derive conclusions about future observing systems or
analysis procedures in case the quality requirements
cannot be met with the current infrastructure andapproaches.

109

List of members
Claudio Abbondanza (USA)Sabine Bachmann (Germany)
Liliane Biskupek (Germany)
Christian Bizouard (France)
Xavier Collilieux (France)
Aletha de Witt (South Aftica)
Anastasiia Girdiuk (Germany)
David Gordon (USA)Robert Heinkelmann (Germany), Chair, IERS Analysis Coordinator
Christopher Jacobs (USA)
Shuanggen Jin (China)
Hana Krasna (Austria)
Sebastien Lambert (France)
Karine Le Bail (USA)
Daniel MacMillan (USA)Zinovy Malkin (Russia), representative of IAG SC 1.4
David Mayer (Austria)
Manuela Seitz (Germany), Vice-Chair
Benedikt Soja (USA)Nickolas Stamatakos (USA)Corresponding members
Alberto Escapa (Spain), representative of IAU Comm. A2
Richard Gross (USA)
Florian Seitz (Germany), representative of IAU Comm. A2
Jean Souchay (France)
Daniela Thaller (Germany), Director of IERS Central Bureau
Proposed cycle
Classical cycles: IAG WG (4 year cycle), IAU WG (3 year
cycle), IERS WG (2 year cycle). A 4-year cycle is proposedin order to be compliant with IAG bylaws as the initiative
and thus the primary affiliation of this JWG is with IAG.

110

The Geodesist’s Handbook 2020

Commission 2 – Gravity Field
President: Adrian Jäggi (Switzerland)
Vice President: Mirko Reguzzoni (Italy)
https://com2.iag-aig.org/

Terms of Reference
The accurate determination of the gravity field and its temporal variations is one of the three fundamental pillars ofmodern geodesy (besides of geometry/kinematics and Earthrotation). This is essential for applications in positioning andnavigation, civil and aerospace engineering, metrology, geophysics, geodynamics, oceanography, hydrology, cryospheric sciences and other disciplines related to the Earth’s
climate and environment. IAG Commission 2 was established at the IUGG in Sapporo in summer 2003 for promoting, supporting, and stimulating the advancement ofknowledge, technology, and international cooperation in thegeodetic domain associated with the Earth’s gravity field.
Since most of the scientific themes are of long-term interest, large parts of the structure of Commission 2 are continued on the same basis as in the previous period 2015-19.
Main drivers for the activities of the present period 2019-23
are related to the IAG resolutions adopted at the XXVIIIUGG General Assembly 2019 in Montreal, concerning theestablishment of the International Height Reference System(IHRS) and the establishment of the Infrastructure for theInternational Gravity Reference Frame (IGRF).
Commission 2, at the start of the new period, consists ofsix sub-commissions (SCs), plus some Joint Study Groups(JSG) and Joint Working Groups (JWG), all of them jointlywith other Commissions and/or services. The sub-commissions cover the following scientific topics:x Terrestrial (land, marine, airborne) gravimetry and relative/absolute gravity networks;
x Geoid, Physical Height Systems and Vertical Datum
Unification;x Satellite gravity missions;x Regional geoid determination;x Satellite altimetry;x Gravity inversion and mass transport in the Earth system.
Commission 2 has strong links to other commissions,
GGOS, IGFS, ICCT and other components of IAG. Connections to these components are created through joint working
groups (JWGs) and joint study groups (JSGs) that provide across-disciplinary stimulus for work in several topics of interest to the commission, and the joint organization of meetings.
The main tasks of Commission 2 in the period 2019-23
are among others:
x Establishment of a Global Absolute Gravity Reference
System (GAGRS) to replace the International Gravity
Standardization Net 1971 (IGSN71), which no longer
fulfills the requirements and accuracy of a modern gravity reference; especially to include time-dependent gravity variations;x Supporting the realization of an International Height
Reference System (IHRS);
x Supporting the realization of a Global Geodetic Reference System (GGRS);x Analysis of current and future satellite data (CHAMP,GRACE, GOCE, GRACE-FO) and the release of improved global gravity field models (satellite only models
and in combination with terrestrial data and satellite altimetry);x Promoting future gravity mission constellations for assuring the continued monitoring of global gravity andmass transport processes in the Earth system;x Assuring the future of the comparison campaigns of absolute gravimeters;x Investigating modern relativistic methods and geodetic
metrology with special focus on gravity field and height
determination;

Commission 2 – Gravity Fieldx Fostering regional gravity and geoid determination andintegration of regional models into a global reference;x Understanding of physics and dynamics of the Earthsub-systems and mass transport processes in the Earthsystem;x Providing contributions to operationalization of masstransport modelling and stimulation of new applications;
x Fostering communication with user communities;
x Assisting the IGFS and its components in improving
their visibility and their services;x Assisting the regional sub-commissions in establishingcontacts and in acquiring data.
The necessary WGs and SGs can be established at any
time and they can be dissolved when they reached theirgoals or if they are not active.
Objectives
The main objectives of Commission 2 are as listed in the
IAG by-laws:x Terrestrial, marine and airborne gravimetryx Satellite gravity field observations
x Gravity field modelingx Time-variable gravity fieldx Geoid and height determinationx Satellite orbit modeling and determinationx Satellite altimetry for gravity field modeling
Structure
Sub-Commissions
SC 2.1: Land, Marine and Airborne Gravimetry
Chair: Derek van Westrum (USA)SC 2.2: Geoid, Physical Height Systems and Vertical Datum Unification
Chair: George Vergos (Greece)
SC 2.3: Satellite Gravity Missions
Chair: Frank Flechtner (Germany)
SC 2.4: Regional Geoid Determination
Chair: Hussein Abd-Elmotaal (Egypt)
SC 2.4a: Gravity and Geoid in Europe
Chair: Heiner Denker (Germany)
SC 2.4b: Gravity and Geoid in South America
Chair: Maria Cristina Pacino (Argentina)
SC 2.4c: Gravity and Geoid in North and Central America
Chair: Xiaopeng Li (USA)SC 2.4d: Gravity and Geoid in Africa
Chair: Hussein Abd-Elmotaal (Egypt)
SC 2.4e: Gravity and Geoid in Asia-Pacific
Chair: Cheinway Hwang (China-Taipei)
SC 2.4f: Gravity and Geoid in Antarctica
Chair: Mirko Scheinert (Germany)
SC 2.5: Satellite Altimetry

111

Chair: Xiaoli Deng (Australia)
SC 2.6: Gravity Inversion and Mass Transport in the Earth
SystemChair: Wei Feng (China)
Joint Study Groups
JSG 3.1: Geodetic, seismic and geodynamic constraints on
GIA (Joint with: Comm 1, Comm 3)
Chair: R. Steffen (Sweden)
JSG T.28: Forward gravity field modelling of known mass
distributions (Joint with: ICCT, Comm 3, GGOS)
Chair: D. Tsoulis (Greece)
JSG T.35: Advanced numerical methods in physical geodesy (Joint with: ICCT, GGOS)
Chair: R. Čunderlík (Slovakia)
JSG T.23: Spherical and spheroidal integral formulas of thepotential theory for transforming classical and new
gravitational observables (Joint w.: ICCT, GGOS)
Chair: M. Šprlák (Australia / Czech Republic)
JSG T.26: Geoid/quasi-geoid modelling for realization of
the geopotential height datum (Joint with: ICCT,GGOS)
Chair: J. Huang (Canada), Y.M. Wang (USA)JSG T.25: Combining geodetic and geophysical information
for probing Earth’s inner structure and its dynamics(Joint with: ICCT, Comm 3)
Chair: R. Tenzer (China)
JSG T.34: High resolution harmonic analysis and synthesisof potential fields (Joint with: ICCT, GGOS)
Chair: S. Claessens (Australia)
JSG T.30: Dynamic modeling of deformation, rotation andgravity field variations (Joint w.: ICCT, Comm 3)
Chair: Y. Tanaka (Japan)
JSG X.X: Machine learning in geodesy (Joint with: ICCT,Comm 1, Comm 3, Comm 4, GGOS)
Chair: B. Soja (USA)JSG T.37: Theory and methods related to high-resolution
digital topographic and bathymetric models (Joint
with: ICCT, Comm 1, Comm 3, GGOS)
Chair: D. Carrion (Italy)
Joint Working Groups
JWG 2.1.1: Establishment of the International Gravity Reference Frame (joint with IGFS, BGI, IGETS)
Chair: Hartmut Wziontek (Germany)JWG 2.1.2: Unified file formats and processing software forhigh-precision gravimetry Frame (joint with IGFS,IGETS, BGI)
Chair: Ilya Oshchepkov (Russia)
JWG 2.2.1: Error assessment of the 1 cm geoid experiment(joint with ISG, IGFS)
Chair: Martin Willberg (Germany)112

JWG C.3: Geodesy for the Cryosphere: advancing the useof geodetic data in polar climate modelling (Joint
with: ICCC, Comm 3)
Chair: Bert Wouters (Netherlands)
JWG C.4: Sea level and vertical land motion (Joint with:
ICCC, Comm 1, Comm 4, GGOS)
Chair: Roelof Rietbroek (Germany)JWG C.5: Understanding the monsoon phenomenon from ageodetic perspective (Joint with: ICCC, Comm 3,
Comm 4, GGOS)
Chair: Balaji Devaraju (India)JWG C.6: Numerical Simulations for Recovering ClimateRelated Mass Transport Signals (Joint with: ICCC,
GGOS)
Chair: Roland Pail (Germany)JWG C.7: Satellite geodetic data assimilation for climate research (Joint with: ICCC, GGOS)
Chair: Mehdi Khaki (Australia)
JWG C.8: Methodology of comparing/validating/testing climate simulations to/with geodetic data (Joint with:
ICCC, ICCT)
Chair: Jürgen Kusche (Germany)JWG Q.1: Quantum gravimetry in space and on ground(Joint with: IAG Project QuGe)
Chair: F. Pereira (France)
JWG Q.2: Laser interferometry for gravity field missions(Joint with: IAG Project QuGe)
Chair: M. Murböck (Germany)JWG Q.3: Relativistic geodesy with clocks (Joint with: IAG
Project QuGe)
Chair: G. Petit (France)

The Geodesist’s Handbook 2020

Program of Activities
The Gravity Field Commission fosters and encourages research in the areas of its sub-entities by facilitating the exchange of information and organizing Symposia, either independently or at major conferences in geodesy. The activities of its sub-entities, as described below, constitute the activities of the Commission, which will be coordinated by theCommission and summarized in annual reports to the IAG
Bureau.
The principal symposia that will be organized jointly by
Commission 2 and the IGFS in the next period will be heldin Austin in September 2020 and in 2022 (location TBD).
The other two symposia where a Commission 2 meeting will
be held are the IAG Scientific Assembly 2021 in Beijing,
China, and the IUGG General Assembly 2023 in Berlin,
Germany.
The status of Commission 2, including its structure andmembership, as well as links to the internet sites of its subentities and parent and sister organizations and services, will
be updated regularly and can be viewed on the web site:
https://com2.iag-aig.org/.
Steering Committee
President Commission 2: Adrian Jäggi (Switzerland)
Vice President Comm. 2: Mirko Reguzzoni (Italy)
Chair Sub-Comm. 2.1: Derek van Westrum (USA)
Chair Sub-Comm. 2.2: George Vergos (Greece)
Chair Sub-Comm. 2.3: Frank Flechtner (Germany)
Chair Sub-Comm. 2.4: Hussein Abd-Elmotaal (Egypt)
Chair Sub-Comm. 2.5: Xiaoli Deng (Australia)
Chair Sub-Comm. 2.6: Wei Feng (China)
Representative of IGFS: Riccardo Barzaghi (Italy)
Representative of ICCT: Pavel Novák (Czech Republic)
Member-at-Large: Laura Sanchez (Germany)
Member-at-Large: Min Zhong (China)
Immediate Past President: Roland Pail (Germany)
The steering committee will meet at least once per year.
These meetings are open for all interested IAG members.

Commission 2 – Gravity Field

113

Sub-Commissions, Working Groups andStudy Groups

commission will encourage regional meetings and workshops dedicated to specific problems when and where appropriate.

SC 2.1: Gravimetry and Gravity Network

Program of Activities

Chair: Derek van Westrum (USA)Vice-Chair: Przemyslaw Dykowski (Poland)
Terms of Reference
Geodesists and geophysicists utilize gravity and gravity gradient datasets from a wide variety of sources: local relative
gravity campaigns, pointwise absolute gravity observations,gravity variation in time at fixed locations, and continental
scale observations from marine and airborne platforms.
These observations need to be consistent with each other,
consistent with satellite-based results, and have well defined
accuracy/uncertainty determinations. IAG Sub-commission
2.1, "Land, Marine and Airborne Gravimetry” aims to bring
together scientists from all over the globe that are interested
in the instruments, techniques, and analysis of terrestrial,
marine and airborne gravity and gravity gradient measurements.
Objectives
SC2.1 provides the scientific community with the means toassess the accuracy of absolute gravity observations throughthe organization of regular international absolute gravimetercomparisons. These efforts are in cooperation with the metrology community: the Consultative Committee on Massand Related Quantities, its Working Group on Gravimetry(CCM WGG), and other Regional Metrology Organizations
as well as all interested scientific institutions. The relationship allows for direct traceability of gravity data to international standards.
SC2.1 supports the dissemination of the results of these
activities through an international absolute gravity database,which in turn, will support the ongoing realization of a new
and improved International Gravity Reference Frame.
SC2.1 supports sharing expertise and experience in performing gravity surveys on moving platforms (Marine, Airborne) allowing for the collection of the highest possible
quality gravity data using the most up to date techniques.
To facilitate the exchange of all terrestrial gravity data
and metadata, SC2.1 is actively supporting the creation of a
unified file format in an open source environment.
Finally, SC2.1 promotes research and development into
new instruments and techniques by stimulating communication and cooperation between scientific groups. The sub-x Host the JWG2.1.1, “Establishment of an International
Gravity Reference Frame”, along with IGFS, BGI andIGETS
x Host the JWG 2.1.2 “Unified file formats and processing
software for high-precision gravimetry,” along with
IGFS, BGI and IGETS
x Host the SG2.1.1 “Developments in near Earth gravimetry: instruments, analysis, and applications”
x Provide access to the results of comparisons of absolutegravimeters via the AGrav database at BKG-BGIx Appoint the Steering Committee consisted of the members experienced in the fields of gravimetry related to theactivities of SC2.1 and the contact persons for European,
East Asia and Western Pacific, South America andNorth America Gravity Networks.
Support IAG Commission 2 Symposia such as GGHS.

SG 2.1.1: Developments in Gravity Instrumentation, Analysis, and Applications
Chair: Derek van Westrum (USA)Vice-Chair: Przemyslaw Dykowski (Poland)
Terms of Reference
SG2.1.1 is focused on methods and instrumentation used incollecting and analyzing terrestrial (non-satellite) gravity
and gravity gradiometry data. New developments in both“classic” and quantum absolute instruments, as well as
novel relative instruments, are happening a rapid pace andare of great interest to the geodetic community. In addition,communication of such developments between the geodesy
community and metrology community is essential.
SG2.1.1 also supports research in the analysis of gravity
data. Examples include standard absolute corrections, barometric loading, reduction of relative gravity networks, software, and file formats.
SG2.1.1 also promotes innovations in the use of gravity
and gravity gradient data. As examples, time varying gravity
signals are being used to fine tune ice melt models, biological processes, and of course, geoid change.

114

The Geodesist’s Handbook 2020

Objectives

Objectives

x Communication between research groups developing
novel instruments and the community of gravity
scientists
x Coordination of scientific efforts regarding mobile
platforms.
x Promotion and coordination in the establishment andmeasurements of regional gravity networks.
x Organization of scientific workshops and meetings forthe discussion of techniques and methods of terrestrial
gravity measurements.

Within IAG Sub-Commission 2.1 “Land, Marine and Airborne Gravimetry” the realization of the International Gravity Reference Frame (IGRF) will be initiated. The IGRF is
the implementation of the International Gravity Reference
System (IGRS). The IGRS is defined by the observation of
the instantaneous acceleration of free fall, the traceability ofthese observations to the International System of Units (SI),and a set of conventional corrections for the time independent components of gravity effects. The IGRF as the realization of the IGRS is based on observations with absolute gravimeters (AG) which are monitored at reference stations andduring comparisons. The IGRF further defines a set of conventional models for the correction of temporal gravity
changes. Finally, the IGRF demands a compatible infrastructure accessible to end-users.
The JWG focuses on the establishment of such an infrastructure in cooperation with IGFS, GGOS, internationaland national institutions, agencies, and governmental bodies. This infrastructure should consist of reference stations
on the national level for the monitoring of AGs. On the international level, comparison stations will provide the facilities to check the consistency of AGs within their reported
uncertainty estimates, and core stations will link to space
geodetic techniques and the International Height Reference
Frame (IHRF).
The absolute gravity database “AGrav” which already isa fixed part of the BGI (International Gravimetric Bureau)
services is proposed to serve as a central inventory to document all IGRF stations and related AG observations.
A close cooperation with the International Geodynamics
and Earth Tide Service (IGETS) supports the continuous
monitoring at the gravity reference stations. The collaboration with the Working Group on Gravimetry of the Consultative Committee on Mass and Related Quantities (CCMWGG) ensures good practice in the field of AG comparisons.
The activities should be further aligned with the JWG on
the Implementation of the International Height Reference
Frame.

Members
Chair: Derek van Westrum (USA)Vice Chair: Przemyslaw Dykowski (Poland)
Mirjam Bilker-Koivula (Finland)
Sylvain Bonvalot (France)
John Crowley (Canada)
Yoichi Fukuda (Japan)
Silvia Alicia Miranda (Argentina)
Ilya Oshchepkov (Russia)
Wu Shuqing (China)
Hartmut Wziontek (Germany)JWG 2.1.1: Establishment of the International Gravity Reference Frame(joint with IGFS, BGI, IGETS)

Chair: Hartmut Wziontek (Germany)
Vice-Chair: Sylvain Bonvalot (France)
Terms of Reference
One task of IAG's Commission 2 “Gravity Field” is the establishment of the International Gravity Reference Systemand Frame (IGRF). These activities are motivated by the
IAG Resolutions No. 2 of 2015 (IUGG General Assembly
Prague) and No. 4 of 2019 (IUGG General Assembly Montreal). The IAG Sub-Commission 2.1 “Land, Marine andAirborne Gravimetry” promotes consistency and compatibility of gravity and gravity gradient datasets and assessment of their accuracy. The International Gravity Field Service IGFS coordinates the servicing of the geodetic and geophysical community with gravity field related data, software and information. A modern and precise absolute gravity reference frame will not only contribute to the establishment of the Global Geodetic Reference Frame (GGRF) of
the UN, but will also serve as a long-term and precise gravity reference for the IAG Global Geodetic Observing System (GGOS).

Members
Mirjam Bilker Koivula (Finland)
Przemyslaw Dykowski (Poland)
Andreas Engfeldt (Sweden)
Reinhard Falk (Germany)
Jaakko Mäkinen (Finland)
Urs Marti (Switzerland)Jack McCubbine (Australia)
Ilya Oshchepkov (Russia)
Vojtech Palinkas (Czech Republic)

Commission 2 – Gravity Field

Victoria Smith (UK)
Ludger Timmen (Germany)
Claudia Tocho (Argentina)
Christian Ullrich (Austria)
Michel van Camp (Belgium)
Derek van Westrum (USA)
Marc Véronneau (Canada)
Leonid Vitushkin (Russia)
Shuqing Wu (China)
Toshihiro Yahagi (Japan)
Corresponding Members
Jonas Ågren (Sweden)
Mauro Andrade de Sousa (Brazil)
Daniel Barnes (USA)
Henri Baumann (Switzerland)
Denizar Blitzkow (Brazil)
Jean-Paul Boy (France)
Ana Cristina O. Cancoro de Matos (Brazil)
In-Mook Choi (Korea)
Alfredo Esparza (Mexico)
Olivier Francis (Luxemburg)
Yoichi Fukuda (Japan)
Alessandro Germak (Italy)
Joe Henton (Canada)
Jacques Hinderer (France)
Domenico Iacovone (Italy)
Shuanggen Jin (China)
Janis Kaminskis (Latvia)
Jeff Kennedy (USA)Jakub Kostelecky (Czech Republic)
Jan Krynski (Poland)
Jacques Liard (Canada)Jose Manuel Serna Puente (Spain)
Camilo Matiz (Colombia)
Koji Matsuo (Japan)
Leidy Johanna Moisés Sepúlveda (Colombia)
Per-Anders Olsson (Sweden)
Tomasz Olszak (Poland)
Diego Piñón (Argentina)
Andrea Prato (Italy)
Rene Reudink (Netherlands)
Axel Rülke (Germany)
Laura Sanchez (Germany)
Roman Sermyagin (Russia)
Heping Sun (China)
V.M. Tiwari (India)
Objectives
x Review of existing software, data types, data formats
and processing standards in high-precision gravimetry;115

JWG 2.1.2: Unified file formats and processing software for high-precision gravimetry frame(joint with IGFS, IGETS, BGI)

Chair: Ilya Oshchepkov (Russia)
Vice-Chair: Vojtech Pálinkáš (Czech Republic)
Terms of Reference
Absolute gravity measurements have become widely usedin geodesy since the 1970s when several transportable absolute gravimeters were introduced, since then their number
has increased dramatically and continues to do so. The absolute gravimeters are used not only in geodesy, but also inmetrology, geophysics, hydrology and other applications.
The IAG's Commission 2 “Gravity Field” and its JWG 2.1.1
are working on the establishment of the International Gravity Reference System/Frame (IGRS/IGRF), which will bebased solely on the absolute gravity measurements. The latter task will require a possibility for re-processing of all historical, current and future data, as well as their long-term
availability for all interested parties.
The current ability to exchange and to re-process raw
data of absolute gravity measurements is limited by the factthat each manufacturer uses their own proprietary softwareand different data storage formats. Also differences in theimplementation of processing standards may exist. In sucha situation it is difficult to ensure reproducibility and traceability to the SI of an individual experiment. Another difficulty arises from the requirement for a re-processing of old
measurements after the introduction of new processing
standards, when neither data nor software are available anymore.
The JWG 2.1.2 aims to create a unified, meter and software independent, format for storing and sharing not only
the processing results and metadata, but also the raw data ofgravity measurements. Different software will be evaluatedand discrepancies will be discovered and resolved. Perspectively, an open source software should be established toeliminate the above mentioned problems, as well as to implement a standard procedure for handling absolute gravity
measurements for the IGRF. The activities need a close cooperation with the manufacturers of absolute gravimeters inorder to align instrument specific data handling and a transparent processing and to implement a common exchange
format.
develop requirements for a unified format and data processing software.
x Test of the compatibility of existing software

116

x Develop a unified data storage format for high-precision
gravity measurements: description, converter and software implementation.
x Develop a unified processing software to process any
high-precision gravity measurements with a wide support for any processing procedure.
Members
Brian Ellis (USA)Jacques Liard (Canada)
Jeffrey Kennedy (USA)Jaakko Mäkinen (Finland)
Sergey Svitlov (Germany)
Pierre Vermeulen (France)
Marc Véronneau (Canada)
Hartmut Wziontek (Germany)
Sylvain Bonvalot (France)
Vadim Nagormyi (USA)
Igor Sizikov (Russia)
Christian Ullrich (Austria)
Axel Rülke (Germany)
Domenico Iacovone (Italy)
Alessandro Germak (Italy)
Shuqing Wu (China)
Derek Van Vestrum (USA)
Mirjam Bilker-Koivula (Finland)
Przemyslaw Dykowski (Poland)

SC 2.2: Geoid, Physical Height Systems andVertical Datum Unification
Chair: George Vergos (Greece)
Vice-Chair: Rossen S. Grebenitcharsky (Saudi Arabia)
Terms of Reference
A global height reference frame with high accuracy and stability is required to determine the global changes of the
Earth. A major step towards this goal was taken by the IAG
resolution (No. 1) for the definition and realization of an International Height Reference System (IHRS), adopted at the
IUGG 2015 meeting in Prague and the IAG resolution (No.
3) for the establishment of the International Height Reference Frame (IHRF), adopted at the IUGG 2019 meeting inMontreal.
Given the work carried out for the general methodological scheme for geoid and potential determination, the data
prerequisites and practical studies, it has become apparent
that the IHRS should be globally realized with common
standards in terms of the processing strategy. Moreover, theuse of all available data sources, e.g., GNSS-derived

The Geodesist’s Handbook 2020heights, satellite altimetry, topography/bathymetry, local
gravity (terrestrial, airborne and marine) as well as the latest
global geopotential models, should be employed in order toproperly model the high-frequency part of the gravity field
spectrum. Such combination of heterogenous data has been
deemed a mandatory in order to reduce the omission error
as well as to properly model the contribution of topography.
Traditional levelling might also be integrated on a regional or local scale. Finally, the unification of local/nationalvertical reference frames to regional ones and their link to
the IHRF is of main importance, employing local geoid realizations and datum definitions.
The IAG SC 2.2 aims at bringing together scientists andgeodesists concerned with methodological questions in
geoid and potential determination, who in different ways
contribute to reach the above-mentioned goal of a global
height system realization and unification. It includes topics(state of art methodologies for processing, analyzing, utilizing data, unifying datums, etc.), and ranging from regional
gravimetric geoid determination to the realization and implementation of IHRS in view of the existing regional/local/national height system realizations and 3D vertical datum (geoid) definitions.
Objectives
The IAG Sub-Commission 2.2 (SC2.2) promotes and supports scientific research related to methodological questions
in geopotential, geoid and height determination, both fromthe theoretical and practical perspectives. The former refers
in particular on methodological questions and practical numerical applications contributing to the realization of IHRS
with the required sub-centimeter accuracy, the combinationof local/regional vertical reference frames and their unification to the IHRF. This includes for instance:x Realization of the International Height Reference
System (support to the Joint Working Group with the
GGOS Focus Area Unified Height System“Implementation of the International Height Reference
Frame (IHRF)”)x Height system unification at regional scales andunification to the IHRF.
x Studies on W0 determination.
x Studies on data requirements, data quality, distribution
and sampling rate to reduce the omission error to thesub-centimeter level in different parts of the world.
x Contributions of alternate data sources, such as altimetry
sea surface heights and GNSS geometric heights togeopotential modeling and geoid determination atreference benchmarks.
x Investigation of the theoretical framework required tocompute the sub-centimeter geoid (support of ICCT SG:

Commission 2 – Gravity Field

x

x
x

x

x

x

x

Geoid/quasi-geoid modelling for realization of thegeopotential height datum)
Investigation of the error budget od potential
determination and vertical reference frames unification(support to Commission 2 WG: Error assessment of the
1 cm geoid experiment)
Investigation and benchmarking of alternative regional
geoid determination methods and software.
Studies on theoretical and numerical problems related tothe solution of the geodetic boundary value problems(GBVPs) in geoid determination,
Studies on time variations of the gravity field andheights due to Glacial Isostatic Adjustment (GIA) andland subsidence.
Development of relativistic methods for potential
difference determination using precise atomic clocks(support of Working Group X.3).
Investigating the role of traditional levelling in future
regional/local height system realizations combined withall available data linked to Earth’s geopotential
determination.
Investigating the utilizations of already defined nationaland regional geoid models together with new types ofGeodetic Earth Observations (GEOs) and based ontheoretical and practical developments linked to mixed
GBVPs.

Program of Activities
x Organizing meetings and conferences.
x Organization of local/regional workshops for thepromotion of IHRF related studies.
x Inviting the establishment of Special Study Groups onrelevant topics.
x Reporting activities of SC2.2 to the Commission 2.
x Communication/interfacing between different groups/
fields relevant to the realization of IHRS.
x Conceptual and methodological support to working
groups for national & regional vertical datums andreference frames definitions as realizations of IRHS.

117

JWG 2.2.1: Error assessment of the 1 cm
geoid experiment(joint with ISG, IGFS)

Chair: Martin Willberg (Germany)
Vice-Chair: Tao Jiang (China)
Terms of Reference
The realization of the International Height Reference System (IHRS) will be based on reference stations, which arecalculated from a local combination of global gravity fieldmodels and regional gravity observations. This process,which is called regional geoid/gravity modeling is realizedwith different philosophies and theories inside the geodetic
community. However, the final quality of the IHRS depends
heavily on the consistency of all included modeling methods. Consequently, in the previous IAG period, within
JWG 2.2.2 an effort was made to evaluate the differences invarious regional geoid/gravity modeling approaches andstandardize them to a specific degree.
Within ‘the 1 cm geoid experiment’ 15 participatinggroups have calculated a regional geoid/gravity model in thearea of Colorado, US. Thereby, all groups used identical input data sets consisting of terrestrial and airborne gravity
observations. After two iterations within ‘the 1 cm geoid experiment’, differences of a few centimeters remain between
the final results of the contributing groups. Manifold reasons
might be responsible for this difference, but major aspects
are assumed to be differences in the procedure, the topographic reduction, and the individual data handling. Until
now, the quality assessment of individual solutions was
mainly analyzed by their variation from a joint mean value,
which was interpreted as reference. However, the Colorado
area contains a Geoid Slope Validation Survey (GSVS),
where positions, gravity values and deflections of the vertical were measured with very high quality along a set of 223
benchmarks. These values and the results of the GSVS processing are not yet published, but will be open to the public
soon, thereby providing an improved reference (for thisJWG).
The objectives of this JWG are to validate the results, toidentify and quantify potential error sources, and to develop
and improve methods for deriving realistic error estimatesof the gravity potential values at the IHRS stations. Once
available, the differences of individual geoid/height anomaly results to the improved reference from the GSVS shallbe analyzed. The most possible reasons for these differences
should be worked out. Especially, a modified computation
set-up shall be defined, which enables to separate methodrelated and data-driven error contributions. This will be important to quantify the error level caused by different regional gravity modelling methods. If possible, these errors

118

shall be further reduced within an additional iteration step.
Furthermore, different methods should be examined fortheir ability to estimate an appropriate error budget for the
final results. This is of great importance, as the assessmentof the total error is needed for the reference stations in the
IHRS. Lessons from this JWG should then be transferred to
the JWG for ‘Implementation of the International Height
Reference Frame – IHRF’.
Program of Activities
x Analyze the difference of various solutions to the GSVS
referencex Quantify the main error contributors of regional geoid
modeling
x Estimation of the total error budget
x Derive recommendations for the IHRS realization fromthe viewpoint of regional gravity field modelingx Organize conference sessions
x Report activities
Members
Chair: Martin Willberg (Germany)
Vice-Chair: Tao Jiang (China)
Laura Sánchez (Germany)
Yan Ming Wang (USA)
Vassilios Grigoriadis (Greece)
Marc Véronneau (Canada)
Sten Claessens (Australia)
Qing Liu (Germany)
Rene Forsberg (Denmark)Hussein Abd-Emotaal (Egypt)
Koji Matsuo (Japan)
Bihter Erol (Turkey)
Jonas Ågren (Sweden)
Kevin Ahlgren (USA)
Matej Varga (Czech/Croatia)
Riccardo Barzaghi (Italy)
Representative person USP (Brazil)

The Geodesist’s Handbook 2020

SC 2.3: Satellite Gravity Missions
Chair: Frank Flechtner (Germany)
Vice-Chair: Matthias Weigelt (Germany)
Terms of Reference
The successful launches of the German CHAMP (2000), theUS/German GRACE (2002), the ESA GOCE (2009) andUS/German GRACE-FO (2018) missions have led to a revolution in global gravity field mapping by space-borne observation techniques. These missions are the only measurement systems which can directly observe mass distribution
and mass transport in the Earth system based on proven new
concepts and technologies, such as high-low satellite-to-satellite tracking (SST) using the GPS constellation, low-low
SST based on micro-wave and laser ranging, and satellite
gravity gradiometry (SGG), as well as space-borne accelerometry.
GRACE has produced 15+ years consistent long- to medium-wavelength global gravity field models and its temporal changes till June 2017 which are extended since May
2018 by GRACE-FO data. GOCE provided high- accuracy
and high-resolution static gravity field models. In combination with complementary gravity field information from terrestrial data and satellite altimetry, an even higher spatial
resolution can be achieved. Consequently, these satellite
missions provide valuable contributions to many geoscientific application fields, such as geodesy, hydrology, oceanography, glaciology, and solid Earth physics.
Objectives
The focus of SC 2.3 will be to promote and stimulate thefollowing activities:
x providing the scientific environment for thedevelopment of the next generation of static andtemporal gravity field solutions based on observations
from the satellite gravity missions CHAMP, GRACE,
GOCE, and GRACE-FO, as well as optimum combination with complementary data types (SLR, terrestrial
and air-borne data, satellite altimetry, etc.),x developing alternative methods and new approaches for
global gravity field processing with special emphasis on
functional and stochastic models and optimum data
combination,x fostering the exchange of knowledge and data amongprocessing entities,
x communication and interfacing with gravity field model
user communities (climatology, oceanography/altimetry
glaciology, solid Earth physics, geodesy, ...) as well as
relevant IAG organizations such as the GGOSCommission 2 – Gravity Field

Committee on Satellite and Space Missions and the
GGOS Bureau of Products and Standards,
x identification, investigation and definition of enabling
technologies for future gravity field missions such as
observation types, technologies or mission architectures,
andx triggering new gravity field mission proposals andsupporting their implementation.
Program of Activities
The sub-commission will establish, if necessary, Working
Groups on relevant topics. The Steering Committee will
work closely with members and other IAG commissions andsub-commissions to obtain mutual goals. Also it will promote and jointly sponsor special sessions at IAG Symposia
and other workshop/conferences.

SC 2.4: Regional Geoid Determination
Chair: Hussein Abd-Elmotaal (Egypt)
Vice-Chair: Xiaopeng Li (USA)Terms of Reference and Objectives
Sub-commission 2.4 is concerned with the following areasof investigation:
x Regional gravity and geoid sub-commissions: data sets,
involved institutions, comparison of methods andresults, data exchange, comparison with global models,connection of regional models
x Gravimetric geoid modelling techniques and methods,
available software, new alternative geoid determination
techniques
x GNSS/levelling geoid determination: methods,
comparisons, treating and interpretation of residuals,common treatment of gravity and GNSS/levelling for
geoid determinationx Geoid applications: GNSS heights, sea surface
topography, integration of geoid models in GNSS
receivers, vertical datums.
x Other topics: topographic effects, downward andupward continuation of terrestrial, airborne, satellite data
specifically as applied to geoid modelling.
Program of Activities
Sub-Commission 2.4 is going to initiate and coordinate regional gravity and geoid sub-commissions. It will encourage
and support the data exchange between agencies and willassist local, regional and national authorities in their projectsof gravity field determination. It will help in organizing
courses and symposia for gravity field determination.

119

Steering Committee
Chair SC2.4: Hussein Abd-Elmotaal (Egypt)
Chair SC2.4a: Heiner Denker (Germany)
Chair SC2.4b: Maria Cristina Pacino (Argentina)
Chair SC2.4c: Xiaopeng Li (U.S.)
Chair SC2.4d: Hussein Abd-Elmotaal (Egypt)
Chair SC2.4e: Cheinway Hwang (China-Taipei)
Chair SC2.4f: Mirko Scheinert (Germany)

SC 2.4a: Gravity and Geoid in Europe
Chair: Heiner Denker (Germany)
Terms of Reference
The primary objective of the sub-commission is the development of improved regional geoid and quasigeoid models
for Europe, which can be used for applications in geodesy,
oceanography, geophysics and engineering, e.g., height determination with GNSS techniques, vertical datum definition and unification, dynamic ocean topography estimation,
geophysical modelling, and navigation. Another emerging
field is related to the development of new optical clocks inphysics with relative uncertainties at the level of 10-18, as inaccordance with the laws of general relativity, such clocks
are sensitive to the gravity potential at the level of 0.1 m2/s2,
equivalent to 1 cm in height.
The geoid and quasigeoid modelling will be based
mainly on terrestrial gravity and terrain data in combination
with state-of-the-art global geopotential models. In this context, upgraded terrestrial data sets as well as the utilizationof GRACE and GOCE based global geopotential models led
to significant improvements. The evaluation of the latest European gravimetric quasigeoid models by GNSS and levelling data indicates an accuracy potential of 1 – 2 cm on anational basis, and 2 – 4 cm at continental scales, provided
that high quality and resolution input data are available
within the area of interest. Further improvements can be expected from the inclusion of upgraded gravity field data sets,
especially in areas with hitherto insufficient input data.
Program of Activities
x Utilization of state-of-the-art global geopotential
models.
x Identification and acquisition of new terrestrial data sets,
including gravity, terrain, and GPS/levelling data.
x Merging and validation of all data sets.
x Investigation of refined mathematical modelling
techniques and numerical tests.
x Computation of new geoid and quasigeoid models.
x Evaluation of the results by GNSS/levelling data.

120

The Geodesist’s Handbook 2020

Chair: Maria Cristina Pacino (Argentina)
Vice-Chair: Gabriel do Nascimento Guimarães (Brazil)

x To encourage and eventually support local organizations
in different countries endeavoring to increase the gravity
data coverage, to improve the existing digital terrain
models, to carry out GPS observations on the levelling
network and to compute a high resolution geoid.
x To organize and/or encourage the organization ofworkshops, symposia or seminars on gravity and geoid
determination in South America.
x To test and to use future geopotential models derived
from the modern missions (GRACE and GOCE) as wellas any new combined model.
x To support the IAG Sub-Commission 1.3b (Reference
Frame for South and Central America, SIRGAS) in theactivities related to the unification of the existing vertical
datums.
x Establish close connections with SC2.4c (Gravity andGeoid in North and Central America) to have a goodoverlap of data coverage in Central America and the
Caribbean.

Terms of Reference and Objectives

Delegates

The Sub Commission 2.4b entitled Gravity and Geoid inSouth America, as part of the Commission 2 of IAG, wasestablished as an attempt to coordinate efforts to establish a
new Absolute Gravity Network in South America, to carryout gravity densification surveys, to derive a geoid modelfor the continent as a height reference and to support localorganizations in the computation of detailed geoid models
in different countries.
Besides, a strong effort is being carried out in several
countries in order to improve the distribution of gravity information, to organize the gravity measurements in the continent and to validate the available gravity measurements.
The main objectives of the project are:x To re-measure existent absolute gravity stations and toencourage the establishment of new stations.
x To validate fundamental gravity network from different
countries in order to establish a single and common
gravity network for South America.
x To adjust national gravity networks and to link them
together.
x To obtain and to maintain files with data necessary forthe geoid computation like gravity anomalies, digitalterrain models, geopotential models and satellite
observations (GPS) on the levelling network of different
countries.
x To provide a link between the different countries and the
IGFS in order to assure access to proper software andgeopotential models for local geoid computation.
x To compute a global geoid model for South and Central
America using the available data. To encouragecountries to cooperate by releasing data for this purpose.

Chair: Maria Cristina Pacino (Argentina)
Co-Chair: Gabriel do Nascimento Guimarães (Brazil)
Henry Montecino Castro (Chile)
Oscar Carranco (Ecuador)
Ana Crisitina Oliveira Concoro de Matos (Brasil)
Ayelén Pereira (Argentina)
Roberto Teixeira Luz (Brasil)
Silvia Alicia Miranda (Argentina)
Ivonne Gatica Placencia (Chile)
Norbertino Suárez (Uruguay)
Jorge Faure Valbi (Uruguay)x Study of applications, such as vertical datum definition
and unification, dynamic ocean topography estimation,
ground truth for optical clocks, etc.
Delegates
The regional sub-commission for Europe SC2.4a cooperates
with national representatives from most of the countries in
Europe and reports to sub-commission 2.4. The existing
contacts and successful cooperation with the respective persons and national and international agencies shall be continued and extended.

SC 2.4b: Gravity and Geoid in South America

SC 2.4c: Gravity and Geoid in North andCentral America
Chair: Xiaopeng Li (USA)Vice-Chair: David Avalos (Mexico)
Terms of Reference and Objectives
The primary objective of this Sub-commission is the development of a regional gravity field and geoid model covering
the region of North America and Central America by 2022
in order to achieve a common vertical datum. The region
involved will encompass Iceland, Greenland, Canada, theU.S.A. (including Alaska and Hawaii), Mexico, countries
forming Central America, the Caribbean Sea and the northern parts of South America. This model will serve as the official realization of the vertical datum for countries that wantto adopt it.

Commission 2 – Gravity Field

The intention is to ensure that a suitable North American
Geoid is developed to serve as a common datum for everyone in the region. All countries in the region would beserved by having access to a common model for translating
oceanographic effects to terrestrial datums for various scientific, commercial, engineering and disaster prepared-ness
applications. Likewise, it shall serve as the basis for theforthcoming International Great Lakes Datum in 2022
(IGLD 2020).
The achievement of a geoid model for North and Central
America will be accomplished by coordinating activities
among agencies and universities with interest in geoid theory, gravity, gravity collection, gravity field change, geophysical modelling, digital elevation models (DEM), digitaldensity models (DDM), altimetry, dynamic ocean topography, levelling and vertical datums. Of particular interest will
be relating geoid and ocean topography models to ocean topography and tidal benchmarks, taking advantage of the recent satellite altimetry and geopotential field products.
The determination of a geoid model for North and Central America is not limited to a single agency, which willcollect all necessary data from all countries. The Sub-commission encourages theoretical diversity in the determination of a geoid model among the agencies. Each agency
takes responsibility or works in collaboration with neighboring countries in the development of a geoid model for theirrespective country with an overlap (as large as possible)
over adjacent countries. Each solution will be compared, thediscrepancies will be analyzed, and the conclusions will be
used to improve on the next model.
Program of Activities
The Sub-commission will support geoid activities in countries where geoid expertise is limited by encouraging moreadvanced members to contribute their own expertise andsoftware. The Sub-commission will encourage training andeducation initiative of its delegates (e.g., ISG geoid school,
graduate studies and IPGH technical cooperation projects).
Starting on 2011 the Sub-commission will organize regularmeetings with representatives of Central American and Caribbean countries to promote an increase of expertise as wellas to create a wide network of specialists.
The chair (or a delegate representative) of the Sub-commission will meet with the equivalent European and SouthAmerican projects to discuss overlap regions and to work
towards agreements to exchange data. The delegates of theSub-commission will keep close contact with all related
Study Groups of the IAG. The Sub-commission is open to
all geodetic agencies and universities across North and Central America with an interest in the development of a geoid
model for the region. The meetings of the Sub-commission

121

2.4c are open to everyone with interests in geodesy, geophysics, oceanography and other related topics.
The delegates will communicate primarily using e-mail.
In addition, starting on November 9, 2015, Canada (CGS),
USA (NGS) and Mexico (INEGI) will organize audio/videoconferences every four weeks to discuss activity plans andpresent results. The sub-commission also plans to organize
annual meetings if enough delegates can be present. Preferably, these meetings will be held during international conferences;. Minutes of meetings will be prepared and sent toall delegates of the Sub-commission.
Delegates
Chair: Xiaopeng Li (USA)Vice-Chair: David Avalos (Mexico)Rene Forsberg (Denmark)Jianliang Huang (Canada)
Dan Roman (USA)
Laramie Potts (USA)Yan Min Wang (USA)
Vinicio Robles (Guatemala)Carlos E. Figueroa (El Salvador)
Anthony Watts (Cayman Islands)
Oscar Meza (Honduras)
Alvaro Alvarez (Costa Rica)
Wilmer Medrano (Nicaragua)
Christopher Ballesteros (Panama)

SC 2.4d: Gravity and Geoid in Africa
Chair: Hussein Abd-Elmotaal (Egypt)
Vice-Chair: S.A. Benahmed Daho (Algeria)
Terms of Reference
The African Gravity and Geoid sub-commission (AGG) belongs to the Commission 2 of the International Associationof Geodesy (IAG). The main goal of the African Gravity andGeoid sub-commission is to determine the most complete
and precise geoid model for Africa that can be obtained fromthe available data sets. Secondary goals are to foster cooperation between African geodesists and to provide highlevel training in geoid computation to African geodesists.
Objectives and Activities
The objectives and activities of the sub-commission aresummarized as follows:x Identifying and acquiring data sets - gravity anomalies,
DTMs, GPS/levelling, seismic Moho.
x Training of African geodesists in geoid computation.

122

x Merging and validating gravity data sets.
x Computing African geoid models.
x Evaluating the computed geoid models using
GPS/levelling data.
x Updating the geoid models using new data/strategies toobtain better geoid accuracy (dynamic process).
Delegates
Chair: Hussein Abd-Elmotaal (Egypt)
Vice-Chair: S.A. Benahmed Daho (Algeria)
Addisu Hunegnaw (Ethiopia)
Ahmed Abdalla (Sudan)
Atef Makhloof (Egypt)
Ayman Hassan (Egypt)
Bernhard Heck (Germany)
Charles Merry (South Africa)
Hassan Fashir (Sudan)
Ismail Ateya Lukandu (Kenya)
John B.K. Kiema (Kenya)
Joseph Awange (Kenya)
Joseph Kamguia (Cameroun)
Karim Owolabi (Namibia)
Kurt Seitz (Germany)
Mostafa Abd-Elbaky (Egypt)
Mostafa Ashry (Egypt)
Norbert Kühtreiber (Austria)
Patroba Odera (Kenya)Peter Nsombo (Zambia)
Prosper Ulotu (Tanzania)
Walyeldeen Godah (Sudan)

SC 2.4e: Gravity and Geoid in the Asia-Pacific
Chair: Cheinway Hwang (China-Taipei)
Vice-Chair: Wenbin Shen (China)
Context
There are about 48 counties in the Asia-Pacific (AP) region.
Many countries in the region have invested considerable resources on improved geoid models. Recent progress in satellite altimetry greatly increases coastal marine gravity accuracy. Satellite remote sensing data have been used to generate digital elevation models that are needed for geoid modeling. Many countries now increase their GNSS/leveling observation campaigns to collect data to assess and to control
the qualities of gravimetric quasi/geoid models. All such datasets allow to improve geoid models in the Asia Pacific region.

The Geodesist’s Handbook 2020

Terms of Reference and Objectives
This sub-commission is a continuation of the previous subcommission and will continue to promote gravity data collection, geoid processing and evaluating techniques, and geoid applications in the Asia-Pacific region. In particular,
coastal marine gravity will be improved by recent altimetrydata. We will organize workshops to exchange data andtechniques of geoid modeling and assessing.
Program of Activitiesa) Gravity and Related Datax share available gravity datax share available DEMs along common borders
x combine resources for terrestrial gravity surveys alongcommon borders
x promote regional airborne gravity surveys
x determine improved coastal gravity anomalies fromsatellite altimetryb) Gravimetric geoid and hybrid geoid quality control
x share GNSS/levelling and vertical deflection data for
geoid quality control
x promote regional GNSS/leveling and vertical deflection
campaigns
x connect regional vertical datumsc) Education & Researchx organize meetings and workshops to improve modelingand evaluation techniques of gravimetric quasi/geoids,
and to promote their application to height modernizationand vertical datum connection.
x propose technical sessions in scientific and professional
conferences
x propose matters of common concern/interest
Delegates
Chair: Cheinway Hwang (China-Taipei)
Vice-Chair: Wenbin Shen (China)
Jay Hyoun Kwon (Korea)
Will Featherstone (Australia)
Koji Matsuo (Japan)
Ami Hassan Md Din (Malaysia)
Chalermchon Satirapod (Thailand)
Kosashi Prijatna (Indonesia)
Dinh Toan Vu (Vietnam)
Ronaldo Gatchalian (Philippines)
Ropesh Goyal (India)
Matt Amos (New Zealand, corresponding member only)

Commission 2 – Gravity Field

SC 2.4f: Gravity and Geoid in Antarctica
Chair: Mirko Scheinert (Germany)
Vice-Chair: Fausto Ferraccioli (UK)
Terms of Reference
Antarctica is the region that still features the largest data
gaps in terrestrial gravity. Global gravity field solutions suffer from the lack of terrestrial data in Antarctica as well asfrom the polar data gap originating from the orbit inclinationof dedicated satellite gravity field missions (esp. GOCE
with a polar data gap of 1,400 km diameter).
The coverage with terrestrial (ground-based and airborne) gravity data in Antarctica has been improved during
the last years. Efforts were successfully accomplished to
publish a first Antarctic-wide gravity anomaly grid(Scheinert et al. 2016) and to record data over the polar datagap (Forsberg et al. 2017). However, the gravity data coverage in Antarctica is still insufficient. The data are heterogeneous and exhibit inconsistencies. Due to the vast extensionof the Antarctic continent, its hostile environment and the
difficult logistic conditions it is a long-lasting task to close
the Antarctic data gaps in terrestrial gravity.
SC 2.4f shall pursue this objective and shall facilitate thenecessary coordination to release an updated grid of terrestrial gravity data for Antarctica. Terrestrial gravity data areneeded for the global high-resolution determination of the
Earth’s gravity field and/or for a validation of global gravity
field models, for a regional improvement of the Antarctic
geoid and for geophysical inversion to improve ourknowledge on the subglacial topography and inner structureof the Earth.
Thus, SC 2.4f plays an important role to improve the cooperation between all interested scientists of geodesy and ofneighbouring disciplines, mainly geophysics.
Program of Activities
x Promoting the collection of surface and airborne gravity
data in Antarctica;
x Promoting new gravity surveys in Antarctica, especiallyairborne gravimetry;x Promoting the establishment and (re-)measurement ofreference gravity stations utilizing absolute gravity
meters;x Promoting the scientific exchange of latest
developments in technology (esp. airborne gravimetry)and data analysis;x Evaluation of existing and new surface and airborne
gravity data, validation of global gravity field models in
Antarctica;

123

x Investigation of optimum strategy for the combinationof gravity data of different sources;
x Release of updated gridded gravity anomaly dataset(s)for Antarctica to the scientific public;x Organization of special workshop on airborne geodesy
and geophysics (especially aerogravimetry) with focus
on Antarctica;
x Focus group for all scientists interested in Antarctic
gravity and geoid, and cooperation with similar data
initiatives, especially within the Scientific Committee on
Antarctic Research (SCAR);
Delegates
Chair: Mirko Scheinert (Germany)
Don Blankenship (USA)
Alessandro Capra (Italy)
Fausto Ferraccioli (UK)
Christoph Förste (Germany)
René Forsberg (Denmark)Larry Hothem (USA)Graeme Eagles (Germany)
German L. Leitchenkov (Russia)
Jaakko Mäkinen (Finland)
Yves Rogister (France)
Koichiro Doi (Japan)
Michael Studinger (USA)Corresponding Members
Matt Amos (New Zealand)

SG 2.4.1: Downward Continuation of Airborne Gravity Data for Local Geoid Improvement
Chair: Xiaopeng Li (USA)Vice-Chair: Jianliang Huang (Canada)
Terms of Reference
Many countries have used or will use pure gravimetric geoid/quasi-geoid models as their height datum. This requires
high accurate and high resolution local gravity data coverage. Airborne gravimetry is widely used for this purpose because of its efficiency both in terms of time and cost. One
important step of using airborne gravity data in local geoid
modeling is to downward continue the airborne gravity datafrom flight altitudes to the (quasi)geoid computation level.
The topic of downward continuation (DWC) has beenstudied for many decades without very conclusive answers
on how different methods compare with each other. Often a124time, geoid modelers just pick one approach and use it without thorough comparisons. On the other hand, there are vast
amounts of airborne gravity data collected by the GRAV-D
project at NGS NOAA of the United States and by manyother groups around the world. These airborne gravity data
are collected on flight lines where the height of the aircraft
actually varies significantly, and this causes challenges forusers of the data. A downward continued gravity grid either
on the topography or on the geoid is still needed for many
applications such as improving the resolution of a local geoid model. Several classical and new downward continuation methods, such as, Least Squares Collocation and Residual Least Squares Collocation (RLSC), the Inverse Poisson
Integral, Truncated Spherical Harmonic Analysis, and Radial Basis Functions (RBF), are tested on both simulated
data sets and real GRAV-D airborne gravity data. Comprehensive theoretical and numerical comparisons are required
to provide useful guidelines for correctly handling airborne
gravity in local geoid computation.
Objectives
The main objectives of this SG are to:x Review the theories of the downward continuation of
airborne gravity data.
x Provide an official forum for in-depth discussion of very
approaches.
x Develop efficient software to perform all consideredapproaches.
x Conduct in-depth analysis of the downward continuation
results.
x Identify main problems and give recommendations.
x Publish downward continued airborne gravity grid andtool boxes.
Program of Activities
x Circulating and sharing information, ideas, progress
reports, papers and presentations.
x To launch a proposal for state-of-the-art cooperation on
the topic of downward continuation.
x Development/improvement of downward continuation
tools.
x Presenting research findings at major international
geodetic or geophysical conferences, meetings, andworkshops.
x Focus on error assessment of results produced by various
methods.
x To open a web page to published downward continued
airborne gravity grid products and related software tool
boxes.

The Geodesist’s Handbook 2020

Members
Chair: Xiapeng Li (USA)Vice Chair: Jianliang Huang (Canada)
René Forsberg (Denmark)Cheinway Hwang (Taiwan)
Roland Klees (Netherlands)
Cornelis Slobbe (Netherlands)
Martin Willberg (Germany)

SC 2.5: Satellite Altimetry
Chair: Xiaoli Deng (Australia)
Vice-Chair: C.K. Shum (USA)Terms of Reference
Satellite altimetry missions (e.g., Geosat, TOPEX/Poseidon,
ERS-1/2, Envisat and Jason-1/2/3) have been providing vital measurements of global ocean surface topography since1991. The latest altimetry missions (e.g., HY2a/2b, Ka-band
altimetry SARAL/Altika, SAR and SARIn altimetry CryoSat-2 and Sentinel-3A/B, and laser altimetry ICEsat-2) areproviding higher resolution observations. The upcoming Jason-CS/Sentinel-6 mission includes two identical satellites
scheduled to launch in 2020 (satellite A) and 2025 (satelliteB), which will continue measuring the sea level for at leasta decade. The future Surface Water and Ocean Topography(SWOT) satellite mission equipped with radar interferometry, due to launch in 2021, will substantially improve measurements of sea surface heights and surface water hydrology
at finer scales that has not been possible before. In addition,
the in situ GNSS reflectometry (GNSS-R) and the NASACYGNSS 8-satellite constellation have been providing water/sea level, land cover, water/snow extents, wave and windmeasurements.
Altimetry observations cover the global oceans, cryosphere, sea-ice, ice-covered oceans and inland water bodies, providing invaluable geodetic and climatic information
for studying the Earth and ocean dynamics (e.g., sea level,
ocean wave and wind speed, ocean surface topography,
tides, soil moisture, snow depth, ice sheet, ice caps, mountain glacier, inland water and solid Earth deformation), andgeophysical features (e.g., marine gravity field, mean sea
surface and bathymetry).
The growing altimetry datasets are driving technologicalleaps forward for satellite geodesy and oceanography. At thesame time, they will bridge an observational gap on a spatial-temporal domain critical for solving interdisciplinary
problems of considerable societal benefit. The purpose ofthis IAG sub-commission is to promote innovative research

Commission 2 – Gravity Field

using historic and future altimeter observations to study local, regional, and global geophysical processes, with emphasis on emerging cross-disciplinary applications using
satellite altimetry, and in combination with other in situ data
sets and techniques including hydrography data, GNSS-R,
CYGNSS, SAR/InSAR and GRACE/GOCE.
Objectives
Sub-Commission 2.5 will:x Establish a close link between this sub-commission andthe International Altimeter Service (IAS) and data
product providers, in order to (1) establish scientificforums to discuss new results, (2) bring new algorithms
from expert research into data production, and (3)encourage development of data products that more
directly facilitate cross-disciplinary applications using
satellite altimetry;x Promote innovative applications of satellite altimetry,
includingevaluations
andcross-disciplinary
applications of future satellite altimetry;x Continue developing techniques to improve altimeterdata quality, aiming towards the development of new
data products across the coastal zones including thecoastal ocean, estuaries and inland water bodies;
x Focus on capabilities of the very high spatial resolution
from SAR and SARAL altimeters, as well as upcoming
SWOT, for precisely modelling the marine gravity field,
mean sea surface, bathymetry and ocean mean dynamic
topography, as well as temporal variations induced bysolid Earth processes and the global terrestrial water
cycle; andx Promote cross-disciplinary research on the shapes andtemporal variations of land/ice/ocean surfaces, such as
studies of long-term ocean variability, regional andglobal sea level changes, mountain glaciers/ice-sheet
ablations/accumulations,permafrost
degradation,
coastal and ice-shelf ocean tides, vertical displacements
at major tectonic-active zone, land subsidence and othergeophysical processes.
Program of Activities
This sub-commission willx Organize independent workshops or special sessions inmajor meetings to promote altimetric applications ininterdisciplinary earth sciences, and to increase thevisibility of IAG in altimetric science; andx Provide independent forums for potentially improved
altimetry data processing and data product access, toencourage innovative and interdisciplinary scientificresearch and applications of satellite altimetry.

125

SC 2.6: Gravity Inversion
Transport in the Earth System

and

Mass

Chair: Wei Feng (China)
Vice-Chair: Roelof Rietbroek (Germany)
Terms of Reference
Spatial and temporal variations of gravity are related to the
dynamics of the Earth’s interior, land surface, oceans, cryosphere, and atmosphere. The geoid maps equilibrium dynamic processes in the ocean and in the Earth’s mantle andcrust, and large-scale coherent changes in gravity result
from mass transports in atmosphere, hydrosphere, cryosphere, and the ocean, and across these. The gravity field,
derived from terrestrial and space gravimetry (SLR,
CHAMP, GRACE, GOCE, GRACE-FO, NGGM, …) with
unprecedented accuracy and resolution, provides a unique
opportunity to investigate gravity- solid earth coupling, thestructure of the globe from the inner core to the crust, andmass transports such as those associated within the global
water cycle. Gravimetry also contributes to a better understanding of the interactions in the Earth system, and to its
response to climate change and the anthropogenic fingerprint.
Objectives
x To further the understanding of the physics anddynamics of the Earth’s interior, land surface,cryosphere, oceans and atmosphere using gravity andother geodetic and geophysical measurement
techniques.
x To promote the study of solid Earth mass (re)distribution from gravity and gravity gradient tensor
variations, e.g. crust thickness, isostatic Moho
undulation, mass loadings, basin formation, thermal
effects on density, deformations, as well as interactions
with the Earth’s interior.
x To advance the investigation of mass transports in the
Earth system, and, in particular, to contribute to theunderstanding of the global water cycle, of the storageof water in cryosphere and hydrosphere, of the fluxes
across these sub-systems and the atmosphere, and of sea
level.
x To contribute to the operationalization of mass transportmonitoring, e.g. for water resource monitoring.
x To aid in reconciling multiple geodetic observations at
various spatio-temporal scales for mass transportmonitoring and interpretation.

126

x To stimulate new techniques and potential applicationsof gravimetry and mass transport monitoring, e.g. quantum gravimeter, optical clock, new satellite gravimetry
concept,x To communicate with gravity-related communities inoceanography, hydrology, cryosphere, solid Earth, geodesy, etc.

The Geodesist’s Handbook 2020

Objectives

Chair: Wenbin Shen (China)
Vice-Chair: Cheinway Hwang (China-Taipei)

x Hydrological change over river basins, lake levelvariation, permafrost, vertical deformation, mountainglacier change, atmospheric circulation of the Tibetan
Plateau, and their interpretations from altimeter, GNSS,GRACE, GRACE-FO, and gravimeters;x Geopotential and orthometric height determinations andunification of world height datum systems;
x Long-term monitoring of surface processes fromsatellite altimeters such as ICESat, TOPEX, Jason-1, -2,
and -3, ERS-1, -2, ENVISAT, and Sentinel series;x Results of satellite and terrestrial-based gravimetricobservations;x Results of GNSS observations, GNSS meteorology, andionosphere;x Geophysical interpretations and consequences ofgravity, GNSS, satellite altimetry, and seismic
observations;
x SAR and LiDAR detections of surface deformation,
especially over the Tibetan Plateau;x Crust structure and density refinement especially in the
Tibetan region using multi-datasets;

Terms of Reference

Members

Program of Activities
The sub-commission will establish Work Groups (WGs) on
relevant topics. The Steering Committee will work closelywith members and other IAG commissions and sub-commissions to obtain mutual goals. Also it will promote andjointly sponsor special sessions at IAG Symposia and otherworkshop/conferences.

WG 2.6.1: Geodetic observations and physical interpretations in the Tibetan Plateau

Mass transport and (re-)distribution of the Tibetan Plateau
is a research hotspot in the field of geoscience, relevant toglobal climate, glaciers, lakes, permafrost and deep geodynamics. The mountain building processes and their dynamic
mechanisms of the Tibetan Plateau are still unclear and remain a key topic of research in geosciences. As multipletype of data continue rapidly to grow on the Tibetan Plateau,advanced techniques in signal processing are needed to effectively extract targeted signals. Cross-correlations between different data types are important keys to discover theconnections between the data, and to understand the causes
and the consequences of the phenomena of interest.
This working group will concentrate on but not limit to
the studies of hydrological change, crustal deformation, regional gravity field and its variation, mass migration andMoho variation, geodynamic and cryospheric processes andclimate change of the Tibetan Plateau, based on various observations from space-borne and terrestrial sensors, such as
GNSS, GRACE, GRACE-FO, satellite altimetry, InSAR,
and ground gravity. Relevant investigations and studies will
significantly promote the understanding and revealing of the
uplift processes and dynamic mechanisms of mass transport
in the Tibetan Plateau.

Chair: Wenbin Shen (China)
Vice-Chair: Cheinway Hwang (China-Taipei)
Carla Braitenberg (Italy)
Benjamin Fong Chao (China-Taipei)
Tonie van Dam (Luxembourg)
Xiaoli Deng (Australia)
Hao Ding (China)
Xiaoli Ding (Hong Kong, China)
Jeffrey T. Freymueller (USA)
Yuanjin Pan (China)
Jim Ray (USA)
Mirko Reguzzoni (Italy)
Lorenzo Rossi (Italy)
Xiaodong Song (USA)CK Shum (USA)Heping Sun (China)
Wenke Sun (China)
Robert Tenzer (Hong Kong, China)
Leonid Zotov (Russia)

Commission 3 – Earth Rotation and Geodynamics

127

Commission 3 – Earth Rotation and Geodynamics
President: Janusz Bogusz (Poland)
Vice President: Cheng-Li Huang (China)
https://com3.iag-aig.org/

Terms of Reference
The Earth must be considered as a dynamic system throughthe study of the global gravity field and its temporal variations, and the global and local deformation at the surface inorder to define the Earth’s internal structure and dynamics.
Consequently, geodynamics is the science that studies how
the Earth moves and deforms in response to forces acting on
the Earth, whether they derive from outside or inside of ourplanet. This includes the entire range of phenomena associated with Earth rotation and Earth orientation in space suchas polar motion, Universal Time (UT) or Length Of Day(LOD), precession and nutation, the observation and understanding of which are critical to the transformation between
terrestrial and celestial reference frames. On the other hand,space and terrestrial geodetic techniques provide key observations to investigate a broad range of geophysical processes, thanks to their high accuracy, precision, and reliable
georeferencing.
The modern geodesy successfully supports research anddata analysis devoted to variations in Earth rotation, gravitational field and geocenter, caused by mass redistribution
within and mass exchange among the Earth’s fluid sub-systems, i.e., the atmosphere, ocean, continental hydrosphere,
cryosphere, mantle, and core along with geophysical processes associated with ocean tides and the hydrological cycle. It also includes tidal processes such as solid Earth andocean loading tides, and crust and mantle deformation associated with tectonic motions and isostatic adjustment etc.
Geodesy is an important tool for exploring the geometry
and temporal evolution of magma plumbing systems, aswell as for monitoring and hazards assessment during volcanic unrest and eruption. Angular momenta and the related
torques, gravitational field coefficients, and geocenter shifts
for all geophysical fluids are the relevant quantities. They
are observed using global-scale measurements and are stud-

ied theoretically as well as by applying state-of-the-art models; some of these models are already constrained by suchgeodetic measurements.
During the last few decades many geophysicists havecome to use geodynamics in a more restricted sense to address processes such as plate tectonics and Post Glacial Rebound (PGR) that are dominantly endogenic in nature. Because the Earth as a mechanical system responds to both endogenic and exogenic forces, and because these responses
are sometimes coupled, Commission 3 studies the entire
range of physical processes associated with the motion andthe deformation of the solid Earth.
Present-day ice mass changes induce an immediate elastic deformation of the Earth, while the integrated history ofmass changes induces an additional viscoelastic deformation. Traditionally, these have been considered separately, which is a good approximation for long-ago loadchanges and regions of high mantle viscosity. The presentday and recent past load changes must be modeled together
as the rapid viscoelastic relaxation is substantial and not easily separated from the immediate elastic changes.
Reference frames of GIA models are likely computed in
the center of mass of the solid Earth frame, while the International Terrestrial Reference Frame (ITRF) is defined withorigin at the center of mass of Earth system (including all
fluids). This means a frame origin transformation is required
to allow direct comparison to measurements in ITRF andambiguity currently exists over the exact transformation between the two.
Among their many applications, geodetic measurements
can now contribute to the study of the different phases of theseismic cycle, as they allow recording static and dynamic
displacements during large earthquakes, as well as the slow
postseismic and interseismic deformation contributing significantly to the process of monitoring natural hazards and128risks. The purpose of Commission 3 is to promote, disseminate, and, where appropriate, to help coordinate research inthis broad arena.
Sub-Commission 3.1 (Earth Tides and Geodynamics)
addresses direct and indirect tidal phenomena that affect theposition of fiducial sites and have to be corrected to provide
accurate spatial referencing. Such referencing is needed forthe observation and monitoring of changes of the Earth’s
surface at global, regional and local scales. Therefore, there
is a considerable contribution of tidal research to global geodynamics and climate change by providing important constraints to geophysical models.
Sub-Commission 3.2 (Volcano Geodesy) addresses explosion in the quality and quantity of volcano geodetic data,
which has created a need for new approaches to data analysis, interpretation, and modeling required for data fusion andjoint interpretation, both between geodetic datasets and withother types of volcano monitoring results.
Sub-Commission 3.3 (Earth Rotation and GeophysicalFluids) addresses the space-time variation of atmosphericpressure, seafloor pressure and the surface loads associatedwith the hydrological cycle, and Earth’s (mainly elastic) responses to these mass redistributions.
Sub-Commission 3.4 (Cryospheric Deformation) addresses past and present changes in the mass balance of the
Earth's glaciers and ice complexes which both induce present-day deformation of the solid Earth on a range of spatial
scales, from the very local to global.
Sub-Commission 3.5 (Seismogeodesy) addresses studying the plate boundary deformation zones and integration ofgeodetic and seismological monitoring of seismically active
areas by increasing and/or developing infrastructures dedicated to broadband observations from the seismic wave
band to the permanent displacement.
Commission 3 interacts with Global Geodetic Observing
System (GGOS), other Commissions and Services of the
IAG as well as with other organizations such as the International Astronomical Union (IAU), International Associationof Seismology and Physics of the Earth’s Interior (IASPEI),International Association of Volcanology and Chemistry of
the Earth’s Interior (IAVCEI) and International Associationof Cryospheric Sciences (IACS).
Objectives
x To promote cooperation and collaboration on the theory,modelling and observation of Earth rotation and geodynamics.
x To ensure development of research in Earth rotation andgeodynamics by organizing meetings, symposia, andsessions at conferences and general assemblies, by creating working groups on specific topics, and by encouraging the exchange of ideas and data and the comparison

The Geodesist’s Handbook 2020of methods and results with the goal of improving accuracy, content, methods, theories, and understanding ofEarth rotation and geodynamics.
x To serve the geophysical community by facilitating interactions with organizations that provide the dataneeded to study Earth rotation and geodynamics.
Structure
Sub-Commissions
SC 3.1: Earth Tides and Geodynamics
Chair: Carla Braitenberg (Italy)
SC 3.2: Volcano Geodesy (joint with IAVCEI)
Chair: Emily Montgomery-Brown (USA)SC 3.3: Earth Rotation and Geophysical Fluids
Chair: Jianli Chen (USA)SC 3.4: Cryospheric Deformation
Chair: Jeff Freymueller (USA)SC 3.5: Seismogeodesy
Chair: Jean-Mathieu Nocquet (France).
Joint Study GroupJSG 3.1: Geodetic, Seismic and Geodynamic Constraints on
Glacial Isostatic Adjustment (joint with IASPEIand IAG Commissions 1 and 2)
Chair: Rebekka Steffen (Sweden)
Joint Working Groups
JWG 3.1: Improving Theories and Models of the Earth’s
Rotation (joint with IAU)
Chair: José Ferrándiz (Spain)
JWG 3.2: Global combined GNSS velocity field (joint with
IAG Commissions 1 and 2)
Chair: Alvaro Santamaría-Gómez (France)
Program of Activities
Commission 3 fosters and encourages research in the areasof its sub-entities by facilitating the exchange of informationand organizing symposia, either independently or at major
conferences in geodesy or geophysics. Some events will befocused narrowly on the interests of the Sub-Commissions
and other entities listed above, and others will have abroader commission-wide focus.
Steering Committee
President Commission 3: Janusz Bogusz (Poland)
Vice President Comm. 3: Chengli Huang (China)
Chair Sub-Comm. 3.1: Carla Braitenberg (Italy)
Chair Sub-Comm. 3.2: Emily Montgomery-Brown (USA)
Chair Sub-Comm. 3.3: Jianli Chen (USA)
Chair Sub-Comm. 3.4: Jeff Freymueller (USA)
Chair Sub-Comm. 3.5: Jean-Mathieu Nocquet (France)

Commission 3 – Earth Rotation and Geodynamics

Representative of IERS: Robert Heinkelmann (Germany)
Representative of IGFS: Nico Sneeuw (Germany)
Representative of IGETS: Hartmut Wziontek (Germany)
Member-at-Large: Matt King (Australia)
Member-at-Large: Laura Fernández (Argentina)

Sub-Commissions
SC 3.1: Earth Tides and Geodynamics
Chair: Carla Braitenberg (Italy)
Vice-Chair: Séverine Rosat (France)
Terms of Reference
SC 3.1 addresses the entire range of Earth tidal phenomena
and dynamics of the Earth, both on the theoretical as well ason the observational level. The Earth tide affects many typesof high precision instrumentation, be it measurements of position, deformation, potential field or acceleration. The tidal
phenomena influence both terrestrial and satellite-borne acquisitions. The tidal potential is a driving force that can be
accurately calculated, and the tidal response observable as
deformation and variations in Earth orientation and rotation
parameters gives information on Earth’s rheology.
Instruments sensitive enough to detect the tidal signal,
record a large range of periodic and aperiodic phenomena as
ocean and atmospheric tidal loading, ocean, atmosphericand hydrospheric non-tidal effects, deformation related tothe earthquake cycle and even to gravitational waves, aswell as plate tectonics and intraplate deformation.
The periods range from seismic normal modes over to the
Earth tides and the Chandler Wobble and beyond, ending at
the nutation period. Thus, the time scales range from seconds to years and for the spatial scales from local to continental dimensions. As tidal friction is affecting Earth rotation, all the physical properties of the Earth contribute to the
explanation of this phenomenon. Therefore, the research on
tidal deformation due to changes of the tidal potential aswell as ocean and atmospheric loading are a prerequisite toconstrain Earth’s rheological properties.
Further, direct and indirect tidal phenomena affect theposition of fiducial sites and have to be corrected to provide
accurate spatial referencing. Such referencing is needed forthe observation and monitoring of changes of the Earth’s
surface at global, regional and local scales. Therefore, there
is a considerable contribution of tidal research to global geodynamics and climate change by providing important constraints to geophysical models.
Modern instrumental developments for which tidal phenomena are relevant are gravimeters and gradiometers based

129

on superconductivity (SG), atom interferometry, microelectromechanical-system (MEMS) gravimeters, Inertial
Measurement Units, gravitational wave antennas, satellite
gravimetry and atomic clocks. The improvements in gravimetric instrumentation leads to the use of gravimetry as atool to detect underground mass changes, as naturally occurring hydrologic draughts or fluids injected into the underground for the purpose of temporary storage or for otherpurposes.
The Earth must be studied as a dynamic system throughthe study of the global gravity field and its temporal variations, and the global and local deformation at the surface inorder to define the Earth’s internal structure and dynamics.
In the next few years, instrumental developments in portableabsolute gravimeters can be expected, and further innovations can be envisaged from the ring laser technology.
The SC 3.1 will follow the instrumental developments
and infer innovative applications. These geophysical observations together with other geodetic observations and geological information provide the means to better understandthe structure, dynamics and evolution of the Earth system.
The existence of a network of superconducting gravimeters allows continuous monitoring of the gravity signal atselected stations with a precision of better than 10-10. The
range of applications of SGs has become very wide and applicable not only to Earth tides investigations, but also to
support studies on Earth’s seismic cycle and hydrologicalmass estimates. The SG network has had scientifically close
relation to the SC 3.1 and IGETS (International Geodynamics and Earth Tide Service), which distributes the data.
Therefore, the Chair of SC 3.1 is responsible for the close
cooperation with the IGETS to provide effective servicewith science coupling.
Objectives
Objectives of SC 3.1 include:
x to study and implement new observational techniques
and improve existing ones, including clinometric and extensometric techniques;x to demonstrate the importance of long term geodetic stations;x to predict the signals observable with space geodetic
techniques based on high precision terrestrial long term
time series;
x to advance tidal data analyses and prediction methods;
x to enhance the models on the interaction among solid
Earth, ocean, and atmospheric tides;
x to research the effects of the atmosphere and hydrology
on gravity and other geodetic observations;x to study the response of the Earth at tidal and non-tidal
forcing frequencies;x to study the interplay between tides and Earth rotation;

130

x to study tides on the planets;
x to study the effects of ocean loading and global water
distribution;
x to establish and coordinate working groups on specifictopics of interest and relevancy to the understanding ofour planet;x to develop, coordinate and promote international conferences, programs and workshops on data acquisition,
analysis and interpretation related to the research fields
mentioned above;
x to contribute to the definition and realization of the International Terrestrial Reference Frame via advanced
geodynamic models at global, regional and local scales;
x to promote the systematic calibration and intercomparison of absolute and relative gravimeters (superconducting, MEMS as well as traditional spring instruments) ;x to promote interdisciplinary research in Earth and planetary tides;
x to support the IAG Global Geodetic Observing System(GGOS) in the field of:o the integral effect on Earth rotation of all angular momentum exchanges inside the Earth, between land,
ice, hydrosphere and atmosphere, and between the
Earth, Sun, Moon, and planets,
o the geometric shape of the Earth’s surface (solid
Earth, ice and oceans), globally or regionally, and its
temporal variations, whether they are horizontal orvertical, secular, periodical or sudden,o the Earth’s gravity field-stationary and time variable
mass balance, fluxes and circulation.
Program of Activities
x Organization of International Symposium on Geodynamics and Earth Tide (GET Symposium held every
four years) as well as other thematic conferences together with other Commission 3 SCs if possible.
x Awarding of the outstanding scientists with the Paul
Melchior Medal, formerly known as the Earth Tides
Commission Medal.
x Organization of special sessions at international meetings.
x Organization of the comprehensive SC meeting together
with the IGETS.
x Publishing the outcome of the researches, either asstand-alone publications or as proceedings or special issues of scientific journals.
x Cooperating with other Joint Study Groups (JSG), Joint
Working Groups (JWG) or Inter-Commission Projects(ICP) and Committees (ICC).
x Cooperate with GGOS, as mentioned above.

The Geodesist’s Handbook 2020

SC 3.2: Volcano Geodesy (joint with IAVCEI)
Chair: Emily Montgomery-Brown (USA)Vice-Chair: Alessandro Bonforte (Italy)
Terms of Reference
Geodesy is an important tool for exploring the geometry andtemporal evolution of magma plumbing systems, as well as
for monitoring and hazards assessment during volcanic unrest and eruption. Geodetic techniques include measurements of both deformation (to determine the magnitude, location, and geometry of subsurface sources of pressurechange) and gravity (to assess subsurface mass variations).
Recent decades have seen an explosion in the quality andquantity of volcano geodetic data, which has created a needfor new approaches to data analysis, interpretation, andmodeling. In addition, geodetic data can have different temporal and spatial resolutions, as well as different origins(ground-, air-, and space-based), and they are best utilizedin conjunction with other non-geodetic datasets, like seismicity and gas emissions. New tools are therefore neededfor data fusion and joint interpretation, both between geodetic datasets and with other types of volcano monitoring
results. This is especially relevant now given the expansion
in GEO’s Geohazard Supersites and Natural Laboratories
initiative to volcanic sites around the globe.
We feel that an IAVCEI (International Association on
Volcanology and Chemistry of the Earth's Interior) Commission on Volcano Geodesy is needed to organize the diverse community and promote a better understanding ofmagmatic processes through geodesy.
Objectives
Objectives of SC 3.2 include:x foster communication within the volcano geodesy community, particularly between senior and early-career researchers, between scientists from different countries,
and between volcano observatories;
x facilitate a coordinated geodetic response to volcanic unrest and eruptions around the world, including the acquisition of, and access to, satellite data;x ensure high-level geodetic capability at the world’s volcanoes through the sharing of best practices; development, testing, and distribution of open-source analysis
and modeling tools; standardization of techniques for themeasurement and interpretation of geodetic changes; exploitation of new technologies; and capacity-building
activities;

Commission 3 – Earth Rotation and Geodynamics

x support the establishment and maintenance of databasesfor volcano geodetic observations, as well as the interoperability between these and other sources of geological,
geochemical, and geophysical data related to volcanoes;
x promote volcano geodesy as a tool with broad implications and diverse applications in research, monitoring,and crisis response by serving as a bridge between geodesy and other branches of volcanology; connecting geodesists within the academic community, volcano observatories, space agencies, industry, government institutions, and other organizations; and advocating for thecommitment of appropriate resources;x encourage and enable collaborations between geodesy
and other disciplines, given that interdisciplinary approaches to volcano research and hazards assessment offer the best prospects for improving overall understanding of volcanic processes and their impacts;
x implementation and dissemination of new standard approaches, protocols and best practices;x promotion of common initiatives and projects with other
IAG and IAVCEI entities.
Program of Activities
x Organize a scientific conference to define big scientificquestions that could be addressed with Volcano Geodesy.
x Organize a scientific workshop with the goals of training
early career volcano geodesists, sharing current research, and comparing codes on a standardized synthetic
data set.
x Set up and use of social networks for advertising the activities and news and encourage people to use it widely.

SC 3.3: Earth Rotation and GeophysicalFluidsChair: Jianli Chen (USA)Vice-Chair: Michael Schindelegger (Germany)
Terms of Reference
Mass transport in the atmosphere-hydrosphere-mantle-coresystem, or the “global geophysical fluids”, causes observable geodynamic effects on broad time scales. Although relatively small, these global geodynamic effects have beenmeasured by space geodetic techniques to increasing, unprecedented accuracy, opening up important new avenues ofresearch that will lead to a better understanding of global
mass transport processes and of the Earth’s dynamic response. Angular momenta and the related torques, gravitational field coefficients, and geocenter shifts for all geophysical fluids are the relevant quantities. They are observed

131

using global-scale measurements and are studied theoretically as well as by applying state-of-the-art models; some ofthese models are already constrained by such geodetic
measurements.
Objectives
The objective of the SC3.3 is to serve the scientific community by supporting research and data analysis devoted to variations in Earth rotation, gravitational field and geocenter,
caused by mass redistribution within and mass exchange
among the Earth’s fluid sub-systems, i.e., the atmosphere,
ocean, continental hydrosphere, cryosphere, mantle, andcore along with geophysical processes associated withocean tides and the hydrological cycle. The SC complements and promotes the objectives of GGOS with its central
theme "Global deformation and mass exchange processes inthe Earth system" and the following areas of activities:
x quantification of angular momentum exchange and masstransfer;x deformation due to mass transfer between solid Earth,atmosphere, and hydrosphere including ice.
Program of Activities
x To promote the exchange of ideas and results as well asof analysis and modeling strategies, sessions at international conferences and topical workshops will be organized.
x In addition, SC 3.3 interacts with the sister organizations
and services, particularly with the IERS Global Geophysical Fluids Centre and its operational component
with four Special Bureaus (atmosphere, hydrology,
ocean, combination) and its nonoperational component
for core, mantle, and tides.
x SC 3.3 will have close contacts to the GGOS activities,
in particular to the activities of the newly established
GGOS Committee “Contributions to Earth System Modelling”.

SC 3.4: Cryospheric Deformation (joint withIACS)

IAG co-Chair: Jeff Freymueller (USA)
IACS co-chair: Bert Wouters (Netherlands)
Vice-Chair: Natalya Gomez (Canada)
Terms of Reference
Past and present changes in the mass balance of the Earth's
glaciers and ice complexes induce present-day deformationof the solid Earth on a range of spatial scales, from the very
local to global. Geodetic observations that validate, or may

132

be assimilated into, models of glacial isostatic adjustment(GIA) and/or constrain models of changes in present-day ice
masses through measurements of elastic rebound are of paramount importance, as are “paleo-geodetic” observations
like the history of relative sea level.
Present-day ice mass changes induce an immediate elastic deformation of the Earth, while the integrated history ofmass changes induces an additional viscoelastic deformation. Traditionally, these have been considered separately, which is a good approximation for long-ago loadchanges and regions of high mantle viscosity. In regions of
low mantle viscosity (e.g. West Antarctica and Iceland), thepresent-day and recent past load changes must be modeled
together as the rapid viscoelastic relaxation is substantial
and not easily separated from the immediate elastic changes.
In all cases, present-day geometric measurements (e.g., uplift rates) measure the sum of elastic and viscoelastic deformations, and these components cannot be separated without
additional models or observations.
Present-day gravity changes have a different sensitivity
to the elastic and viscoelastic components. In addition, it is
now clear that 1-D Earth models are no longer sufficient for
many problems, but 3-D models pose computational challenges, and careful inter-comparison of 3-D models is required to better understand model differences.
Reference frames of GIA models are likely computed in
the center of mass of the solid Earth frame, while the International Terrestrial Reference Frame (ITRF) is defined withorigin at the center of mass of Earth system (including all
fluids). This means a frame origin transformation is required
to allow direct comparison to measurements in ITRF andambiguity currently exists over the exact transformation between the two.
This SC has a long history as part of IAG. At the Montreal IUGG, it was decided to make this a joint sub-commission with IACS. Within IAG, SC3.4 historically has focusedon resolving technical measurement issues. With the new
cross-Association sub-commission, we will have a better
opportunity to enhance collaboration and dissemination ofthese measurements within the glaciological community.
Objectives
Objectives of SC 3.4 include:x improvement of ice loading/unloading histories;
x improvement of Earth rheological models;x assessment of elastic loading and viscoelastic GIA models using present day geodetic data of all types, or paleosea level data;x assessing the impact of cryospheric deformation on geodetic reference frames and estimates of plate motions,and the differences between the frames of GIA models
and the ITRF;

The Geodesist’s Handbook 2020x assessing impact of lateral variations in Earth rheology
on interpretations of geodetic and geological data.
Program of activities
x Organize a workshop focused on observation and modeling of cryospheric changes and GIA. There is an opportunity to organize what would likely be a 2-day workshop in conjunction with an upcoming WCRP Grand
Challenge workshop, planned for November 2020 inVictoria BC, Canada. In terms of workshops, we willseek partners to enhance cross-disciplinary aspects of
the workshops, and have begun discussions with the
WRCP/CLIVAR program, the PALSEA program, and
JSG 3.1: Geodetic, Seismic and Geodynamic Constraints on Glacial Isostatic Adjustment (Rebekka Steffen, Chair). We have approached IRIS about using their
Earth Model Collaboration effort for the disseminationand inter-comparison of 3-D viscosity models, and they
are eager to include these important Earth models.
x Organize a second workshop in 2022, possibly jointlywith the PALSEA community on a topic such as GIA
and past and present changes in sea level, geomorphology and landscape evolution. We have begun discussions with PALSEA on this, although their future activities will depend on a funding renewal.
x Organize a working group to analyze frame differences(especially frame origin) between GIA models and
ITRF. It should be possible to transform global GIA
model predictions into any reference frame, including
Center of mass of Earth System and Center of Figure.
We should encourage future modeling efforts to compute the needed frame transformations.
x Develop an online archive of 1D and 3D Earth rheological models to enhance dissemination and inter-comparison of these models. The IRIS Earth Models Collaboration (http://ds.iris.edu/ds/products/emc/) offers a promising suite of tools and archive capability, and they are
eager to work with us. The IRIS EMC includes opensource software tools for dealing with their model format, and we will try to encourage development of tools
to compare and use these viscosity models, and to transform seismic velocity models into effective viscosity
models.
x Organize an effort to benchmark 3D GIA modeling approaches, similar to the benchmarking exercise done a
few years ago for 1D codes.
x Encourage the completion of ongoing Activities from2015-2019 that were approaching completion as of thelast report (Shfaqat Abbas Khan and Matt King, leaders):
o establish and publish a list of PSMSL tide gauges
that are subject to large, time-variable elastic deformation associated with present-day glacier massCommission 3 – Earth Rotation and Geodynamics

change,o compile a database of predictions for relative sea
level changes at tide gauges, gravity field, and 3D
deformation rates at geodetic sites and on global orregional grids for a set of reasonable GIA models,
both for the deglaciation after LGM and more recent
ice changes. While this database may not lead to consensus about the “best” model, it will clarify therange of predictions made by models that have some
support within the broader community.

SC 3.5: Seismogeodesy (joint with IASPEI)
Chair: Jean-Mathieu Nocquet (France)
Vice-Chair: Takuya Nishimura (Japan)
Position replacement every 2 years.
Terms of Reference
Space and terrestrial geodetic techniques provide key observations to investigate a broad range of geophysical processes, thanks to their high accuracy, precision, and reliable
georeferencing. Thanks to the technological evolution witnessed in the past decades, crustal movements of few millimeters can be now detected and monitored over time, opening new prospects for the study of Earth kinematics and geodynamics.
Among their many applications, geodetic measurements
can now contribute to the study of the different phases of theseismic cycle, as they allow recording static and dynamic
displacements during large earthquakes, as well as the slow
postseismic and interseismic deformation. However, thefoundation for fully exploiting the potential of geodetic
measurements is the development of a multidisciplinary approach to their interpretation.
The joint IAG-IASPEI SC on Seismogeodesy aims to facilitate the cooperation between the geodetic and the seismological communities to improve our current understanding of the different seismic processes. The investigated phenomena range from large destructive events, to slow earthquakes and tremors. The works of the SC focus on both theoretical aspects and observational challenges. Particular effort is dedicated to identifying gaps of knowledge and opportunity for progress, particularly in the field of hazard assessment and early warning systems.

133

Objectives
Objectives of SC 3.5 include:
x to actively encourage the cooperation between all geoscientists studying the plate boundary deformation
zones, by promoting the exploitation of synergies between different fields;
x to reinforce joint and integrated geodetic and seismological monitoring of seismically active areas by increasing
and/or developing infrastructures dedicated to broadband observations from the seismic wave band to thepermanent displacement;
x to be a reference group for the integration of the mostadvanced geodetic and geophysical techniques by developing consistent methodologies for data reduction, analysis, integration, and interpretation;
x to act as a forum for discussion and scientific support forinternational geoscientists investigating the kinematics
and mechanics of the plate boundary deformation zone;
x to promote the use of standard procedures for geodetic
data acquisition, quality evaluation, and processing, particularly GNSS data and InSAR data;x to promote earthquake geodesy, the study of seismically
active regions with large earthquake potential, and geodetic application to early warning system of earthquakes
and tsunamis for hazard mitigation;
x to promote the role of geodesy in tectonic studies for understanding the seismic cycle, transient and instantaneous deformation, and creeping versus seismic slip on
faults.
Program of Activities
x Building on the experience of the WEGENER Initiative,
to continue as a framework for geodetic cooperation in
the study of the plate boundary zones.
x To develop scientific programs in earthquake geodesy
for subduction zones and possible occurrence of giant
earthquakes and associated tsunamis.
x To foster the use of space-borne, airborne, marine andhybrid techniques such as GNSS, LIDAR, GNSSAcoustic, seafloor pressure gauges, radar, optical, andgravity satellite missions including GOCE, GRACE,ENVISAT, SENTINELLE, ALOS, etc. for earth observation.
x To define effective integrated observational strategies
for these techniques to reliably identify and monitor
crustal movements and gravity variations over all timescales.
x To facilitate and stimulate the integrated exploitation ofdata from different techniques in the analysis and interpretation of geo-processes.

134

x To organize periodic workshops and meetings with special emphasis on interdisciplinary research and interpretation and modeling issues.
x To organize special sessions at international meetings.
x To publish the outcome of the researches, either asstand-alone publications or as proceedings or special issues of scientific journals.

Joint Study Group 3.1: Geodetic, Seismic
and Geodynamic Constraints on Glacial
Isostatic Adjustment(joint with IASPEI and IAG Commissions 1 and 2)
Chair: Rebekka Steffen (Sweden)
Vice-Chair: Erik R. Ivins (USA)Terms of Reference
The solid Earth’s memory of past glacial loading has beenmodelled throughout the past 100 years using much of thesame formalism and attention to Earth structure that is foundin the study of surface wave seismology. Glacial Isostatic
Adjustment (GIA) models and geodynamics models use, as
fundamental source of data, both seismologically based internal mantle structure models and geodetic time series. It istherefore the focus of this working group to allow cross fertilization of models, data and conceptual frameworks ofthese two communities, geodynamics and GIA, with the development of an interdisciplinary approach to better determination of the Earth’s internal rheological structure.
The compatibility of the spatial and time scales overwhich rheological frameworks operate effectively is essential. This JSG shall also task itself with analysis of the currently applied GIA modelling parametrizations, data constraints and emerging geodetic data sets, such as GPS, gravity change, and both relative and absolute sea-level variations. In this interdisciplinary study it will be essential to
improve the operative definition of the lithosphere.
We seek to identify critical assessments that can be performed to more tightly constrain the relationships between
effective mantle viscosity for use in geodynamics and GIA
models that are compatible with the results of advanced seismic imaging of 3-D mantle structure and geodetic time series. Consequently, this Study Group is joined between
Commission 1 on Reference Frames, Commission 2 on
Gravity Field and Commission 3 on Earth Rotation and Geodynamics with promising cooperation with IASPEI Commission on Earth Structure and Geodynamics.
Objectives
Objectives of JSG 3.1 include:

The Geodesist’s Handbook 2020

x to review the integration of geophysical, seismological,
and geodynamical modelling as well as fundamental
mineral physics into GIA models, with a special emphasizes on their model results (including gravity changes
and GNSS rates);
x to formulate general principles for defining the lithosphere for GIA models and assessment of the rheologicalprinciples and geophysical observables relevant to thatdefinition;
x to study the relative merits of GIA data types. These datatypes include GNSS horizontal and vertical motion, tidegauges, gravity changes, observed with both terrestrial
and space, techniques, and seismicity, in form of paleo,
historic and recent earthquakes. These data are especially powerful when combined with one another. Special emphasis should be placed on evaluating the spatial
distribution of data and the length of time series required
for GIA modelling;
x to assess the role of GIA model impact on products derived from modern space gravimetry (GRACE) for bothocean and hydrological sciences;x to intercompare model based transient response of postseismic relaxation following Mw > 7.0 earthquakes to theconstitutive laws assumed valid in GIA models;
Program of Activities
x Organize a workshop discussing the objectives fromabove.
x Publishing a report on the definition of the GIA lithosphere.
x Organization of an international joint workshop in 2021
or 2022 (possibly in collaboration with SC 3.4 “Cryospheric Deformation”, with JSG 0.21 “Dynamic modeling of deformation, rotation and gravity field variations”, and even further related IAG (and IASPEI) working groups).
x Contribution to international meetings and conferences(e.g., EGU, AGU).
x Organization of a session at the IUGG meeting in Berlinin 2023.
x Common publications by JSG members.
x Managing a website with updates on the development of
the JSG.
Members
Kristel Chanard (France)
Mark Hoggard (USA)Paula Koelemeijer (UK)
Tanghua Li (Singapore)
Glenn Milne (Canada)
Bart Root (Netherlands)

Commission 3 – Earth Rotation and Geodynamics

Andrew Schaeffer (Canada)
Kate Selway (Australia)
Bernhard Steinberger (Germany)
Doug Wiens (USA)

Joint Working Group 3.1: Improving Theories and Models of the Earth’s Rotation(joint with IAU)

Chair: José Ferrándiz (Spain)
Vice-Chair: Richard Gross (USA)Terms of Reference
The main purpose of this JWG is proposing consistent updates of the Earth rotation theories and models and their validation. The associated tasks will thus contribute to the implementation of the 2018 IAU Resolution B1 on Geocentricand International Terrestrial Reference Systems andFrames, and the 2019 IAG Resolution 5 on Improvement of
the Earth’s Rotation Theories and Models. The last resolution is the most specific for the WG assignment and mandates:
x to encourage a prompt improvement of the Earth rotation
theory regarding its accuracy, consistency, and ability tomodel and predict the essential EOPs;
x that the definition of all the EOPs, and related theories,
equations, and ancillary models governing their time
evolution, must be consistent with the reference frames
and the resolutions, conventional models, products, andstandards adopted by the IAG and its components;
x that the new models should be closer to the dynamicallytime-varying, actual Earth, and adaptable as much as
possible to future updating of the reference frames andstandards.
The work will be performed in close cooperation other IAG
components, particularly GGOS, the IERS, and current
WGs dealing with the Earth rotation and standards from specific perspectives, as well as with the IAU Commissions A2
and A3. Continuous coordination will be sought throughcommon members and correspondents.
Program of Activities
At short term, intended as two years in this context, the JWG
is committed to derive supplementary models for the Celestial Pole Offsets (CPO) evolution, in part of semi-empiricaland semi-analytical nature, and able to increase significantly
the explained variance of the current theories and models.
According to the recommendations of the 2019 GGOSIERS Unified Analysis Workshop, the priority tasks ofbuilding such models will include:

135

x updating the amplitudes of the leading nutations of the
IAU2000 theory and testing shortened series for certain
operational purposes;
x correcting the inconsistencies found in the precessionnutation models;x test the available FCN models (for explaining CPO variance) and consider whether the IERS should recommend FCN models or not.
The two years term being too short to develop and publish afully dynamically consistent theoretical approach to support
those models, that activity will likely continue till the end of
the term. Theoretical developments must also address to advancing in all the aspects made explicit on resolution 5, likeusing a consistent framework for all the Earth Orientation
Parameters, with regard to reference systems and frames,
background models, standards, and adaptation of the developments to the current knowledge of the dynamic Earth,from its inner components to its outer layers. The chairing
people may assign specific tasks with delimited scopes tovolunteer members and correspondents, according to theirexpertise, availability and initiative.
Structure and operation
Taking into account the different methods and expertise required for the treatment of the different kinds of EOP andthat their theoretical treatment must be as consistent as theirdetermination from observations, we propose to structure
the JWG in three Sub-WGs, which should work in parallel
for the sake of efficiency. To guarantee that the SWGs arelinked together as closely as the needs of consistency demand, the Chair and Vice-Chair of the WG, Ferrándiz and
Gross, will be involved in all SWGs as will the President of
the IAU Commission A2, F. Seitz, and the Vice-presidentof IAG Commission 3, C. Huang. Besides, a number of people will be affiliated to more than one SWG.
1. Precession/Nutation
Chair: Alberto Escapa ((Spain)
Members:
T. Baenas (Spain),W. Chen (China),
V. Dehant (Belgium),
C. Huang (China),
J. Vondrak (Czech Republic)
Correspondents:
D. Angermannn (Germany),
C. Bizouard (France),
N. Capitaine (France),
J. Getino (Spain),
J. Hilton (USA),
G. Kaplan (USA),
J.C. Liu (China),

136

J.F. Navarro (Spain),
J. Ray (USA),R. Ray (USA),
C. Ron (Czech Republic),
H. Schuh (Germany),
F. Seitz (Germany),
W.B. Shen (China),
D. Thaller (Germany).
2. Polar Motion and UT1Chair: Aleksander Brzezinski (Poland)Members:S. Böhm (Austria),
B.F. Chao (Taipei),
J. Nastula (Poland),F. Seitz (Germany),
W.B. Shen (China).
Correspondents:
D. Angermann (Germany),
C. Bizouard (France),
W. Chen (China),
R. Dill (Germany),
H. Dobslaw (Germany),
L. Fernández (Argentina),
Z. Malkin (Russia),
J. Ray (USA),
D. Salstein (USA),
H. Schuh (Germany),
J. Vondrak (Czech Republic),
L. Zotov (Russia)
3. Numerical Solutions and Validation
Chair: Robert Heinkelmann (Germany)
Members:
S. Belda (Spain),
C. Bizouard (France),
Z. Malkin (Russia),
M. Schindelegger (Austria),
B. Soja (USA).
Correspondents:
D. Angerman (Germany),
B.F. Chao (Taipei),
W. Chen (China),
J. Hilton (USA),J. Mueller (Germany),
J. Ray (USA),
H. Schuh (Germany),
F. Seitz (Germany),
D. Thaller (Germany),
M. Thomas (Germany),
P. Zhu (Belgium).

The Geodesist’s Handbook 2020

JWG 3.2: Global combined GNSS velocity
field (joint IAG Commissions 1 and 2)
Chair: Alvaro Santamaría-Gómez (France)
Vice-Chair: Roelof Rietbroek (Germany)
Terms of ReferenceThis Working Group aims at combining and comparing
available GNSS velocity fields obtained by different groups
from both network and PPP solutions. It continues the activities of former JWG3.2 “Constraining vertical land motionof tide gauges” with the inclusion of the last reprocessed solutions derived or related to the ITRF2020 realization while
also extending the scope to the horizontal component of thevelocity field.
GNSS velocities estimated by different groups usuallydiffer due to the choices made concerning the GNSS dataprocessing (corrections applied and noise level of the series), the completeness of the series, the removed position
discontinuities and the alignment to a terrestrial reference
frame. The position discontinuities that populate the GNSS
time series have probably the biggest impact on the velocity
estimates. Even when using exactly the same series, it iscommon that different groups provide different velocity estimates and uncertainties mainly due to the different choicesof position discontinuities.
The main outcome of the Working Group will be a combined velocity field that takes into account the repeatabilityof the estimates by the different groups. It is expected thatthe combined GNSS velocity field will be useful for the scientific community in the areas of tectonics, sea-level change
and GIA modeling among others.
The differences of the combined GNSS velocity fieldwith respect to velocity fields obtained from other techniques (other space geodetic techniques, TGs, satellite altimetry) will be assessed. For instance, differences between
tide gauge records and between tide gauges and satellite altimetry can provide constraints on the vertical velocities at
the tide gauges. Observations from gravimeters, InSAR andother space geodetic techniques (e.g., DORIS) have the potential to provide valuable information on the velocities.
Program of Activities
x Collect velocity fields from GNSS and other techniques.
x Combine the GNSS velocity fields.
x Assess the differences between the combined GNSS velocity field and other velocity fields.
Members
Thomas Frederikse (USA),Paul Rebischung (France).

Commission 4 – Positioning and Applications

137

Commission 4 – Positioning and Applications
President: Allison Kealy (Australia)
Vice President: Vassilis Gikas (Greece)
https://com4.iag-aig.org/

Terms of Reference
IAG Commission 4 intends to bring together scientists, researchers and professionals dealing with the broad area of
positioning and its applications. For this purpose, it will promote research that leverages current and emerging positioning techniques and technologies to deliver practical and theoretical solutions for GNSS smartphone positioning technologies, multi frequency, multi constellation GNSS, positioning integrity and quality, alternatives and backups to
GNSS, sensor fusion, atmospheric sensing, modelling, andapplications based on geodetic techniques. Commmission 4
will carry out its work in close cooperation with the IAG
Services and IAG entities, as well as via linkages with entities within scientific and professional organizations.
Recognizing the central role of Global Navigation Satellite Systems (GNSS) in providing the positioning requirements today and into the future, Commission 4 will focus on
research for improving models and methods that enhance
and assure the positioning performance of GNSS-based positioning solutions for an increasing diversity of end-user
applications. It also acknowledges the increasing levels of
threat and vulnerabilities for GNSS only positioning and investigates technologies and approaches that address these.
The Sub-Commissions will develop theory, strategies
and tools for modeling and/or mitigating the effects of interference, signal loss and atmospheric effects as they apply to
precise GNSS positioning technology. They will address thetechnical and institutional issues necessary for developing
backups for GNSS, integrated positioning solutions, automated processing capabilities and quality control measures.
Commission 4 will also deal with geodetic remote sensing, using Synthetic Aperture Radar (SAR), Light Detection
and Ranging (LiDAR) and Satellite Altimetry (SA) systems
for geodetic applications.
Additional WGs and SGs can be established at any time,and existing can be dissolved, if they are inactive.

Objectives
The main topics dealt by Commission 4 are as listed in the
IAG By-laws:x Terrestrial and satellite-based positioning systems development, including sensor and information fusion;x Navigation and guidance of platforms;
x Interferometric laser and radar applications (e.g., Synthetic Aperture Radar);x Applications of geodetic positioning using three dimensional geodetic networks (passive and active networks),
including monitoring of deformations;x Applications of geodesy to engineering;x Atmospheric investigations using space geodetic techniques.

Structure
Sub-Commissions
SC 4.1: Emerging Positioning Technologies and GNSS
Augmentation
Chair: Laura Ruotsalainen (Finland)
SC4.2: Multi-frequency Multi-constellation GNSS
Chair: Suelynn Choy (Australia)
SC 4.3: Atmosphere Remote Sensing
Chair: Michael Schmidt (Germany)
SC 4.4: GNSS Integrity and Quality Control
Chair: Pawel Wielgosz (Poland)
Joint Study Groups
JSG T.32: High rate GNSS
Chair: Mattia Crespi (Italy)(joint with ICCT, description see ICCT)JSG T.24: Integration and co-location of space geodetic observations and parameters

138

Chair: Krzysztof Sośnica (Poland)(joint with ICCT, description see ICCT)JSG T.31: Multi-GNSS theory and algorithms
Chair: Amir Khodabandeh (Australia).
(joint with ICCT, description see ICCT)
Steering Committee
President: Allison Kealy (Australia)
Vice President: Vassilis Gikas (Greece)
Chair SC4.1: Laura Ruotsalainen (Finland)
Chair SC4.2: Suelynn Choy (Australia)
Chair SC4.3: Michael Schmidt (Germany)
Chair SC4.4: Paweł Wielgosz (Poland)Members at large:
Ana Paula Camargo Larocca (Brazil)
Jiyun Lee (Korea)
Services Representatives
IVS:
Robert Heinkelmann (Germany)
IGS:
Sharyl Byram (USA)The Geodesist’s Handbook 2020

positioning. As well, safety critical applications such as navigation of autonomous systems require use of multiple technologies.
The SC 4.1 focuses on research using specific technologies, like computer vision for navigation or use of 3D point
clouds for situational awareness, platforms like smartphones
with low-cost positioning sensors, fusion of multi-sensor
measurements and applications such as autonomous systems and localization at urban canyons.
Objectives
x Developing methods for multi-sensor navigationx Studying and solving navigation problems for safety
critical applications such as autonomous driving.
x Formation of 3D point clouds for spatio-temporal monitoringx Development of computer vision technologies for navigation
x Use of smartphone as a positioning platformx Localization in deep urban canyons

Representative of External Bodies

Program of activities

ISPRS: Charles Toth (USA)
FIG:
Allison Kealy (Australia)
ION: Larry Hothem (USA)x To promote research collaboration among groups fromgeodesy and other branches worldwide dealing withemerging positioning research and applications
x To organize and/or participate in scientific and professional meetings (workshops, conference sessions, etc.)
x To maintain a web page concatenating the Sub-Commission activities and reports
x To encourage special issues on research, applications,and activities related to the topics of this Sub-Commission
x Close co-operations with other elements of the IAG
structure and other international organizations such as
FIG , ION and ISPRS

Sub-Commissions
SC 4.1: Emerging Positioning Technologies and GNSS Augmentations
Chair: Laura Ruotsalainen (Finland)
Vice-Chair: Ruizhi Chen (China)
Terms of Reference
The global availability of position, velocity and time information due to the maturation of GNSS technologies is creating an increasing demand for more and more accurate andreliable solutions for navigation in also GNSS challenging
areas.
At present, navigation is mainly based on the use of
Global Navigation Satellite Systems (GNSS), providing
good performance in open outdoor environments. However,navigation solution with sufficient accuracy and integrity isneeded in urban canyons and indoors, where GNSS is significantly degraded or unavailable. For overcoming the
aforementioned navigation challenges, research has beenvery active for decades for finding a suitable set of othermethods for augmenting or replacing the use of GNSS in

Overview of Joint Study Groups (JSG) andWorking Groups (WG) of the SC 4.1
x WG 4.1.1 Multi-Sensor Systems
x WG 4.1.2 Autonomous Navigation for Unmanned Systems
x WG 4.1.3 3D Point Cloud based Spatio-temporal Monitoringx WG 4.1.4 Computer Vision in Navigationx WG 4.1.5 Localization at Asian urban canyons
x SSG 4.1.1 Positioning using smartphones

Commission 4 – Positioning and Applications

WG 4.1.1: Multi-Sensor Systems
Chair: Allison Kealy (Australia)
Vice-Chair: Gunther Retscher (Austria)
Description
This group is a joint working group between IAG and FIG.
It focuses on the development of shared resources that extend our understanding of the theory, tools and technologies
applicable to the development of multi-sensor systems.
Objectives
The group has a major focus on:
x performance characterization of positioning sensors andtechnologies that can play a role in augmenting core
GNSS capabilities,x theoretical and practical evaluation of current algorithms
for measurement integration within multi-sensor systems,x the development of new measurement integration algorithms based around innovative modeling techniques inother research domains such as machine learning and genetic algorithms, spatial cognition etc.,
x establishing links between the outcomes of this WG andother IAG and FIG WGs (across the whole period),x generating formal parameters that describe the performance of current and emerging positioning technologies
that can inform IAG and FIG members.
Specific projects to be undertaken include:
x international field experiments and workshops on a
range of multi sensor systems and technologies.
x evaluation of UAV capabilities and the increasing roleof multi-sensor systems in UAV navigation.
x investigation of the role of vision based measurements
in improving the navigation performance of multi-sensor systems.
x development of shared resources to encourage rapid research and advancements internationally.
Members
N/A

WG 4.1.2: Autonomous Navigation for Unmanned Systems
Chair: Ling Pei (China)
Vice-Chair: Giorgio Guglieri (Italy)

139

Description
Unmanned systems (e.g., UAV, driverless vehicles, and robots) have become increasingly important for data acquisition in numerous geospatial applications. In recent years,
technological advancements have facilitated the manufacturing of various types of intelligent sensors, such as cameras, LiDAR, motion, wireless, magnetic, light, and ultrasonic ones. These sensors and their enabling multi-sensor
autonomous systems have potential to be promoted into thegeospatial world such as autonomous vehicles, robotics,
smart cities, geolocation, condition monitoring, and context
awareness.
The Working Group will focus on the challenges for autonomous navigation using unmanned systems. Althoughextensive research efforts have been paid to sensors, algorithms, architectures, and applications of unmanned systems, it is still challenging to establish smart, autonomous,and disruptive implementations. Examples of the challenges
include enabling robust navigation data acquisition in challenging environments, using crowdsourcing techniques togenerate and use multi-source navigation databases, designing low-cost low-power autonomous navigation systems,
and cloud and edge computation of multi-sensor navigation
data, etc.
Objectives
The group has a major focus on:x Specification, characterization, and evaluation of the autonomous navigation system requirements in various
scenarios
x Technological challenges and emerging applications of
UAVs
x New sensors, platforms, and sensors for unmanned vehicle navigation
x Regulations and social impacts on unmanned vehicles
x Scalable multi-sensor integration architectures and technologies for unmanned vehicles
x Self-improving and adaptive navigation systems
x Location-based interactive between autonomous vehicles and humanx Artificial intelligent techniques for environment perception, awareness, data processing, and decision making in
unmanned vehicles
x Advanced computation techniques in autonomous navigation systems
Specific projects to be undertaken include:
x Specification, characterization, and evaluation of thesystem requirements
x Optimal set of sensors and technologies for robust unmanned navigation

140

The Geodesist’s Handbook 2020

x Advantages, challenges, analysis, and application of selected systems
x Relation between autonomous navigation and existingnavigation applications
x Relation between autonomous vehicles and humanx Adaptation of navigation sensors and algorithms in various environments

x Evaluate the fusion of heterogeneous data like 3D point
clouds and ground-based synthetic aperture radar (GBSAR) data with respect to structural health monitoring
applications of, e.g., infrastructure buildings.
x Algorithms will be implemented in Python, Matlab, C++
and for basic 3D point cloud operations open source libraries, e.g., point cloud library (PCL) will be used.

Members

Specific projects to be undertaken include:
x Strengthen the international visibility by cooperatingwith FIG Commission 6, e.g. at the FIG Working Week
2020 (The Netherlands, Amsterdam), 10 - 14 May 2020
x Corinna is the Co-Chair of FIG Commission 6 and thus
stands for the perfect link between both organisations
and their WGs
x A session with up to 6 contributions in the frame of WG
is already set up
x Motivate people/network to contribute, e.g., by ResearchGate, Linkedin
x ISPRS laser scanning community, in particular, Marco
Scaioni (Italy), Roderik Lindenbergh; the WG tries to bepresent at the upcoming ISPRS Congress in Nice in June
2020.
x Establish, verify and provide reference and benchmark
data sets for 3D Point Cloud Based Spatio-Temporal
Monitoring via an open access internet platform

You Li (Canada)
Laura Ruotsalainen (Finland)
Margarida Coelho (Portugal)
Marko Ševrović (Croatia)

WG 4.1.3: 3D Point Cloud Based SpatioTemporal Monitoring
Chair: Jens-Andre Paffenholz (Germany)
Vice-Chair: Corinna Harmening (Austria)
Description
The WG will focus on spatio-temporal monitoring of artificial and natural objects with the aid of 3D point clouds acquired by means of multi-sensor-systems (MSS). The emphasis will primarily be placed on laser scanning technology
and to a certain extent on digital cameras, satellite andground-based synthetic aperture radar (GB-SAR). In general, monitoring applications over a certain period of timerequire a geo-referencing of the acquired data with respect
to a known datum. In addition, a kinematic MSS requires
the determination of the time-dependent seven degrees of
freedom (translation, rotation and scale) with regard to a referencing. Both aforementioned key facts will be included in
the WG themes.
Objectives
The group has a major focus on:x Data evaluation, algorithm development in the directionof meaningful comparison of 3D point clouds of different epochs/measurement times (similar to classical deformation monitoring)x Evaluate the object’s abstraction for epochal comparisonby means of discrete point-wise, area-based and shapebased approaches. One suitable method to investigate
will be B-spline surfaces.
x Investigate and develop suitable algorithms for change
tracking/detection and deformation analysis over time in
3D point clouds for instance by means of feature point
tracking or shape matching.

Members
Michele Crosetto (Spain)
Petra Helmholz (Australia)
Christoph Holst (Germany)
Florian Schill (Germany)
Further members will be actively acquired by an email callas well as within the special session “3D point cloud based
spatio-temporal monitoring” at the FIG Working Week
2020 in Amsterdam, where the first WG 4.1.3 face-to-facemeeting will take place.

WG 4.1.4: Vision Aided Positioning andNavigation
Chair: Andrea Masiero (Italy)
Vice-Chair: Kai-Wei Chiang (China)
Description
The Work Group will focus on the integration of visual information with other sensor measurements in order to enhance navigation in challenging working conditions, such asindoors and urban canyons. The goal is that of compensating for the degradation of GNSS positioning performance,

Commission 4 – Positioning and Applications

providing a robust positioning solution in a wide range ofconditions, both indoors and outdoors. The WG will take
into consideration several cases of interest, focusing in particular on pedestrian navigation, unmanned aerial vehicles,
and terrestrial vehicles in urban environments.
In particular, the Work Group focuses on:x Specifications of the system performance requirements
to satisfy usability conditions for the considered casestudies.
x Assessment of the usability of vision for aiding navigation in the different case studies, including the investigation of suitable integration methods of other sensors suchas TOF cameras and LiDAR.
x Selection of best algorithms and technologies for integrating sensor information and fulfilling the system requirements.
x Analysis of the system performance for all the considered cases in different operating conditions.
Specific projects to be undertaken include:
x Reporting on the system requirements for ensuring usability conditions in the considered cases
x Reporting on the most suitable algorithms for integrating
visual information in the considered case studies
x Reporting on the performance analysis of the system
x Reporting on criticalities and potential issues in the developed solution
x Establishing links between the outcomes of this WG andother IAG, FIG and ISPRS WGs addressing sensor fusion for enhancing positioning and navigation results inchallenging operating conditions.
Members
Vassilis Gikas (Greece)
Harris Perakis (Greece)
Paolo Dabove (Italy)
Laura Ruotsalainen (Finland)
Rui Alexandre Matos Araujo (Portugal)
Vincenzo Di Pietra (Italy)

WG 4.1.5: Positioning and Navigation in
Asian Urban Canyons
Chair: Li-Ta Hsu (Hong Kong)
Co-Chair: Kubo Nobuaki (Japan)
Background
This group is a joint working group between IAG and ION.
Accurate positioning and localization in urban canyons remain a challenging problem for systems with navigation requirements, such as autonomous driving vehicles (ADV)and unmanned aerial vehicles (UAV). The urban canyons

141

are typical in megacities like Hong Kong and Tokyo. The
globally referenced GNSS positioning can be significantly
degraded in urban canyons, due to the blockage from tallbuildings.
The visual positioning, LiDAR positioning can be considerably affected by numerous dynamic objects. To facilitate the development and study of robust, accurate and safe
positioning solutions in urban canyons with multiple sensors, we form a working group to jointly build an integrated
dataset collected in diverse challenging urban scenarios inHong Kong and Tokyo that provides full-suit sensor data,
which includes GNSS, INS, LiDAR and cameras.
Locations for data collection
Urban canyons in Tokyo, Japan, and Hong Kong, which we
believe are the most challenging positioning areas in the city
environments.
Objectives
x Open-sourcing localization sensor data, including
GNSS, INS, LiDAR and cameras collected in Asian urban canyons, including Tokyo and Hong Kong.
x Raising the awareness of the urgent navigation requirement in highly-urbanized areas, especially in Asian-Pacific regions.
x Providing an integrated online platform for data sharing
to facilitate the development of navigation solutions of
the research community.
x Benchmarking positioning algorithms based on the
open-sourcing data.
Specific projects to be undertaken include:
x Proposing a special session on “Positioning and Navigation in Asian Urban Canyons” in ION Pacific PNT 2021.
These chairs of the session will disseminate the dataset
and encourage the researcher to make use of this opensourcing data to present in the session.
x Disseminating the open-source dataset in the major academic conferences that related to positioning and navigation.
x Identifying the experts in the field to design the assessment criteria for different positioning algorithms. Positioning methods such as GNSS SPP, PPP, RTK and 3D
mapping aided (3DMA) GNSS will be considered in thefirst stage. Then, GNSS/INS integration and LiDAR,
visual odometry will be considered in the second stage.
Finally, the multi-sensor integration using all the sensors
will be considered.
x Building a website to let the researchers upload their paper and result that evaluated based on the open-source
data in terms of the proposed criteria.

142

The Geodesist’s Handbook 2020

x Reporting the performance of the state-of-the-art positioning and integration algorithms in the urban canyons
every 2 years.
x Identifying the challenges of using different sensors inurban canyons.

SC4.2: Multi-frequency Multi-constellation
GNSS

Members

Terms of Reference

Junichi Meguro (Japan)
Taro Suzuki (Japan)
Wu Chen (Hong Kong)
Zhizhao Liu (Hong Kong)

The year 2020 marks a new era of multi-constellation GNSS
with increased number of available satellites in different orbits, diverse signals/frequencies, and new correction products and services. This ongoing modernization offers exciting prospects for further improvement of high precision
GNSS PNT and open up new areas of research and innovation.
For example, the increased number of satellites and signals-in-space improves the performance of precise positioning applications; the available of addition frequency signals(beyond L1 and L2) enables new concepts for signal quality
assessment and improved carrier phase ambiguity resolution
techniques; multi-GNSS satellite metadata to allow determination of GNSS-based terrestrial reference frame scale, orbit determination; as well as new services such as Precise
Point Positioning (PPP) and emergency warning services.
Recognizing the central role of GNSS in enabling highprecision PNT, SC4.2 will foster research to address interoperability of high precision GNSS, which includes
standards, theory, algorithms development and applicationsof multi-GNSS. In addition, SC4.2 will encourage researchin emerging areas such as carrier phase positioning and ambiguity resolution for mass-market GNSS positioning; aswell as GNSS PNT and LEO constellation.
SC4.2 will coordinate activities to promote and deliver
practical and theoretical solutions for engineering and scientific applications and also will stimulate strong collaboration with the IAG Services (IGS) and relevant scientific andprofessional sister organizations such as FIG, ION andIEEE.

SG 4.1.1: Positioning Using Smartphones
Coordinators: Gunther Retscher (Austria), Ruizhi Chen
(China)Terms of Reference (ToR)/Description
With the increasing ubiquity of smartphones and tablets, users are now routinely carrying a variety of sensors with themwherever they go. These devices are enabling technologies
for ubiquitous computing, facilitating continuous updates ofa user’s context. They have built-in GNSS (Global Navigation Satellite Systems), Wi-Fi (Wireless Fidelity), Bluetooth, cameras, MEMS-based inertial sensors, etc. Sensor
fusion techniques are required to enable robust positioning
and navigation in complex environments needed by consumer users, vehicles, and pedestrians. The SG will be dealing with current developments of such technologies andtechniques.
Objectives
Within the next four years we will focus on:x Specification, characterization, and evaluation ofsmartphone positioning and navigation system requirements
x Emerging technologies and techniques and their usage
x Absolute and relative positioning technologies and techniques
x Usage of signals-of-opportunity from different systems,
such as Wi-Fi, Ultra-wide Band (UWB), BluetoothiBeacons, etc.
x Inertial MEMS-based sensors positioning and their integration
x Vision-based positioning with smartphone cameras
x Development of robust sensor fusion algorithms
Members
Brian Bai (Australia)
Thilantha Dammalage (Sri Lanka)

Chair: Suelynn Choy (Australia)
Vice Chair: Sunil Bisnath (Canada)

Objectives
The objectives of SC4.2 are:x Identify and investigate important scientific and technical issues in multi-frequency multi-constellation
GNSS
x Encourage international collaboration in new areas of research and innovationx Promote interoperability and compatibility of GNSS
x Promote development of GNSS applications in the Asia
Pacific region and contribute to capacity building of
GNSS education and training

Commission 4 – Positioning and Applications

x Encourage partnerships across research, government
and industry on applications of multi-frequency multiconstellation GNSS

WG 4.2.1: Interoperability of GNSS precise
positioning (Joint WG between IAG and IGS)
Chair: Allison Kealy / Suelynn Choy TBA (Australia)
Vice-Chair: Sharyl Byram (USA)Objective
To promote interoperability of GNSS precise positioning tosupport a wide range of science and engineering applications which will benefit society. Activities include:(1) encourage sharing and dissemination of knowledge ofsatellite parameters and receiver properties which are essential for high precision GNSS applications; and(2) investigate new techniques and algorithms to ensure interoperability of correction products for precise point
positioning (PPP).
This WG will work in close scientific collaboration with
IGS, FIG and ICG.

WG 4.2.2: Ambiguity resolution for lowcost GNSS positioning
Chair: Xiaohong Zhang (China)
Vice-Chair: Robert Odolinski (New Zealand)
Description
In the past few decades the American GPS and Russian
GLONASS have been the dominant satellite systems in Geodesy and Geophysics applications. Recent developments in
Global Navigation Satellite Systems (GNSSs) involve theChinese BeiDou Navigation Satellite System (BDS), Japanese Quasi-Zenith Satellite System (QZSS), European Galileo, and modernization of triple-frequency GPS andGLONASS signals.
Through the many more line of sights and frequencies
obtained in a combined multi-GNSS model, one can improve the positioning reliability and accuracy when compared to using any of the satellite systems separately. The
challenges lie however in formulating rigorous models andalgorithms to link these satellite observations to the parameters of interests.
Low-cost multi-GNSS receiver development has taken a
revolutionary role in precise positioning applications in thepast few years. By combining several GNSSs, it has been
demonstrated that a competitive low-cost positioning performance can be obtained to that of using survey-grade

143

GNSS receivers and antennas. Smartphone manufacturers
have started to take advantage of such low-cost GNSS chips,
which has led to precise positioning applications insmartphones as well. The research conducted will focus onalgorithms and methods for integer ambiguity resolution on
low-cost handheld devices, to facilitate optimal modellingof precise positions and atmospheric delays (ionosphere andtroposphere), to investigate the quality control methods for
low-cost GNSS precise positioning, to develop a robust algorithms of integration G㹌SS with MEMS and other lowcost sensors.
Members
Yang Gao (Canada)
Wu Cheng (China)
Amir Khodabandeh (Australia)
Dinesh Manandhar (Japan)
Nacer Naciri (Canada)
Baocheng Zhang (China)

WG 4.2.3: GNSS and LEO constellation
Chair: Xingxing Li (Germany)
Vice-Chair: Safoora Zaminpardaz (Australia)
Description
There has been significant development in building large
LEO constellations of satellites to provide a positioning,navigation and timing service. These LEO constellations
give us a great opportunity to create new LEO-augmented
GNSS technologies and applications, and even to open up
new research areas. However there are many challenges.
This WG is devoted to promote research, develop models
and algorithms, and study theoretical and practical foundations for LEO-augmented GNSS technologies. The main research focus will include, but not limited to, LEO-augmented GNSS precise positioning with rapid convergence,
integrated precise orbit determination, LEO-GNSS meteorology and ionospheric sounding methodology, terrestrialreference frame realization, etc. Many efforts will also bemade to stimulate strong collaborations among researchers
and international organizations.
Members
Bofeng Li (China)
Maorong Ge (Germany)
Oliver Montenbruck (Germany)
Yansong Meng (China)
Xiaohong Zhang (China)

144

The Geodesist’s Handbook 2020

Toshiaki Tsujii (Japan)
Hyung Keun Lee (Korea)
Ben K.H. Soon (Singapore)
Horng-Yue Chen (China)
Michael Moore (Australia)
Dudy Darmawan (Indonesia)
Trong Gia Nguyen (Vietnam)

charge state. From the geodetic point of view the atmosphere is nowadays not only seen as a disturbing quantity
which has to be corrected but also as a target quantity, sincealmost all geodetic measurement techniques, such as GNSS,
satellite altimetry, VLBI, SLR, DORIS and radio occultations, provide valuable information about the state of andthe dynamics within the atmosphere. One up-to-date challenge is to combine all these data efficiently to extract asmuch information as possible. Space weather events, gravity waves, natural hazards, climate change and autonomous
driving are a few modern catchwords in this context.
For many decades the International GNSS Service (IGS)
is delivering high-precision tropospheric and ionospheric,i.e. atmospheric products. The Ionosphere Associated Analysis Centers (IAAC), for instance, provide routinely mapsof the Vertical Total Electron Content (VTEC), i.e. the integral of the electron density along the height to correct measurements for ionospheric influences, usually disseminatedwith latencies of days to weeks and based on post-processed
observations and final orbits to the user. Precise GNSS applications, however, such as autonomous driving or precision farming, require the use of high-precision and high-resolution atmospheric correction models in real-time. Thus,
real-time modelling of the atmosphere is one of the key tasksof the SC 4.3.
Space weather and especially its impacts and risk aregaining more and more importance in politics and sciences,since our modern society is highly depending on spaceborne techniques, e.g., for communication, navigation andpositioning. Coupling processes between different atmospheric layers and interrelations with climate change areother up-to-date topics. Besides sounding the atmosphereand studying space weather effects by modern evaluation
methods, the promising GNSS reflectometry technique(GNSS-R) is another research topic within the SC 4.3.
The SC 4.3 focuses on a coordinated research in understanding processes within and between the different atmospheric layers using space-geodetic measurements and observations from other branches such as astrophysics or heliophysics. Furthermore, it is concentrated on developing new
strategies, e.g., for prediction and detection of small and medium atmospheric structures.

SC 4.3: Atmosphere Remote Sensing

Objectives

Lang Bian (China)
Denise Dettmering (Germany)
Jan Dousa (Czech Republic)
Inigo del Portillo (USA)Xiaodong Ren (China)
Tyler G. R. Reid (USA)
Adrian Jäggi (Switzerland)
Qile Zhao (China)
Jose van den Ijssel (Netherlands)
Da Kuang (USA)
Daniel Koenig (Germany)
Wenhai Jiao (China)
Rothacher Markus (Switzerland)
Baoguo Yu (China)

WG 4.2.4: Multi-GNSS in Asia
Chair: Chalermchon Satirapod (Thailand)
Vice-Chair: Hung-Kyu Lee (Korea)
As the Asia Oceania GNSS downstream market continues
to grow rapidly, the role of the WG is to further promote
GNSS scientific research, development and applications in
the region. It will also focus on education and capacity
building such as training, research, and networking activities to encourage the next generation of GNSS researchers.
The working group will work in close cooperation with
Multi-GNSS Asia (MGA) to promote applications of GNSS
and SBAS such as in surveying, construction, agriculture,transportation and logistics, as well as emergency responseand disaster management.
Members

Chair: Michael Schmidt (Germany)
Vice-Chair: Ehsan Forootan (Wales)
Terms of Reference
The Earth’s atmosphere can be structured into various layers
depending on physical parameters such as temperature orx Studying and solving problems of atmosphere researchfor up-to date applications such as autonomous driving.
x Bridging the gaps between modern geodetic observation
techniques such as radio occultations or GNSS reflectometry, measurements from other scientific branches
such as astrophysics and geophysics with the geodetic
community

Commission 4 – Positioning and Applications

x Exploration of the synergies between geodesy and otherscientific branches such as astrophysics and geophysics
x Investigation of ionosphere phenomena such currents orscintillations
x Support of atmosphere prediction models based on the
combination of data from different observation techniques, e.g. by developing sophisticated estimation proceduresx Improvement of precise positioning and navigation on
the basis of new atmosphere models
x Development of real- and near real-time techniques foratmosphere monitoring
Program of activities
x To promote research collaboration among groups fromgeodesy and other branches worldwide dealing with atmosphere research and applications
x To organize and/or participate in scientific and professional meetings (workshops, conference sessions, etc.)
x To maintain a web page concatenating the Sub-Commission activities and reports
x To encourage special issues, e.g. of Journal of Geodesy,on research, applications, and activities related to the
topics of this Sub-Commission
x Close co-operations with other elements of the IAG
structure, such as IAG Commission 1, the ICCT, the
ICCC and GGOS.

Overview about Joint Study Groups(JSG), Working Groups (WG) and Joint
Working Groups (JWG) of or related to theSC 4.3x JWG 4.3.1 Real-time ionosphere monitoring and modelling (joint with IGS and GGOS)
x WG 4.3.2 Prediction of ionospheric state and dynamics
x WG 4.3.3 Ionosphere scintillations
x JWG 4.3.4 Validation of VTEC models for high-precision and high resolution applications (joint with IGS,GGOS and Comm. 1)
x WG 4.3.5 Sensing small-scale structures in the lower atmosphere with tomographic principles
x WG 4.3.6 Real-time troposphere monitoringx WG 4.3.7 Geodetic GNSS-R
x JSG from other leading commissions joint with Commission 4, SC 4.3:
o JSG 1 (JSG T.27): Coupling processes between
magnetosphere, thermosphere and ionosphere (IAG
ICCT, joint with GGOS Focus Area on Geodetic
Space Weather Research)

145

x JWGs from other leading commissions joint with Commission 4, SC 4.3:
o JWG 1: Electron density modelling (GGOS Focus
Area on Geodetic Space Weather Research)o JWG 2: Improvement of thermosphere models(GGOS Focus Area on Geodetic Space Weather Research, joint with ICCC)o JWG 3: Improved understanding of space weather
events and their monitoring by satellite missions(GGOS Focus Area on Geodetic Space Weather Research);o JWG 1.x.x: Intra- and inter-technique atmosphericties (Comm. 1)
o JWG x: Zenith Total Delays and gradients quality
control for climate (ICCC, joint with Comm. 4)

JWG 4.3.1: Real-time ionosphere monitoring and modelling (Joint with IGS and GGOS)
Chair: Zishen Li (China)
Vice-Chair: Ningbo Wang (China)
Terms of Reference (ToR) / Description
The WG focuses on the methodology development for realtime ionosphere monitoring and modelling with the use ofmultiple space-geodetic observations, in particular the inclusion of ionospheric observables from the new GNSS constellations (e.g. Galileo and BeiDou), altimetry, DORIS andradio occultation (RO) techniques aside from the groundbased GPS/ionosonde measurements. The approaches forthe retrieval of precise ionospheric parameters (e.g. total
electron content), generation of two- and/or three-dimensional ionosphere maps on regional and global scales, independent validation and potential combination of ionosphericinformation from different providers in real-time will be developed and analysed. The dissemination of real-time ionospheric information following RTCM, 5G or other standards
will be discussed in support of both scientific researches andtechnological applications. The connections to IGS, iGMAS, IDS, IRI, NeQuick and other communities will also
be involved for the possible establishment of joint WGs orexperimental campaigns on real-time ionosphere monitoring.
Objectives
Within the next four years we will focus on:
x close connections to different scientific communities(e.g. IGS, iGMAS and IDS) for the coordination of
RT/NRT ground- and space-based measurements in support of real-time ionosphere monitoring.

146

x comparison of different approaches for real-time ionosphere modelling by the combination of multi-constellation observations with distinct characteristics (e.g. biases and time latencies).
x development of methods for the independent validationand potential combination of real-time ionospheric information from different providers.
x discussions on the distribution of real-time ionosphericinformation within scientific and technological communities (e.g. target parameter, data format and time latency).
x generation and dissemination of experimental twoand/or three-dimensional ionospheric information in
support of real-time ionosphere monitoring and associated scientific applications.
x possible joint sub working groups or experimental campaigns on real-time ionosphere monitoring in close scientific collaboration with IGS and IDS WGs, COSPAR
IRI and NeQuick WGs, among others.
Members
Alberto Garcia-Rigo (Spain)
Alexis Blot (France)
Andre Hauschild (Germany)
Andreas Goss (Germany)
Andrzej Krankowski (Poland)
Attila Komjathy (USA)Cheng Wang (China)
Eren Erdogan (Germany)
German Olivares (Australia)
Kenji Nakayama (Japan)
Libo Liu (China)
Manuel Hernández-Pajares (Spain)
Nicolas Bergeot (Belgium)
Ningbo Wang (China)
Qile Zhao (China)
Raul Orús (Netherland)Reza Ghoddousi-Fard (Canada)
Wookyoung Lee (Korea)
Xingliang Huo (China)
Yunbin Yuan (China)
Zhizhao Liu (China)
Zishen Li (China)

The Geodesist’s Handbook 2020

WG 4.3.2: Prediction of ionospheric stateand dynamics
Chair: Mainul Hoque (Germany)
Vice-Chair: Eren Erdogan (Germany)
Terms of Reference (ToR) / Description
Ionospheric disturbances can affect technologies in spaceand on Earth disrupting satellite and airline operations, communications networks, navigation systems. As the world becomes ever more dependent on these technologies, ionospheric disturbances as part of space weather pose an increasing risk to the economic vitality and national security.
Having the knowledge of ionospheric state in advance during space weather events is becoming more and more important.
With the modernization of Global Navigation Satellite
Systems (GNSS), the use of multi-constellation, multi-frequency observations including new signals enables continuous monitoring of the Earth’s ionosphere using worldwide
distributed sensor stations. Other ground based techniquessuch as vertical sounding (VS), Incoherent Scatter Radar(ISR), Very Low Frequency (VLF) or Radio Beacon (RB)measurements provide complementary ionospheric observations.
The radio occultation (RO) technique provides one of
the most effective space-based methods for exploring planetary atmospheres. The availability of numerous medium
Earth orbit satellites deployed by GPS, GLONASS, Galileo,
BeiDou navigation systems allows continuous monitoringof the Earth’s ionosphere and neutral atmosphere by tracking GNSS signals from low Earth orbiting (LEO) satellites.
Other space-based techniques include ionosphere estimation using dual-frequency altimeter data (e.g. TOPEX-Poseidon, Jason 2 & 3 missions), using radio beacon measurements from DORIS (geodetic orbit determination and positioning system) receivers onboard LEO satellites and GNSS
reflectometry.
The availability of ionospheric data from different sensors has increased in many folds during the last decades. In
one hand the ionosphere has been sounded by a large number of sensors providing a vast database. On the other hand,the accuracy of the measuring techniques has been improved significantly.
As an example, the IGS is routinely generating ionospheric total electron content (TEC) maps from GNSS data
since 1998. The inter-dependency of different space weather
parameters (e.g., TEC, peak electron density and height, solar flux, geomagnetic indices, interplanetary magnetic fieldcomponents etc.) paves the way for determining ionosphericprediction algorithm. With the availability of fast computing

Commission 4 – Positioning and Applications

machines as well as the advancement of the machine learning techniques and Big Data algorithms, the prediction ofionospheric state and dynamics is possible in near real time.
Objectives
Within the next four years we will focus on:
x study the inter-dependency of different space weather
parameters (e.g., TEC, solar flux, geomagnetic indices,interplanetary magnetic field components etc.) during
quiet and perturbed conditions, trend analysis and algorithm development for predicting space weather parameters
x develop global as well as regional prediction approaches
considering that the high latitude phenomena/processes
are different from the low latitude phenomena/processes
and hemispherical asymmetry (e.g., South Atlantic
Anomaly)x modelling the phenomena which are closely connected
to nighttime filling of the ionosphere such as theNighttime Winter Anomaly (NWA), Weddell Sea
Anomaly (WSA) and the Okhotsk Sea Anomaly (OSA).
It is assumed that the midsummer nighttime anomaly(MSNA) and related special anomalies such as the WSA
and the OSA are closely related to the NWA via enhanced wind-induced uplifting of the ionosphere.
Members
Mainul Hoque (Germany)
Eren Erdogan (Germany)
Mahdi Alizadeh (Iran)
Enric Monte (Spain)
Fabricio Prol (Germany)
Liangliang Yuan (China)
Ke Su (China)
Adria Rovira Garcia (Spain)
Murat Durmaz (Turkey)

WG 4.3.3 Ionosphere scintillations
Chair: Jens Berdermann (Germany)
Vice-Chair: Lung-Chih Tsai (China)
Terms of Reference (ToR) / Description
Trans-ionospheric radio signals of global navigation satellite systems (GNSS) like GPS, GLONASS, GALILEO and
BeiDou may suffer from rapid and intensive fluctuations of
their amplitude and phase caused by small-scale irregularities of the ionospheric plasma. Such disturbances occur frequently in the equatorial region during the evening hours
due to plasma flow inversion or during geomagnetic storms

147in the polar region. This phenomenon is called radio scintillation and can strongly disturb or even disrupt the signaltransmission.
The main effects of scintillation on trans-ionospheric radio system are signal loss and phase cycle slips, causing difficulties in the signal lock of receivers. All GNSS signals
are affected, but the influence of the small scale irregularities is expected to differ since the signals are transmitted bydifferent carrier frequencies and are constructed in different
ways. Furthermore, the sensitivity of receivers in respect toscintillation events differ between various GNSS receiver
types and an advanced analysis using “bitgrabber” systems
are needed to rate their vulnerability.
In spite of the importance of irregular density variations
for the science of the ionosphere and for space weather operations, no fully sufficient global model for such disturbances is available.
Objectives
Within the next four years we will focus on:
x understanding the climatology of ionospheric scintillations, namely, its variation with latitude, season, local
time, magnetic activity and solar cycle,
x investigation of the GNSS signal frequency and receiver
impact on signal loss and phase cycle slips during scintillation events
x global modelling and forecasting of scintillations taking
into account temporal and regional (Polar and Equatorial
region) differences.
Members
Charles L. Rino (USA)Michael Schmidt (Germany)
Rui Fernandes (Portugal)
Chi-Kuang Chao (China)
Kai-Chien Cheng (China)
Alexei V. Dmitriev (China)
Yoshihiro Kakinami (Japan)
Suvorova Alla (China)
Sudarsanam Tulasiram (India)
Kuo-Hsin Tseng (China)
Ernest Macalalad (Philippines)
Chinmaya Kumar Nayak (India)

148

JWG 4.3.4: Validation of VTEC models forhigh-precision and high resolution applications (Joint with IGS)
Chair: Anna Krypiak-Gregorczyk (Poland)
Vice-Chair: Attila Komjathy (USA)Terms of Reference (ToR) / Description
Global and regional VTEC models are routinely used inSpace Weather studies, but also in high-precision applications like e.g. GNSS positioning. There are currently many
analysis centers and research groups providing operational
and test VTEC maps. Indeed, the global ionospheric maps
(GIMs) are being systematically produced and openly provided by the IGS Ionosphere Working Group (IIWG) since
1 June 1998. IGS GIMs are developed as an official productof IIWG by performing a weighted mean of the various
Analysis Centers (AC) VTEC maps. There are also important empirical models like the International Reference
Ionosphere (IRI) or NeQuick that are based on statisticalanalysis of the results of measurements.
However, IGS ACs and other groups use different mathematical models and estimation techniques resulting different resolutions, accuracies and time delays of their products.
Therefore, there is a need to compare and validate existing
VTEC models in order to better understand their performance and quality, and hence to better understand the ionosphere and foster VTEC models usage in geosciences community.

The Geodesist’s Handbook 2020

Mainul Hoque (Germany)
Reza Ghoddousi-Fard (Canada)
Shuanggen Jin (China)
Wojciech Jarmołowski (Poland)
Yunbin Yuan (China)
Manuel Hernández-Pajares (Spain)
Haixia Lyu (Spain)
Qi Liu (Spain)
Raul Orus-Perez (The Netherlands)
Tam Dao (Australia)
Beata Milanowska (Poland)- Corresponding Member

WG 4.3.5: Real-time Troposphere Monitoring
Chair: Cuixian Lu (China)
Vice-Chair: Galina Dick (Germany)
Terms of Reference (ToR) / Description

Within the next four years we will focus on:
x close connections to different scientific communities –primarily to IGS and GGOS
x comparison of GNSS-derived VTEC maps and empirical models
x VTEC validation with external data, such as altimetry,
DORIS, Swarm, radio occultation (RO) and groundbased ionosonde measurements
x VTEC validation is precise GNSS positioning
x development of new validation techniques

The main objective of this WG is to develop, optimize andassess new real-time or ultra-fast GNSS tropospheric products, and exploit the full potential of multi-GNSS observations in weather forecasting. Tropospheric zenith total delays, tropospheric linear horizontal gradients, slant delays,
integrated water vapour (IWV) maps or other derived products in sub-hourly fashion are foreseen for future exploitation in numerical and non-numerical weather nowcasting or
severe weather event monitoring.
The use of Precise Point Positioning (PPP) processing
strategy will play a key role in developing new products because it is an efficient and autonomous method, it is sensitive to absolute tropospheric path delays, it can effectively
support real-time or ultra-fast production, it may optimally
exploit data from all GNSS multi-constellations, it can easily produce a full variety of parameters such as zenith total
delays, horizontal gradients or slant path delays and it may
also support as reasonable as high temporal resolution of all
the parameters. Last, but not least, the PPP is supported withthe global orbit and clock products provided by the real-time
service of the International GNSS Service (IGS).

Members

Objectives

Anna Krypiak-Gregorczyk (Poland)
Attila Komjathy (Usa)Andreas Goss (Germany)
Bruno Nava (Italy)
Dieter Bilitza (Usa)Eren Erdogan (Germany)
Gu Shengfeng (China)
Heather Nicholson (Canada)

Within the next four years we will focus on:
x development of real-time multi-GNSS processing algorithms and strategies for high-resolution, rapid-update
NWP and nowcasting applications.
x development of new/enhanced GNSS tropospheric products and exploit the full potential of multi-GNSS (GPS,GLONASS, Galileo and BeiDou) observations for use
in the forecasting of severe weather.

Objectives

Commission 4 – Positioning and Applications

x development and validate methods for initialization of
NWP models using new/enhanced operational multiGNSS tropospheric products and for use in nowcasting.
x assessing the benefit of new/enhanced GNSS products(real-time, gradients, slants…) for numerical and nonnumerical nowcasting.
x stimulate the development of application software forsupporting routine production.
x demonstrate real-time/ultra-fast production, assess applied methods, software and precise orbit and clock
products.
x setup a link to the potential users, review product format
and requirements.
Members
Kefei Zhang (Australia)
Xiaoming Wang (Australia)
Fabian Hinterberger (Austria)
Eric Pottiaux (Belgium)
Thaleia Nikolaidou (Canada)
Xingxing Li (China)
Junping Chen (China)
Pavel Václavovic (Czech Republic)
Henrik Vedel (Danish)
Rosa Pacione (Italy)
Yoshinory Shoji (Japan)
Felix Norman Teferle (Luxembourg)
Siebren de Haan (The Netherlands)
Jonathan Jones (United Kingdom)John Braun (USA)Galina Dick (Germany)
Tomasz Hadaś (Poland)

WG 4.3.6: Sensing small-scale structuresin the lower atmosphere with tomographic
principles
Chair: Gregor Moeller (Switzerland)
Vice-Chair: Chi Ao (USA)Terms of Reference (ToR)/Description
The working group on troposphere tomography intends tobring together researchers and professionals working on tomography-based concepts for sensing the neutral atmosphere with space-geodetic and complementary observation
techniques, sensitive to the water vapour distribution in thelower atmosphere.
While geodetic GNSS networks are nowadays the backbone for troposphere tomography studies, further local densifications, e.g. at airports or cities are necessary to achieve

149

very fine spatial and temporal resolution. Besides, InSAR
interferograms, GNSS radio occultation or microwave radiometer profiles are a valuable asset, which can provide thenecessary complementary information for stabilizing the tomography system. Furthermore, in the next decade CubeSat
missions are expected, which are designed for tomography
processing. These constellations can operate independently
from ground-based networks and due to a more favourable
observation geometry, will allow for sensing globally thewater vapour distribution in the neutral atmosphere with increased spatial resolution.
Objectives
Within the next study period (2019-2023), the working
group on troposphere tomography intends to address current
challenges in tropospheric tomography with focus on spacebased measurements using tomography principles. Hereby,
the main objectives are:x Evaluating approaches for the densification of existingdual-frequency geodetic networks;
x Working towards a dynamical tomography model adaptable to varying input data (continuous-time image
reconstruction, trade-off between model resolution andvariance size);x Setting up a benchmark campaign for the combinationof ground-based GNSS with radio occultation and otherobservation techniques like InSAR;
x Assessing existing ray-tracing approaches for the reconstruction of space-based observations;x Working on standards for data exchange (SINEX TRO
2.0 or other formats).
Members
Natalia Hanna (Austria)
Zohreh Adavi (Austria)
Eric Pottiaux (Belgium)
Hugues Brenot (Belgium)
Chaiyaporn Kitpracha (Germany)
Witold Rohm (Poland)
Andre Garcia Sa (Portugal)
Endrit Shehaj (Switzerland)
Karina Wilgan (Switzerland)
Kuo-Nung (Eric) Wang (USA)
George Hajj (USA)150

WG 4.3.7: Geodetic GNSS-R
Chair: Sajad Tabibi (Luxembourg)
Vice-Chair: Felipe Nievinski (Brazi)
Terms of Reference (ToR) / Description
The radio waves broadcast by Global Navigation Satellite
Systems (GNSS) satellites have been used for unanticipatedpurposes, such as remote sensing of the environment. The
most prominent example for a novel application from recent
years is the usage of reflected GNSS signals as a new tool
for remote sensing. GNSS Reflectometry (GNSS-R) has
been used to exploit signals of opportunity at L-band forground-based sea and lake level studies at several locationsin the last few years. Although geodetic-quality antennas aredesigned to boost the direct transmission from the satellite
and to suppress indirect surface reflections, the delay of reflections with respect to the line-of-sight propagation can beused to estimate the water-surface level in a stable terrestrialreference frame. GNSS-R has started to make an impact inthe disciplines of geodesy and remote sensing, with diverse
applications such as sea-level, snow depth, and soil moisturemonitoring, observations are highly relevant to the goals of
the Global Geodetic Observing System (GGOS). Thus, theoverall aim of this working group is to further demonstrateand consolidate the value of GNSS-R for the geodesy,
oceanography, cryosphere, and hydrology communities.
Objectives
Within the next four years we will focus on:
x identification of GNSS-R products which have a strong
relation to IAG services and goals.
x maintain interactions with neighboring societies (such as
the IEEE Geoscience and Remote Sensing Society,
GRSS) and cooperate with technological, engineering,and operational entities related to GNSS (e.g., the International GNSS Service, IGS), identifying common goals
and detecting potential synergies.
x organization of working meetings with GNSS-R experts,
while also inviting stakeholders from the geodetic community to participate in such events.
x maintain the GNSS-R site guidelines for installing
multi-purpose GNSS stations
x maintain the inventory of GNSS stations used for reflectometry purposes, currently available for sea-level applications, possibly extending it to other applications as
well.
x organization of a near-operational demonstration projecton GNSS-R for coastal sea level monitoring.
x organization of algorithm inter-comparison exercises.
These can be based on either synthetic data or field

The Geodesist’s Handbook 2020

measured GNSS data. Validation will be based, respectively, on the simulation configuration or independent insitu data (e.g., tide gauges for sea level applications).
The treatment of external corrections, such as atmospheric effects, should be considered. Challenging conditions should also be addressed, such as large tidal range(~ 4-5 m) and the impact of multi-GNSS revisit time on
tidal constituent.
Members
Dave Purnell (Canada)
Chung-Yen Kuo (China)
Clara Chew (USA)
Estel Cardellach (Spain)
Jens Wickert (Germany)
Jihye Park (USA)
Joerg Reinking (Germany)
Karen Boniface (Italy)
Kegen Yu (China)
Kristine Larson (USA)Manuel Martín-Neira (ESA)
Maximilian Semmling (Germany)
Nikolaos Antonoglou (Germany)
Ole Roggenbuck (Germany)
Rüdiger Haas (Sweden)
Simon Williams (UK)Thomas Hobiger (Germany)
Wei Liu (China)

Overview about Joint Study Groups(JSG), Working Groups (WG) and Joint
Working Groups (JWG) led by other IAG
components (Commissions, ICCT, ICCC,
GGOS)
JWG 1.1.1: Intra- and Inter-Technique Atmospheric Ties
(Led by Commission 1 Reference Frames, joint with Commission 4, Sub-commission 4.3)
Chair: Kyriakos Balidakis (Germany)
Vice-Chair: Daniela Thaller (Germany)
Terms of Reference (ToR) / Description
The differences between atmospheric parameters (mainly
zenith delays and gradients) at co-located stations that observe nearly simultaneously, and stem from external systems (e.g., meteorological sensors or weather models) areCommission 4 – Positioning and Applications

understood as atmospheric ties. Atmospheric ties mainly exist because of differences in (i) the observing frequency, (ii)the relative position, and (iii) the observing system set-up.
The acquisition of accurate atmospheric delay corrections is of paramount importance for mm-level positioning
employing space geodetic techniques. Atmospheric delay
corrections may stem from dedicated instruments such as
water vapor radiometers, meteorological sensors, numerical
weather models, or from the geodetic data itself. While thelatter is fairly common for modern GNSS and VLBI, observation geometry and accuracy limitations inherent to othersystems such as SLR and DORIS impede the accurate atmospheric parameter estimation, thus hindering among else
positioning.
To this end, it might be useful to compare and combine
atmospheric parameters at co-located sites, in a manner similar to the combination of station and satellite coordinates,
as well as Earth rotation parameters (via local, space, andglobal ties, respectively). The multi-technique combination
is indispensable to the distinction between real signals andundesired technique-specific artefacts.
Nowadays, the multi- technique combination is facilitated by the increasing investments in state-of-the-art geodetic infrastructure at co-located sites. However, a host of
systematic and random errors render the combination via atmospheric ties a difficult task. Moreover, since atmosphericdelays are dependent upon essential climate variables (pressure, temperature, and water vapor), differences in longterm atmospheric delay time derivatives at co-located stations might offer an insight into local climate change.
Objectives
The purpose of this working group is to answer the questions:x How can one relate atmospheric parameter estimates andthe time derivatives thereof that refer to different place,time, and observing system? What are the limits in distance, time lag, and observing system?
x What is the optimal way to combine atmospheric parameters?
x Which are the risks from including atmospheric ties in a
multi-technique terrestrial reference frame combination?
Specific program activities
Comparison of atmospheric delay estimates from singletechnique geodetic analysis (GNSS, SLR, VLBI, and DORIS) Comparison of atmospheric delays from state-of-theart meso-beta scale weather models (e.g., ERA5 and
MERRA2), and high-resolution WRF runs Assessment of151

spatial and temporal correlation between atmospheric parameters Assessment of multi-technique combination employing atmospheric ties on the single site and global TRF
level
Members
Balidakis, Kyriakos (Germany)
Boisits, Janina (Austria)Drożdżewski, Mateusz (Poland)
Heinkelmann Robert (Germany)
Kitpracha, Chaiyaporn (Germany)
Lemoine Frank (USA)
Nilsson, Tobias (Sweden)Sośnica Krzysztof (Poland)
Thaller Daniela (Germany)
Wang Xiao-Ya (China)
Zus Florian (Germany)JWG C.2: Quality control methods for climate applications of geodetic tropospheric parameters(Led by ICCC, joint with Commission 4, Sub-Commission
4.3)
Chair: Rosa Pacione (Italy)
Vice-Chair: Marcelo Santos (Canada)
Introduction
Zenith Total Delay (ZTD) estimates are determined on aregular basis by several processing centers. For example, the
IGS Analysis Centers have all their own independent ZTD
solutions but, unlike other estimated parameters (e.g., orbits
and satellite clocks) they are not combined. The official IGS
ZTD product is the result of an independent and dedicatedsolution based on a precise point positioning solution. On
the other hand, EUREF performs combination of ZTD estimates on a regular basis as well as the IVS, which combines
ZTD estimates coming from VLBI sessions. Nonetheless,not all IGS and IVS analysis centers make available their
ZTD estimates.
GNSS is reaching the “maturity age” of 30 years whenclimate normals of ZTD and gradients can be derived. But
what would be the best series to serve the climate community? What series would offer the most realistic trends? As
the IGS moves towards its third reprocessing campaign(REPRO3) where all ACs are to be make available their own
ZTD and gradient estimates, as the IVS is moving towards
its ACs also providing ZTD and gradient estimates and as
the PPP-derived IGS product continues to be produced,
there is a huge opportunity to perform quality control, using

152

the tools of combination of parameters, to assess what
would be the ZTD and gradient product best suited to bemade available to climate studies.
Objectives
Potential scientific questions include:
x Are there advantages of combining ZTD estimates overnot combining them? Is there any ‘loss of information’in performing combinations?
x Would there be difference in trends derived from them?
If so, how much implication for feeding information toclimate?
x Can we trust in a combined ZTD as we trust any combined products (e.g., orbits, clock, site coordinates)?
x What the best combination strategy can be done (notnecessarily to combine exactly the same way as otherproducts)?
x Under what criteria can we use spectral analysis todemonstrate that a ‘good’ combined product have thesame properties of the contributing solutions?
x What metrics should be used to ascertain that the optimal
set of ZTD estimates, gradients and their trends, are provided to the climate community?
Activities
x Collaborate with IGS and IVS in the forthcoming reprocessing campaign.
x Participate actively in IAG, AGU and EGU conferences
and organize sessions
x Organize working group meetings, splinter group meetings at the said symposia
Members
Fadwa Alshawaf (Germany)
Kyriakos Balidakis (Germany)
Sharyl Byram (USA)Galina Dick (Germany)
Gunnar Elgered (Sweden)
Olalekan Isioye (South Africa)
Jonathan Jones (UK)Michal Kačmařík (Czech Republic)
Anna Klos (Poland)
Haroldo Marques (Brazil)
Thalia Nikolaidou (Canada)Tong Ning (Sweden)
Mayra Oyola (USA)
Eric Pottiaux (Belgium)
Paul Rebischung (France)
Roeland Van Malderen (Belgium)
Yibin Yao (China)

The Geodesist’s Handbook 2020

JSG 1 (JSG T.27): Coupling processes between magnetosphere, thermosphere andionosphere(Led by ICCT; joint with GGOS, Focus Area on Geodetic
Space Weather Research and Commission 4, Sub-Commission 4.3)
Chair: Andres Calabia Aibar (China)
Introduction
Consequences of upper-atmosphere conditions on humanactivity underscore the necessity to better understand andpredict effects of the magnetosphere-ionosphere-thermosphere (MIT) processes and of their coupling. This will prevent from their potential detrimental effects on orbiting, aerial and ground-based technologies. For instance, major concerns include the perturbation of electromagnetic signals
passing through the ionosphere for an accurate and secureuse of global navigation satellite systems (GNSS), and thelack of accurate aerodynamic-drag models required for accurate tracking, decay and re-entry calculations of low Earthorbiters (LEO), including manned and unmanned artificial
satellites. In addition, ground power grids and electronics ofsatellites could be influenced, e.g., by the magnetic field
generated by sudden changes in the current system due tosolar storms.
Monitoring and predicting Earth’s upper atmosphereprocesses driven by solar activity are highly relevant to science, industry and defense. These communities emphasize
the need to increment the research efforts for better understanding of the MIT responses to highly variable solar conditions, as well as detrimental space weather effects on ourlife and society. On one hand, electron-density variations
produce perturbations in speed and direction of various electromagnetic signals propagated through the ionosphere, andreflect as a time-delay in the arrival of the modulated components from which pseudo-range measurements of GNSS
are made, and an advance in the phase of signal’s carrier
waves which affects also carrier-phase measurements. On
the other hand, an aerodynamic drag associated with neutral-density fluctuations resulting from upper atmospheric
expansion/contraction in response to variable solar and geomagnetic activity increases drag and decelerates LEOs,
dwindling the lifespan of space-assets, and making theirtracking difficult.
Through interrelations, dependencies and coupling patterns between ionosphere, thermosphere and magnetospherevariability, this JSG aims to improve the understanding of
coupled processes in the MIT system, and considerations of
the solar contribution. In addition, tides from the lower atmosphere forcing can feed into the electrodynamics; they
have a composition effect leading to changes in the MIT

Commission 4 – Positioning and Applications

153

JWG 1: Electron density modellingsystem. In this scheme, our tasks are addressed to exploit theknowledge of the tight MIT coupling by investigating multiple types of magnetosphere, ionosphere and thermosphereobservations. The final outcome will help to enhance thepredictive capability of empirical and physics-based models
through interrelations, dependencies and coupled patterns ofvariability between essential geodetic variables.

Chair: Fabricio dos Santos Prol (Germany)
Vice-Chair: Alberto Garcia-Rigo (Spain)

Objectives

Terms of Reference (ToR)/Description

x Characterize and parameterize the global modes of MIT
variations associated with diurnal, seasonal, and space
weather drivers, as well as the lower atmosphere forcing.
x Determine and parameterize the mechanisms responsible for discrepancies between observables and the present models.
x Detect and investigate coupled processes in the MIT system for the deciphering of physical laws and principles
such as continuity, energy and momentum equations andsolving partial differential equations.

The main goal of this group is to disseminate and evaluate
established methods of 3D electron density estimation interms of electron density, peak height, Total Electron Content (TEC), or other derived products that can be effectively
used for GNSS positioning or for analyzing perturbed conditions due to representative space weather events. It isplanned to generate products, showing the general error
given by such 3D electron density estimations and, also, distribute information regarding to space weather conditions.
To achieve this main goal, the following objectives are defined.

Program of activities
x Presenting research findings at major international geodetic or geophysical conferences, meet-ings, and workshops.
x Interacting with related IAG Commissions and GGOS.
x Monitoring research activities of the JSG members andof other scientists, whose research interests are related tothe scopes of SGx Organizing a session at the Hotine-Marussi Symposium2022.
x Organizing working meetings at international symposia
and presentation of research results at appropriate sessions.
Members
Andres Calabia Aibar (Chair, China)
Piyush M. Metha (USA)Liang Yuan (China)
Astrid Maute (USA)Gang Lu (USA)Toyese Tunde Ayorinde (Brazil)
Charles Owolabi (Nigeria)
Oluwaseyi Emmanuel Jimoh (Nigeria)
Emmanuel Abiodun Ariyibi (Nigeria)
Olawale S. Bolaji (Nigeria)(Led by GGOS; joint with Commission 4, Sub-Commission
4.3)

Objectives
x Develop a database, where the methods from the groupmembers will be able to be evaluated in terms of GNSS,
radio-occultation, DORIS, in-situ data, altimeters,
among other electron density and TEC measurements.
x Evaluate established methods for 3D electron density estimation in order to define their accuracy related to specific parameters of great importance for Space Weather
and Geodesy.
x Generate products indicating the space weather conditions and expected errors of the methods.
x Carry out surveys in order to detect if the products arelinked to the user’s specific needs. Based on an analysisof the user needs, re-adaptations will be identified in order to improve the products in an iterative process. It isplanned to define which parameters are of interest for theusers and to detect additional information that may berequired.
Members
Andreas Goss (Germany)
Bruno Nava (Italy)
David Themens (Canada)
Feza Arikan (Turkey)
Gopi Seemala (India)
Haixia Lyu (Spain)
Johannes Norberg (Finland)
Katy Alazo (Italy)
Mainul Hoque (Germany)
Marcio Muella (Brazil)

154

Michael Schmidt (Germany)
Mir-Reza Razin (Iran)
Orhan Arikan (Turkey)
Shuanggen Jin (China)
Secil Karatay (Turkey)
Solen Yildiz (Turkey)
Tatjana Gerzen (Germany)
Yenca Migoya-Orue (Italy)

JWG 2: Improvement of thermospheremodels(Led by GGOS; joint with IAG Commission 4, Sub-Commission 4.3 and ICCC)
Chair: Christian Siemes (The Netherlands)
Vice-Chair: Kristin Vielberg (Germany)
Terms of Reference (ToR) / Description
Mass density, temperature, composition and winds are important state parameters of the thermosphere that affect dragand lift forces on satellites. Since these significantly influence the orbits of space objects flying at altitudes below 700
km, accurate knowledge of the state of the thermosphere isimportant for applications such as orbit prediction, collision
avoidance, evolution of space debris, and mission lifetime
predictions. Drag and lift forces can be inferred from space
geodetic observations of accelerometers, which complement other positioning techniques such as GNSS, satellite
laser ranging or radar tracking of space objects. The objective of the working group is to improve thermosphere models through providing relevant space geodetic observations
and increasing consistency between datasets by advancing
processing methods. Broadening the observational data basis with geodetic space observations, which are available
now for a time span of 20 years, will also benefit climatological studies of the thermosphere.
Objectives
x Review space geodetic observations and state-of-the-art
processing methods
x Advance processing methods to increase consistency between observational datasets
x Improve thermosphere models through providing accurate and consistent space geodetic observations
x Study the impact of improved observational datasets andadvanced processing methods on orbit determinationand prediction
x Use of improved thermosphere models and observational data sets to forward the investigation of thermosphere variations in the context of climate change

The Geodesist’s Handbook 2020

Members
Michael Schmidt (Germany)
Armin Corbin (Germany)
Ehsan Forootan (UK)Mona Kosary (Iran)
Lea Zeitler (Germany)
Christopher Mccullough (USA)
Sandro Kraus (Austria)
Saniya Behzadpour (Austria)
Aleš Bezděk (Czech Republic)

JWG 3: Improved understanding of space
weather events and their monitoring bysatellite missions(Joint with IAG Commission 4, Sub-Commission 4.3)
Chair: Alberto Garcia-Rigo (Spain)
Vice-Chair: Benedikt Soja (Switzerland)
Terms of Reference (ToR) / Description
Space weather events cause ionospheric disturbances thatcan be detected and monitored thanks to estimates of thevertical total electron content (VTEC) and the electron density (Ne) of the ionosphere. Various space geodetic observation techniques, in particular GNSS, satellite altimetry,
DORIS, radio occultations (RO) and VLBI are capable ofdetermining such ionospheric key parameters. For the monitoring of space weather events, low latency data availability
is of great importance, ideally real time, to enable triggering
alerts. At present, however, only GNSS is suited for thistask. The use of the other techniques is still limited due latencies of hours (altimetry) or even days (RO, DORIS,
VLBI).
The JWG 3 will investigate different approaches to monitor space weather events using the data from different space
geodetic techniques and, in particular, combinations thereof.
Simulations will be beneficial to identify the contribution ofdifferent techniques and prepare for the analysis of real data.
Different strategies for the combination of data will be investigated.
Furthermore, the geodetic measurements of the ionospheric parameters will be complemented by direct observations of the solar corona, where solar storms originate, as
well as of the interplanetary medium. Spacecrafts like
SOHO or ACE have monitored the solar corona and the solar wind for decades and will be beneficial, together withdata from other spacecrafts like SDO, in assessing the performance of geodetic observations of space weather events.
Data from Parker Solar Probe, which will allow even greater

Commission 4 – Positioning and Applications

insights, has just recently been made publicly available. Geodetic VLBI is also capable of measuring the electron density of the solar corona when observing targets angularly
close to the Sun and will be useful for comparisons.
Other solar-related satellite missions such as Stereo,
DSCOVR, GOES, etc. provide valuable information such as
solar radiation, particle precipitation and magnetic field variations. Other indications for solar activity - such as theF10.7 index on solar radio flux, SOLERA as EUV proxy orrate of Global Electron Content (dGEC), will also be investigated. The combination and joint evaluation of these data
sets with the measurements of space geodetic observation
techniques is still a great challenge. Through these investigations, we will gain a better understanding of space
weather events and their effect on Earth’s atmosphere andnear-Earth environment.
Objectives
x Selection of a set of historical representative space
weather events to be analysed.
x Determination of key parameters and products affectedby the selected space weather events.
x Identification of the main parameters to improve realtime determination and the prediction of ionospheric/plasmaspheric VTEC and Ne estimates as well
as ionospheric perturbations in case of extreme solar
weather conditions.
x Improving the (near) real time determination of the electron density within the ionosphere and plasmasphere todetect space weather events.
x Combination of measurements and estimates derived
from space geodetic observation techniques by conducting extensive simulations, combining different data sets
and testing different algorithms.
x Comparison and validation using external data, in particular data from spacecraft dedicated to monitoring thesolar corona.
x Interpretation of the results. Correlate acquired
data/products with space weather events’ impact on geodetic applications (e.g. GNSS positioning, EGNOS
performance degradation).
Members
Anna Belehaki (Greece)
Anthony J Mannucci (USA)Jens Berdermann (Germany)
Xiaoqing Pi (USA)
Enric Monte (Barcelona)
Denise Dettmering (Germany)
Consuelo Cid (Spain)
Rami Qahwaji (UK)155

Jinsil Lee (Republic of Korea)
Benedikt Soja (Switzerland)
Alberto Garcia-Rigo (Barcelona)

SC 4.4: GNSS Integrity and Quality Control
Chair: Pawel Wielgosz (Poland)
Vice-Chair: Jianghui Geng (China)
Secretary: Grzegorz Krzan (Poland)
Terms of Reference
GNSS constellation is rapidly developing by growing thenumber of satellites and available signals and frequencies.
In addition to two already operational GPS and GLONASS
systems, the new Galileo and BDS systems achieved initial
operational capabilities. Both GPS and GLONASS are currently undergoing a significant modernization, which adds
more capacity, more signals, better accuracy and interoperability, etc. In addition, a rapid development in the massmarket GNSS chipsets has to be also acknowledged.
These new developments in GNSS provide opportunities to create new high-precision GNSS technologies andapplications and also to open new research areas. This, however, results in new challenges in multi-GNSS data processing, which primarily concern the positioning integrity
and reliability. Recognizing the central role of GNSS inproviding high accuracy positioning information, SC4.4
will foster research activities that address integrity, quality
control and relevant applications of GNSS in case of multiconstellation and multi-frequency environment. SC4.4 will
coordinate activities to deliver practical and theoretical solutions for engineering and scientific applications. Among
those applications there are structural and ground deformation monitoring, precise navigation, GNSS remote sensing, geodynamics, etc.
SC4.4 will also encourage strong collaboration with the
IAG Services (primarily IGS) as well as with relevant entities within scientific and professional sister organizations(FIG, IEEE and ION).
Objectives
The major objective of SC4.4 is to promote collective research on GNSS Integrity and Quality Control methods andtheir novel applications to facilitate timely dissemination ofscientific findings, to stimulate strong collaborations among
researchers and international organizations and the industry.

156

Program of Activities
x to identify and investigate important scientific and technical issues in GNSS integrity and quality control methods and their applications,x to stimulate strong collaborations among researchers,
x to organize international conferences and workshops,
x to promote the use reliable GNSS techniques and products in interdisciplinary scientific research and engineering applications.

Working and Study Groups of Sub-Commission 4.4
WG 4.4.1: Quality Control and Integrity
Monitoring of Precise Positioning
Chair: Ahmed El-Mowafy (Australia)
Vice-Chair: Christian Tiberius (The Netherlands)
Description
Global Navigation Satellite Systems (GNSS) are the prime
source of precise position information for a variety of applications including intelligent transport systems, autonomous
driving, precision agriculture, and deformation monitoring.
For such applications, even small errors can incur serious
consequences like loss of human lives, liability, and damage
to infrastructure, as the provided position information needs
to be of high level of reliability.
Any positioning platform, either based on standalone- oraugmented-GNSS, is subject to a series of vulnerabilities,
e.g. signal faults, interference and carrier phase cycle-slips,
which can dramatically deteriorate the reliability of the position solutions. As such, it is crucial to have proper ‘Quality
Control’ mechanisms in place for timely detection of hazardous faults. In addition, monitoring the integrity of thesystem is an essential part of this quality control procedure,
to ensure that the resulting positioning errors are boundedby protection levels that are determined according to the allowable risk probability.
The constituent components of a quality control and integrity monitoring procedure will vary depending on the positioning sensors in use, the positioning method, and the performance requirements. This will in turn raise the need fora thorough research into factors contributing to the qualityof a positioning platform as well as their interactions, so as
to enable the development of optimal application-dependent
quality control and integrity monitoring procedures.
Objectives
x The main objectives of this working group are:

The Geodesist’s Handbook 2020

x to derive optimal statistical testing regimes that are capable of detection and exclusion of multiple alternative
fault hypotheses using the underlying positioning models,x to characterize the link between the statistical testing andparameter estimation exercised in data processing so as
to develop rigorous quality control frameworks for evaluating the reliability of the position solutions,x to develop integrity monitoring algorithms for precise
positioning methods such as RTK and PPP.
x to disseminate the developed algorithms and numericalresults through journal papers and conference proceedings.
Members
Ahmed El-Mowafy (Australia)
Christian Tiberius (The Netherlands)
Chris Rizos (Australia)
Mathieu Jöerger (USA)
Juan Blanch (USA)Krzysztof Nowel (Poland)
Amir Khodabandeh (Australia)
Nobuaki Kubo (Japan)
Kan Wang (Australia)
Yang Gao (Canada)
Safoora Zaminpardaz (Australia)
Markus Rippl (Germany)

WG 4.4.2: Geophysical Applications ofHigh-Rate GNSS
Chair: Brendan Crowell (USA)
Description
The proliferation of high-rate Global Navigation Satellite
System (GNSS) data has enabled advances in geophysicalmonitoring well beyond the original intent of such systems.
It has been well demonstrated that models of large and rapid
deformation events, such as earthquakes and volcanic eruptions, are improved considerably by including high-rate
GNSS observations because of the ability to directly track
ground motions from strong shaking out to the permanent
offsets. Likewise, the models of the impacts of these events(i.e. ground motions, tsunami predictions) are improved for
applications such as early warning and rapid response. In
addition to direct measurements of the deformation field,
high-rate GNSS can offer additional applications in weather
forecasting, space weather through ionospheric tracking,and environmental probing with GNSS reflectometry. Highrate GNSS observations can also be applied to engineering

Commission 4 – Positioning and Applications

seismology problems such as long-period peak ground motions and can help determine the post-event resiliency of engineered structures. The use of this data for geophysical operations is still in its infancy, and robust algorithms, especially for the quality control and reliability assessment ofhigh-rate GNSS, are required to be developed to ensure future use.
Objectives
The primary objectives for this working group are:x Objectively characterize the limitations of high-rate
GNSS data and determine avenues for improvement,
x Determine the roadblocks to greater adaptation of highrate GNSS methods,
x Identify stakeholders outside the group that would benefit from high-rate GNSS data, such as monitoring agencies,
x Improve global access to high-rate GNSS data and methodologies.
MembersNA

WG 4.4.3:
Reliability of Low-cost &Android GNSS in navigation and geosciences
Chair: Jacek Paziewski (Poland)
Vice-Chair: Robert Odolinski (New Zealand)

157

Objectives
The main research will focus on the following objectives:x To perform a comprehensive characterization of lowcost receiver/smartphone signal quality, including carrier-to-noise density ratio and measurement noise,x To identify and investigate of the anomalies present insmartphone observables,x To assess the low-cost receiver/smartphone GNSS positioning performance,x To develop of novel processing algorithms addressing
low-cost receiver/smartphone GNSS observables characteristics,
x To call out new geophysical applications based on
GNSS smartphone signals.
Members
Jacek Paziewski (Poland)
Robert Odolinski (New Zeland)
Rafal Sieradzki (Poland)Martin Hakansson (Sweden)
Amir Khodabandeh (Australia)
Xiaohong Zhang (China)
Eugenio Realini (Italy)
Umberto Robustelli (Italy)
Vassilis Gikas (Greece)
Rene Warnant (Belgium)
Xiaopeng Gong (China)
Augusto Mazzoni (Italy)
Dimitrios Psychas (The Netherlands)
Guangcai Li (China)
Safoora Zaminpardaz (Australia)

Description
Nowadays, we may observe a rapid development in the
mass-market GNSS chipsets including those which are usedin smart devices. A real milestone on the way to the introduction of smartphones into location-based applications was
the introduction of Android Nougat 7 OS and, therefore
making their GNSS raw observations accessible to the general public. This in turn, induced a development of algorithms enhancing the accuracy of positioning with massmarket devices. Hence, now it is feasible to determine theposition with low-cost GNSS chipset with a degree of precision which was previously achievable only by surveygrade receivers with advanced processing algorithms.
This working group will endeavor to address and investigate issues related to the usage of low-cost receiver andsmartphone GNSS observations to navigation, positioning
and selected geoscience applications.

JSG 4.4.4: Assessment and validation of
IGS products and open-source scientificsoftware (Joint WG between IAG and IGS)
Chair: Yidong Lou (China)
Vice-Chair: Peng Fang (USA)
Description
High-precision GNSS applications require not only thehigh-accuracy GNSS products but also the high-precision
software. The IGS (International GNSS Service) has been
maintaining public available high-quality products for decades, including the GNSS satellite ephemerides, geocentric
coordinates of IGS tracking stations, earth rotation, atmospheric parameters and biases, to satisfy the objectives of awide range of scientific research and applications, which has
greatly benefited the GNSS community.

158

With the modernization of GPS and GLONASS and thein-service of Galileo, Beidou and QZSS, the precision andtimelines of IGS products are continuously improved andtypes are under expansions. On the other hand, however, we
seldom have credible open-source high-precision scientificsoftware for enormous users. The open-source of more highprecision/scientific software can significantly boost the utilization of IGS products in the scientific community andpromote the popularization of GNSS in high-precision applications.
Although a few software packages have been open
sourced recently, they may be far from enough to demonstrate their applicability in high-precision applications, andquestions like how the performance of these current opensource software is and what kinds of applications they cansatisfy remain unclear. This study group is therefore set up
mainly to investigate the performance of different software
comprehensively, improve their capability through international coordination, encourage the open-source of more professional software, and bridge the IAG and IGS regarding
the applications of IGS products in diverse fields.
Objectives
The main objectives of this working group are:x to investigate the performance and reliability of different
open-source scientific software comprehensively, so as
to provide important references to users for choosing themost suitable software in different applications
x to provide a platform to facilitate the communications
between the developers and users of the open-sourcehigh-precision/scientific software, so as to promote theimprovement of algorithms and potential scientific application.
x to collect and disseminate information of open-sourcehigh-precision/scientific software for the scientific community,
x to act as a bridge between the IAG and IGS regarding
the applications of the high-precision IGS products in diverse fields.
Members
Yidong Lou (China)Peng Fang (USA)Weixing Zhang (China)
Jan Dousa (Czech)
Feng Zhou (China)
D. Ibáñez (Spain)
Xiaolei Dai (China)
Yuanqing Pan (China)
Pavel Vaclavovic (Czech Republic)
Fu Zheng (China)

The Geodesist’s Handbook 2020

Berkay Bahadur (Turkey)
Haojun Li (China)

WG 4.4.5: Spoofing and Interference of
GNSS
Chair: Lakshay Narula (USA)Vice-Chair: Chengjun Guo (China)
Description
Global navigation satellite system (GNSS) signals are relatively weak, and thus susceptible to intentional and unintentional radio frequency interference (RFI). GNSS interference can lead to denial-of-service (by intentional or unintentional jamming), or can make the victim deduce a false position fix and/or a false clock offset (by intentional spoofing). Such interference is of serious concern for civil aviation, freight transportation, financial trading, military operations, etc. The last few years have seen a dramatic rise in
GNSS RFI activity across the world, with verified reports ofGPS spoofing in Ukraine/Black Sea, Syria, Shanghai, andsome other parts of China.
As low-cost GNSS jammers continue to be an issue, theGNSS spectrum is facing a renewed threat from terrestrial
communications in neighboring frequency bands. With lowcost software-defined radios, a GNSS spoofer can now be
downloaded from the internet. As safety-of-life applications
like self-driving cars and air taxis look for reliable and secure positioning and navigation techniques, GNSS spoofing
and interference issues are becoming an important concern
for the GNSS research community.
Current GNSS RFI countermeasures range from encryption of signals to interference detection via sensor fusion,and from use of directional antennas to monitoring of ADC
gain. This working group will bring together experts in thefield of GNSS spoofing and interference to consolidate thecurrent body of knowledge on the topic, identify promising
future directions, and to debate on the efficacy of the current
and proposed countermeasures to GNSS RFI.
Objectives
The primary objectives of this working group are to examine
and identify promising future directions on the following
topics:x GNSS resilience against jamming, including jammingfrom terrestrial communication networks (e.g. Ligado)
and on-chip communication (e.g., USB3).
x Sensor fusion for GNSS spoofing detection.
x Current proposals for navigation message and/or spreading code authentication and encryption for non-militaryuse, e.g., Galileo High Accuracy Service.

Commission 4 – Positioning and Applications

x The role of upcoming massive low earth orbit (LEO) satellite constellations in resilience to GNSS jamming andspoofing.
x Attacks and defenses for secure clock synchronization.
x Global GNSS RFI monitoring and situational awarenessvia dedicated and/or opportunistic probes.
In addition, this working group will encourage GNSS interference wardriving to collect data evidence of interesting159

and credible GNSS RFI activity in different parts of theworld.
MembersNA

160

The Geodesist’s Handbook 2020

Inter-Commission Committee on Theory (ICCT)
President: Pavel Novák (Czech Republic)
Vice President: Mattia Crespi (Italy)
http://icct.iag-aig.org

Terms of Reference
The Inter-Commission Committee on Theory (ICCT) was
formally approved and established after the IUGG XXI Assembly in Sapporo, 2003, to succeed the former IAG Section IV on General Theory and Methodology and, more importantly, to interact actively and directly with other IAG
entities, namely commissions, services and the Global Geodetic Observing System (GGOS). In accordance with the
IAG by-laws, the first two 4-year periods were reviewed in
2011. IAG approved the continuation of ICCT at the IUGGXXIII Assembly in Melbourne, 2011. At the IUGG XXIV
Assembly in Prague, 2015, ICCT became a permanent entity within the IAG structure.
Recognizing that observing systems in all branches ofgeodesy have advanced to such an extent that geodetic
measurements(i) are now of unprecedented accuracy and quality, can readily cover a region of any scale up to tens of thousands ofkilometres, yield non-conventional data types, and canbe provided continuously;
and consequently,(ii) demand advanced mathematical modelling in order toobtain the maximum benefit of such technological advance, ICCT(1) strongly encourages frontier mathematical and physical research, directly motivated by geodetic needand practice, as a contribution to science and engineering in general and theoretical foundations of geodesy in particular;(2) provides the channel of communication amongst different IAG entities of commissions, services and projects on the ground of theory and methodology, anddirectly cooperates with and supports these entities
in the topical work;(3) helps IAG in articulating mathematical and physicalchallenges of geodesy as a subject of science and in
attracting young talents to geodesy. ICCT strives toattract and serve as home to all mathematically motivated and oriented geodesists as well as to appliedmathematicians; and(4) encourages closer research ties with and gets directly
involved in relevant areas of Earth sciences, bearing
in mind that geodesy has always been playing an important role in understanding the physics of the
Earth.
Objectives
The overall objectives of the ICCT are:x to act as international focus of theoretical geodesy,x to encourage and initiate activities to advance geodetic
theory in all branches of geodesy,x to monitor developments in geodetic methodology.
To achieve the objectives, the ICCT interacts and collaborates with the IAG Commissions, GGOS and other IAG related entities (services, projects).
Structure
The structure of Inter-Commission Committees is specified
in the IAG by-laws. The ICCT Steering Committee consistsof the President, Vice-President, Past-President, representatives from each of the IAG Commissions, GGOS and of two
members-at-large.
ICCT activities are undertaken by study groups. By theinter-commission nature of ICCT, these study groups arejoint study groups, affiliated to one or more of the Commissions and/or to GGOS.

Inter-Commission Committee on Theory (ICCT)Program of Activities
The ICCT's program of activities include:
x participation as (co-)conveners of geodesy sessions atmajor conferences such as IAG, EGU and AGU,
x organization of Hotine-Marussi symposia,
x initiation of summer schools on theoretical geodesy,x and maintaining a website for dissemination of ICCT related information.
Steering Committee
President
Pavel Novák (Czech Rep.)
Vice-President Mattia Crespi (Italy)
Past-President Nico Sneeuw (Germany)
Representatives of IAG entities:
Commission 1 Christopher Kotsakis (Greece)
Commission 2 Mirko Reguzzoni (Italy)
Commission 3 Janusz Bogusz (Poland)Commission 4 Allison Kealy (Australia)
GGOS
Michael Schmidt (Germany)
IGFS
Riccardo Barzaghi (Italy)
IERS
Jürgen Müller (Germany)
Members at large:
IAG
Bofeng Li (China)
IAG
Marcelo Santos (Canada)
Joint Study Groups
The following list names ICCT joint study groups (JSG) for
the 2019-2023 period. Their chairs are indicated in boldface.
The numbers behind the names denote the affiliation of JSG
to the IAG Commissions or GGOS.
JSG T.23 Spherical and spheroidal integral formulas of thepotential theory for transforming classical andnew gravitational observables
M. Šprlák (Czech Rep.) 2, GGOS
JSG T.24 Integration and co-location of space geodetic observations and parameters
K. Sośnica (Poland) 1, 2, 3, 4, GGOS
JSG T.25 Combining geodetic and geophysical information for probing Earth’s inner structure and its
dynamics
R. Tenzer (Hong Kong) 2, 3, GGOS
JSG T.26 Geoid/quasi-geoid modelling for realization of
the geopotential height datum
J. Huang (Canada) 2, GGOS
JSG T.27 Coupling processes between magnetosphere,
thermosphere and ionosphere
A. Calabia (China) 4, GGOS
JSG T.28 Forward gravity field modelling of known mass
distributions
D. Tsoulis (Greece) 2, 3, GGOS

161

JSG T.29 Machine learning in geodesy
B. Soja (Switzerland) 2, 3, 4
JSG T.30 Dynamic modeling of deformation, rotation andgravity field variations
Y. Tanaka (Japan) 2, 3, GGOS
JSG T.31 Multi-GNSS theory and algorithms
A. Khodabandeh (Australia) 1, 4, GGOS
JSG T.32 High-rate GNSS for geoscience and mobility
M. Crespi (Italy) 1, 3, 4, GGOS
JSG T.33 Time series analysis in geodesy and geodynamics
W. Kosek (Poland) 1, 3, 4, GGOS
JSG T.34 High resolution harmonic analysis and synthesisof potential fields
S. Claessens (Australia) 2, GGOS
JSG T.35 Advanced numerical methods in physical geodesy
R. Čunderlík (Slovakia) 2, GGOS
JSG T.36 Dense troposphere and ionosphere sounding
G. Savastano (Luxembourg) 4, GGOS
JSG T.37 Theory and methods related to combination ofhigh-resolution topographic/bathymetric models
in geodesy
D. Carrion (Italy) 2, GGOS

JSG T.23: Spherical and spheroidal integral formulas of the potential theory fortransforming classical and new gravitational observables
Chair: M. Šprlák (Czech Republic)
Affiliation: Commission 2 and GGOS
Introduction
The gravitational field represents one of the principal properties of any planetary body. Physical quantities, e.g., thegravitational potential or its gradients (components of gravitational tensors), describe gravitational effects of any
mass body. They help indirectly in sensing inner structuresof planets and their (sub-)surface processes. Thus, they represent an indispensable tool for understanding inner structures and processes of planetary bodies and for solving challenging problems in geodesy, geophysics and other planetary sciences.
Various measurement principles have been developed
for collecting gravitational data by terrestrial, marine, airborne or satellite sensors. From a theoretical point of view,
different parameterizations of the gravitational field havebeen introduced. To transform observable parameters intosought parameters, various methods have been introduced,
e.g., boundary-value problems of the potential theory have

162

been formulated and solved analytically by integral transformations.
Transforms based on solving integral equations of Stokes, Vening-Meinesz and Hotine have traditionally been ofsignificant interest in geodesy as they accommodated gravity field observables in the past. However, new gravitational data have recently become available with the advent ofsatellite-to-satellite tracking, Doppler tracking, satellite altimetry, satellite gravimetry, satellite gradiometry and chronometry. Moreover, gravitational curvatures have alreadybeen measured in laboratory. New observation techniques
have stimulated formulations of new boundary-value problems, equally as possible considerations on a tie to partial
differential equations of the second order on a two-dimensional manifold. Consequently, the family of surface integral
formulas has considerably extended, covering now mutualtransformations of gravitational gradients of up to the thirdorder.
In light of numerous efforts in extending the apparatus
of integral transforms, many theoretical and numerical issues still remain open. Within this JSG, open theoreticalquestions related to existing surface integral formulas, suchas stochastic modelling, spectral combining of various gradients and assessing numerical accuracy, will be addressed.
We also focus on extending the apparatus of spheroidal integral transforms which is particularly important for modelling gravitational fields of oblate or prolate planetary bodies.
Objectives
This JSG plans to:x Study noise propagation through spherical andspheroidal integral transforms.
x Propose efficient numerical algorithms for precise
evaluation of spherical and spheroidal integral
transformations.
x Develop mathematical expressions for calculating the
distant-zone effects for spherical and spheroidal integral
transformations.
x Study mathematical properties of differential operatorsin spheroidal coordinates which relate various
functionals of the gravitational potential.
x Formulate and solve spheroidal gradiometric andspheroidal curvature boundary-value problems.
x Complete the family of spheroidal integral transforms
among various types of gravitational gradients and to
derive corresponding integral kernel functions.
x Investigate optimal combination techniques of various
gravitational gradients for gravitational field modellingat all scales.

The Geodesist’s Handbook 2020

Program of Activities
x Presenting findings at international geodetic or
geophysical conferences, meetings and workshops.
x Interacting with IAG Commissions and GGOS.
x Monitoring research activities of JSG members andother scientists whose research interests are related toscopes of this JSG.
x Organizing a session at the Hotine-Marussi Symposium2022.
x Providing a bibliographic list of publications fromdifferent branches of the science relevance to scopes ofthis JSG.
MembershipMichal Šprlák (Czech Republic), chair
Sten Claessens (Australia)
Mehdi Eshagh (Sweden)
Ismael Foroughi (Canada)Peter Holota (Czech Republic)
Juraj Janák (Slovakia)
Otakar Nesvadba (Czech Republic)
Pavel Novák (Czech Republic)
Vegard Ophaug (Norway)
Martin Pitoňák (Czech Republic)
Michael Sheng (Canada)
Natthachet Tangdamrongsub (USA)Robert Tenzer (Hong Kong)

JSG T.24: Integration and co-location of
space geodetic observations and parameters
Chair: K. Sośnica (Poland)
Affiliation: Commissions 1, 2, 3 and 4, GGOS
Introduction
Many geodetic parameters can be retrieved using various
techniques of space geodesy. For instance, all satellite techniques are sensitive to a geocenter motion and gravity field
variations. However, some techniques are affected more bysystematic observation errors than other techniques. Earth’s
rotation parameters from sub-daily to daily temporal scales
can be determined using all techniques of space geodesy
with higher or lower accuracy, and with better or worse temporal resolutions. Precise orbits of satellites may be basedon a single technique or multiple techniques that shall mitigate system-specific orbital systematic errors.
Recently, a series of satellite missions co-locating different space geodetic techniques has been launched:Inter-Commission Committee on Theory (ICCT)x SLR and GNSS: Galileo (all satellites), GLONASS (allsatellites), QZSS (all satellites), IRNSS (all satellites),
GPS (2 satellites), BeiDou/COMPASS (selectedsatellites), CHAMP, GRACE-A/B, GOCE, SWARMA/B/C, ICESat-2, COSMIC-2, Terra-SAR, TanDEM-X,
GRACE Follow-On A/B, etc.
x DORIS and SLR: TOPEX/Poseidon, ENVISAT,CRYOSAT-2, SARAL and Jason-1 (after 2009),
x VLBI and SLR: RadioAstron,
x VLBI, SLR, and GNSS: APOD,
x DORIS, GNSS and SLR: Jason-2/3, HY-2A and
Sentinel-3A/B,
x SLR, VLBI, GNSS and DORIS: GRASP and E-GRASP(planned missions).
SLR retroreflectors are passive and relatively cheap devices; thus, they are installed on-board many low- and highorbiting satellites. Many low-orbiting satellites for ocean
monitoring are equipped with DORIS and GNSS receivers
for precise orbit determination, and with SLR retroreflectors
for the orbit validation. DORIS receivers are installed on
many satellites which require precise ephemeris and orbit
below 2000 km. Missions dedicated to Earth’s gravity fieldrecovery are typically equipped with GNSS receivers and
SLR retroreflectors. Most of the GNSS satellites areequipped with SLR retroreflectors (except for GPS). VLBI
telescopes are typically slow as they are dedicated to tracking extra-galactic quasars. Hence, many VLBI telescopes
have problems with tracing fast-moving low-orbiting targets
that are planned for co-location on-board satellites. However, first experiments using the APOD satellite with a
VLBI transmitter and SLR retroreflector was successfully
performed in Australia. Unfortunately, the APOD GPS receiver failed soon after the satellite launch which caused
some issues with the accuracy of the determined orbit when
the number of SLR observations was insufficient.
Despite many LEO satellites equipped with two or threetechniques of space geodesy, the full potential of the co-location on-board LEO has not yet been entirely explored interms of deriving combined geodetic parameters. SLR observations to LEO are typically used only for validation ofGPS-based or DORIS-based orbits. SLR observations to
LEO and GNSS do not contribute at all to realization of theInternational Terrestrial Reference System despite GNSS
and LEO satellites contributing to GNSS and DORIS solutions, respectively.
Recently, the International Laser Ranging Service initiated a series of special tracking campaigns dedicated to
tracking new LEO and GNSS spacecraft which increased
the amount of collected data with a perspective of their fullco-location in space. The combination of solutions based on
GNSS, SLR, LLR, DORIS and VLBI requires a profoundinvestigation of biases and systematic effects affecting all

163

individual techniques. Neglecting systematic effects maylead to degradation of solutions and to absorption of various
systematic effects by global geodetic parameters.
The main goal of this JSG is to investigate methods tocombine global geodetic parameters derived from multiple
techniques of space geodesy with the major focus on thosemissions capable of co-locating and integrating different observation techniques. We aim at improving quality and reliability of global geodetic parameters and realization of theterrestrial reference system through integration of different
microwave techniques with laser techniques. We will also
explore benefits emerging from co-locating geodetic techniques on-board low and high-orbiting satellites. We aim at
detailed analyses related to system-specific issues and systematic effects emerging from combining different techniques of space geodesy, and at the assessment of their contributions to combined global geodetic parameters.
Objectives
x Determination of global geodetic parameters using
combined space geodetic observations.
x Determination of geocenter motion from: SLR
observations to passive and active satellites, DORIS,
Galileo, GPS, GLONASS, and BeiDou or possibly also
VLBI (using inverse methods).
x Separation of geophysical signals in the geocentermotion from the technique-specific and system-specificerrors, employing the co-location in space between SLR
and GNSS using Galileo, BeiDou, and GLONASS
satellites for deriving common parameters.
x Analysis of potential usability of SLR observations toactive LEO satellites together with GNSS and DORIS
data for deriving global geodetic parameters.
x Analysis of daily pole coordinates and of length-of-day
variations using combined SLR and microwave
observations to different GNSS and LEO satellites withDORIS receivers, and the comparison with respect to
LLR and VLBI results.
x Determination of sub-daily Earth’s rotation parametersfrom VLBI, GPS, GLONASS, Galileo and SLR
observations to LEO and geodetic satellites.
x Precise orbit determination of LEO and GNSS satellites
using combined SLR and microwave observations –GNSS and DORIS.
x Estimation of geodetic parameters using GNSS
employing time-variable gravity field models derived
from SLR, active LEOs and GRACE. Assessment of thevulnerability of satellite orbits to low-degree Earth’s
gravity field depending on the satellite heights.
x Homogenization of tropospheric delay models for colocated space geodetic stations. Separation of the wet
and hydrostatic tropospheric delay; analysis of the164horizontal gradients for optical and microwave
techniques.
x Combination of SLR observations to various LEO
missions: Sentinel-3A/3B, GRACE, GRACE-FO,
GOCE, SWARM-A/B/C, Jason-2/3 to realize theterrestrial reference frames.
x Determination of time-variable low-degree gravity fieldusing SLR observation to passive geodetic satellites and
GNSS-based orbits of LEO satellites to fill a gap
between GRACE and GRACE-FO missions,x Estimation of Earth’s rotation parameters by combining
LLR, SLR and GNSS, and their comparison with VLBI
results.
Program of activities
x To launch a questionnaire for the current integration oftechniques and finalized co-location in spaceexperiments.
x To open a web page with information concerning the colocation in space, the combination of global geodetic
parameters and the exchange of ideas, provision andupdating the bibliographic list of references of research
results and relevant publications from different
combination centers.
x To launch a proposal for two state-of-the-art review
papers on co-location on-board LEO and GNSS andcombination of global geodetic parameters co-authoredby JSG members.
x To organize a session at the Hotine-Marussi Symposium2022.
x To promote sessions and presentation of the research
results at international symposia both related to Earthscience, e.g., IAG/IUGG, EGU, AGU, EUREF, IGS andILRS.
Membership
Krzysztof Sośnica (Poland), chair
Mathis Blossfeld (Germany)
Janina Boisits (Austria)
Grzegorz Bury (Poland)
Florian Dilssner (Germany)
Susanne Glaser (Germany)
Toshimichi Otsubo (Japan)
Erik Schnoemann (Germany)
Dariusz Strugarek (Poland)Daniela Thaller (Germany)
Tzu-Pang Tseng (Australia)
Radosław Zajdel (Poland)
Julian Zeitlhöfler (Germany)

The Geodesist’s Handbook 2020

JSG T.25: Combining geodetic andgeophysical information for probing
Earth’s inner structure and its dynamics
Chair: R. Tenzer (Hong Kong)
Affiliation: Commissions 2 and 3, GGOS
Introduction
The seismic tomography is primarily used to provide imagesof the Earth’s inner structure based on the analysis of seismic waves due to earthquakes and (controlled) explosions.
This technique involves several different methods for processing P-, S- and surface waves on the principle of solving
inverse problems for finding locations of reflection and refraction of wave pathways in order to create topographic
models. In this way, 3D models of P- and S-wave seismic
velocity anomalies are obtained which can be interpreted as
structural, thermal or compositional variations inside theEarth. Focusing on the Earth’s density structure, the conversion between seismic velocities and mass densities are
adopted to construct regional or global seismic density models of the crust and the mantle. Two major limiting aspects
restrict possibilities of recovering Earth’s density structure
realistically. The first one is practical. Since active seismic
experiments are relatively expensive, large parts of theworld are not yet covered sufficiently by seismic surveys,
most remarkably most of world’s oceans as well as remoteparts of Antarctica, Greenland, Africa and South America.
The other aspect is of a theoretical nature. The determination of mass density from seismic data could be ambiguous
while affected by many uncertainties, meaning that the relationship between seismic velocities and mass densities is notunique. Actually, the density structure inside the Earth iscontrolled by many factors such a thermal state or mineralcomposition.
Gravity data has been used to interpolate the information
about the Earth’s density structure (or density interfaces)
where seismic data coverage is uneven or sparse. The National Geospatial-Intelligence Agency in conjunction with
its partners from around the world has begun to develop a
new global gravitational model, EGM2020, which should be
released publically in 2020. EGM2020 should significantly
improve the accuracy (as well as the actual resolution) of the
global Earth’s gravity field. This will be achieved by incorporating new data sources and procedures. Updated satellite
gravity information from the GOCE and GRACE missions
will better support the lower harmonics, globally. Multiple
new acquisitions (terrestrial, airborne and shipborne) ofgravimetric data over specific regions, will provide improved global coverage and resolution over the land as well
as for coastal and some oceanic areas. Ongoing accumulation of satellite altimetry data will contribute to refinement

Inter-Commission Committee on Theory (ICCT)and accuracy improvement of the marine gravity field, mostnotably in polar and near-coastal regions. A significant improvement is also anticipated over large remote regions in
Africa, South America, Greenland and Antarctica.
EGM2020 will provide opportunities to improve the current
knowledge about the Earth’s inner structure and processes
particularly in regions with a low seismic data coverage.
Gravimetric interpretation of the Earth’s inner density structure is, however, a non-unique problem because infinity
many density configurations could be attributed just to the
one gravity field solution. Moreover, the gravity inversion
is (in a broader mathematical context) an ill-posed problem.
To overcome partially theoretical deficiencies and practical restrictions of both, seismic and gravimetric methods
for the recovery of the Earth’s inner density structure, techniques for a combined or constrained inversions of gravity
and seismic data are optimally applied, while incorporating
additional geophysical, geological and geodynamic constraints. Many such methods already exist or could be developed and further improved within the framework of scientific activities of members of this (multidisciplinary)study group over the next four years. This is achievable,
given their expertise in the field of geodesy, geophysics,
mathematics and to some extent also geology.
We expect that our research activities will substantiallycontribute to the current knowledge of the lithosphericstructure, focusing on continental regions of Africa andSouth America and other continents where seismic data aresparse. Our ongoing research already involves Antarctica
and central part of Eurasia. Moreover, a special attention
will be given to study the lithospheric structure beneath theIndian Ocean, which is probably the most complex, but theleast understood. Despite the lithosphere is the most heterogeneous layer inside the Earth, large lateral structural irregularities are still present even deeper within the mantle below the lithosphere-asthenosphere boundary that are mainly
attributed to the mantle convection pattern. The combined
gravity and seismic data will be exploited in order to improve existing global or continental-scale mantle density
models. A further improvement of the knowledge on the
Earth’s inner structure is important, among many other subjects, also for a better understanding of the response of thelithosphere to the mantle convection. This involves numerous study topic, including but not limited to the compensation stage of the crust/lithosphere, the lithospheric strength,mechanisms behind the oceanic subduction, the relation between the mantle convection pattern and the global tectonic
configuration (and its spatio-temporal variations), the glacial isostatic adjustment, volcanic processes, or geo-hazard.
The members of this study group will address some of these
aspects within the following overall objectives.

165

Objectives
The main objectives of the JSG are as follows:x Improvement of (regional and continental-scale)lithospheric density models based on combining
geodetic and geophysical data and additional geologicalconstraining information, focusing mainly on regionswith insufficient seismic data coverage. Special
emphasis will be given to Africa, Greenland and SouthAmerica. Studies will involve also Indian and Pacific
Oceans.
x Development of a preliminary global density model ofthe mantle bellow the lithosphere-asthenosphereboundary based on the combined analysis of seismic andgravity data, focusing on the seismic data conversion tomass densities within the gravimetric inversion scheme
constrained by geothermal, geochemical, geodynamic
and other information.
x Contribution to a better understanding of the interaction
between the mantle dynamics and the lithospheric stateand structure.
Program of Activities
Presenting research findings at major international geodetic
or geophysical conferences, meetings and workshops.
Interacting with related IAG Commissions and GGOS.
Monitoring research activities of the JSG members and ofother scientists, whose research interests are relevant to thescopes of the JSG.
Organizing a session at the Hotine-Marussi Symposium
2022.
Providing bibliographic list of publications from different branches of science relevant to JSG scopes.
Membership
Robert Tenzer (Hong Kong), chair
Aleksej Baranov (Russia)
Mohammad Bagherbandi (Sweden)
Carla Braitenberg (Italy)
Wenjin Chen (China)
Róbert Čunderlík (Slovakia)
Franck EK Ghomsi (Cameroon)
Mirko Reguzzoni (Italy)Lars Sjöberg (Sweden)

166

JSG T.26: Geoid/quasi-geoid modelling
for realization of the geopotential height
datum
Chair: J. Huang (Canada)
Affiliation: Commission 2 and GGOS
Introduction
The geopotential height datum is realized by a gravimetricgeoid/quasi-geoid model. The geoid/quasi-geoid model can
now be determined with the accuracy of a few centimeters
in a number of regions around the world; it has been adopted
in some as a height datum to replace spirit-leveling networks, e.g., in Canada and New Zealand. A great challenge
is the 1-2 cm accuracy anywhere to be compatible with theaccuracy of ellipsoidal heights measured by the GNSS technology. This requires an adequate theory and its numericalrealization, to be of the sub-centimeter accuracy, and theavailability of commensurate gravity data and digital elevation models (DEMs).
Geoid/quasi-geoid modelling involves the combinationof satellite, airborne and surface gravity data through the remove-compute-restore method, employing various modelling techniques such as the Stokes integration, least-squares
collocation, spherical radial base functions or spherical harmonics. Satellite gravity data from recent gravity missions(GRACE and GOCE) enable to model the geoid components with the accuracy of 1-2 cm at the spatial resolutionof 100 km. Airborne gravity data are covering more regionswith a variety of accuracies and spatial resolutions such as
the US GRAV-D project. They often overlap with surface
gravity data which are still essential in determining the highresolution geoid model.
In the meantime, DEMs required for the gravity reduction have achieved higher spatial resolutions with a global
coverage. In order to understand how accurately the geoid
model can be determined, the 1 cm geoid experiment was
carried out in a test region in Colorado, USA by more thanten international teams. The state-of-the-art airborne data
was provided for this experiment by US NGS. The test results reveal that differences between geoid models by theseteams are at the level of 2-4 cm in terms of the standard deviation with a range of decimeters. Reducing these differences is necessary for realization of geopotential height datums and the International Height Reference System(IHRS). This will require a thorough examination and assessment of both methods and data.
Objectives
The scope of this JSG covers all aspects of geoid/quasigeoid modelling, in particular focuses on:

The Geodesist’s Handbook 2020

x Adoption of physical parameters such as GM.
x Determination and adoption of W0.
x Geo-center convention with respect to the International
Terrestrial Reference Frame (ITRF).
x Adoption of a Geodetic Reference System.
x Identification of data requirements and gaps.
x Gravity data gridding methods.
x Downward continuation of high-altitude airborne
gravity data.
x Spatial and spectral modelling of topographic effects
considering mass density variation.
x Combination of satellite, airborne and surface gravity
data.
x Separation between the geoid and quasi-geoid.
x Estimation of data and geoid/quasi-geoid model errors.
x External validation data and methods for thegeoid/quasi-geoid model.
x Dynamic geoid/quasi-geoid modelling.
x New geodetic boundary-value problems.
Program of Activities
The JSG will achieve its objectives through:x Involving and supporting new generation of geoid
modelers.
x Organizing splinter meetings in coincidence with major
IAG conferences and a series of online workshops.
x Circulating and sharing information, ideas, progress
reports, papers and presentations.
x Organizing a session at the Hotine-Marussi Symposium2022.
x Supporting and cooperating with IAG commissions,services, GGOS and other study and working groups on
gravity modelling and height system, in particular
GGOS IHRS working group, and International Service
for the Geoid (ISG).
Membership
Jianliang Huang (Canada), chair
Jonas Ågren (Sweden)
Riccardo Barzaghi (Italy)
Heiner Denker (Germany)
Bihter Erol (Turkey)
Christian Gerlach (Germany)
Christian Hirt (Germany)
Juraj Janák (Slovakia)
Tao Jiang (China)
Robert W. Kingdon (Canada)
Xiaopeng Li (USA)Urs Marti (Switzerland)
Ana Cristina de Matos (Brazil)
Pavel Novák (Czech Republic)

Inter-Commission Committee on Theory (ICCT)Laura Sanchez (Germany)
Matej Varga (Croatia)
Marc Véronneau (Canada)
Yanming Wang (USA)Xinyu Xu (China)

JSG T.27: Coupling processes between
magnetosphere,
thermosphereandionosphere
Chair: A. Calabia (China)
Affiliation: Commission 4 and GGOS
Introduction
Consequences of upper-atmosphere conditions on humanactivity underscore the necessity to better understand andpredict effects of the magnetosphere-ionosphere-thermosphere (MIT) processes and of their coupling. This will
prevent from their potential detrimental effects on orbiting,aerial and ground-based technologies. For instance, major
concerns include the perturbation of electromagnetic signals
passing through the ionosphere for an accurate and secureuse of global navigation satellite systems (GNSS), and thelack of accurate aerodynamic-drag models required for accurate tracking, decay and re-entry calculations of low Earthorbiters (LEO), including manned and unmanned artificial
satellites. In addition, ground power grids and electronics ofsatellites could be influenced, e.g., by the magnetic field generated by sudden changes in the current system due to solar
storms.
Monitoring and predicting Earth’s upper atmosphereprocesses driven by solar activity are highly relevant toscience, industry and defense. These communities
emphasize the need to increment the research efforts for better understanding of the MIT responses to highly variable
solar conditions, as well as detrimental space weather effects on our life and society. On one hand, electron-density
variations produce perturbations in speed and direction ofvarious electromagnetic signals propagated through theionosphere, and reflect as a time-delay in the arrival of themodulated components from which pseudo-range measurements of GNSS are made, and an advance in the phase of
signal’s carrier waves which affects also carrier-phase measurements. On the other hand, an aerodynamic drag associated with neutral-density fluctuations resulting from upper
atmospheric expansion/contraction in response to variable
solar and geomagnetic activity increases drag and decelerates LEOs, dwindling the lifespan of space-assets, and making their tracking difficult.
Through interrelations, dependencies and coupling patterns between ionosphere, thermosphere and magnetosphere167

variability, this JSG aims to improve the understanding of
coupled processes in the MIT system, and considerations of
the solar contribution. In addition, tides from the lower atmosphere forcing can feed into the electrodynamics; they
have a composition effect leading to changes in the MIT
system. In this scheme, our tasks are addressed to exploit theknowledge of the tight MIT coupling by investigating multiple types of magnetosphere, ionosphere and thermosphereobservations. The final outcome will help to enhance thepredictive capability of empirical and physics-based models
through interrelations, dependencies and coupled patterns ofvariability between essential geodetic variables.
Objectives
x Characterize and parameterize global modes of MIT
variations associated with diurnal, seasonal and space
weather drivers as well as the lower atmosphere forcing.
x Determine and parameterize mechanisms responsiblefor discrepancies between observables and present
models.
x Detect and investigate coupled processes in the MIT
system for the deciphering of physical laws andprinciples such as continuity, energy and momentum
equations and solving partial differential equations.
Program of Activities
x Presenting research findings at major international
geodetic or geophysical conferences, meetings, andworkshops.
x Interacting with related IAG Commissions and GGOS.
x Monitoring research activities of the JSG members andof other scientists, whose research interests are related tothe scopes of SGx Organizing a session at the Hotine-Marussi Symposium2022.
x Organizing working meetings at international symposia
and presentation of research results at appropriatesessions.
Membership
Andres Calabia Aibar (China), chair
Emmanuel Abiodun Ariyibi (Nigeria)
Toyese Tunde Ayorinde (Brazil)
Olawale S. Bolaji (Nigeria)
Oluwaseyi Emmanuel Jimoh (Nigeria)
Gang Lu (USA)Naomi Maruyama (USA)
Astrid Maute (USA)
Piyush M. Metha (USA)Charles Owolabi (Nigeria)
Liang Yuan (China)

168

JSG T.28: Forward gravity field modellingof known mass distributions
Chair: D. Tsoulis (Greece)
Affiliation: Commissions 2 and 3, GGOS
Introduction
The geometrical definition of the shape and numerical evaluation of the corresponding gravity signal of any given mass
distribution express a central theme in gravity field modelling. Involving different theoretical and computational aspects of the potential field theory and including the elementof interpreting the computed signal by comparing it with theobserved gravity field, the specific research topic determines a characteristic interface between geodesy and geophysics.
Theoretical and methodological aspects of mass modelling concern a wide range of applications, from computing
gravity anomalies and geoid to reducing satellite gradiometry data or solving an extended family of integral equations of the potential theory. Directly linked to real massdensity distributions in the Earth's interior, the problem ofcomputing the potential function of given mass density distributions and its spatial derivatives up to higher orders defines the core of forward gravity field modelling, while also
constituting an integral part of an inverse modelling
flowchart in geophysics.
The availability of an abundance of terrestrial and satellite data of global coverage and increasing spatial resolution
provides a challenging framework for revisiting known theoretical aspects and especially investigating computational
limits and possibilities of forward gravity modelling induced by known mass distributions. Satellite observations provide global grids of gravity related quantities at satellite altitudes, global crustal databases offer detailed layered information of the shape and consistency of the Earth's crust,
while satellite methods produce digital elevation models
that represent a continental part of the topographic surface
with unprecedented resolution.
The current datasets enable the consideration of several
theoretical, methodological and computational aspects offorward gravity field modelling. For instance, dense digital
elevation models provide a unique input dataset that challenges the evaluation of precise terrain effects, especially inareas of very steep terrain. At the same time and due to theavailability of new data, the complete theoretical frameworkthat evaluates the gravity effect of a given distribution using
analytical, numerical or spectral techniques emerges again
at the forefront of research, examining both ideal bodies andreal distributions. Finally, the existence of detailed information of the structure in the Earth's interior provides an opportunity to revisit synthetic Earth reference models by

The Geodesist’s Handbook 2020

computing the actual gravity effect induced by these distributions and validate it against the observed gravity signal
obtained by the available gravity field models.
Objectives
x Examine new theoretical developments (numerical,
analytical or spectral) in expressing the gravity signal ofideal geometric distributions.
x Perform validation studies of precise terrain effects overrugged mountainous topography.
x Compute the gravity effect of structures in the Earth's
interior and embed this effort in the frame of a synthetic
reference Earth model.
Program of Activities
x Participation in forthcoming IAG conferences with
splinter meetings and proposed sessions.
x Preparation of joint publications with JSG members.
x Organization of a session at the Hotine-Marussi
Symposium 2022.
Membership
Dimitrios Tsoulis (Greece), chair
Carla Braitenberg (Italy)
Christian Gerlach (Germany)
Ropesh Goyal (India)
Olivier Jamet (France)
Michael Kuhn (Australia)
Pavel Novák (Czech Republic)
Konstantinos Patlakis (Greece)
Daniele Sampietro (Italy)
Matej Varga (Croatia)
Jérôme Verdun (France)

JSG T.29: Machine learning in geodesy
Chair: B. Soja (Switzerland)
Affiliation: Commissions 2, 3 and 4
Introduction
Due to the exponential increase in computing power overthe last decades, machine learning has grown in importancefor several applications. In particular, deep learning, i.e.,
machine learning based on deep neural networks, typically
performed on extensive data sets (“big data”), has become
very successful in tackling various challenges, for example,
image interpretation, language recognition, autonomous decision making or stock market predictions. Several scientificdisciplines have embraced the capability of modern machineInter-Commission Committee on Theory (ICCT)

learning algorithms, including astronomy and many fields
of geosciences.
The field of geodesy has seen a significant increase inobservational data in recent years, in particular from Global
Navigation Satellite Systems (GNSS) with tens of thousandsof high-quality permanent stations, multiple constellations,and increasing data rates. With the upcoming NISAR mission, the InSAR community needs to prepare for handlingdaily products exceeding 50 GB. In the future, the next-generation Very Long Baseline Interferometry (VLBI) Global
Observing System (VGOS) will deliver unprecedented
amounts of data compared to legacy VLBI operations. Traditional data processing and analysis techniques that rely
largely on human input are not well suited to harvest suchrich data sets to their full potential. Still, machine learningtechniques are not yet adopted in geodesy.
Machine learning in geodesy has the potential to facilitate the automation of data processing, detection of anomalies in time series and image data, their classification into
different categories and prediction of parameters into the future. Machine learning and, in recent years, deep learning
methods can successfully model complex spatiotemporal
data through the creation of powerful representations at hierarchical levels of abstraction. Furthermore, machine learning techniques provide promising results in addressing thechallenges that arise when handling multi-resolution, multitemporal, multi-sensor, multi-modal data.
The information contained in GNSS station position
time series is essential as it can help derive important conclusions related to hydrology, earthquakes, or volcanism
using machine learning. Other important applications aretropospheric and ionospheric parameters derived from
GNSS where automated detection and prediction could be
beneficial for improved severe weather forecasting andspace weather monitoring, respectively. InSAR data will benefit in particular from efficient image processing algorithms based on machine learning, facilitating the detectionof regions of interest. In several of these cases, the development of scalable deep learning schemes can contribute tomore effectively handling and processing of large-scale spatiotemporal data.
Traditional machine learning techniques for geodetic
tasks include convolutional neural networks for image data
and recurrent neural networks for time series data. Typically, these networks are trained by supervised learning approaches, but certain applications related to autonomous
processing will benefit from reinforcement learning.
The field of machine learning has expanded rapidly inrecent years and algorithms are constantly evolving. It is theaim of this JSG to identify best practices, methods, and algorithms when applying machine learning to geodetic tasks.
In particular, due to the “black box” nature of many machine

169

learning techniques, it is very important to focus on appropriate ways to assess the accuracy and precision of the results, as well as to correctly interpret them.
Objectives
x Identify geodetic applications that could benefit frommachine learning techniques, both in terms of whichdata sets to use and which issues to investigate.
x Create an inventory of suitable machine learningalgorithms to address these problems, highlighting theirstrengths and weaknesses.
x Perform comparisons between machine learning
methods and traditional data analysis approaches, e.g.,
for time series analysis and prediction.
x Focus on error assessment of results produced bymachine learning algorithms.
x Identify open problems that come with the automationof data processing and generation of geodetic products,
including issues of reliability.
x Develop best practices when applying machine learning
methods in geodesy and establishing standardized
terminology.
Program of Activities
x Create a web page about machine learning in geodesy toprovide information and raise awareness about this
topic. The page will include:o inventory of algorithms, see above,o benchmark datasets to test the performance of thesealgorithms,
o comprehensive record of previous activities/ publications related to machine learning in geodesy,o description of activities by the JSG members.
x Work toward a state-of-the-art review paper aboutmachine learning in geodesy co-authored by the JSG
members.
x Promote sessions and presentation of the research results
at international scientific assemblies (IAG/IUGG, EGU,
AGU) and technique-specific meetings (IGS, IVS, ...).
Membership
Benedikt Soja (USA), chair
Kyriakos Balidakis (Germany)
Clayton Brengman (USA)
Jingyi Chen (USA)Maria Kaselimi (Greece)
Ryan McGranaghan (USA)
Randa Natras (Germany)
Simone Scardapane (Italy)

170

JSG T.30: Dynamic modeling of deformation, rotation and gravity field variations
Chair: Y. Tanaka (Japan)
Affiliation: Commissions 2 and 3, GGOSThe Geodesist’s Handbook 2020

o
o
o
o

Integration of diverse data.
Effective processing of a large quantity of data.
Data assimilation.
Application of various theories to real observations
for new scientific findings.

Introduction

Program of Activities

Advancements in the Global Geodetic Observation System(GGOS), and terrestrial, aerial and marine geodetic observations have enabled us to monitor deformation, rotationand gravity field variations of the Earth with the unprecedented accuracy, which are caused by geophysical phenomena having various space-time scales. In addition, recent
developments of global networks for solid-Earth observations and technologies for laboratory experiments have allowed us to obtain higher-quality and finer-resolution geophysical data for elasticity, density, viscosity, pressure, electromagnetic and thermal structures, etc., reflecting three dimensional heterogeneities in the internal Earth.
The improved geodetic and geophysical data motivate us
to interpret the various phenomena, based on dynamic modelling. Through the modelling, we are able to identify thecauses of the detected space-time variations and to deepen
the understanding of the phenomena. Furthermore, it would
help appeal the usefulness of GGOS.
This JSG consists of scientists working on dynamic modelling using diverse approaches. The targets of the modelling include local, regional and global variations which occur near the surface down to the inner core. To share different perspectives for modelling stimulates the activities ofeach member and can produce and/or evolve collaborative
studies. For which reason, we form a forum within the
ICCT.

x To launch an e-mail list to share information concerning
research results and to interchange ideas for solving
related problems.
x To open a web page to share information, such as
publication lists and its update.
x To promote international workshops focusing on theabove research theme.
x To propel collaborations with closely related joint study
groups such as geodetic, seismic and geodynamic
constraints on glacial isostatic adjustment, cryosphericdeformation and assessing impacts of loading onreference frame realizations.
x To have sessions at international meetings andworkshops (EGU, AGU, IAG, Hotine-Marussi
Symposium, etc.) as needed.

Objectives
x Development/improvement of forward modelling:o Natural phenomena: earthquake, volcano, plate motion, surface fluids, glacial isostatic adjustment(GIA), tides and Earth rotation, etc.
o Properties of the Earth structure to be modelled: elasticity, viscoelasticity, plasticity, poroelasticity,
electromagnetic, thermal and chemical properties,
heterogeneities and anisotropies in the Earth structure, etc.
o Modelling approaches: analytical, semi-analyticaland fully numerical methods and associated approximation methods, etc.
o Comparison between different theories.
o Opening developed software (if possible).
x Development or improvement of inversion andsimulation methods:

Membership
Shin-Chan Han (Australia)
Taco Broerse (Netherlands)
José Fernández (Spain)
Guangyu Fu (China)
Hom Nath Gharti (USA)
Pablo J. González (Spain)
Cheinway Hwang (Taiwan)
Volker Klemann (Germany)Zdeněk Martinec (Ireland)Daniel Melini (Italy)
Anthony Mémin (France)
Craig Miller (New Zealand)
Jun’ichi Okuno (Japan)
Riccardo Riva (Netherlands)
Jeanne Sauber (USA)
Giorgio Spada (Italy)
Yoshiyuki Tanaka (Japan), chairPeter Vajda (Slovak Republic)
Wouter van der Wal (Netherlands)

Inter-Commission Committee on Theory (ICCT)JSG T.31: Multi-GNSS theory and algorithms

171

Chair: A. Khodabandeh (Australia)
Affiliation: Commissions 1 and 4, GGOS

conducted on both individual and collaborative bases. The
output of the group study is to provide the geodesy and
GNSS communities with well-documented models and algorithmic methods through the journals and conference proceedings.

Introduction

Membership

The family of modernized and recently-developed global
and regional navigation satellite systems is being further extended by plentiful Low Earth Orbit (LEO) navigation satellites that are almost 20 times closer to Earth as comparedto current GNSS satellites. This namely means that navigation sensory data with much stronger signal power will beabundantly available, being in particular attractive in
GNSS-challenged environments. Next to the developmentof new navigation signal transmitters, a rapid growth in thenumber of mass-market GNSS and software-defined receivers would at the same time demand efficient ways of dataprocessing in terms of computational power and capacity.
Such a proliferation of multi-system and multi-frequency measurements, that are transmitted and received bymixed-type sensing modes, raises the need for a thoroughresearch into the future of next-generation navigation satellite systems, thereby appealing rigorous theoretical frameworks, models and algorithms that enable such GNSS-LEO
integration to serve as a high-accuracy and high-integrity
tool for Earth-, atmospheric- and space-sciences.

Amir Khodabandeh (Australia), chair
Ali Reza Amiri-Simkooei (Iran)
Gabriele Giorgi (Germany)
Bofeng Li (China)
Robert Odolinski (New Zealand)
Jacek Paziewski (Poland)
Dimitrios Psychas (The Netherlands)
Jean-Marie Sleewagen (Belgium)
Peter J.G. Teunissen (Australia)
Baocheng Zhang (China)

Objectives
The main objectives of this JSG are to:x Identify and investigate challenges that are posed by the
integration of multi-GNSS and LEO observations.
x Develop and study proper theory for GNSS integrity andquality control.
x Conduct an in-depth analysis of the mass-market GNSS
sensory data such as those of smart-phones.
x Improve computational efficiency of GNSS parameter
estimation and testing in the presence of a huge numberof GNSS sensing nodes.
x Investigate the problem of high-dimensional integer ambiguity resolution and validation in a multi-system,
multi-frequency landscape.
x Articulate theoretical developments and findings
through the journals and conference proceedings.
Program of Activities
While the investigation will strongly be based on the theoretical aspects of the GNSS-LEO observation modelling andchallenges, they will be also accompanied by numericalstudies of both the simulated and real-world data. Given theexpertise of each member, the underlying studies will be

JSG T.32: High-rate GNSS for geoscienceand mobility
Chair: M. Crespi (Italy)
Affiliation: Commissions 1, 3 and 4, GGOS
Introduction
Global Navigation Satellite Systems (GNSS) have become
for a long time an indispensable tool to get accurate and reliable information about positioning and timing; in addition,
GNSS are able to provide information related to physicalproperties of media passed through by GNSS signals. Therefore, GNSS play a central role both in geodesy and geomatics and in several branches of geophysics, representing acornerstone for the observation and monitoring of ourplanet.
So, it is not surprising that, from the very beginning of
the GNSS era, the goal was pursued to widen as much as
possible the range in space (from local to global) and time(from short to long term) of the observed phenomena, in order to cover the largest possible field of applications, bothin science and in engineering. Two additional primary goals
were, obviously, to get this information with the highest accuracy and in the shortest time.
The advances in technology and the deployment of new
constellations, after GPS (in the next few years the European Galileo, the Chinese Beidou and the Japanese QZSS
will be completed) remarkably contributed to transform thisthree-goals dream in reality, but still remain significant
challenges when very fast phenomena have to be observed,
mainly if real-time results are looked for.

172

Actually, for almost 15 years, starting from the noble
birth in seismology, and the very first experiences in structural monitoring, high-rate GNSS has demonstrated its usefulness and power in providing precise positioning information in fast time-varying environments. At the beginning,high-rate observations were mostly limited at 1 Hz, but thetechnology development provided GNSS equipment (insome cases even at low-cost) able to collect measurements
at much higher rates, up to 100 Hz, therefore opening new
possibilities, and meanwhile new challenges and problems.
So, it is necessary to think about how to optimally process this potential huge heap of data, in order to supply information of high value for a large (and increasing) variety
of applications, some of them listed hereafter without theclaim to be exhaustive: better understanding of the geophysical/geodynamical processes mechanics; monitoring ofground shaking and displacement during earthquakes, also
for contribution to tsunami early warning; tracking the fastvariations of the ionosphere; real-time controlling landslides
and the safety of structures; providing detailed trajectories
and kinematic parameters (not only position, but also velocity and acceleration) of high dynamic platforms such as airborne sensors, high-speed terrestrial vehicles and even athlete and sport vehicles monitoring.
Further, due to the contemporary technological development of other sensors (hereafter referred as ancillary sensors) related to positioning and kinematics able to collecthigh-rate data (among which MEMS accelerometers and gyros play a central role, also for their low-cost), the feasibilityof a unique device for high-rate observations embedding
GNSS receiver and MEMS sensors is real, and it opens,again, new opportunities and problems, first of all related tosensors integration.
In this respect, Android based mass-market devices(smartphones and tablets) are nowadays able to provide 1
Hz raw GNSS measurements (with a growing number ofmodels able to provide multi-constellation and multi-frequency code and phase observations) in addition to theabove-mentioned ancillary sensors measurements.
All in all, it is clear that high-rate GNSS (and ancillary
sensors) observations represent a great resource for future
investigations in Earth sciences and applications in engineering, meanwhile stimulating a due attention from themethodological point of view in order to exploit their fullpotential and extract the best information. This is the why
it is worth to open a focus on high-rate (and, if possible, realtime) GNSS within ICCT.
Objectives
x To realize the inventories of:

The Geodesist’s Handbook 2020o the available and applied methodologies for highrate GNSS, in order to highlight their pros and cons
and the open problemso the present and wished applications of high-rate
GNSS for science and engineering, with a special
concern to the estimated quantities (geodetic,
kinematic, physical), in order to focus on related
problems (still open and possibly new) and draw future challenges
o the technology (hw, both for GNSS and ancillary
sensors, and sw, possibly FOSS), pointing out what
is ready and what is coming, with a special concern
for the supplied observations and for their functionaland stochastic modeling with the by-product of establishing a standardized terminology.
x To address known (mostly cross-linked) problems
related to high-rate GNSS as (not an exhaustive list):
revision and refinement of functional and stochastic
models; evaluation and impact of observations timecorrelation; impact of multipath and constellation
change; outlier detection and removal; issues about
GNSS constellations interoperability; ancillary sensors
evaluation, cross-calibration and integration.
x To address new problems and future challenges whicharise from inventories.
x To investigate about the interaction with present realtime global (IGS-RT, EUREF-IP, etc.) andregional/local positioning services: how can these
services support high-rate GNSS observations and, on
reverse, how can they benefit of high-rate GNSS
observations
Program of Activities
x To launch a questionnaire for the above mentioned
inventory of methodologies, applications andtechnologies.
x To open a web page with information concerning highrate GNSS and its wide applications in science andengineering, with special emphasis on exchange ofideas, raw relevant datasets, provision and updating
bibliographic list of references of research results andrelevant publications from different disciplines.
x To launch the proposal for two (one science and theother engineering oriented) state-of-the-art review
papers in high-rate GNSS co-authored by JSG members.
x To promote sessions and presentation of research results
at international symposia both related to Earth science(IAG/IUGG, EGU, AGU, EUREF, IGS), engineering(workshops and congresses in structural, geotechnical,
mechanical, transport and automotive engineering), andlife sciences (sports and health care).

Inter-Commission Committee on Theory (ICCT)Membership
Mattia Crespi (Italy), chair
Elisa Benedetti (United Kingdom)Mara Branzanti (Switzerland)
Liang Chen (China)
Gabriele Colosimo (Switzerland)
Elisabetta D’Anastasio (New Zealand)
Roberto Devoti (Italy)
Rui Fernandes (Portugal)
Marco Fortunato (Italy)
Athanassios Ganas (Greece)
Pan Li (Germany)
Alain Geiger (Switzerland)
Jianghui Geng (China)
Dara Goldberg (USA)
Kathleen Hodgkinson (USA)
Shuanggen Jin (China)
Iwona Kudlacik (Poland)
Jan Kaplon (Poland)
Augusto Mazzoni (Italy)
Joao Francisco Galera Monico (Brazil)
Héctor Mora Páez (Colombia)
Michela Ravanelli (Italy)
Giorgio Savastano (Luxembourg)
Sebastian Riquelme (Chile)
Peiliang Xu (Japan)

JSG T.33: Time series in geodesy andgeodynamics
Chair: W. Kosek (Poland)
Affiliation: Commissions 1, 3 and 4, GGOS
Introduction
Observations of the space geodesy techniques enable measuring Earth’s gravity variations caused by mass displacement, the change in the Earth’s shape, and the change inthe Earth’s rotation. The Earth’s rotation represented by the
Earth Orientation Parameters (EOP) should be observedwith possibly the smallest latency to provide real-time transformation between the International Terrestrial and Celestial Reference Frames (ITRF and ICRF). Observed by
GRACE missions, redistribution of mass within the fluidlayers relative to the solid Earth induces exchange of angular momentum between these layers and solid Earth, changes in the Earth’s inertia tensor.
Redistribution of masses induce temporal variations ofEarth's gravity field where 1 degree spherical harmonics
correspond to the Earth’s centre of mass variations (longterm mean of them determines the ITRF origin) and 2 de-173

gree spherical harmonics correspond to Earth rotation changes. Satellite altimetry enables observation of changes ingeometry of sea level and space geodesy techniques enable
observations of changes in geometry of the Earth's crust bymonitoring horizontal and vertical deformations of site positions. Sea surface height varies due to thermal expansionof sea water and changes in ocean water mass arising frommelting polar ice cap, mountain glacier ice, as well as due
to groundwater storage. The site positions which are determined together with satellite orbit parameters (in the case of
SLR, GNSS and DORIS) or radio source coordinates (in thecase of VLBI) and Earth orientation parameters (x, y pole
coordinates, UT1-UTC/LOD and precession-nutation corrections dX, dY) are then used to build the global ITRF
which changes due to e.g. plate tectonics, postglacial rebound, atmospheric, hydrology and ocean loading andearthquakes. In these three components of geodesy whichshould be integrated into one unique physical and mathematical model there are changes that are described by spatial
and temporal geodetic time series.
Different time series analysis methods have been applied
to analyze all elements of the Earth’s system for better understanding the mutual relationship between them. The nature of considered signals in the geodetic time series ismostly wideband, irregular and non-stationary. Thus, it isrecommended to apply spectra-temporal analyzes methods
to analyze and compare these series to explain the mutualinteraction between them in different time and different frequency bands. The main problems to deal with is to estimate
the deterministic (including trend and periodic variations)and stochastic (non-periodic variations and random changes
described by different noise characters) components in thesegeodetic time series as well as to apply the appropriate methods of spectra-temporal comparison of these series.
The multiple methods of time series analysis may be encouraged to be applied to the preprocessing of raw data fromvarious geodetic measurements in order to promote the quality level of enhancement of signals existing in these data.
The topic on the improvement of the edge effects in timeseries analysis should be also considered, since they may affect the reliability of long-range tendency (trends) estimatedfrom data series as well as the real-time data processing andprediction. For coping with small geodetic samples one canapply simulation-based methods and if the data are sparse,
Monte-Carlo simulation or bootstrap technique may be
useful.
Measurements by space geodetic techniques provide animportant contribution to the understanding of climatechange. The analysis of Earth rotation and geophysical timeseries as well as global sea level variations shows that there
is a mutual relationship between them for oscillations with

174

periods from a few days to decades. The thermal annual cycle caused by the Earth's orbital motion modified by variable
solar activity induces seasonal variations the Earth’s fluidlayers, thus in the Earth rotation, sea level variations as wellas in the changes of the Earth's gravity field and centre ofmass. The interrelationships between the geodetic time series and changes of global troposphere temperature showthat they provide very important information about the
Earth's climate change (for example global sea level increases faster during El Nino events associated with the increaseof global temperature and in this time the increase of lengthof day can be also noticed). Thus, the spectra-temporal analysis and comparison of geodetic time series should also include time series associated with solar activity.
Objectives
x Study of the nature of geodetic time series to choose
optimum time series analysis methods for filtering,
spectral analysis, time frequency analysis andprediction.
x Study of Earth's geometry, rotation and gravity field
variations and their geophysical causes in different
frequency bands.
x Evaluation of appropriate covariance matrices for thetime series by applying the law of error propagation tothe original measurements, including weighting
schemes, regularization, etc.
x Determination of the statistical significance levels of theresults obtained by different time series analysis
methods and algorithms applied to geodetic time series.
x Comparison of different time series analysis methods inorder to point out their advantages and disadvantages.
x Application and development of time frequency analysis
methods to detect the relationship between geodetic timeseries and time series associated with the solar activity
in order to solve the problems related to the climatechange.
x Recommendations of different time series analysis
methods for solving problems concerning specificgeodetic time series.
x Detection of reliable station velocities and theiruncertainties with taking into account their non-linear
motion and environmental loadings and identification ofsite clusters with similar velocities
x Deterministic and stochastic modelling and prediction of
troposphere and ionosphere parameters for real time
precise GNSS positioning.
x Better Earth Orientation Parameters short-term
prediction using the extrapolation models of the fluid
excitation functions.

The Geodesist’s Handbook 2020

Program of Activities
x Organization of a session on time series analysis in
geodesy at the Hotine-Marussi Symposium in 2022.
x Co-organization of the PICO sessions "Mathematicalmethods for the analysis of potential field data andgeodetic time series" at the European Geosciences
Union General Assemblies in Vienna, Austria.
Membership
Wieslaw Kosek (Poland), chair
Orhan Akyilmaz (Turkey)
Johannes Boehm (Austria)
Xavier Collilieux (France)
Olivier de Viron (France)
Laura Fernandez (Argentina)
Richard Gross (USA)
Mahmut O. Karslioglu (Turkey)
Anna Kłos (Poland)
Hans Neuner (Germany)
Tomasz Niedzielski (Poland)
Sergei Petrov (Russia)
Waldemar Popiński (Poland)
Michael Schmidt (Germany)
Michel Van Camp (Belgium)
Jan Vondrák (Czech Republic)
Dawei Zheng (China)
Yonghong Zhou (China)

JSG T.34: High-resolution harmonic series of gravitational and topographic potential fields
Chair: S. Claessens (Australia)
Affiliation: Commission 2 and GGOS
Introduction
The resolution of models of the gravitational and topographic potential fields of the Earth and other celestial bodies in the Solar System has increased steadily over the lastfew decades. These models are most commonly represented
as a spherical, spheroidal or ellipsoidal harmonic series.
Harmonic series are used in many other areas of sciencesuch as geomagnetism, particle physics, planetary geophysics, biochemistry and computer graphics, but geodesists areat the forefront of research into high-resolution harmonic series.
In recent years, there has been increased interest and activity in high-resolution harmonic modelling (to sphericalharmonic degree and order (d/o) 2190 and beyond). In 2019,

Inter-Commission Committee on Theory (ICCT)the first model of the Earth’s gravitational potential in excess of d/o 2190 was listed by the International Centre for
Global Earth Models (ICGEM). All high-resolution models
of gravitational potential fields rely on forward modellingof topography to augment other sources of information. Harmonic models of solely the topographic potential are also
becoming more common. Models of the Earth’s topographic
potential up to spherical harmonic d/o 21,600 have been developed, and ICGEM has listed topographic gravity fieldmodels since 2014.
The development of high-resolution harmonic models
has posed and continues to pose both theoretical and practical challenges for the geodetic community.
One challenge is the combination of methods for ultrahigh d/o harmonic analysis (the forward harmonic transform). Least-squares-type solutions with full normal equations are popular, but computationally prohibitive at ultrahigh d/o. Alternatives are the use of block-diagonal techniques or numerical quadrature techniques. Optimal combination and comparison of the different techniques, including studying the influence of aliasing, requires further
study.
A related issue is the development of methods for the
optimal combination of data sources in the computation ofhigh-degree harmonic models of the gravitational potential.
Methods used for low-degree models cannot always suitably
be applied at higher resolution.
Another challenge is dealing with ellipsoidal instead ofspherical geometry. Much theory has been developed andapplied in terms of spherical harmonics, but the limitationsof the spherical harmonic series for use on or near the
Earth’s surface have become apparent as the maximum d/oof the harmonic series has increased. The application of
spheroidal or ellipsoidal harmonic series has become morewidespread, but needs further theoretical development.
A specific example is spectral forward modelling of the
topographic potential field in the ellipsoidal domain. Various methods have been proposed, but these are yet to becompared from both a theoretical and numerical standpoint.
There are also still open questions about the divergence effect and the amplification of the omission error in sphericaland spheroidal harmonic series inside the Brillouin surface.
A final challenge are numerical instabilities, underflow/overflow and computational efficiency problems in theforward and reverse harmonic transforms. Much progresshas been made on this issue in recent years, but further improvements may still be achieved.
Objectives
The objectives of this JSG are to:x Develop and compare combined full least-squares,
block-diagonal least-squares and quadrature approaches

175

to very high-degree and order spherical, spheroidal andellipsoidal harmonic analysis.
x Develop and compare methods to compute highresolution harmonic potential models using ellipsoidal
geometry, either in terms of spherical, spheroidal or
ellipsoidal harmonic series.
x Study the divergence effect of ultra-high degree
spherical, spheroidal and ellipsoidal harmonic series
inside the Brillouin sphere, spheroid and/or ellipsoid.
x Study efficient methods for ultra-high degree and orderharmonic analysis (the forward harmonic transform) fora variety of data types and boundary surfaces, as well as
harmonic synthesis (the reverse harmonic transform) ofvarious quantities.
Program of Activities
To facilitate achievement of these objectives, the group will
provide a platform for increased collaboration between
group members, encouraging exchange of ideas and research results. Working meetings of group members will beorganized at major international conferences.
Membership
Sten Claessens (Australia), chair
Hussein Abd-Elmotaal (Egypt)Blažej Bucha (Slovakia)
Christoph Förste (Germany)
Toshio Fukushima (Japan)
Ropesh Goyal (India)
Christian Hirt (Germany)
Norbert Kühtreiber (Austria)
Kurt Seitz (Germany)
Elmas Sinem Ince (Germany)
Michal Šprlák (Czech Republic)
Philipp Zingerle (Germany)

JSG T.35: Advanced numerical methods
in physical geodesy
Chair: R. Čunderlík (Slovakia)
Affiliation: Commission 2 and GGOS
Introduction
Advanced numerical methods and high performance computing (HPC) facilities provide new opportunities in many
applications in geodesy. The goal of this JSG is to apply
such numerical methods to solve various problems of physical geodesy, mainly gravity field modelling, processing satellite observations, nonlinear data filtering or others. It fo-

176

cuses on a further development of approaches based on discretization numerical methods like the finite element
method (FEM), finite volume method (FVM) and boundary
element method (BEM) or the meshless collocation techniques like the method of fundamental solutions (MFS) or
singular boundary method (SOR). Such approaches allow
gravity field modelling in spatial domain while solving thegeodetic boundary-value problems (GBVPs) directly on thediscretized Earth’s surface. Their parallel implementations
and large-scale parallel computations on clusters with distributed memory allow high-resolution numerical modelling.
The JSG is also open to new innovative approaches
based for example on the computational fluid dynamics(CFD) techniques, spectral FEM, advection-diffusion equations, or similar approaches of scientific computing. It isalso open for researchers dealing with classical approachesof gravity field modelling like the spherical or ellipsoidal
harmonics that are using HPC facilities to speed up theirprocessing of enormous amount of input data. This includes
large-scale parallel computations on massively parallel architectures as well as heterogeneous parallel computations
using graphics processing units (GPUs).
Objectives
The objectives of this JSG are to:x Design the FEM, BEM and FVM numerical models forsolving GBVPs with the oblique derivative boundary
conditions.
x Develop algorithms for a discretization of the Earth’s
surface based on adaptive refinement procedures (theBEM approach).
x Develop algorithms for an optimal construction of 3D
unstructured meshes above the Earth’s topography (theFVM or FEM approaches).
x Design numerical models based on MFS or SBM forprocessing the GOCE gravity gradients in spatial domain.
x Design algorithms for 1D along track filtering of satellitedata, e.g., from the GOCE satellite mission.
x Develop numerical methods for nonlinear diffusion filtering of data on the Earth’s surface based on solutionsof the nonlinear heat equations.
x Investigate innovative approaches based on the computational fluid dynamics (CFD) techniques, spectral FEM
or advection-diffusion equations.
x Apply parallel algorithms using MPI procedures.
x Apply large-scale parallel computations on clusters with
distributed memory.

The Geodesist’s Handbook 2020

Program of Activities
x Active participation in major geodetic conferences.
x Working meetings at international symposia.
x Organization of a conference session.
Membership
Róbert Čunderlík (Slovakia), chair
Petr Holota (Czech Republic)
Michal Kollár (Slovakia)
Marek Macák (Slovakia)
Matej Medľa (Austria)
Karol Mikula (Slovakia)
Zuzana Minarechová (Slovakia)
Otakar Nesvadba (Czech Republic)
Yoshiyuki Tanaka (Japan)
Robert Tenzer (Hong Kong)
Zhi Yin (Germany)

JSG T.36: Dense troposphereionosphere sounding

andChair: G. Savastano (Luxembourg)
Affiliation: Commission 4 and GGOS
Introduction
Global Navigation Satellite Systems Radio Occultation(GNSS-RO) have become an important technique to globally sound the Earth’s atmosphere from space. This technique overcomes some of the main limitations of groundbased remote sensing instruments, increasing the amount of
tropospheric and ionospheric data measured over the oceans
and under sampled regions.
Up until few years ago, GNSS-RO observations weremainly supported by expensive satellite missions (e.g. COSMIC-1), which implies also considerably high operationalcosts. A great opportunity was brought in the field bynanosatellites, which are a satellite of low mass and size,
usually under 500 kg. These satellites can significantly reduce the large economic cost of launch vehicles and thecosts associated with construction.
In recent years, commercial RO providers (e.g., Spire
Global) shifted the paradigm and started operationally producing GNSS-RO data from CubeSats in Low Earth Orbit(LEO). This data was demonstrated to be comparable inquality to larger satellite constellations (e.g., COSMIC-1),
but with a denser spatial and temporal coverage. The newparadigm proposed by these commercial companies is thatnanosatellites, especially in large numbers, may be more
beneficial than using fewer, larger satellites in tasks such as
gathering scientific data.

Inter-Commission Committee on Theory (ICCT)

Independent assessments of these commercial data quality were carried out by JPL, UKMO, ESA, NOAA, andNRL, which convinced the international RO communitythat commercial data are ready to be assimilated by NWP
centres and used by scientists to investigate different research topics.
Often, these nanosatellites carry different scientific payloads collecting a large amount of different data (e.g.,
GNSS-POD solutions, GNSS top ionosphere TEC observations), that could be exploited for several scientific investigations. Furthermore, contemporary technological advancesof other low-cost sensors (e.g., in-situ atmospheric sensors,
MEMS accelerometers and gyros) opens new opportunityand problems, first of all related to data fusion, validationand sensor integration.
Spire will share data samples (e.g., podGps, atmPhs,
podTec, atmPrf) within the members of the study group, inorder to promote the development of new algorithms andmethodologies for remote sensing of the Earth.
It is clear that this unprecedented dense coverage of troposphere and ionosphere sounding enabled by commercial
GNSS-RO CubeSats and dense network of ground-based
GNSS receivers represents a great opportunity for future investigations in Earth sciences. This brings the attention to
the methodological point of view in order to exploit theirfull potential and extract the best information. This is thereason why it is worth opening a focus on dense troposphereand ionosphere sounding using GNSS-RO and groundbased GNSS techniques within ICCT.
Objectives
x To realize inventories of:o commercial and publicly available GNSS-RO andground-based GNSS observations, with a distinction
between troposphere and ionosphere observations,and a classification based on the different acquisition
parameters (e.g., sampling rate, vertical or temporal
resolution, altitude range of acquisition, trackingmode),o present and wished applications of dense troposphereand ionosphere sounding for science and engineering, with a special concern to the estimated physicalquantities (e.g., temperature, pressure and TEC), in
order to focus on related problems (still open andpossibly new) and draw future challenges.
x To address known problems related to dense troposphereand ionosphere sounding using GNSS-RO observations
as (not an exhaustive list): atmospheric anomalies detection, localization and classification; revision and refinement of inversion techniques; temporal variability of receivers DCBs and evaluation of their impact in the calibrated process; data quality assessment and validation;

177

outlier detection and removal; in-situ sensors evaluation,
cross-calibration and integration.
x To describe the different analytical and physical implication of combining observations collected with different observational geometries, such as: ground-based receivers tracking signals transmitted by GNSS satellites
in MEO and GEO orbits; space-based receivers tracking
GNSS signals at different elevation angles (from positive to negative and vice versa). Furthermore, investigate
the different ways of combining together these remotesensing observations to retrieve fundamental atmospheric parameters, and disentangle the spatial and temporal variability of the atmosphere.
Program of Activities
x To organize a session at the forthcoming Hotine-Marussi
symposium 2022.
x To convene at international conferences such as
IAG/IUGG, EGU, AGU.
Membership
Giorgio Savastano (Luxembourg), chair
Matthew Angling (UK)Elvira Astafyeva (France)
Riccardo Biondi (Italy)
Mattia Crespi (Italy)
Kosuke Heki (Japan)
Addisu Hunegnaw (Luxembourg)
Alessandra Mascitelli (Italy)
Giovanni Occhipinti (France)
Michela Ravanelli (Italy)
Eugenio Realini (Italy)
Lucie Rolland (France)
Felix Norman Teferle (Luxembourg)
Jens Wickert (Germany)

JSG T.37: Theory and methods related to
combination of high-resolution topographic/ bathymetric models in geodesy
Chair: D. Carrion (Italy)
Affiliation: Commission 2 and GGOS
Introduction
Topographic and bathymetric models constitute a fundamental input for geodetic computations, e.g. for the evaluation of terrain effects for local and global geoid estimation.
In this regard, the Shuttle Radar Topography Mission(SRTM) provided a very significant contribution to theknowledge of terrain heights over land. Great advantages

178

provided by SRTM are the homogeneity of its spatial resolution and its (almost) global coverage. In addition, the spatial resolution of SRTM is adequate for the majority of geodetic applications.
The situation is quite different concerning currently
available bathymetric models: in this case, the resolution is
not homogeneous around the Earth and the level of accuracy
can vary considerably from one area to another. In addition,
when considering the transition between land surface andsea bottom, the combination of topographic and bathymetricmodels can be challenging, due to the limitations linked toresolution and accuracy of data and to local datum inconsistencies, which could be neglected in global models.
Different combined products are available at global
level, such as SRTM+, however the poor knowledge of thesea bottom or datum issues, may lead to problems in geodetic computations and should be further investigated. Apartfrom geodetic applications, the precise knowledge of theland-sea transition is crucial for modelling of other environmental processes in the coastal zone, such as the impact ofsea level change and extreme sea level events such as storm
surges and tsunamis.
This JSG aims at studying the available topographic andbathymetric models and at exploring their limitations, inparticular concerning the transition along the coasts.
Objectives
x Highlight the issues of the topography/sea bottom transition through literature examples.

The Geodesist’s Handbook 2020

x Analyse available data on global and local topographic
and bathymetric models, highlighting the issues, based
also on personal research experience.
x Verify the quality of the transition through test cases.
x Suggest best practices for combination of models.
x Identify the need for data acquisition in specific areas.
Program of Activities
x Explore available data and literature research.
x Propose review papers concerning the state of the art
knowledge on the combination of topographic and bathymetric models.
x Cooperate with IAG Commissions and other JSGs.
x Organize meetings, workshops and sessions at selected
conferences, e.g. during Hotine-Marussi 2022.
Membership
Daniela Carrion (Italy), chair
Riccardo Barzaghi (Italy)
Mattia Crespi (Italy)
Vassilios Grigoriadis (Greece)
Karsten Jacobsen (Germany)
Kevin Kelly (US)Michael Kuhn (Australia)
Cornelis Slobbe (Netherlands)
Roberto Teixeira Luz (Brazil)
Ana Cristina de Matos (Brazil)
Dan Palcu (Brazil)
Ionut Sandric (Romania)
Georgios S. Vergos (Greece)

Inter-Commission Committee on Geodesy for Climate Research

179

Inter-Commission Committee on Geodesy for Climate Research(ICCC)
President: Annette Eicker (Germany)
Vice-President: Carmen Boening (USA)Internet site: https://iccc.iag-aig.org/
Twitter: @IAG_climate

Terms of Reference
The Inter-Commission Committee on Geodesy for Climate
Research (ICCC) was formally approved and establishedduring the 27th IUGG General Assembly in Montreal 2019to advance the use of geodetic observations for climate research.
The growing data record from numerous geodetic observation techniques (GNSS station observations, satellite radio occultation and reflectometry, satellite gravimetry, satellite altimetry, InSAR, VLBI, GNSS-controlled tidegauges, etc.) provides a new quantitative view on various
variables that are relevant for climate research, such as tropospheric water vapor, thermospheric neutral density, terrestrial water storage, ice sheet and mountain glacier mass , steric and barystatic sea level, sea surface winds, ocean waves,subsurface and surface currents, or sea ice extent and -thickness. Many of these are listed as Essential Climate Variables(ECV) according to the definition by the Global Climate
Observing System (GCOS).
Geodetic methods provide unique information on the
Earth's surface geometry, its large-scale mass transports
such as fluctuations in Earth’s water cycle, and the global
energy imbalance. Time series of geodetic data start to reveal a complex picture of natural climate variability, longterm climate change and anthropogenic modifications.
Combined with other observations by means of, e.g., global
or regional Earth system simulations or reanalyses, they provide excellent tools to improve our understanding of climate-related processes. Furthermore, due to their advantage
of being independent of other data commonly used to driveand evaluate coupled climate models, geodetic observations
have strong potential for either being used as input for numerical models as constraints (e.g. water budget, sea levelbudget) or for a posteriori model assessment.

While it is generally recognized that geodetic data provide invaluable information for studying the planet’s changing climate, programmatic obstacles, technical limitations
such as the length of time series, and scientifically open
questions have been identified that hamper the broader
recognition of geodesy as an important source of information for climate research. In order to better promote andfacilitate the use of genuinely geodetic data in the climate
community, and to better explore the synergies between the
different geodetic branches with respect to observing climate signals, we propose to establish an Inter-Commission
Committee on “Geodesy for Climate Research”. It will bebased on the work started in the 2015-2019 IAG period’s
Joint Working groups 2.6.1 “Geodetic Observations for Climate Model Evaluation” and 4.3.8 “GNSS Tropospheric
Products for Climate”. It will continue the roadmap initiatedat the workshop “Satellite Geodesy for Climate Studies”(Bonn 2017), which brought together geodesists representing all different observation techniques and climate scientists in a dedicated framework.
The topic of the suggested ICC is positioned at the interface between geodesy and climate science and is of high relevance for the entire scientific discipline geodesy. Various
geodetic observables provide complementary information
on climate change processes. Examples include (but are notlimited to) the following: climate change related masstransport (e.g. ice melting, sea level rise, changes in the continental and oceanic water cycle as well as their impact onwater resources) are among the primary signals derived
from (satellite) gravity observations and can also be detected directly by geometrical measurements of volume
change (satellite altimetry for water bodies/ice, InSAR overaquifers) or indirectly via crustal deformations induced bysurface loads (terrestrial GNSS, InSAR, VLBI). Further-180

more, by changing the Earth’s moments of inertia and relative momentum term, mass transports also lead to measurable variations in Earth orientation parameters.
Climate change related variations of the atmosphere affect the propagation of geodetic signals and thus can be inferred from long time series of VLBI and ground and satellite based GNSS observations. Finally, a stable global geodetic reference frame (GGRF) is an indispensable requirement for providing a uniform reference for monitoring
global change processes, as has recently been recognized by
the corresponding UN resolution1. However, synergies between the different geodetic observing systems for monitoring climate change have not yet been fully exploited and theinteraction with the climate communities needs to be intensified in order to achieve a broader – and better recognized– use of geodetic data for climate research.
Objectives
x To deepen the understanding of the potential (and limitations) of geodetic measurements for the observation,
analysis and identification of climate signals
x To advance the development of geodetic observing systems, analysis techniques and data products regarding
their sensitivity to and impact on Essential Climate Variables, this way also supporting activities of the IPCC
x To advance the improvement of numerical climate models, climate monitoring systems, and climate reanalysis
efforts through incorporating geodetic observations
x To stimulate scientific exchange and collaboration between the geodetic and the climate science communities
x To make geodetic variables more user-friendly by sharing them publicly and explaining their usefulness
Program of Activities (tentative):x The ICC will establish a workshop series to intensify theexchange between different geodetic communities andthe climate monitoring and modeling communities.
x The ICC will create opportunities for communicationand discussion through suggesting/organizing sessions
at international scientific meetings and conferences.
x The ICC will develop reference (best-practice) methods
for evaluating/improving climate models with geodetic
data and publish these methods (e.g. in a ‘white paper’).
x The ICC will seek to organize special issues on its topic
in appropriate international journals.
x The ICC will work towards a better recognition of geodesy as an essential provider of precise information about
long-term changes in the Earth system.

The Geodesist’s Handbook 2020

x The ICC will establish links to other climate science related bodies, e.g. the IUGG Union Commission on Climatic and Environmental Change (CCEC) or the
IAMAS International Commission on Climate (ICCL).
x The ICC will maintain a website for dissemination of
ICC related information
List of Joint Working Groups:
JWG C.1: Climate Signatures in Earth Orientation Parameters
Chair: Jolanta Nastula (Poland)
Vice-Chair: Henryk Dobslaw (Germany)(Affiliation: Commission 3, GGOS, IERS)JWG C.2: Quality control methods for climate applicationsof geodetic tropospheric parameters
Chair: Rosa Pacione (Italy)
Vice-Chair: Marcelo Santos (Canada)(Affiliation: Commission 4, IGS, IVS)JWG C.3: Geodesy for the Cryosphere: advancing the useof geodetic data in polar climate modelling
Chair: Bert Wouters (Netherlands)
Vice-Chair: Ingo Sasgen (Germany)(Affiliation: Commission 2, Commission 3,
GGOS)
JWG C.4: Sea level and vertical land motion
Chair: Roelof Rietbroek (Germany)
Vice-Chair: Riccardo Riva (Netherlands)(Affiliation: Commission 1, 2 & 4, GGOS)JWG C.5: Understanding the monsoon phenomenon from ageodetic perspective
Chair: Balaji Devaraju (India)
Vice-Chair: Matthias Weigelt (Germany)(Affiliation: Commissions 2, 3 & 4, GGOS)JWG C.6: Numerical Simulations for Recovering ClimateRelated Mass Transport Signals
Chair: Roland Pail (Germany)
Vice-Chair: Wei Feng (China)(Affiliation: Commission 2, GGOS, IGFS)JWG C.7: Satellite geodetic data assimilation for climate research
Chair: Mehdi Khaki (Australia)(Affiliation: Commission 2, GGOS)JWG C.8: Methodology of comparing/validating climate
simulations with geodetic data
Chair: Jürgen Kusche (Germany)(Affiliation: Commisison 2, ICCT)
Steering Committee:
President: Annette Eicker (Germany)
Vice-President: Carmen Boening (USA)
Representative of Comm.1: Christopher Kotsakis (Greece)

Inter-Commission Committee on Geodesy for Climate Research

Representative of Comm.2: Wei Feng (China)
Representative of Comm.3: M. Schindelegger (Germany)
Representative of Comm.4: Anna Klos (Poland)
Representative of GGOS: Mayra Oyola (USA)
Representative of IAMAS: Vincent Humphrey (USA)Member at Large: Felipe Nievinski (Brazil)

Joint Working Groups
Joint Working Group JWG C.1: Climate
Signatures in Earth Orientation Parameters
Affiliation: Commission 3, GGOS, IERS
Chair: Jolanta Nastula (Poland)
Vice-Chair: Henryk Dobslaw (Germany)
Introduction
Earth orientation parameters comprising variations of boththe position of the rotational pole and the spin rate are precisely observed by modern space geodetic techniques forseveral decades already. Moreover, optical astrometric observations extending back in time over more than 100 years
provide even carry information about the mass transport andmass distribution processes acting on Earth at historicaltimes that might be explored to quantify slow and subtle variations in the Earth's climate. This working group will study
the various contributors of the global and interactively coupled climate system to the observed changes of the Earth's
orientation on time-scales from days to centennials. It will
explore possibilities to validate numerical climate models
and its individual components by means of assessing the angular momentum budget and the associated torques. The
working group will further investigate predictive limits ofvarious Earth system state and flux variables in order to aid
short- and long-term prediction of polar motion and changes
in the length-of-day, and might ultimately foster the incorporation of Earth Orientation Parameters into contemporaneous global re-analyses of the Earth System by means ofdata assimilation.
Objectives
x Detection of climatic signals in Earth's rotation fromdays to centennials
x Modelling of climatic trends on the Earth rotation fromdays to centennials
x Assessment of angular momentum budgets of global numerical climate and Earth system models
x Fusion of Earth rotation parameters and global geophysical fluid models by means of data assimilation

181

Activities
x Establishment of the "best practices" for deriving angular momentum and torque estimates from numerical climate model datax Contributions to the future development of the Global
Geophysical Fluid Centre (GGFC) of the International
Earth Rotation and Reference Systems Service (IERS)
x Active participation at major geodetic conferences via
both session proposals and contributing abstracts
x Annual working group meetings aligned to a major geodetic conference
Members
Christian Bizouard (France)
Sigrid Boehm (Austria)
Aleksander Brzezinski (Poland)
Benjamin Fong Chao (Taiwan)
Yavor Chapanov (Bulgaria)
Jianli Chen (USA)Alexandre Couhert (France)
Robert Dill (Germany)
Alberto Escapa (Spain)
José Manuel Ferrandiz (Spain)
Laura Fernandez (Argentina)
Franziska Goettl (Germany)
Richard Gross (USA)Robert Heinkelmann (Germany)
Sébastien Lambert (France)
Vladimir Pashkevich (Russia)
Elena Podladchikova (Belgium)
Cyril Ron (Czech Republic)
David Salstein (USA)Michael Schindelegger (Germany)
Nikolay Sidorenkov (Russia)
Leonid Zotov (Russia)

Joint Working Group JWG C.2: Quality
control methods for climate applicationsof geodetic tropospheric parameters
Chair: Rosa Pacione (Italy)
Vice-Chair: Marcelo Santos (Canada)
Affiliation: Commission 4, IGS, IVS
Introduction
Zenith Total Delay (ZTD) estimates are determined on aregular basis by several processing centers. For example, the
IGS Analysis Centers have all their own independent ZTD
solutions but, unlike other estimated parameters (e.g., orbits
and satellite clocks) they are not combined. The official IGS

182

ZTD product is the result of an independent and dedicatedsolution based on a precise point positioning solution. On
the other hand, EUREF performs combination of ZTD estimates on a regular basis as well as the IVS, which combines
ZTD estimates coming from VLBI sessions. Nonetheless,not all IGS and IVS analysis centers make available their
ZTD estimates. GNSS is reaching the “maturity age” of 30
years when climate normals of ZTD and gradients can bederived. But what would be the best series to serve the climate community? What series would offer the most realistic
trends? As the IGS moves towards its third reprocessing
campaign (REPRO3) where all ACs are to be make available their own ZTD and gradient estimates, as the IVS ismoving towards its ACs also providing ZTD and gradientestimates and as the PPP-derived IGS product continues tobe produced, there is a huge opportunity to perform quality
control, using the tools of combination of parameters, to assess what would be the ZTD and gradient product best suited
to be made available to climate studies.
Objectives
Potential scientific questions include:
x Are there advantages of combining ZTD estimates overnot combining them? Is there any ‘loss of information’in performing combinations?
x Would there be difference in trends derived from them?
If so, how much implication for feeding information toclimate?
x Can we trust in a combined ZTD as we trust any combined products (e.g., orbits, clock, site coordinates)?
x What the best combination strategy can be done (notnecessarily to combine exactly the same way as otherproducts)?
x Under what criteria can we use spectral analysis todemonstrate that a ‘good’ combined product have thesame properties of the contributing solutions?
x What metrics should be used to ascertain that the optimal
set of ZTD estimates, gradients and their trends, are provided to the climate community?
Activities
x Collaborate with IGS and IVS in the forthcoming reprocessing campaign.
x Participate actively in IAG, AGU and EGU conferences
and organize sessions
x Organize working group meetings, splinter group meetings at the said symposia
Members
Fadwa Alshawaf (Germany)
Kyriakos Balidakis (Germany)

The Geodesist’s Handbook 2020

Sharyl Byram (USA)Galina Dick (Germany)
Gunnar Elgered (Sweden)
Olalekan Isioye (South Africa)
Jonathan Jones (UK)Michal Kačmařík (Czech Republic)
Anna Klos (Poland)
Haroldo Marques (Brazil)
Thalia Nikolaidou (Canada)Tong Ning (Sweden)
Mayra Oyola (USA)
Eric Pottiaux (Belgium)
Paul Rebischung (France)
Roeland Van Malderen (Belgium)
Yibin Yao (China)

Joint Working Group JWG C.3: Geodesy
for the Cryosphere: advancing the use ofgeodetic data in polar climate modelling
Affiliation: GGOS, Commission 2 & 3
Chair: Bert Wouters (Netherlands)
Vice-Chair: Ingo Sasgen (Germany)
Introduction
Over the last two decades, tremendous progress has been
made in the development and use of geodetic methods toobserve the rapidly emerging changes in the cryosphere.
Variations in mass, elevation, grounded ice extent and flow
speed are now being monitored on a routine basis using geodetic techniques such as gravimetry, (In)SAR, altimetry,
GNSS and the like. Additionally, observations of land motion provide indirect information on the past evolution of ice
masses. These geodetic observations have led to a leap forward in our understanding of the cryosphere as part of theclimate system, and unambiguously have shown that the
Earth’s ice sheets and glaciers are increasingly losing massand now represent the largest land-based contribution to
global mean sea level rise.
Yet, compared to other fields of climate science (e.g. hydrology, oceanography and atmospheric sciences), inclusion of geodetic data is lagging behind in cryosphere modelling and remains mostly limited to validation of model
output at large spatial scales. Data assimilation and the combination of multiple observables are still at an early development stage and rarely used to exploit the full potential of
the geodetic measurements. To date, it remains a challenge
incorporate the geodetically observed transitions in the cryosphere into future simulations. Within this JWG, we aim tobridge the currently existing gap between the geodetic andmodelling communities, as detailed in our objectives below.

Inter-Commission Committee on Geodesy for Climate Research

Objectives
Within this JWG, we aim to:x identify current bottlenecks in using geodetic data forvalidation and assimilation efforts in ice sheet and glacier modelling
x communicate the possibilities and limitations of geodetic data to the modelling community
x document the wishes of the modelling community forgeodetic data (resolution, projection, uncertainty definitions, etc.)
x identify geodetic data relevant for the evaluation of projection ensembles
x based on the above, list a set of recommendations for thegeodetic community to advance the use geodetic data inmodelling efforts.
x Explore potential of future geodetic observables for theiruse in glaciology
Program of Activities
x Summarize and gather state-of-the-art papers on geodetic observation techniques and data on the IAG website for non-geodetic audiences
x In close collaboration with the representatives of the cryosphere modelling community or through a open survey,
identify requirements and derive concepts of geodetic
data assimilation into ice sheet and glacier modelling
x List a set of recommended processing steps and standards for the geodetic community on the IAG website orin a white paperx Schedule a yearly strategic splinter meeting to review
progress and define strategic tasks for the upcoming year
x Acknowledge and promote work of talented young scientist contributing into the aims of JWG, through ayearly award or promotion on the ICCC website
x Communicate activities through IAG’s social media accounts
Members
Mike Bevis (USA)Matthias Braun (Germany)
William Colgan (Denmark)Christoph Dahle (Germany)
Olga Engels (Germany)
Xavier Fettweis (Belgium)
Dana Floricioiu (Germany)
Heiko Goelzer (Netherlands)
Natalya Gomez (USA)Martin Horwath (Germany)
Michalea King (USA)
Kristine Larson (USA)Jan Lenaerts (USA)183

Lin Liu (Hong Kong)
Malcolm McMillan (UK)
Brice Noël (Netherlands)
Masashi Niwano (Japan)
Louise Sandberg Sørensen (Denmark)Mirko Scheinert (Germany)
Nicole Schlegel (USA)David Wiese (USA)

Joint Working Group JWG C.4: Regional
Sea level and vertical land motion
Affiliation: Commissions 1, 2 & 4, GGOS
Chair: Roelof Rietbroek (Germany)
Vice-Chair: Riccardo Riva (Netherlands)
Introduction
Global mean sea-level change is an excellent overall indicator of the state of the climate and the cryosphere, but societal
impact is better represented by regional to local sea-levelchange, which can be very different from the global mean.
Regional sea-level change may be more accurately described by dedicated time series, which incorporate
knowledge of the designated coastal zone and vertical landmotion. The non-uniform response of sea level to terrestrial
mass changes causes regions in the far field of melting glaciers and ice sheets to be more sensitive to mass loss. Furthermore, long-term changes in wind fields, ocean heat uptake and circulation can change regional sea level. Finally,
the difference between relative and geocentric sea level canbe significant in places where vertical land motion is present. This can be caused by the ongoing glacial isostatic adjustment of the solid earth, but also by local subsidence fromgroundwater extraction and sediment compaction and loading.
The construction of sea-level change records which reconcile satellite measurements (e.g. radar altimetry, satellite
gravimetry, lidar) with terrestrial measurements (GNSS stations, tide gauges and terrestrial gravimetry) on both global
and regional level remains a challenging topic. This working
group aims to increase the understanding of local/regional
geophysical signals present in geodetic measurements, withthe aim of encouraging a more widespread use of geodetic
datasets in multi-disciplinary fields.
Objectives
x Encourage the use of geodetic datasets for multi-disciplinary studies related to sea-level changes.
x Communicate the need for a consistent treatment of observations and models of sea-level change and verticalland motion to non-geodetic scientific communities.

184

x Advance the science of regional and global sea-level research by identifying open questions and gathering stateof-the-art work.
x Communicate and coordinate activities with other relevant working groups (specifically: Geodesy for the Cryosphere), in particular on the topic of vertical land motion.
Program of Activities
x Summarize and gather state-of-the-art papers on sea
level on the IAG website for non-geodetic audiences.
x Create an inventory of geodetic datasets useful for sealevel research, to be organised according to agreed
standards and made freely available. Provide and gather,under a creative commons license, free to use visuals forcommunicating aspects of (regional) sea-level change
and its (geodetic) observing system.
x Schedule a yearly strategy meeting to review the past
year and define tasks for the upcoming year.
x Organize inter-JWG communication directly related tothe study of vertical land motion, involving participantsfrom the JWG Geodesy for the Cryosphere (e.g., sharedweb-page on IAG site, mutual participation in yearlystrategy meetings).
x Communicate activities through IAG’s social media accounts.
x Report activities back to relevant IAG working groups.
Members
Adrian Borsa (USA)Francisco Calafat (UK)Don Chambers (USA)
Sönke Dangendorf (Germany)
Thomas Frederikse (USA)
Ropesh Goyal (India)
Erik Ivins (USA)Marta Marcos (Spain)
Alvaro Santamaria (France)
Aimée Slangen (Netherlands)
Karen Simon (Netherlands)
Giorgio Spada (Italy )Guy Woppelmann (France)

Joint Working Group JWG C.5: Understanding the monsoon phenomenon froma geodetic perspective
Affiliation: Commissions 2, 3 & 4, GGOS
Chair: Balaji Devaraju (India)
Vice-Chair: Matthias Weigelt (Germany)

The Geodesist’s Handbook 2020

Introduction
The monsoon phenomenon is one of the large-scale atmospheric circulation processes that drives the water cycle affecting nearly one-third of the global population. It is predominantly acting in the Inter-Tropical Convergence Zone
and it controls the agricultural productivity of the countries
that fall within this region. Researchers from multiple disciplines have tried to understand and model the monsoon. A
century of research efforts has led to a greater understandingof the monsoon phenomenon, but research gaps and open
questions remain. Improved understanding will lead to better modelling of the monsoon as well as better forecasting,which will help mitigate some of the potential hazards andrisks. Currently, meteorological forecasts on timing and duration of the monsoon, its strength, and its regional distribution are limited. Furthermore, it has been observed that ongoing climate change is linked to and alters the monsoon
phenomenon. Many studies point to a weakening of themonsoon, which would mean reduced rainfall to the regionsthat it feeds. The consequences of such weakening could be
disastrous and will threaten food and water security for theregion. Therefore, it becomes imperative to observe, monitor and understand the monsoon with every possible means.
The bulk of research on monsoon has been mainly conducted by meteorologists, oceanographers, atmospheric andclimate scientists with oceanographic, hydrological and hydrometeorological datasets and modelling. In the recent
years, geodetic sensors have been recognized as a very insightful tool for studying climate processes and their spatiotemporal changes. This has been made possible by the increased accuracy and spatial coverage of geodetic sensors,which has enabled detecting the response of the Earth's
shape and gravity field to climate-related processes. At thesame time geodetic sensors and their data have become integral to Earth system science, and represent critical monitoring tools. Of all geodetic methods satellite altimetry, satellite gravimetry and GNSS positioning have contributed
significantly towards understanding sea level change, sea
ice change, ice sheet and glacier mass balance, and the hydrological cycle, to name a few. Further, they have opened
new pathways in Earth system science including the demandfor improved ground networks for calibration. With the advent of satellite-based GNSS reflectometry, geodetic sensors are providing observations of soil moisture and windspeed at unprecedented horizontal scale and temporal resolution.
There is currently a deluge of geodetic sensor data spanning periods of 20 to 100 years, and therefore, perfectly suitable for climate change analysis. It presents a great opportunity to explore the signatures of various environmental

Inter-Commission Committee on Geodesy for Climate Researchand geophysical phenomena. The monsoon is one such phenomenon whose signatures in geodetic sensor data havelargely remained underexplored. Some attempts have been
made in the past to use geodetic sensor data in monsoon research. For example, satellite altimetry has been used to estimate the geostrophic contribution of monsoon currents.
Similarly, precipitable water vapour estimates from continuously observing GNSS stations have been used to study thevariations in monsoon precipitation. Nevertheless, the full
integration of geodetic sensors data into monsoon modelling
has not be achieved yet.
In this context we like to propose a working group to
analyse geodetic sensor data in order to identify geodetic
variables that are sensitive to the monsoon process, and thesignatures that the monsoon leaves in geodetic data. Furthermore, we would like to explore the possibilities of complementing/supplementing monsoon forecast models, andthereby, improve their efficacy. The geodetic sensors to be
used include, but are not limited to, satellite altimetry, continuously operating GNSS stations, tide gauges, gravimetricsatellites (for example, GRACE, GRACE-FO and SLR), interferometric/polarimetric SAR, and terrestrial gravimeters.
We will complement the geodetic sensors with meteorological data, remote sensing data and reanalysis products inglobal and regional climate models (such as PRECIP, BCCCSM1.1, ECMWF-SYS4, NCEP-CFS2) to achieve our objectives.
Objectives
x Identify geodetic sensors, and in turn their observables,that are most sensitive to the monsoon phenomenon
x Identify the signatures (amplitudes, scales) of the monsoon phenomenon in geodetic sensor datax Study the evolution of the monsoon phenomenon in timeand space through geodetic sensor datax Identify limitations and/or the necessity for additional
and/or more accurate measurements including in situ
networksx Quantify the sensitivity to error sources, for example,
tidal or non-gravitational force modellingx Compare geodetic sensor data with reanalysis products
in global and regional climate models
x Identify the possibility of assimilating geodetic sensor
data into monsoon prediction models
x Understand relationships between extreme events andthe monsoon phenomenon
Program of Activities
x Participate actively in IAG, AGU, AOGS and EGU conferences and organize sessions

185

x Organize working group meetings, splinter group meetings at the said symposia
x Collate geodetic sensor data along with their quality information and enable public accessibility via web services
x Conduct dedicated workshops and seminars on monsoon
research with focus on geodetic sensor datax Organize a special issue in a journal or an edited book
Members
Alexander Braun (Canada)
Karim Douch (Germany)
Vagner G. Ferreira (China)
Qiang Chen (Luxembourg)
Subimal Ghosh (India)
Zhizhou Liu (Hong Kong)
Chandrakanta Ojha (USA)Mohammad Sharifi (Iran)Alka Singh (USA)
Nico Sneeuw (Germany)
Shivam Tripathi (India)
Bramha Dutt Vishwakarma (UK)
Susanna Werth (USA)Peng Yuan (Germany)

Joint Working Group JWG C.6: Numerical
Simulations for Recovering Climate-Related Mass Transport Signals
Affiliation: Commission 2, GGOS, IGFS
Chair: Roland Pail (Germany)
Vice-Chair: Wei Feng (China)
Introduction
Gravity field missions are a unique geodetic measuring system to directly observe mass transport processes in the Earthsystem. Past and current gravity missions such as CHAMP,GRACE, GOCE and GRACE-Follow On have improved
our understanding of many mass change processes, such as
the global water cycle, ice mass melting of ice sheets andglaciers, changes in ocean mass being closely related to the
mass-related component of sea level rise, which are subtle
indicators of climate change, on global to regional scale.
Next Generation Gravity Missions (NGGMs) expected to belaunched in the midterm future have set high anticipations
for an enhanced monitoring of mass transport in the Earthsystem with significantly improved spatial and temporal resolution and accuracy. Science and user needs have been collected and consolidated mainly for the application fields hydrology, cryosphere, ocean and solid Earth, and a corresponding resolution on the need of NGGMs was expressed

186

The Geodesist’s Handbook 2020

by IUGG resolution no. 2 adopted in 2015. However, masstransport observations are also very valuable for long-termclimate applications. According to GCOS, in general timeseries of minimum 30 years are needed to decouple naturaland anthropogenic forcing mechanisms. Up to now, this hypothesis has never been checked and evaluated for gravity
field observations.

Martin Horwath (Germany)
Vincent Humphrey (USA)Erik Ivins (USA)
Laura Jensen (Germany)
Laurent Longuevergne (France)
Ingo Sasgen (Germany)
Bert Wouters (Netherlands)

Objectives

Joint Working Group JWG C.7: Satellite
geodetic data assimilation for hydro-climate research

The main objective of this working group is to set-up andrun long-term numerical simulation studies to evaluate theusefulness of gravity field missions for climate-related applications. As a first step, mass transport time series containing long-term changes of climate relevant signals have to begenerated in close interaction with climate modelers. They
shall then be used for the numerical simulations on the recoverability by means of different NGGM concepts, e.g.
GRACE-type in-line single-pair missions, Bender doublepair mission being composed of a polar and an inclined satellite pair, or high-precision high-low tracking missions following the MOBILE concept. In this respect, special emphasis shall be given to the separability of natural and anthropogenic forcing mechanisms in dependence of thelength of the measurement time series, the quantification ofrobustness of derived trends and systematic changes, and theevaluation of their impact to climate modeling.
Program of Activities
The following activities shall be performed:
x Generation of mass transport time series for a time-spanof at least 30 years containing climate-relevant signals
x Numerical closed-loop simulations for various mission
concepts that are currently in discussion as potential candidates for an NGGM
x Evaluation of recoverability of climate-related signals
from these mass transport time series
x Detectability of climate change pathways in the future
mass transport time seriesx Investigation of separability of natural and anthropogenic forcing processes
x Evaluation of impact for climate model applications towards societal applications
x Evaluation of the detectability of thresholds for early
warning
Members
Alejandro Blazquez (France)
Qiang Chen (Luxembourg)
Lijing Cheng (China)
Henryk Dobslaw (Germany)
Andreas Groh (Germany)

Affiliation: Commission 2 and GGOS
Chair: Mehdi Khaki (Australia)
Introduction
The recent advancements in the space geodetic techniques
have gained a lot of attention for improving our understanding of Earth's climate system and its hydrology. Traditionally, various types of models such as hydrologic and atmospheric models have been used for modelling/simulating andpredicting hydro‐meteorological processes at regional andglobal scales. Nevertheless, due to various sources of uncertainties such as imperfect modelling, data limitations on
both temporal and spatial resolutions, their errors, as well as
limited knowledge about empirical model parameters, theaccuracy of model simulations can be degraded. Assimilation of satellite geodetic data such as satellite gravimetry,satellite radar and radiometer measurements, synthetic-aperture radar (SAR) and radar interferometry data, and satellite altimetry has been shown to be effective for improving
the models’ performance and their forecasting skills. This
allows us to better study, for example, water resources andtheir distributions, mass variations and balance, extreme
events such as droughts and floods, ice transfer, and help toadapt to long-term environmental challenges posed by climate changes on continental scales.
Data assimilation (DA) facilitates this data integrationby constraining the models’ simulations based on observations and error associated with them. The method has become more popular with the advent of the space era sincescientific observational methods were not limited any more
to terrestrial only and offer high spatiotemporal resolution
data with global coverage. Specifically, the application ofsatellite geodetic measurement has been proven to successfully improve various models such as atmospheric and oceanic models, hydrological models and also coupled (e.g.,
land-atmosphere) systems. For example, the Gravity Recovery And Climate Experiment (GRACE) terrestrial water
storage (TWS) data has been used to enhance land surface
model performance. Satellite radar altimetry data over theInter-Commission Committee on Geodesy for Climate Researchocean has been used for enhancing oceanic models. Altimetry-derived surface water over land has been recently applied for improved routing as well as rainfall-runoff estimates. Satellite soil moisture, e.g., from Soil Moisture andOcean Salinity (SMOS) radiometer and Soil Moisture Active Passive (SMAP) has been used for hydrologic DA andmore recently for land-atmosphere coupled DA to better
study soil moisture feedback to atmospheric components.
The use of space geodetic techniques for DA can be further
extended with the development of new missions such as
NASA's Surface Water and Ocean Topography (SWOT)
global surface water, GRACE Follow-on, and Cyclone
Global Navigation Satellite System (CYGNSS) soil moisture. Therefore, satellite geodetic DA has a great potential
in hydro-climate studies and it requires more concentrations
within the geodesy community. The main objective of establishing this working group within IAG is to bring together people with this expertise to share their knowledge,
address the current challenges, and draw more attention to
the application of geodetic techniques for DA.
Objectives
x To investigate the contributions of space geodetic DA in
Earth systems.
x To develop and analyze theoretical and numerical methods for the efficient integration of satellite measurements with models.
x To better analyze model-data uncertainties in satellite
DA and their influence on the model’s simulations.
x To explore the application of satellite DA for model calibrations
x To investigate the application of new geodetic platforms
for DA objectives.
Program of Activities
x To actively participate in geodetic meetings and promote
space geodetic DA, and to monitor current progress andidentify challenges.
x To share efforts, ideas, and information regarding theworking group objectives.
x To organize related sessions at international events.
x To provide opportunities for more collaborations between group members (within the joint working groups)
on satellite DA and publishing important findings.
x To create a web page with information relevant to theworking group, bibliographic list of publications, andavailable research opportunities to also share significant
DA outcomes with the public.
Members
Joseph Awange (Australia)

187

Luca Brocca (Italy)
Harrie-Jan Hendricks Franssen (Germany)
Ibrahim Hoteit (Saudi-Arabia)
Jayaluxmi Indu (India)
Gabrielle J. M. De Lannoy (Belgium)
Hamid Moradkhani (USA)
Christian Massari (Italy)
John T. Reager (USA)Jan Saynisch (Germany)
Ashkan Shokri (Australia)
Natthachet Tangdamrongsub (USA)
Yoshihide Wada (Austria)
Benjamin Zaitchik (USA)

Joint Working Group JWG C.8: Methodology of comparing/validating/testing climate simulations to/with geodetic data
Affiliation: Commission 2, ICCT
Chair: Jürgen Kusche (Germany)
Introduction
Climate model simulations provide a unique tool for understanding past and present climates, and projecting future climate under given scenarios. Comparing simulations to observed data is of key importance for understanding uncertainties and systematic errors, attributing causal relations
among competing hypotheses, and lending confidence topredictions. One way geodesy contributes to climate sciences is via providing a unique data record for comparing,
validating and testing climate model simulations, e.g. withrespect to observed sea level change, mass redistribution orwater vapor timeseries. However, what is required from geodesy is beyond ‘just’ providing long and stable data sets,
and challenges must be addressed that require revisiting themethodology.
Climate model simulations often consist of large, singleor multi-model ensembles that need to be evaluated as awhole (i.e. not just the ensemble mean which averages out
real variability). Model simulations encompass hundreds ofdynamically linked variables with increasing spatial andtemporal resolution, as e.g. in climate monitoring applications. Simulations are prone to drifts and biases, and climate
science is not only interested in ‘deterministic’ (or mean)outcomes but e.g. in how statistics of extreme events or turbulent phenomena like eddy kinetic energy varies over time.
Testing climate models e.g. for the anthropogenic fingerprint requires that such statistics are derived from (geodetic)
data, where uncertainties must be assigned that characterizeboth measurement and sampling errors. This will require

188

that geodetic methods are critically reviewed and new approaches e.g. that deal with large data quantities and ensembles and/or the reconstruction of data gaps, and that capture
statistics beyond the mean and RMS be developed. Moreover, as geodetic techniques evolve (and are integrated with
non-geodetic observables), new climate observables as e.g.
Earth’s Energy Budget come into reach and new methods
must be developed.
Objectives
x To contribute to the understanding of past, present andfuture climate via comparing/validating/testing climate
models with geodetic datax To promote and advance the development of rigorous
methods across climate science and geodesy
x To safeguard the proper evaluation of the complex geodetic data sets, which are often built from multiple techniques, over overlapping or non-overlapping time periods, in the presence of background model and other analysis technique changes, in the presence of instrumental
errors and biases and the intricacies of geodetic reference frames (i.e. develop ‘best-practice’ examples)x To facilitate communication of climate scientists and geodesists with respect to methodological issues

The Geodesist’s Handbook 2020

x To enable the reanalysis of long geodetic data sets
Program of Activities
x The WG will first seek to stimulate exchange and collaboration across geodesists from different background(atmospheric remote sensing, altimetry, GRACE) andclimate scientists.
x It will organize splinter meetings along conferences andpromote session proposals e.g. at EGU and AGU conferences.
x It will eventually seek to consolidate the geodesy methodology and disseminate results in form of a white paper/ review paper.
Members
Henryk Dobslaw (Germany)
Petra Friedrichs (Germany)
Vincent Humphrey (USA)
Laura Jensen (Germany)
Anna Klos (Poland)
Felix Landerer (USA)Ben Marzeion (Germany)
Anne Springer (Germany)

Inter-Commission Committee on Marine Geodesy (ICCM)

189

Inter-Commission Committee on Marine Geodesy (ICCM)
President: Yuanxi Yang (China)
Vice President: Heidrun Kopp (Germany)

Terms of Reference
The Inter-Commission Committee on Marine Geodesy(ICCM) was first proposed by the Chinese National Committee to the IAG Executive Committee (EC) in Kobe, Japan in 2017 and then passed at the Sixth/Seven Meetingsof the IAG EC, 2018. The Inter-Commission Committee
on Marine Geodesy (ICCM) was formally approved andestablished following the IUGG General Assembly inMontreal, Canada, 2019.
With over seventy percent of the planet’s surface andthe most important zones of crustal formation and destruction covered by the oceans, monitoring and understanding
the oceans and the seafloor is of highest relevance to secure
the human sustainable development. The oceans provide
enormous biological and mineral resources while at thesame time modulate the climate and weather patterns andserve as an important sink for atmospheric carbon. The
oceans and seafloor are crucial to the evolution not only oflife, but of the Earth system, yet 80% of marine realm remain unexplored [NOAA]. The research foci of the discipline Marine Geodesy have enormous economic and scientific potential, however, at present large gaps in ocean surveys, seafloor mapping and remote sensing exist which necessitate IAG’s immediate attention.
Research contributions to Marine Geodesy have advanced tremendously during the last two decades:(i) seafloor geodetic networks have been initiated and established by countries or regions including North andCentral America, Europe, New Zealand and Japan, andin the near future more coastal countries may start seafloor observatory plans,(ii) advanced GNSS/acoustic GPS-A techniques haveachieved centimeter accuracy in seafloor geodetic posi-

tioning, crucial to marine geohazard monitoring, including undersea earthquakes volcanic eruptions, and submarine landslides as well as monitoring of seafloor infrastructure;(iii) multi-ocean environment monitoring data are available
to potentially improve seafloor geodetic positioning ormonitoring of steric sea level and circulations, including
temperature and salinity profiles of the Array for Realtime Geostrophic Oceanography (Argo), expendable
bathythermograph (XBT) data, ocean-bottom pressure(OBP) data and surface and subsurface ocean current observations.
ICCM strongly encourages research to:(1) develop and implement a precise seafloor reference frame
to enhance marine positioning, navigation and timing(PNT) techniques, and promotes international cooperations to bridge scientific research gaps including the component of the international terrestrial reference frame(ITRF) in the coastal and the deep ocean;(2) enhance frontier research topics on monitoring changesof the ocean and seafloor, such as sea level change, seafloor tectonic motion and seismological events, steric andmass oceanic variations, changes of the surface and subsurface currents, and changes of waves and wind patterns;(3) refine a series of marine geodetic models, including barotropic and baroclinic ocean tide models, marine geoid
models, dynamic topography models, and coastal reference models such as the mean high water (MHW) and thehigh-water line (HWL); and(4) improve the accuracy and resolution of the global seafloor topography particularly in the coastal regions by advancing new seafloor geodetic data acquisitions, innovative data processing, and exploring new topography inversion tools.

190

The Geodesist’s Handbook 2020

Objectives

Structure

The overall objectives of the ICCM arex to shorten the gaps between theory and applications inmarine geodesy, and to encourage transdisciplinary integration of the contemporary geodetic sensors, including marine geophysical sensors, oceanic sonar andphysical oceanography instrumentation;
x to improve the global realization of the International
Terrestrial Reference Frame (ITRF) by connecting theseafloor geodetic network component with the ITRF,
and to improve current marine geodetic models by including the space, surface and subsurface geodetic observations;x to encourage development of marine geodetic methodology, especially for the fusion methods of multi-marine
geodetic observations;x to promote international collaborations in regional marine geodetic surveys, and to develop and establish international conventions for marine geodetic data processing, the seafloor reference frame, and other standards.
To achieve these aims, ICCM will interact and collaborate with the IAG Commissions, GGOS and other IAG
related entities (services, projects).

The general structure of Inter-Commission Committees is
specified in the IAG By-laws (§17). The Steering Committee
includes the president, the vice-president, the past president, one
representative appointed by each Commission, and two representatives of the IAG services. The ICCM activities will be
structured in study groups. Due to the inter-commission character of the ICCM, these study groups are always joint study
groups, affiliated to one or more of the Commissions, GGOS
and/or IAG services. The Joint Study Groups will be established during the first period of the ICCM.

ICCM Activities
The anticipated ICCM activities include:
x service as (co-)conveners of geodesy sessions at major
conferences such as IAG, EGU, AGU, AOGS, IUGG,
etc.
x organization of marine geodesy symposia, and publication of special issues of international journals such as
Marine Geodesy, Journal of Geodesy, and Advanced
Space Research.
x creation and maintenance of a website for the dissemination of ICCM related information and data products.

Steering Committee
President:
Yuanxi Yang (China)
Vice President: Heidrun Kopp (Germany)
Representatives
Commission 1: Geoffrey Blewitt (USA)Commission 2: Roland Pail (Germany)
Commission 3: Manabu Hashimoto (Japan)
Commission 4: Marcelo Santos (Canada)
GGOS: Hansjörg Kutterer (Germany)
IGFS: Riccardo Barzaghi (Italy)
IERS: Jürgen Müller (Germany)

Members
Ole Baltazar Andersen (Danish)
Rongxing Li (China)
Ian Church (Canada)
Keiichi Tadokoro (Japan)
Pierre Sakic (Germany)
Morelia Urlaub (Germany)
Valérie Ballu (France)
Xiaoli Deng (Australia)
Tianhe Xu (China)
Felipe Nievinski (Brazil)
Shuqiang Xue (China)
Sajad Tabibi (Luxembourg)
Fanlin Yang (China)
Lifeng Bao (China)

Novel Sensors and Quantum Technology for Geodesy (QuGe)

191

IAG Project – Novel Sensors and Quantum Technology for Geodesy (QuGe)
President: Jürgen Müller, Germany
Vice President: Marcelo Santos, Canada
http://quge.iag-aig.org

Terms of Reference
The novel developments in quantum physics of the previous
decade, including new technologies and related measurement concepts, will open up enhanced prospects for satellite
geodesy, terrestrial gravity sensing and reference systems.
In close collaboration between physics and geodesy, thisnew IAG project shall exploit the high potential of quantum
technology and novel measurement concepts for various innovative applications in geodesy.
Climate change often is reflected in mass variations on
Earth. And, many mass change processes in the hydrosphere, geosphere and atmosphere are widely imprinted ingravitational data. However, gravitational data with better
spatial-temporal resolution and higher accuracy is required,
which can only be achieved by employing innovative quantum technology concepts. Highly stable and accurate reference systems provide the fundamental backbone to monitor
the change processes in the Earth system, where clocks willplay a central role in the future.
QuGe will serve as a unique platform for developing andevaluating those novel concepts and observation systems,
where also further applications, like in exploration and navigation, may benefit. Technology development and space
mission requirements have to be linked to geodetic andgeophysical modelling in a synergetic way.
Optical ranging between test masses in satellites, atominterferometric accelerometry and gradiometry, and chronometric levelling with clocks are the needed approaches toovercome the problems of classical concepts in geodesy.
With these novel techniques, mass variations on almost all
spatial and temporal scales can be observed with unprecedented accuracy and will serve as input for a multitude ofapplications in geosciences, from the monitoring of smaller

groundwater basins and geodynamic effects to the observation of the complex global mass transport processes in theoceans.
The combination of expertise from quantum physics andgeodesy in QuGe, integrating engineering skills and fundamental research, serves as an excellent basis to advance thefrontiers of gravimetric Earth observation and the realization of reference systems.

Objectives
QuGe will put its focus on three major pillars
1) Atom interferometry for gravimetry on ground and inspace (quantum gravimetry) will allow for a comprehensive set of applications, such as fast local gravimetricsurveys and exploration, or the observation of gravimetric Earth system processes with high spatial and temporal resolution. In space, atom interferometry will enableaccelerometry and inertial sensing in a modernistic way.
The use of atom interferometry in hybrid systems withelectrostatic accelerometers may allow to cover a wide
spectral range for future inertial sensing and navigation.
It will benefit satellite navigation, but also serve as a basis for developing the next generation of gradiometer
missions (GOCE follow-on).
2) Laser-interferometric ranging between test masses inspace with nanometer accuracy belongs to these novel
developments as well, where technology developed forgravitational wave detection and successfully tested in
the LISA/pathfinder mission is being prepared for geodetic measurements. GRACE-FO already demonstrates
this new development. Even more refined concepts, liketracking a swarm of satellites, might be realized within
the next years. Optical techniques may also be applied
for test mass sensing in future accelerometers, and evencombined to next generation gradiometry in space.

1923) Frequency comparisons of highly precise optical clocks
connected by optical links give access to differences of
the gravity potential over long distances (relativistic
geodesy). In the future, relativistic geodesy with clocks
will be applied for defining and realizing height systems
in a new way, locally as well as globally. As further application, clock measurements will provide long-wavelength gravity field information. Moreover, accurate
clocks help to improve the accuracy of the International
Atomic Time standard TAI. They are important for all
space geodetic techniques as well as for the realizationof reference systems and their connections. Another application example is the possible use of high-performance clock networks to support GNSS.
In all three research areas, along with the research on measurement systems and techniques, the analysis models haveto be put on a sound theoretical basis. This requires dedicated geodetic and relativistic modelling of the various involved gravity field quantities and measurement concepts.

Structure
Working Groups:
WG Q.1: Quantum gravimetry in space and on ground
WG Q.2: Laser interferometry for gravity field missions
WG Q.3: Relativistic geodesy with clocks
Steering Committee
President:
Jürgen Müller (Germany)
Vice-President: Marcelo Santos (Canada)
WG chairs:see below
Representatives of the four Commissions:
IAG Comm. 1: Erricos Pavlis (USA)IAG Comm. 2: Adrian Jäggi (Switzerland)
IAG Comm. 3: Federica Migliaccio (Italy)
IAG Comm. 4: Suelynn Choy (Australia)
Representatives of Services:
IGFS:
Sylvain Bonvalot (France)
GGOS:
Ulrich Schreiber (Germany)
Members-at-large:
Wenbin Shen (China)
Gabriel Guimarães (Brazil)
Representative of External Bodies
Partly already proposed as members of the WGs. Additional
members, e.g., from industry could be A. Bresson(ONERA), S. Seidel (OHB), B. Desruelle (MuQuans) andothers.

The Geodesist’s Handbook 2020

Working Groups of the Project
The new WGs will closely collaborate with other components of IAG such asx IAG SC 2.6 “Gravity and Mass Transport in the Earth
System” (Wei Feng, Wuhan China)x IAG SC 2.3 "Satellite Gravity Missions" (Frank
Flechtner, Potsdam, Matthias Weigelt, Hannover,Germany)x IAG Inter-Commission Committee on Geodesy for
Climate Research – Annette Eicker, Roland Pail,
Munich, Germanyx Further collaborations, e.g., with ICCT, IERS, WG on
IHRF, JWG on IGRF, etc. will be fixed after start.

WG Q.1: Quantum gravimetry in spaceand on ground
Chair: Franck Pereira (France)
Vice-Chair: Michele van Camp (Belgium)
Description
On ground, quantum sensors based on matter wave interferometry with cold atoms are very well suited for rapid andvery precise gravity sensing. They can be used as registration instruments and as absolute gravimeters with sub-μGal
accuracy. Mobile devices are developed for field campaigns
and large-scale stationary devices for achieving extreme
precision. While the former enable new strategies for local
and regional gravity surveys, the latter will provide a new
gravity standard in the future.
In space, the long-term stability and low noise level ofquantum sensors will allow improving the spatial gravity
field models in GOCE-type gradiometer missions. The determination of mass transport processes on Earth at low andmedium degrees in GRACE-type missions will benefit fromquantum accelerometers providing the measurement of thespecific non-conservative forces. In addition, hybrid systems (i.e. a combination of electrostatic and atom-interferometric accelerometers) can cover a wider spectral range
which will greatly support navigation and inertial sensing
on ground and in space.
The goal of this WG is to elaborate the major benefit andmost promising applications of atom interferometry for gravimetry and inertial sensing in space and on ground.
Objectives
x Terrestrial quantum gravimeters and applications
scenarios (including airborne and marine instruments)
x (Hybrid) accelerometers for space missions andspacecraft navigation

Novel Sensors and Quantum Technology for Geodesy (QuGe)x Atom interferometric gradiometryx Elaboration of further applications / space demonstrator(e.g. pathfinder) like atmosphere research, relativity
tests, etc.
x Elaboration of synergies between different science
topics in a single mission (Earth observation andfundamental physics, navigation and space exploration,
several scenarios for Earth observation, e.g. gravimetry,atmospheric research and magnetometry)
Members (preliminary)
R. Pail (TU Munich)
A. Landragin (Syrte Paris)
P. Bouyer (LP2N Bordeaux)E. Rasel (LUH Hannover
C. Schubert (LUH Hannover)
T. Lévèque (CNES Toulouse)
O. Carraz (ESA)
L. Mondin (ESA)
A. Rülke (BKG Frankfurt)
M. Krutzik (HU Berlin)
F. Migliaccio (Univ. Milano)
M. Reguzzoni (Univ. Milano)

WG Q.2: Laser interferometry for gravity
field missions
Chair: Michael Murböck (Germany)
Vice-Chair: Bob Spero (USA)
Description
GRACE has excellently demonstrated the great potential ofinter-satellite tracking to determine time-variable gravitational signals which are related to mass transport processes inthe Earth system. Examples are ice mass loss in Greenlandand Antarctica, ground water loss in Asia, droughts in USA,
quantification of the global water cycle, mass contribution
to sea level rise, mass variation due to land uplift in North
America and Scandinavia, or mass changes related toearthquakes. To increase the resolution and to extend thetime series, GRACE-FO was launched in May 2018 also
carrying a Laser Ranging Interferometer (LRI) as demonstrator which is able to approach an accuracy of tens of
nm for inter-satellite ranging.
Optical sensing of the motion of test masses in the gravitational field with nanometer accuracy and beyond can berealized in various measurement concepts such as for ranging between satellites like in GRACE-FO or future swarms
of satellites. Further concepts apply LRI for sensing single
test-mass motion (accelerometry) or multiple test-mass

193

constellations within one satellite (GOCE-type gradiometry).
The overall goal of this WG is to study optical sensing
for inter-satellite tracking, accelerometry and gradiometry,
and its applications for next generation gravity field missions.
Objectives
x Interferometric Laser Ranging between swarms ofsatellites
x Accelerometry with optical readout and application
scenarios
x Gradiometry with optical readout
x New concepts for future satellite gravity missions
Members (preliminary)V. Müller (AEI Hannover)
G. Heinzel (AEI Hannover)
J. Kusche (Uni Bonn)
F. Landerer (JPL Pasadena)
D. Wiese (JPL Pasadena)
P. Bender (JILA Boulder)G. Metris (OCA, France),
Ch. Le Poncin-Lafitte (Syrte Paris)
S. Jin (Shanghai China)
M. Rothacher (ETH Zurich)
B. Spero (JPL Pasadena)
C. Woodruff (JPL Pasadena)
F. Flechtner (GFZ Potsdam)

194

WG Q.3: Relativistic geodesy with clocks
Chair: Gerard Petit (France)
Vice-Chair: Jakob Flury (Germany)
Consultant from Physics: Christian Lisdat, Braunschweig,
Germany
Description
Optical clocks are sensitive to the gravity potential in which
they are operated. The comparison of two clocks will reveal
a frequency offset from the value expected from side-byside comparisons that can directly be related to the potential
difference between both clocks. The best optical clocks now
reach resolutions of 0.1 m2/s2, transportable ones about 2
m2/s2. They can be achieved already after few hours of averaging.
We will evaluate how this technique can be used to generate unified and long-term stable height networks and reference systems. This will include discussion about thefeasibility to realize a datum by reference to a, e.g., spaceborne clock with ideally negligible gravitational interference. Future clock networks might also be used as groundtruth for space missions or even to bridge gaps in satellite
observations.
Other aspects to be addressed are the application of observed time-variable signals in de-aliasing of satellite observations. In cooperation with the two previous WGs, sensor
fusion concepts will be discussed to utilize the different spatial integration characteristics of clocks and the other gravity
sensors to disentangle local and extended signal sources.
In summary, the goals of this WG are using clocks measurements for determining differences of physical heights
and gravity potential for various geodetic applications.

The Geodesist’s Handbook 2020

Objectives
x Clock networks for unification of height systems
x Gravity field recovery on groundx Application to realize reference systems, including
dedicated space clocks
x Further applications (height/potential variations)x Potential satellite missions for long-wavelength gravity
field recovery, including optical links for comparing thespace clocks
Members (preliminary)
N. Newbury (NIST Boulder)
A. Ludlow (NIST Boulder)P. Delva (Syrte Paris)
P. Visser (TU Delft)
H. Margolis (NPL Teddington)
D. Calonico (INRIM, Torino)
C. Lämmerzahl (ZARM Bremen)
W. Shen (Wuhan, China)
U. Schreiber (GO Wettzell)
M. Santos (Uni New Brunswick)
S. Kopeikin (Uni Missouri)
N. Pavlis (NGA, USA)
P. Pottie (Obs de Paris)
S. Merlet (Obs. de Paris/Syrte)
E. Mazurova (MIGAIK, Moscow)
S. Stellmer (Uni Bonn)
J. Kusche (Uni Bonn)
Y. Tanaka (Tokyo Japan)
Hua Guan (WIPM, Wuhan, China)

Communication and Outreach Branch (COB)

195

Communication and Outreach Branch (COB)
President: Szabolcs Rózsa (Hungary)
Secretary: Gyula Tóth (Hungary)
web: http://www.iag-aig.org

Development
The Communication and Outreach Branch (COB) was
created by the IAG Council at its special meeting in
Budapest, 7 September 2001. A Call for Participation was
issued by the IAG Central Bureau (CB) to fill this position.
The offer of the Hungarian Academy of Sciences(HAS)/Budapest University of Technology and Economics(BME) was elected by the Executive Committee (EC) at its
meeting in Nice, 11 April, 2003. The IAG Council at the23rd IUGG/IAG General Assembly (Sapporo, Japan, 30
June-11 July, 2003) has confirmed this election. Thus, the
COB started its activities in July 2003, and in the period of
2019-2023 will be the fifth term in the operation of the COB
by the BME.
The Communication and Outreach Branch is one of thecomponents of the Association. According to the new
Statutes (§5) of the IAG, the COB is the office responsible
for the promotional activities of the IAG and thecommunication with its members.

Terms of Reference
According to §18 of the new By-laws of the IAG:
a) The function of the Communication and OutreachBranch is to provide the Association with communication, educational/public information and outreachlinks to the membership, to other scientific Associations
and to the world as a whole.
b) The responsibilities of the Communication and OutreachBranch shall include the following tasks:(i) Promote the recognition and usefulness of geodesy
in general and IAG in particular.
(ii) Publications (newsletters).
(iii) Membership development.
(iv) General information service and outreach.

c) The Communication and Outreach Branch shall also
assist the IAG General Secretary, in the following tasks
as required:(i) Maintenance of the IAG website.
(ii) Setting up Association schools.
(iii) Setting up meetings and conferences.
d) The IAG Executive Committee establishes the COB ona long-term basis by issuing a Call for Participation.
The responding organization(s) and the IAG Executive
Committee shall then negotiate the Terms of Reference
and other conditionse) The President of the COB shall be elected by the IAG
Council after consideration of a COB proposal.
f) Major decisions related to the operations of the COB
shall be made by a Steering Committee consisting of
the following voting members:(i) Communication and Outreach Branch President.
(ii) IAG Secretary General.
(iii) Editor-in-Chief of the Journal of Geodesy.
(iv) Editor-in-Chief of the IAG Symposia Series.
(v) Up to 5 other members appointed by the Executive
Committee on the recommendation of the
President of the Communication and OutreachBranch.

Program of Activities
According to the structure of the IAG, the individual
membership has been introduced in addition to the
traditional National Members. However, the individual
membership requires a more commercial, member-oriented
operation of the Association. The main purpose of the COB
is to promote communication and interaction among all its
members and to facilitate the work of IAG in general.
Therefore, the COB is a permanent IAG office forpublication, publicity and visibility of the Association.

196

The planned activities of the COB are split into two maingroups:a) communicational activities, andb) membership developments and promotional activities
which enable the growth of the IAG.
One of the major tasks of the COB is to create thechannels of the communication within the Association. Our
intention is to maintain a simple, structured way ofcommunication using various information technologies(IT). The communication of the IAG is done using thefollowing channels:x the official IAG website (see the chapter IAG on theInternet in this issue),x publication of the IAG Newsletters and the Geodesist’s
Handbook in cooperation with the IAG Office.
The official IAG website acts on one hand as the mostimportant interface to the outside community, and on theother hand it is the first pillar of the communication
infrastructure of the Association. Therefore, the content of
the website is defined to support both roles.
The server operating at the IAG COB, handles mailinglists, which is one of the major source of information for themembers. The members receive the announcements andNewsletters via e-mail and through the website.
The electronic version of the IAG Newsletter ispublished monthly on the IAG website and is distributed tothe members in PDF format via e-mail. A selection of theNewsletter articles is published in the Journal of Geodesy.
COB is active in the membership developments andpromotional activities. The major channel of thepromotional activities is the IAG website. Additionally,
several brochures and leaflets are available for download
and printing, which
x introduce the IAG to the global community,x emphasize the mission statement of IAG, andx describe the advantages of being an IAG member.
Our intention is that these brochures should be available
at every conference organized and/or sponsored by IAG.
Therefore the COB should also represent IAG at all major
meeting (including not only IUGG General Assemblies,
IAG Scientific Assemblies, AGU and EGS meetings, butalso at IAG-sponsored meetings) with different IAG
materials (brochures, etc). These brochures are also madeavailable for download from the IAG website (www.iagaig.org).
Another important task of COB to promote and support
the outreach activities of IAG. Our plan is to collect theexisting materials supporting primary and high-school
education as well as promoting geodesy to students.
Moreover, additional syllabus and exercises are to be
developed.

The Geodesist’s Handbook 2020

Steering Committee
The COB has a Steering Committee (SC) with the following
members:
Ex officio voting members:
COB President: Szabolcs Rózsa (Hungary)
IAG Secretary General: Markku Poutanen (Finland)
Editor-in-Chief of the JoG: Jürgen Kusche (Germany)*
Editor-in-Chief of the IAG Symposia Series:
Jeff Freymueller (USA)*
Other voting members:
Gyula Tóth (Hungary), COB Secretary, Editor of the IAG
Newsletter
Anne Joergensen (Norway, GGRF)
Hussein Abd-Elmotaal (Egypt)
Nancy Wolfe Kotary (USA)TBD (South America)
TBD (Asia-Pacific)*Editors may be substituted by the respective Assistant
Editors
Permanent Guests (non-voting):
Zuheir Altamimi (Germany), IAG President
Richard Gross (USA), IAG Vice-President
Harald Schuh (Germany), IAG Immediate-Past President
The COB operates an office the address of which is asfollows:
IAG Communication and Outreach Branch
c/o Department of Geodesy and Surveying
Budapest Univ. of Technology and Economics
P.O.Box 91, H-1521 Budapest, Hungary
Phone: +36-1-463 3222/3213, Fax: +36-1-463 3192
E-mail: szrozsa@iag-aig.org / iagcob@iag-aig.org

Global Geodetic Observing System (GGOS)

197

Global Geodetic Observing System (GGOS)
Chair of the GGOS Coordinating Board: Basara Miyahara (Japan)
Vice-Chair of the GGOS Coordinating Board: Laura Sanchez (Germany)
Director of the Coordinating Office: Martin Sehnal (Austria)
http://www.ggos.org

GGOS Background

GGOS Vision

Preamble

Advancing our understanding of the dynamic Earth system
by quantifying our planet’s changes in space and time.

The proposal for the Global Geodetic Observing System(GGOS) was developed by the GGOS planning group between 2001 and 2003 according to the Bylaws of the International Association of Geodesy (IAG). The proposal was
accepted by the IAG Executive Committee and the IAG
Council at their meetings during the XXIII IUGG General
Assembly in Sapporo in July 2003. GGOS was endorsed by
the IUGG through Resolution No. 3 at the same General Assembly.
Changes in the IAG Bylaws in 2007 resulted in GGOS
being recognized as an integral component of IAG alongwith Services and Commissions. This transformed the statusof GGOS from that of an IAG Project to an IAG component.
Specific to GGOS are IAG Bylaw numbers 1(d) and 15.
During 2009‐2016, and again in 2017, revisions to the structure of GGOS were discussed leading in 2018 to the Termsof Reference, primarily to update changes to the organizational structure of GGOS.
According to the IAG Bylaws 1(d): “The Global Geodetic Observing System (GGOS) works with the IAG Services to provide the geodetic expertise and infrastructurenecessary for the monitoring of the Earth system and globalchange research.”

GGOS Mission
x To provide the observations needed to monitor, map, andunderstand changes in the Earth’s shape, rotation, andmass distribution.
x To provide the global geodetic frame of reference that is
the fundamental backbone for measuring andconsistently interpreting key global change processes
and for many other scientific and societal applications.
x To benefit science and society by providing thefoundation upon which advances in Earth and planetarysystem science and applications are built.
We live on a dynamic planet in constant motion that requires long-term continuous quantification of its changes ina truly stable frame of reference. GGOS and its related research and IAG services will address the relevant scienceissues related to geodesy and geodynamics in the 21st century, but also issues relevant to society (global risk management, geo-hazards, natural resources, climate change, severe storm forecasting, sea level estimations and ocean forecasting, space weather, and others). It is an ambitious program of a dimension that requires strong cooperation within
the geodetic, geodynamic and geophysical communities,
and the establishment of strong links to other internationalorganizations. GGOS will provide this integration at thehighest level, in service to the technical community and society as a whole.

198

GGOS Strategic Direction
Overarching Strategic Areas of GGOSThe GGOS Goals, Objectives, and Outcomes are built
around four strategic areas that are directly attributable tothe established GGOS goals. These areas were establishedin the 2011 Strategic Plan and continue to be relevant to theactivities and future efforts of GGOS in subsequent strategicplans. The strategies are related to each goal but are overarching in nature – just as each goal acts in support of othergoals, each strategy has a role in all of the goals.
1. Geodetic Information and Expertise (intangible assets).
GGOS outcomes will support the development andmaintenance of organizational intangible assets, including geodetic information and expertise. The development of this strategic area will benefit all other goals andobjectives.
2. Global Geodetic Infrastructure (advocacy for, and sustenance of, tangible assets). Development of, advocacy
for, and maintenance of existing global geodetic infrastructure is in direct support of each GGOS goal.
3. Services, Standardization, and Support (internal and external coordination). Optimal coordination, support, andutilization of IAG services, as well as leveraging existing IAG resources, are critical to the progress of all
GGOS goals and objectives.
4. Communication, Education, and Outreach (public relations, external education and outreach, internal continuing education and training). Marketing, outreach, andengagement are critical elements for sustaining the organizational fabric of GGOS.

IAG Services, Commissions, and InterCommission Committees in Support of
GGOS
In order to accomplish its mission and goals, GGOS depends on the IAG Services, Commissions and Inter-Commission Committees. The Services provide the infrastructure and products on which all contributions of GGOS are
based. The IAG Commissions and Inter-Commission Committees provide expertise and support for the scientific development within GGOS. In summary, GGOS is IAG's central interface to the scientific community and to society ingeneral.
IAG is a Participating Organization of the Group on
Earth Observations (GEO). GGOS acts on behalf of the

Global Geodetic Observing System: Meeting the Requirements of a Global Society on a Changing Planet in 2020, H.-P. Plag and M. Pearlman(editors), Springer, 2009

1

The Geodesist’s Handbook 2020

IAG in GEO and actively contributes to the Global Earth
Observation System of Systems (GEOSS).
The GGOS 2020 Book1 serves as the initial basis for the
implementation of GGOS, as the observing system of IAG,
and is used to derive work plans based on its recommendations.

GGOS Structure
Overview of Key GGOS Elements
Structural Elements:
The organizational structure of GGOS is comprised of thefollowing key elements which are depicted in Fig. 1:
GGOS Consortium – is the collective voice for all GGOS
matters.
GGOS Coordinating Board – is the central oversight anddecision-making body of GGOS.
GGOS Executive Committee – serves at the direction of theCoordinating Board to accomplish day-to‐day activities
of GGOS tasks.
GGOS Science Panel – advises and provides recommendations to the Coordinating Board relating to the scientificcontent of the GGOS 2020 book and its updates; and represents the geodetic and geoscience community at
GGOS meetings.
GGOS Coordinating Office – coordinates the work within
GGOS and supports the Chair, the Executive Committee
and the Coordinating Board; and coordinates GGOS external relations.
GGOS Bureau of Products and Standards – tracks, reviews,
examines, evaluates all actual standards, constants, resolutions and products adopted by IAG or its components
and recommends their further use or proposes the necessary updates.
GGOS Bureau of Networks and Observations – develops a
strategy to design, integrate and maintain the fundamental geodetic infrastructure including communication anddata flow; monitors the status of the networks and advocates for implementation of core and other co-locatednetwork sites and improved network performance.
GGOS Affiliates – are national or regional organizations thatcoordinate geodetic activities in that country or region.
GGOS Affiliates allow increased participation in
GGOS, especially by organizations in under-represented
areas of Africa, Asia-Pacific, and South and Central
America.

Global Geodetic Observing System (GGOS)

GGOS Committees, Working Groups and Focus Areas (formerly known as Themes) – address overarching issues
common to several or all IAG components, and are amechanism to bring the various activities of the Services, Commissions and Inter-Commission Committees
together, or to link GGOS to external organizations. Focus Areas are cross-disciplinary and address specific focus areas where GGOS contributors work together to address broader and critical issues.
Fundamental Supporting Elements of GGOS
IAG – promotes scientific cooperation and research in geodesy on a global scale and contributes to it through its various research bodies. GGOS is the Observing System of
the IAG.
IAG Services, Commissions and Inter‐Commission Committees – are the fundamental supporting elements of
GGOS. GGOS works with these IAG components to

199

provide the geodetic infrastructure that is necessary formonitoring the Earth system and for global change research. GGOS, built upon the existing IAG Services andtheir products, will provide a framework for existing or
future Services and will strive to ensure their long-term
stability.
GGOS Inter-Agency Committee (GIAC) – was a forum thatsought to generate a unified voice to communicate with
Governments and Intergovernmental organizations(GEO, CEOS, UN bodies) in all matters of global andregional spatial reference frames and geodetic research
and applications. GIAC was dissolved when the United
Nations Committee of Experts on Global Geospatial Information Management (UN-GGIM) Working Group on
the Global Geodetic Reference Frame (GGRF) was elevated to the permanent Subcommittee on Geodesy of the
UN-GGIM.

Fig. 1 Organization structure of GGOS (December 2019)

200

United Nations Committee of Experts on Global Geospatial
Information Management (UN-GGIM) – led by United
Nations Member States, UN-GGIM aims to address
global challenges regarding the use of geospatial information and to serve as a body for global policymaking
in the field of geospatial information management.
UN-GGIM Subcommittee on Geodesy (SCoG) – provides anintergovernmental forum for cooperation and exchangeof dialogue on issues relating to the maintenance, sustainability and enhancement of the Global Geodetic Reference Frame (GGRF).

Details of the Structure of GGOS
GGOS Consortium
The GGOS Consortium is the voice and essentially the large
steering committee of GGOS. It reviews GGOS progress
and activities and nominates and votes for the candidates forthe elected positions on the GGOS Coordinating Board.
The GGOS Consortium is comprised of up to two designated representatives from each IAG Service, Commission,and Inter-Commission Committee and one representativefrom each GGOS Affiliate. The Chair of an IAG Service
Governing or Directing Board, and the Director of the Central Bureau or Coordinating Office, as well as Commission
and Inter-Commission Committee Presidents and Vice Presidents and Chairs of GGOS Affiliates may be those designated members. However, no person may represent two or
more components, and no one may have more than one vote.
The presiding Chair of GGOS is ex-officio the Chair of theConsortium. GGOS Consortium decisions are based on consensus. Decisions requiring a vote are decided by simple
majority of the votes cast. The quorum is met when at least
fifty percent of members are present, but electronic voting
is acceptable provided a quorum responds.
The Consortium is the nominating and electing body for the
GGOS Coordinating Board. The Consortium will meet atleast once a year. Observers may participate in meetings of
the Consortium at the discretion of the Chair.
GGOS Coordinating Board
The Coordinating Board (CB) is the decision making bodyof GGOS. Decisions are based upon consensus, wheneverpossible. Decisions requiring a vote are decided by simple
majority of the votes cast. The quorum for a valid vote isparticipation of fifty percent of the voting members of theCoordinating Board. Votes may be held in person at meetings, or by appropriate electronic means at the discretion of
the GGOS Executive Committee. The Coordinating Board

The Geodesist’s Handbook 2020

will meet at least once yearly, although twice yearly is preferable. Observers may participate in meetings of the Coordinating Board at the discretion of the Chair.
Coordinating Board Members
Voting members:
GGOS Chair (votes in case of a tie)
1
GGOS Vice-Chair
1
GGOS Science Panel Chair (ex-officio)
1
GGOS Coordinating Office Director (ex-officio)
1
GGOS Manager of External Relations (ex-officio)
1
GGOS Bureau Directors (ex-officio)
2
GGOS Affiliate Representatives(elected by the Consortium)
2
IAG President or designated representative(ex-officio)
1
IAG Service Representatives(elected by the Consortium)
4
IAG Commission and Inter-Commission Committee
Representatives (elected by the Consortium)
2
Members-at-Large (elected by the GGOS CB)
3
Total Voting Members
19
Non-voting members:
GGOS Committee and Working Group Chairs(ex-officio)
6
GGOS Focus Area Leads (ex-officio)
4
GGOS Web and Social Media Manager (ex-officio) 1
Immediate Past Chair of GGOS (ex officio)
1
Total Non-Voting Members
12
Total membership of Coordinating Board
19 Voting Members
12 Non-Voting Members
31 Total members
Chair
The Chair of the GGOS Coordinating Board is determinedaccording to the IAG Bylaws. The Chair of the GGOS Coordinating Board is also known as the GGOS Chair. The
GGOS Chair presides over meetings of the GGOS Consortium, Coordinating Board, and Executive Committee. The
Chair is the principal spokesperson and representative of
GGOS to the IAG and outside organizations.
Vice Chair
The Vice Chair of the GGOS Coordinating Board is electedby the Coordinating Board. The Vice Chair assists the Chairand serves as the Chair in the absence of the Chair or whena motion involving the Chair is being discussed.

Global Geodetic Observing System (GGOS)

201

Members-at-Large

GGOS Science Panel

Members-at-Large are invited to join the Coordinating
Board in order to provide balance in representation of geographical regions or unique capabilities. The Chair, with theassistance of the Coordinating Office, appoints an Election
Committee to organize the voting process and to ensure
availability of the nominated candidates. The Election Committee then presents the final list of Members-at-Large candidates to the CB for a vote.

The GGOS Science Panel is an independent and multi‐disciplinary advisory board that provides scientific support andguidance to the GGOS steering and coordination entities asrequested. This support may include organization of relevant scientific sessions at conferences, workshops, and otherevents.
The IAG Commissions and Inter-Commission Committees each nominate two candidates and the GGOS Focus Areas each nominate one candidate to the Science Panel subject to approval by the CB. The CB may appoint additional
Members-at-Large to the Science Panel in order to provide
balance in representation of geographical regions or uniquecapabilities. The immediate past Chair of the Science Panelis a Member of the Science Panel.
The Science Panel will elect its own Chair to be approved by the CB.

Appointment of the Chair and Election of Coordinating Board Members
The process for elections to the GGOS Coordinating Board
will follow the four‐year IAG General Assembly, whichtakes place during the IUGG General Assembly (see IAG
Bylaws for more detail). Candidates nominated to serve on
the Coordinating Board as IAG Service, Commission, andInter-Commission Committee representatives must be
members of the GGOS Consortium. Candidates nominatedto serve on the Coordinating Board as GGOS Affiliate representatives must be members of the GGOS Affiliates. The
CB elects the Vice-Chair of the GGOS CB by a vote. However, the GGOS Chair is elected by the IAG in consultation
with the GGOS Coordinating Board.
GGOS Executive Committee
The GGOS Executive Committee (EC) is comprised of thefollowing members:
GGOS Chair
1
GGOS Vice-Chair
1
GGOS Coordinating Office Director
1
GGOS Manager of External Relations
1
GGOS Bureau Directors
2
Voting Members of the CB selected for
EC membership
2
Total
8
Every other year, the GGOS Chair submits a list of his or
her candidates for the two open EC member spaces to the
CB for approval. These candidates must be voting membersof the CB in order to be nominated to the EC.
The Immediate Past Chair of GGOS, the Chair of the
GGOS Science Panel, and the President of IAG or designated representative are all permanently invited guests atmeetings of the Executive Committee. Other observers may
be invited to attend EC meetings (or teleconferences) as
needed.

IAG Services, Commissions and Inter--Commission Committees

GGOS works with these IAG components to provide the geodetic infrastructure necessary for monitoring the Earth system and global change research. GGOS respects the bylaws
and terms of reference for these essential components.
GGOS is built on the existing IAG Services and their products. GGOS is not taking over tasks of the existing, and well
working IAG Services. GGOS will provide a framework forexisting or future Services and strive to ensure their longterm stability.
GGOS Committees, Working Groups and Focus
Areas
GGOS Committees and Working Groups (WG) are established by the Coordinating Board as needed. Working
Groups are established for one 4-year period, Committees
for longer periods of time. The Coordinating Board appoints
their Chairs and prepares and approves their charters. The
members of Committees and Working Groups are nominated by their Chairs and confirmed by the Coordinating
Board.
Focus Areas are cross‐disciplinary and are meant to consider gaps and needed future products. The GGOS CB approves the Focus Areas. The CB appoints Focus Area leads.
Focus Areas outline their charter and propose plans to address the work that they will undertake.
GGOS Coordinating Office
The GGOS Coordinating Office (CO) performs the day‐to‐
day activities in support of GGOS, the Executive Commit-

202

The Geodesist’s Handbook 2020

tee, the Coordinating Board, and the Science Panel, and ensures coordination of the activities of the various components. The CO ensures information flow, maintains documentation of the GGOS activities, and manages specific assistance functions that enhance the coordination across allareas of GGOS, including inter‐services coordination andsupport for workshops. The CO in its long‐term coordination role ensures that the GGOS components contribute to
GGOS in a consistent and continuous manner. The CO also
maintains, manages, and coordinates the GGOS web presence and outreach.
The position of Manager of External Relations resides
within the Coordinating Office. The GGOS Manager of External Relations coordinates GGOS engagement with external organizations such as the Group on Earth Observations(GEO), the Committee on Earth Observation Satellites(CEOS), and the International Science Council (ISC) World
Data System (WDS). The CB elects the Manager of External Relations by a vote.

frastructure needed to maintain the evolving global reference frames, while at the same time ensuring the broader
support of the scientific applications of the collected data.
Coordinating and implementing the GGOS co-located station network is a key focus of the Bureau.

Bureau of Products and Standards

GGOS President/Chair: Basara Miyahara (Japan)
Vice-President/Chair: Laura Sánchez (Germany)
Chair of GGOS Science Panel: Kosuke Heki (Japan)
Director of Coordinating Office: Martin Sehnal (Austria)
Manager of External Relations: Allison Craddock (USA)
Directors of Bureaus of Networks and Observations: Michael Pearlman (USA)
Director of Bureau of Products and Standards:
Detlef Angerman (Germany)
GGOS Japan Affiliate Representatives:
Toshimichi Otsubo (Japan)
IAG President:
Zuheir Altamimi (France)
IAG Service Representative: Riccardo Barzaghi (Italy)
IAG Service Representative: Daniela Thaller (Germany)
IAG Service Representative: Sean Bruinsma (France)
IAG Service Representative:
Robert Heinkelmann (Germany)
IAG Commissions and ICC Representative:
Tonie Van Dam (Luxemburg)
IAG Commissions and ICC Representative:
Adrian Jäggi (Switzerland)Member-at-Large:
María Cristina Pacino (Argentina)
Member-at-Large:
Nicholas Brown (Australia)
Member-at-Large:
Ludwig Combrinck (South Africa)

The Bureau of Products and Standards keeps track of thestrict observations of adopted resolutions, geodetic standards, standardized units, fundamental physical constants andconventions in all official products provided by the geodetic
community. It reviews, examines and evaluates all actual
standards, constants, resolutions and conventions adopted
by ISO, ISC, IUGG, IAU, IAG and its components, and recommends further use or proposes the necessary updates. It
identifies eventual gaps in standards and products, and initiates steps to close them with, e.g., resolutions by the IUGG
and/or IAG Councils.
Bureau of Networks and Observations
The Bureau of Networks and Observations develops a strategy to design, integrate and maintain the fundamental infrastructure in a sustainable way to satisfy the long-term (10–20 years) requirements identified by the GGOS Science
Panel. The Bureau advocates for implementation of core andother co-located network sites to satisfy GGOS requirements, monitors the present state of the networks and projects future status, and supports and encourages infrastructure critical for the development of data products essential
to GGOS. Primary emphasis must be on sustaining the in-

GGOS Affiliates
A GGOS Affiliate is a national or regional organization thatcoordinates geodetic activities in that country or region.
GGOS Affiliates provide a forum for multi-technique,space-geodetic discussions, work to improve the quality ofspace-geodetic observations, and encourages the different
agencies in that country or region that own, operate, andmaintain the space-geodetic infrastructure there to collaborate with each other. To become a GGOS Affiliate, interested organizations submit an application to GGOS which
is approved by the GGOS CB by a vote.
GGOS Coordinating Board (Voting Members):Global Geodetic Observing System (GGOS)

203

GGOS Bureau of Networks and Observations
Director: Michael Pearlman (USA)The Bureau of Networks and Observations develops a strategy to design, integrate and maintain the fundamental infrastructure in a sustainable way to satisfy the long-term (1020 years) requirements identified by the GGOS Science
Panel. Primary emphasis must be on sustaining the infrastructure needed to maintain the evolving global reference
frames, while at the same time ensuring the broader supportof the scientific applications of the collected data. Coordinating and implementing the GGOS co-located station network is a key focus for the Bureau.

GGOS Bureau of Networks & Observationsx IAG Service Network Representatives
x Committee on Performance Simulations andArchitectural Trade-offs
x Committee on Data and Informationx Committee on Satellite Missions

IGFS:

Riccardo Barzaghi (Italy)
George Vergos (Greece)

IVS:

Hayo Hase (Germany)
Dirk Behrend (USA)ILRS:

Toshi Otsubo (Japan)
Jean-Marie Torre (France)

IGS:

Allison Craddock (USA)Gary Johnston (Australia)

IDS:

Jérôme Saunier (France)
Guilhem Moreaux (France)

Tide Gauges:

Elizabeth Bradshaw (UK)Lesley Rickards (UK)Richard Gross (USA)In addition, the IERS Working Group on Site Survey andCo-location also participates in the BN&O activities; thisWorking group is now in the process of reorganization with
Ryan Hippenstiel / NOAA as Chair.

Structure

Objectives

Director: Michael Pearlman (USA);
Secretary: Carey Noll (USA)
Analysis Representative: Erricos Pavlis (USA)The Bureau of Networks and Observations (BNO) supports
the networks capability available to the IAG in its goal toprovide geodetic data products of sufficient quantity, quality
and temporal and spatial resolution to improve our understanding of the dynamic Earth for both scientific understanding and societal needs. Fundamental to achieving
reaching this goal is the maintenance and further development of the globally available terrestrial and celestial reference frames, which are the basis for our metric measurements over space, time, and evolving technology.
The BN&O advocates for implementation of the global
space geodesy network of sufficient capability and geographic coverage to achieve data products essential for

Members:
PLATO Committee:

Daniela Thaller (Germany)
Benjamin Männel (Germany)

Missions Committee: Roland Pail (Germany)
C.K. Shum (USA)
Data and Information: Nicholas Brown (Australia)
Carey Noll (USA)204

GGOS and serves as a coordinating point for the Services tomeet, discuss status and plans, and examine common paths
for meeting GGOS requirements. Committees and working
groups are included in the Bureau in recognition of theirsynergistic role with Bureau activities.
The role of the BNO is to:x Advocate for the expansion and upgrade of the space
geodesy network for the maintenance and improvementof the reference frame and other GGOS priorities; Main
focus will be on the Reference Frame; but the otherapplications need to be accommodated;x Encourage partnerships to build and upgrade network
infrastructurex Organize and expand the GGOS affiliated network;x Monitor network status; projected network evolution
based on input from current and expected future
participants, estimate performance capability 5 and 10
years ahead;x Conduct simulation studies and analyses to assess
impact on reference frame products of: network
configuration, system performance, technique andtechnology mix, co-location conditions, site ties, andnetwork trade of options (PLATO);
x Develop Metadata Systems for a wide range of users
including GGOS; near term strategy for data products(Carey Noll at GSFC) and a more comprehensive
longer-term plan for an all-inclusive system (NickBrown at GA) (Committee on Data and Information);x Provide the opportunity for representatives from theServices and the Standing Committees to meet and share
progress and plans; discuss issues of common interest;
meetings at EGU, AGU, GGOS Days, etc.;x Talks and posters on the Bureau at EGU, AGU, JPGUAGU, AOGS meetings, etc.;
x Letters/documentation to support stations, current/ new
missions, and analysis centers;

The Geodesist’s Handbook 2020

Tasks
x Continue recruiting station membership in the GGOS
Network through the CfP; issue membership certificates(great response);x Continue monitoring network status and plans; develop
next network projection status for 5 and 10 years ahead;x Provide next update of the “Guideline for GGOS Core
Sites and Co-locations Sites” document;
x Work with the IGFS and IHRF, the PSMSL and theother services to integrate relevant parameters fromother ground networks (gravity field, tide gauges, etc.)
into the GGOS network to support GGOS requirements
including the reference frame, a unified height system,
etc.; advocate for installation of GNSS receivers at
appropriate tide gauges; Global Geodetic Observing
System (GGOS)
x Support the technique Services on the promotion ofrecommended
technologies/configurations
andprocedures in the establishment of new sites and theupgrading of current sites, and in the evaluation of
performance of new stations and new capabilities after
they become operational;
x Continue simulation and trade-off studies for network
options (PLATO Committee)
x Continue metadata systems development; target phase 1(data products) for 2020 (Committee on Data andInformation)
x Improve communication and information exchange andcoordination with the space missions; (Committee on
Satellite Missions)x Work with the IERS Working Group on Site Survey andCo-location to improve the quality of site ties andinstrument reference points:
x Continue BNO meetings to meet, discuss status andplans, and examine common interests and requirements;
x Continue presentation at international meetings in BNO
activities and plans;x Continue providing letters and documentation support
x Update the Bureau web pages for public use (to becompatible with the new GGOS website in process;Global Geodetic Observing System (GGOS)

205

Committees of the Bureau of Networks and Observations

BNO C1: Committee on Performance Simulations and Architectural Trade-Offs(joint with IAG Sub-Commission 1.1)

Chair:
Daniela Thaller (Germany)
Vice-Chair: Benjamin Maennel (Germany)
Objective
The PLATO Committee / Working Group has currently 12member groups working on simulations and data analysis
covering the full range of existing ground and space assets,
including VLBI, SLR, GNSS, and DORIS. The main focus
is on how do we use existing observation capabilities (stations, observation concepts, tracking performance, etc.) including co-location in space with existing and new dedicated satellites to best support GGOS planning and implementation.
Project future network capability and examine trade-off
options for station deployment and closure, technology upgrades, the impact of site ties, additional space missions, etc.
to maximize the utility of the GGOS assets:
x Use simulation techniques to assess the impact onreference frame products of network configuration,system performance, technique and technology mix,
colocation conditions, site ties, space ties (added
spacecraft, etc.), analysis and modeling techniques, etc.;
x Use and developing improved analysis methods forreference frame products by including all existing data
and available co-locations (i.e., include all satellites anduse all data types on all satellites);x Make recommendations on network configuration andstrategies based on the simulation and trade-off studies.
Investigations that are being included in the PLATO activity
include studying the impact of:x The full range of existing ground and space assets:o GNSS assets (ground and space)o SLR (beyond Lageos-1 and -2) including ranging to
GNSS satellites;o LLR assets
o VLBI assets including tracking of GNSS satellites;o Co-located assets in space (e.g. GRACE, OSTM/Jason-2)
o Mixture of existing legacy stations and simulated
next generation stations
o Improved GNSS antenna calibrations and clock estimation strategies (GNSS alone or when in combination with SLR, VLBI, and DORIS)x Anticipated improved performance of current systems:
o Simulate the impact of upgrading existing stations
and their procedureso Simulate the impact of additional ground surveys at
colocation sites (site ties)x Potential future space assets: - Co-locate all four
techniques in space on a dedicated satellite
Tasks
x Examining trade-off options for station deployment andclosure, technology upgrades, the impact of site ties,
etc. and project future network capability based on
network configuration projected by the BNO or relevant
IAG services (IGS, ILRS, IVS, IDS);x Investigating the impact of improved SLR tracking
scenarios including spherical satellites, LEOs, and
GNSS satellites and VLBI satellite tracking on reference
frame products;
x Identifying technique systematics by analyzing shortbaselines, data from new observation concepts, andavailable co-locations (e.g., consistent processing of
LEO and ground-based observations);x Investigating the best-practice methods for co-locationin space and assessing the impact of co-location in spaceon reference frame products based on existing satellites
and by simulation studies for proposed missions.

206

BNO C2: Committee on Data and Information
Chair:
Nicholas Brown (Austria)
Vice-Chair: Carey Noll (USA)Objectives
The Committee on Data and Information had two GGOS
objective areas:x Development and implementation of a portal;x Development and implementation of a metadata scheme
Initial work on the portal was done by Bernd Richter. Whenhe retired, the task was transferred to the GGOS Coordinating Office.
Near term Metadata activity (Carey Noll/CDDIS)
CDDIS is implementing collection-level metadata throughthe Earth Observation System Data and Information System(EOSDIS) Common Metadata Repository (CMR). CDDIS
is an EOSDIS Distributed Active Archive Centers (DAACs)
and thus utilizes the EOSDIS infrastructure to manage collection and granule level metadata describing CDDIS archive holdings; these metadata include DOIs associatedwith the CDDIS archive contents. The CMR is accessible
through APIs and can be used in the future by GGOS to findgeodetic data and products available through the CDDIS.
Longer-Term Metadata activity (Nick Brown / Geoscience Australia)
Development of a Geodesy Markup Language (GeodesyML), for the GNSS community; potential for expansion
to the other space geodesy techniques and GGOS. The current study is identifying metadata standards and requirements, assessing critical gaps and the how these might befilled, what changes are needed in the current standards, and
who are the key people who should work on it (more comprehensive scheme). The schema that would be used by its
elements for standardized metadata communication, archiving, and retrieval. First applications would be the automateddistribution of up-to-date station configuration and operational information, data archives and catalogues, and procedures and central bureau communication. One particularplan of great interest is a site metadata schema underway
within the IGS Data Center Working Group. This work is
being done in collaboration with the IGS, UNAVCO, SIO,
CDDIS, and other GNSS data centers. The current activity
is toward a means of exchange of IGS site log metadata utilizing machine-to-machine methods, such as XML and web
services, but it is expected that this will be expanded to theother Services to help manage site related metadata and toother data related products and information. Schema for the

The Geodesist’s Handbook 2020

metadata should follow international standards, like ISO
19xxx or DIF, but should be extendable for technique-specific information, which would then be accessible throughthe GGOS Portal.
Tasks:
Activities underway at CDDIS:
1. Complete collection level metadata related to CDDIS
data and product holdings in the EOSDIS Common
Metadata Repository (CMR)
2. Re-ingest CDDIS data holdings in order to extract
granule level metadata linked to new collection level
records
Activities underway in Geodesy Markup Language (GeodesyML) System
1. Review and document the metadata and standards
requirements of precise positioning users in expectedhigh use sectors (e.g. precision agriculture, intelligent
transport, marine, location-based services etc.).
2. Assess and document the critical gaps in standards
which restrict how Findable Accessible Interoperable
and Reusable (FAIR) precise positioning data is for the
expected high use sectors.
3. Record use cases of standards being applied well andthe benefits it provides to users.
4. Review the “use cases” of geodetic data developed by
Geoscience Australia and the IGS Data Center Working
Group and document what work and time would be
required to ensure these use cases can be met ininternational standards. This could be:o Identify which gaps can be filled by GeodesyMLo Identify which components of GeodesyML would bebetter, handled by / integrated with, existing standards(such as TimeSeriesML, SensorML, Observations andMeasurements) where possible.
o Identify which components of already existing
international geospatial infrastructure can beapproached (such as the European Inspire initiative)o Advise on who we should engage with from the
OGC/ISO community to facilitate a change to a
standard to meet our requirements.
5. Work with Project Partners to develop and test otheruse cases (e.g. integration of geodetic data withgeophysics data (e.g. tilt meters), Intelligent Transport
Sector data, mobile applications). Then, document whatwork and time would be required to ensure these use
cases can be met in international standards.
6. Provide advice on how to best engage with the rightcommunities to learn from their experiences, test theirtools and influence the development of required
standards.

Global Geodetic Observing System (GGOS)BNO C3: Committee on Satellite Missions
Chair:
Roland Pail (Germany)
Vice-Chair: C.K. Shum (USA)Objectives
Improve coordination and information exchange with themissions for better ground-based network response to mission requirements and space-segment adequacy for the realization of GGOS goals
x Advocate, coordinate, and exchange information withsatellite missions as part of the GGOS space
infrastructure, for a better ground-based network
response to mission requirements and space-segment
adequacy for the realization of the GGOS goals.
x Assess current and near-future satellite infrastructure
and their compliance with GGOS 2020 goals;
x Support proposals for new mission concepts andadvocate for needed missions;x Interfacing and outreach with other components of the
Bureau; especially the ground networks component, thesimulation activity (PLATO), as well as the Bureau ofStandards and Products.

207

Tasks
x Continue the regular activities, i.e. updating the twocentral lists, supporting future satellite missions, etc.
x Work with the Coordinating Office to set up andmaintain a Satellite Missions Committee section on the
GGOS website;x Evaluate the contribution of current and near-term
satellite missions to the GGOS 2020 goals;
x Work with GGOS Executive Committee, Focus Areas,and data product development activities (e.g., ITRF) to
advocate for new missions to support GGOS goals;
x Support the Executive Committee and the Science
Committee in the GGOS Interface with space agencies;x Finalize and publish (outreach) of Science and User
Requirements Document for future gravity field
missions.
x Increase the exchange and collaboration with PLATO;
set up a more formal procedure of collaboration; discussneeds and run simulations to study the impact of futuresatellite missions, identify gaps for fulfilling the GGOS
goals, etc.

208

The Geodesist’s Handbook 2020

GGOS Bureau of Products and Standards
Director: Detlef Angermann (Germany)
Vice-Director: Thomas Gruber (Germany)

Members:
M. Gerstl (Germany)
R. Heinkelmann (Germany)
U. Hugentobler (Germany)
L. Sánchez (Germany)
P. Steigenberger (Germany)
Associated Members, Representatives of IAG Services and other entities involved:
R. Barzaghi (Italy)
S. Bonvalot (France)
H. Capdeville (France)
M. Craymer (Canada)
J. Gipson (USA)T. Herring (USA)J. Hilton (USA)L. Hothem (USA)E. Ince (Germany)

K. Kelly (USA)J. Kusche (Germany)
F. Lemoine (USA)J.M. Lemoine (France)
E. Pavlis (USA)M. Reguzzoni (USA)J. Ries (USA)N. Stamatakos (USA)
H. Wziontek (Germany)

GGOS components associated to the BPS:x Committee Earth System Modelling (Chair: M. Thomas)
x Committee Essential Geodetic Variables (Chair: R.
Gross)x BPS Working Group Towards a consistent set of parameters for the definition of a new GRS (Chair: U. Marti)

Objectives
x The Bureau of Products and Standards (BPS) supports
GGOS in its goal to obtain consistent products
describing the geometry, rotation and gravity field of the
Earth. A key objective of the BPS is to keep track ofadopted geodetic standards and conventions across all
IAG components as a fundamental basis for thegeneration of consistent geometric and gravimetricproducts. The work is primarily build on the IAG
Service activities in the field of data analysis andcombinations. The BPS shall act as contact andcoordinating point regarding homogenization ofstandards and IAG products. Moreover the BPS interacts
with external stakeholders that are involved in standards
and conventions, such as the International Organizationfor Standardization (ISO), the Committee on Data for
Science and Technology (CODATA), the International
Astronomical Union (IAU) and the UN GGIM
Subcommittee on Geodesy (SCoG). The objectives of
the BPS may be divided into two major topics/activities:
1. Standards: This includes the compilation of an
inventory regarding standards, constants, resolutions
and conventions adopted by IAG and its components
and a regular update of such a document. The BPS hascompiled an inventory “GGOS Bureau of Products andStandards: Inventory of Standards and Conventions
used for the Generation of IAG Products” (see IAG
Geodesist's Handbook 2016). This inventory provides
an assessment of the present status, identifies gaps andshortcomings concerning the generation of the IAG
products, as well as recommendations. This inventory
needs to be regularly updated since the IAG standards
and products are evolving over time. Finally, the BPS
shall propose the adoption of new standards where
necessary and propagate standards and conventions to
the wider scientific community and promote their use.
In this context, the BPS recommends the developmentof a new Geodetic Reference System GRS20XX basedon the best estimates of the major parameters related toa geocentric level ellipsoid.
2. Products: The BPS shall take over a coordinating role
regarding the homogenization of standards andgeodetic products. The present status regarding IAG
Service products shall be evaluated, including analysis

Global Geodetic Observing System (GGOS)

and combination procedures, accuracy assessment withrespect to GGOS requirements, documentation and
IAG metadata information for IAG products. The
Bureau shall initiate steps to identify user needs andrequirements for geodetic products and shall contributeto develop new and integrated products. The BPS shallalso contribute to the development of the GGOS Portal(as central access point for geodetic products), to ensureinteroperability with IAG Service data products andexternal portals (e.g., GEO, EOSDIS, EPOS, GFZ Data
Services).
Tasks
x The tasks of the Bureau of Products and Standards areto:x act as contact & coordinating point for homogenizationof IAG standards and products
x keep track of adopted geodetic standards andconventions across all IAG components, and initiate
steps to close gaps and deficiencies
x interact with external stakeholders in the field ofstandards and conventions (e.g., IAU, ISO, BIPM,
CODATA, UN-GGIM, …), the BPS director has been
nominated as IAG representative to ISO/TC 211 and as
IAG representative in the UN-GGIM GGRF Working
Group “Data Sharing and Development of Geodetic
Standards”
x update the inventory on standards and conventions used
for the generation of IAG products
x contribute to the re-writing/revising of the IERS
Conventions, the BPS director has been nominated as
Chapter Expert for Chapter 1 “General definitions andnumerical standards“x focus on the integration of geometric and gravimetricobservations and to support the development ofintegrated products (e.g., GGRF, IHRF, atmosphere
products)x contribute to the UN GGIM Subcommittee on Geodesy(SCoG)x contribute to the Committee on Essential Geodetic
Variables (EGVs)
x contribute to the GGOS DOI Working Group

209

Committees and Working Groups of the
Bureau of Products and Standards
GGOS Committee on Earth System Modeling
Chair: Maik Thomas (Germany)
The GGOS Committee on “Earth System Modeling” tends
to promote the development of physically consistent modular Earth system modeling tools that are simultaneously applicable to all geodetic parameter types (i.e., Earth rotation,
gravity field and surface geometry) and observation techniques. Hereby, the committee contributes to:x the interpretation of geodetic monitoring data and, thus,
to a deeper understanding of dynamical and complex
interacting processes in the Earth system responsible forthe observed variations;x the establishment of a link between the geodetic
products delivered by GGOS and numerical processmodels;x a consistent combination and integration of observed
geodetic parameters derived from various monitoring
systems and techniques;x the utilization of geodetic products for theinterdisciplinary scientific community.
Objectives
The overall long-term goal is the development of a physically consistent modular numerical Earth system model forhomogeneous processing, interpretation and prediction ofgeodetic parameters with interfaces allowing the introduction of constraints provided by geodetic time series of global
surface processes, rotation parameters and gravity variations. This ultimate goal implicates the following objectives:
x development of Earth system model components
considering interactions and relationships between
surface deformation, Earth rotation and gravity field
variations as well as interactions and physical fluxes
between relevant compartments of the Earth system;
x promotion of homogeneous processing of geodetic
monitoring data (de-aliasing, reduction) by processmodeling to improve analyses of geodetic parametersets;
x contributions to the interpretation of geodetic
parameters derived from different observation
techniques by developing strategies to separate
underlying physical processes;
x contributions to the integration of geodetic observations
based on different techniques in order to promote

210

The Geodesist’s Handbook 2020

validation and consistency tests of various geodetic
products.
Activities
Major current activities focus on:x the implementation of generalized modules for therealistic consideration of interactions of near-surface
fluids with the geosphere arising, e.g., from surfaceloading and self-attraction;
x implementation of interfaces to geodetic monitoringdata based on Kalman and particle filter approaches inorder to constrain and improve stand-alone model
approaches and to prove consistency of various geodetic
monitoring products;
x feasibility studies for the provision of error anduncertainty estimates of model predictions of geodetic
parameters (Earth rotation, gravity field, surface
deformation) due to imperfect model physics,
initialization, and external forcing.
Important in-progress activities and future efforts focus on:x evaluation of opportunities to constrain dynamicallycoupled model systems with geodetic data products byapplying Kalman filter and inversion techniques;x application of forward modeling and inversion methods
in order to improve model-based predictions of geodetic
quantities and to invert geodetic observations for theunderlying causative processes.

Committee on Essential Geodetic Variables
Chair:

Richard Gross (USA)The GGOS BPS Committee on Essential Geodetic Variables was established in 2018 in order to define a list of Essential Geodetic Variables and to assign requirements tothem. Essential Geodetic Variables (EGVs) are observed
variables that are crucial (essential) to characterizing the geodetic properties of the Earth and that are key to sustainable
geodetic observations. Examples of EGVs might be the positions of reference objects (ground stations, radio sources),
Earth orientation parameters, ground- and space-based gravity measurements, etc. Once a list of EGVs has been determined, requirements can be assigned to them. Examples ofrequirements might be accuracy, spatial and temporal resolution, latency, etc. These requirements on the EGVs canthen be used to assign requirements to EGV-dependent
products like the terrestrial and celestial reference frames.
The EGV requirements can also be used to derive requirements on the observing systems that are used to observe theEGVs. And the list of EGVs can serve as the basis for a gap

analysis to identify observations needed to fully characterize
the geodetic properties of the Earth. During GGOS Days
2017 it was agreed that a Committee within the GGOS Bureau of Products and Standards should be established in order to define the list of Essential Geodetic Variables and toassign requirements to them. This Committee was subsequently established in 2018 and consists of representativesof the IAG Services, Commissions, Inter-Commission
Committees, and GGOS Focus Areas.
Tasks
The tasks of the Committee on Essential Geodetic Variables
are to:x Develop criteria for choosing from the set of all geodetic
variables those that are considered essential
x Develop a scheme for classifying EGVs
x Within each class, define a list of EGVs
x Assign requirements to each EGV
x Document each EGV including its requirements,
techniques by which it is observed, and point-of-contact
for further information about the EGV
x Perform a gap analysis to identify potential new EGVs
x Define a list of geodetic products that depend on each
EGV
x Assign requirements to the EGV-dependent products
x Hold workshops to engage the geodetic community inthe process of defining EGVs, determining theirdependent products, and assigning requirements to them

GGOS Working Group: Towards a consistent set of parameters for the definitionof a new GRS
Chair: Urs Marti (Switzerland)
Terms of Reference
The Geodetic Reference System 1980 GRS80 is still theconventional system for most applications in Geodesy andother Earth sciences. It was defined through the four parameters a (semi-major axis), J2 (Dynamical Form Factor), GM(geocentric Gravitational Constant) and ω (Angular Rotation Velocity). It represents the scientific status of the
1970ies and in its concept, the tidal systems and relativistic
theories are not considered. Since its adaptation, various inconsistencies have been introduced into geodetic standards
and applications, such as new values for GM or a in the
IERS conventions. In 2015, a conventional value for thegravitational potential at sea level W0 was adopted in an
IAG resolution, which is in contradiction to the definition of
GRS80.

Global Geodetic Observing System (GGOS)

This WG will publish a new set of defining parameters
for a modern GRS based on todays knowledge and calculate
all the necessary derived parameters in a consistent way. It
will study the necessity to work towards an IAG resolution
to replace GRS80 as the conventional system and provide
transformation procedures between the two systems. It will
study as well the necessity to define and adopt a conventional global gravity field model for standard applications in
geodesy, navigation and related topics.
This JWG is assigned to the GGOS Bureau of Products
and Standards (BPS) and works together with representatives of IAG Commissions 1 and 2, the Inter-CommissionCommittee on Theory (ICCT), the International Gravity
Field Service (IGFS), the International Earth Rotation andReference Systems Service (IERS) and the Committee on
Essential Geodetic Variables (EGV).
This JWG will focus its activities on the coordination of
the geometric reference frame, the global height system, theglobal gravity network and their temporal changes. The application of Earth orientation parameters and tidal models
and the underlying standard and reference models has to bebrought into consistency.
Objectives and activities
The main objectives and activities of this working group are:x Calculate consistent parameters of a new mean Earthellipsoid and derived quantities
x Study the necessity to replace the global reference
system GRS80 as the conventional system
x Advance the realization of a conventional global
reference gravity field model (combined and satellite
only)

211

x Assist the working group for establishing theInternational Height Reference System (IHRS) in therealization
x Integrating and combining the global gravity networkwith other techniquesx Study the influence of earth orientation parameters, tidal
models and relativistic effects on the realization of aconsistent global reference frame in geometry, heightand gravity
x Foster the free exchange of geodetic data and products
Members
Urs Marti (Switzerland), Chair
Detlef Angermann (Germany), Chair of GGOS BPS, IERS
Richard Gross (USA) IAG Vice President, Committee on
EGV
Ilya Oshchepkov (Russia), GRS, Gravity Networks andHeight Systems
Christopher Kotsakis (Greece), Commission 1
Jonas Ågren (Sweden), Commission 2
Ulrich Meyer (Switzerland) COST-G
Riccardo Barzaghi (Italy), IGFS
Jaakko Mäkinen (Finland), Tidal Systems
Pavel Novak (Czech Republic), ICCTLaura Sánchez (Germany), IHRF
Hartmut Wziontek (Germany), IGRF
John Nolton (USA), GRS
Robert Heinkelmann (Germany), IAU
Sergei Kopeikin (USA), relativistic effects
Erricos Pavlis (USA), ILRS

x

212

Focus Area: Unified Height System
Chair: Laura Sánchez (Germany)
The present objective of Focus Area Unified Height Systemis the implementation of the IAG resolution for the definition and realization of an International Height Reference
System (IHRS) issued during the 2015 IUGG General Assembly. This resolution outlines the conventions for the definition of the IHRS in terms of potential parameters: The
definition is given in terms of potential parameters: the vertical coordinates are geopotential numbers (–'WP = CP =W0 – WP) referring to an equipotential surface of the Earth's
gravity field realized by the conventional value W0 = 62 636
853.4 m2s-2. The spatial reference of the position P for the
potential WP = W(X) is given by coordinates X of the International Terrestrial Reference Frame (ITRF). This Resolution also states that the IHRS coordinates should be related
to the mean-tide system/mean crust.
At present, a main challenge is the realization of the
IHRS; i.e., the establishment of the International Height
Reference Frame (IHRF). It is expected that the IHRF follows the same structure as the ITRF: a global network with
regional and national densifications, whose geopotential
numbers referring to the global IHRS are known. According
to the GGOS objectives, the desired accuracy of these global
geopotential numbers is 1 × 10-2 m2s-2. In practice, the precise realization of the IHRS is limited by different aspects;
for instance, there are no unified standards for the determination of the potential values WP, the gravity field modelling
and the estimation of the position vectors X follow different
conventions, the geodetic infrastructure is not homogeneously distributed globally, etc. Therefore, the achievable accuracy may be restricted to 10 × 10-2 m2s-2 … 100 × 10-2
m2 s-2, which is one or two orders of magnitude lower thanthe desired accuracy.
During the term 2015 – 2019, important advances wereachieved: a global core reference network for the IHRF was
defined and, within the Colorado experiment, it was possible to compare different methodologies for the determination of the reference coordinates WP. The results are very
promising and these activities will be continued in term
2019 – 2023 by the Joint Working Group (JWG) 0.1.3 “Implementation of the International Reference Frame – IHRF”.
This working group is a joint initiative of Joint Working
Group (JWG) of the GGOS Focus Area Unified Height System, the International Gravity Field Service (IGFS), the IAG
Inter-commission Committee on Theory (ICCT) and the
IAG Commissions 2 (Gravity field) and 1 (Reference
Frames). The corresponding terms of reference are describe
in the following.

The Geodesist’s Handbook 2020

Joint Working Group 0.1.3: Implementation of the International Height Reference
Frame (IHRF)
Chair: Laura Sánchez (Germany), Lead of the GGOS Focus
Area Unified Height System
Vice-chair: Riccardo Barzaghi (Italy), Chair of the International Gravity Field Service
Major objectives of the JWG 0.1.3 are:x Based on the Colorado experiment outcomes, toelaborate a document with detailed standards andconventions for the realization and maintenance of theIHRS.
x To compute a first static solution for the IHRF core
network, to evaluate the achievable accuracy under thepresent conditions (data availability, computation
methods, etc.) and to identify key actions to improve thedetermination of the IHRS/IHRF coordinates.
x With the support of the IAG Commission 2, the IGFS
and the ICCT to promote the study ofo quality assessment in the determination of potential
values,o determination of potential changes with time Ẇ,o realization of the IHRS in marine areas.
x In agreement with the IGFS and the IAG Commission 2,
to design a strategy to install an operational
infrastructure within the IGFS to ensure the maintenanceand availability of the IHRF in a long-term basis.
Aspects to be considered areo Updates of the IHRS definition and realization according to future improvements in geodetic theory
and observations.
o Regular updates of the IHRF (e.g. IHRFyyyy) according to new stations, coordinate changes withtime, improvements in the estimation of reference
coordinates and modelling of the Earth’s gravity
field, etc.
o Support in the realisation and utilisation of the
IHRS/IHRF at regional and national level.
o To guarantee an organizational and operational infrastructure to ensure the sustainability of the IHRF.
A strong joint work is planned withx International Gravity Field Service – IGFS, chair: R,
Barzaghi (Italy), vice-chair: G. Vergos (Greece).
x ICCT JSG: Geoid/quasi-geoid modelling for realizationof the geopotential height datum, chairs: J Huang(Canada), YM Wang (USA).
x IAG SC 2.2: Methodology for geoid and physical heightsystems, chair: G. Vergos (Greece).

Global Geodetic Observing System (GGOS)

x IAG Commission 2.2 WG: Error assessment of the 1 cm
geoid experiment, chairs: M Willberg (Germany), T
Jiang (China).
x IAG Commission 2 JWG: On the realization of theInternational Gravity Reference Frame, chairs: H.
Wziontek (Germany), S. Bonvalot (France)
x GGOS-BPS WG: Towards a consistent set of parameters
for a new GRS, chair U Martí (Switzerland).
Members
H.A. Abd-Elmotaal (Egypt)J. Ågren (Sweden)
H. Denker (Germany)
W. Featherstone (Australia)
R. Forsberg (Denmark)
V.N. Grigoriadis (Greece)
T. Gruber (Germany)
G. Guimarães (Brazil)
J. Huang (Canada)
T. Jiang (China)
Q. Liu (Germany)
J. Mäkinen (Finland)
U. Marti (Switzerland)
K. Matsuo (Japan)
P. Novák (Czech Republic)
I. Oshchepkov (Russia)
M. Sideris (Canada)
D. Smith (USA)M. Varga (Croatia)
G. Vergos (Greece)
M. Véronneau (Canada)
Y. Wang (USA)
M. Willberg (Germany)
M. Amos (New Zealand)
D. Avalos (Mexico)
M. Bilker-Koivula (Finland)
D. Blitzkow (Brazil)
S. Claessens (Australia)
X. Collilieux (France)
M. Filmer (Australia)
A.C.O.C. Matos (Brazil)
J. McCubbine (Australia)
R. Pail (Germany)
D. Roman (USA)C. Tocho (Argentina)
H. Wziontek (Germany)

Focus Area: Geohazards
Chair: J. LaBrecque (USA)The Geohazards Monitoring Focus Area of the Global Geodetic Observing System (GGOS) seeks to apply geodeticscience and technology in support of global and regional resiliency to environmental hazards.
The GGOS and its associated IAG services (International GNSS Service (IGS), International VLBI Service forGeodesy and Astrometry (IVS), International DORIS Service (IDS), International Laser Ranging Service (ILRS), International Earth Rotation and Reference Systems Service(IERS), and International Gravity Field Service (IGFS))
provide products that serve as the fundamental geodetic references for science, governments, and industry. The mostnotable of these products serve as the basic reference for positioning and timing information associated with the Global
Navigation Satellite Systems (GNSS) including the International Terrestrial Reference Frame (ITRF), precision orbit

213

and time information and continuing scientific and technicaladvancements to the utilization of the GNSS data.
These and other GGOS products achieved wide global
recognition and acceptance because of their accuracy, timeliness, and continuing technical improvements. These are
the very qualities needed for effective environmental warning. In some cases, the acceptance of geodetic applications
have been immediate and widespread such as the application of GNSS to understanding and modeling earthquake
faults.
However, in other cases geodetic technology has advanced faster than nations can utilize this new capability.
The Geohazards Focus Area seeks to accelerate and guidethe acceptance of new geodetic capability to improve resilience to environmental hazards. The Focus Area will establish working groups comprised of GGOS members and the
responsible agencies of participating nations. The Focus
Area encourages the sharing of intellectual, financial andphysical resources as recommended by the UN-GGIM(http://ggim.un.org).
As its first initiative, the Geohazards Monitoring Focus
Area has issued a Call for Participation (CfP: to researchscientists, geodetic research groups and national agencies insupport of the implementation of the IUGG 2015 Resolution
4: Global Navigation Satellite System (GNSS) Augmentation to Tsunami Early Warning Systems https://office.iagaig.org/iag-and-iugg-resolutions. The CfP responders comprise a working group to be a catalyst and a motivating force
through the definition of requirements, identification of resources, and the encouragement of international cooperationin the establishment, advancement, and utilization of GNSS
for Tsunami Early Warning. The initiative is initially focused upon the Indo-Pacific region following the IUGG
2015 Resolution 4.
Present Status and Progress:
x The Geohazards Focus Area (GFA) is focused upon theimplementation of the IUGG 2015 General Assembly
Resolution #4. The GFA summarized its previous
activities in a 2015 to 2019 quadrennial report to the
IAG.
(https://www.dropbox.com/s/9ivbaqju798y2f9/IAGGeohazards%20Report%202015-2019.pdf?dl=0).
x Since the establishment of GATEW working group, theworking group has grown to 18 members from 12
nations (chart) with the recent inclusion of the Indian
National Centre for Ocean Information (INCOIS). As
listed in the attached membership chart.

214

The Geodesist’s Handbook 2020

Global Geodetic Observing System (GGOS)

x The GATEW worked with other organizations topublish a report on GTEWS 2017 in the UNDRR
GAR19 report in May 2019 https://www.preventionweb.net/ publications/view/66779. The GAR 19 paper
reports on the deliberations and recommendations of the
GTEWS 2017 workshop that GGOS GFA cosponsored.
The GAR 19 white paper articulates the role of GTEWS
technology and the GTEWS 2017 recommendations in
the implementation of the Sendai Framework.
x The strong participation exemplified by the GATEW
membership now serves as the basis of a GEO
community activity Geodesy4Sendai. See page 92 of the
GAR19 report of the GTEWS 2017 workshop
https://www.earthobservations.org/documents/gwp20_22/gwp2020_summary_document.pdf.
x The Geodesy4Sendai activity raises the recommendation of the GTEWS 2017 workshop to ministerial level
discussions.
Planned Actions and Milestones
x 2020 election of a Chair for the GATEW working group/x Establish the GNSS Shield Consortium as recommended
by the GTEWS 2017 workshop.
x Organize the GATEW activities to align with the GEO
Geodesy4Sendai community activity
x GTEWS 2020: The GFA is engaged with partneringorganization in the planning and fund raising isunderway for GTEWS 2020 workshop with a focus upon
implementation of the GTEWS 2017 workshop.
Develop Support for GNSS Consortium:x A proposal to be re-submitted to the US National
Science Foundation by members of the READI Group(a member of the GATEW working group) is viewed asa US contribution to GNSS Shield Consortium asrecommended by the GTEWS 2017 workshop. Similar
efforts by other GATEW is solicited.
x G. Occhipinti (IPGP, France) and M. Crespi (Sapienza
University of Rome, Italy) are preparing a proposal to
the European Commission to apply ionospheric imaging
to the estimation of earthquake and tsunami risk andtheir resulting disasters.
x If they are successful, these efforts by the European and
US membership will be the first contributions to theimplementation of the GTEWS 2017 recommendations.
Please review the recommendations of the GTEWS
2017 and consider how you might support theserecommendations.
Future working groups of the Geohazards Monitoring Focus
Area will support compelling initiatives that improve the re-215

siliency of global and regional societies through the application of geodetic science and technology. The working
groups mandate will be to develop an attainable and valuable goal as recommended by the GGOS Science panel. Eachworking group will define a work-plan with an estimatedtime line that will be subject to periodic review by the
GGOS Coordinating Board.

Focus Area on Geodetic Space Weather
Research
Chair:

Michael Schmidt (Germany)

Space weather means today an own, very up-to-date and interdisciplinary field of research. It describes physical processes in space mainly caused by the Sun’s radiation of energy. The manifestations of space weather are multiple, forinstance, the variations of the Earth’s magnetic field or thechanging states of the upper atmosphere, in particular theionosphere and the thermosphere.
The most extreme known space weather event happened
at September 1, 1859 – the Carrington storm. Other prominent recent, but much weaker events have been the Halloween storm at October 28 – 30, 2003, or the St. Patrick’s
storm at March 17, 2015. The strength of these events, theirimpacts on modern society and the possibility of muchstronger future events have brought several countries suchas US, UK, Japan, Canada and China to recognize the necessity of studying these impacts scientifically, of developing protection strategies and procedures and to establish
space weather data centres and space weather services. As aconsequence of these activities the Focus Area on Geodetic
Space Weather Research (FA GSWR) was initiated and finally implemented into the GGOS structure. The following
statements summarize the necessity of geodesy to deal withthe topic space weather: Geodesy has
x to deal with the ionosphere, since the measurements ofmost of the space-geodetic observation techniques are
depending on the properties of the ionosphere along theray path of an electro-magnetic wave between
transmitter and receiver,x to deal with the thermosphere, since the thermosphericdrag is the most important deceleration effect on LowEarth Orbiting (LEO) satellites below 1000 km andobjects in the re-entry stage,x a long history and large experience in developing andusing sophisticated analysis techniques and modelling
approaches.
To put the aforementioned issues in a nutshell, the main
objectives of the FA GSWR are (1) the improvement of positioning and navigation (PPP), (2) the improvement of pre-216

cise orbit determination (POD) and (3) the study of the coupled processes between magnetosphere, ionosphere andthermosphere (MIT),
Objective (1) aims at the high-precision and the highresolution (spatial and temporal) modelling of the electron
density. This allows to compute a signal propagation delay,
which will be used in many geodetic applications, in particular in positioning, navigation and timing (PNT). Moreover,
it is also important for other techniques using electromagnetic waves, such as satellite- or radio-communications.
Concerning objective (2), satellite geodesy will obviously
benefit when working on POD, but there are further technical matters like collision analysis or re-entry calculation,
which will become more reliable when using high-precisionand high-resolution thermospheric drag models. Objective(3) links the magnetosphere with the first two objectives byintroducing physical laws and principles such as continuity,
energy and momentum equations and solving partial differential equations.
For a long time geodesists looked at the atmosphere justas a disturbing factor whose impacts on electromagnetic signal propagation, i.e. the signal delay and the bending of theray path, have to be corrected by applying atmospheric correction models of sufficient accuracy. On the other hand, as
already mentioned before, the observation data of various
geodetic measurement techniques that are influenced by theatmosphere in different ways provide valuable information
on state and dynamics of the ionosphere. These are of greatinterest also for other disciplines such as meteorology. Today, for Geodetic Space Weather Research geodesy has togo another step forward by introducing physics. To be more
specific, we have to take into account the complete chain of
cause and effect. This means the research has (1) to startwith processes and events on the Sun, (2) to be continued
with the effects on the magnetosphere, the ionosphere, thethermosphere and their coupling processes down to the
Earth’s surface and finally (3) to end by the consideration of
the impact of space weather on (geodetic) applications andmeasurement systems.
Geodetic Space Weather Research is fundamental research, particularly when intending to detect and to survey
structures of the ionosphere, e.g. bubbles, or when studying
special phenomena like electro-jets. Summarizing, geodetic
space weather research has to be based on (a) the use andcombination of all space geodetic observation methods, (b)the use of Sun (solar) observations, (c) real-time modelling,(d) the development of deterministic and stochastic forecast
approaches and (e) assimilation strategies.

The Geodesist’s Handbook 2020

Planned activities of the FA GSWR
x extensive simulation studies which have to be performed
in order to assess the impact of space weather ontechnical systems and to define – as a consequence –necessary actions in case of severe space weather events,
x the development of ionosphere and thermospheremodels as stated above as GGOS products for direct
application,x the establishment of recommendations for applicationsof the models, e.g. in satellite orbit determination,
collision analysis and re-entry computations,x updates of the models as needed and based on the future
improvements of modelling strategies, observing
systems, etc., andx the establishment of roadmaps for improving the models
by including future satellite measurement systems andmissions such as the Formosat-7/COSMIC-2 mission.
To arrive at the above described aims of the FA GSWR one
new Joint Study Groups (JSG) and three Joint Working
Groups (JWG) have to be installed. In detail, these groups
are titled asx JSG 1: Coupling processes between magnetosphere,
thermosphere and ionosphere (implemented at IAG
ICCT and joint with GGOS, Focus Area on Geodetic
Space Weather Research and IAG Commission 4, Subcommission 4.3)
x JWG 1: Electron density modelling (joint with IAG
Commission 4, Sub-commission 4.3)
x JWG 2: Improvement of thermosphere models (joint w.
IAG Commission 4, Sub-commission 4.3 and ICCC)
x JWG 3: Improved understanding of space weather
events and their monitoring by satellite missions (joint
with IAG Commission 4, Sub-commission 4.3);
For more details see the terms of Reference (ToR) andthe descriptions of the JSG and the JWGs presented below.
There will be a strong connection and cooperation between
the four groups. Since the first is covering the coupling processes, i.e. it has to be dealt with many physical problems,
we will install it as JSG at the IAG ICCT.
Other implemented IAG Study Groups (SG) and Working Groups (WG) within the IAG programme will provide
valuable input for the FA GSWR, in particular from theCommission 4, Sub-commission 4.3. Finally, it should be
mentioned that the work within the FA GSWR will be carried out in close relation to the International Association of
Geomagnetism and Aeronomy (IAGA), since this organisation is also concerned with the understanding of properties
related, e.g. to the ionosphere and magnetosphere as well as
the Sun and the solar wind. Partly, the work will be related
to the International Association of Meteorology and Atmospheric Sciences (IAMAS), too.

Global Geodetic Observing System (GGOS)

Overview on one Joint Study Group (JSG)and three Joint Working Groups (JWG):
The running time of these groups is not restricted to the 4year IAG-period from 2019 to 2023, but could last significantly longer.

JSG 1: Coupling processes between magnetosphere, thermosphere and ionosphere
Implemented at IAG ICCT; joint with GGOS, Focus Area
on Geodetic Space Weather Research and Commission 4,
Sub-Commission 4.3
Chair: Andres Calabia Aibar (China, andres@calabia.com)
Vice-Chair: vacantTerms of Reference (ToR) / Description:
Consequences of upper-atmosphere conditions on humanactivity underscore the necessity to better understand andpredict the effects of Magnetosphere-Ionosphere-Thermosphere (MIT) processes and coupling, and prevent from potential detrimental effects on orbiting, aerial, and groundbased technologies. For instance, major concerns include
the perturbation of electromagnetic signals passing throughthe ionosphere for accurate and secure use of Global Navigation Systems (GNSS), and the lack of accurate aerodynamic-drag models required for accurate tracking, decay,
and re-entry calculations of Low Earth Orbit (LEO) objects,
including manned and unmanned artificial satellites. In addition, ground power grids and electronics of satellites could
be influenced, e.g., by the magnetic field generated by sudden changes in the current system due to solar storms. Figure1 illustrates the proposed new structure of the Focus Area
on Geodetic Space Weather Research (FA GSWR) as a double tetrahedron.
Monitoring and predicting the Earth’s upper atmosphereprocesses driven by solar activity is highly relevant to science, industry and defence. These communities emphasize
the need to increment the research efforts for better understanding of the MIT responses to highly variable solar conditions, as well as detrimental space weather effects on ourlife and society. On the one hand, the electron-density variation produces the perturbation in speed and direction ofelectromagnetic signals propagated through the ionosphere,
and reflects as a time-delay in the arrival of the modulated
components from which pseudo-range measurements of
Global Navigation Satellite Systems are made, and an advance in the phases of the signal’s carrier waves which af-

217

fects carrier-phase measurements. On the other hand, aerodynamic-drag associated with neutral-density fluctuations
resulting from upper atmospheric expansion/contraction in
response to variable solar and geomagnetic activity, increases drag and decelerates Low Earth Orbits, dwindlinglifespan of space-assets, and making tracking difficult.
Through the interrelations, dependencies, and coupling
patterns between ionosphere, thermosphere, and magnetosphere variability, the JSG 1 aims to improve the understanding of the coupled processes in the MIT system, andconsiderations of the solar contribution. In addition, tides
from the lower atmosphere forcing can feed into the electrodynamics, and have a composition effect leading to changes
in the MIT system. In this scheme, our tasks are addressed
to exploit the knowledge of the tight MIT coupling by investigating multiple types of magnetosphere, ionosphere,
and thermosphere observations. The final outcome will help
to enhance the predictive capability of empirical and physics-based models through interrelations, dependencies, andcoupled patterns of variability between the essential geodetic variables.
Objectives:
x Characterize and parameterize the global modes of MIT
variations associated with diurnal, seasonal, and space
weather drivers, as well as the lower atmosphere forcing.
x Determine and parameterize the mechanisms
responsible for discrepancies between observables andthe present models.
x Detect and investigate coupled processes in the MIT
system for the deciphering of physical laws andprinciples such as continuity, energy and momentum
equations and solving partial differential equations.
Members:
1.
2.
3.
4.
5.

Piyush M. Metha (Department of Aerospace
Engineering and Mechanics, University of Minnesota,
USA, piyushmukeshmehta@gmail.com)
Liang Yuan (Shanghai Astronomical Observatory,
ChineseAcademyof
Sciences,
China,
llyuan@shao.ac.cn)
Astrid Maute (National Center for AtmosphericResearch, High Altitude Observatory, Colorado, USA,maute@ucar.edu
Gang Lu (High Altitude Observatory, National Center
for Atmospheric, ganglu@ucar.edu)
TBC

218

The Geodesist’s Handbook 2020

JWG 1: Electron density modelling
Joint with Commission 4, Sub-Commission 4.3
Chair: Fabricio dos Santos Prol (Germany) Fabricio.DosSantosProl@dlr.de
Vice-Chair: Alberto Garcia-Rigo (Spain) garciarigo@ieec.cat
Terms of Reference (ToR)/Description:
The main goal of this group is to disseminate and evaluate
established methods of 3-D electron density estimation interms of electron density, peak height, Total Electron Content (TEC), or other derived products that can be effectively
used for GNSS positioning or for analyzing perturbed conditions due to representative space weather events. It isplanned to generate products, showing the general error
given by such 3-D electron density estimations and, also,
distribute information regarding to space weather conditions. To achieve this main goal, the following objectives
are defined.
Objectives:
x Develop a database, where the methods from the groupmembers will be able to be evaluated in terms of GNSS,
radio-occultation, DORIS, in-situ data, altimeters,
among other electron density and TEC measurements.
x Evaluate established methods for 3-D electron density
estimation in order to define their accuracy related to
specific parameters of great importance for Space
Weather and Geodesy.
x Generate products indicating the space weather
conditions and expected errors of the methods.
x Carry out surveys in order to detect if the products arelinked to the user’s specific needs. Based on an analysisof the user needs, re-adaptations will be identified inorder to improve the products in an iterative process. It
is planned to define which parameters are of interest for
the users and to detect additional information that may
be required.
Members:
1.
2.
3.
4.
5.

Andreas Goss (Technical University of Munich,Germany, andreas.goss@tum.de)Bruno Nava (ICTP, Italy, bnava@ictp.it)
David Themens (University of New Brunswick,
Canada, david.themens@gmail.com)
Feza Arikan (Hacettepe University, Turkey, arikan@hacettepe.edu.tr)
Gopi Seemala (Indian Institute of Geomagnetism,
India, GopiSeemala@iigs.iigm.res.in)

6.

Haixia Lyu (Universitat Politecnica de Catalunya,
Spain, haixia.lyu@upc.edu)
7. Johannes Norberg (Finnish Meteorological Institute,Finland, johannes.norberg@fmi.fi)
8. Katy Alazo (ICTP, Italy, kalazo_c@ictp.it)
9. Mainul Hoque (German Aerospace Center, Germany,
Mainul.Hoque@dlr.de)
10. Marcio Muella (Universidade do Vale do Paraíba,
Brazil, Brazil, mmuella@univap.br)
11. Michael Schmidt (Technical University of Munich,Germany, mg.schmidt@tum.de)
12. Mir-Reza Razin (Arak University of Technology, Iran,
mr.ghafari@arakut.ac.ir)
13. Orhan Arikan (Bilkent University, Turkey, oarikan@ee.bilkent.edu.tr)
14. Shuanggen Jin (Nanjing University of Information
Science & Technology, China, sgjin@shao.ac.cn)
15. Secil Karatay (Hacettepe University, Turkey, skaratay@kastamonu.edu.tr)
16. Solen Yildiz (Hacettepe University, Turkey,
solen@ee.hacettepe.edu.tr)
17. Tatjana Gerzen (Technical University of Munich, tatjana.gerzen@tum.de)
18. Yenca Migoya-Orue (ICTP, Italy, yenca@ictp.it)

JWG 2: Improvement of thermospheremodelsJoint with IAG Commission 4, Sub-Commission 4.3 and
ICCC
Chair: Christian Siemes (The Netherlands)
C.Siemes@tudelft.nl
Vice-Chair: Kristin Vielberg (Germany) vielberg@geod.uni-bonn.de)Terms of Reference (ToR) / Description:
Mass density, temperature, composition and winds are important state parameters of the thermosphere that affect dragand lift forces on satellites. Since these significantly influence the orbits of space objects flying at altitudes below 700
km, accurate knowledge of the state of the thermosphere isimportant for applications such as orbit prediction, collision
avoidance, evolution of space debris, and mission lifetime
predictions. Drag and lift forces can be inferred from space
geodetic observations of accelerometers, which complement other positioning techniques such as GNSS, satellite
laser ranging or radar tracking of space objects. The objective of the working group is to improve thermosphere models through providing relevant space geodetic observations

Global Geodetic Observing System (GGOS)

219

and increasing consistency between datasets by advancing
processing methods. Broadening the observational data basis with geodetic space observations, which are available
now for a time span of 20 years, will also benefit climatological studies of the thermosphere.

JWG 3: Improved understanding of space
weather events and their monitoring bysatellite missions

Objectives:

Chair: Alberto Garcia-Rigo (Spain) garciarigo@ieec.cat
Vice-Chair: Benedikt Soja (USA) benedikt.s.soja@jpl.nasa.gov

x Review space geodetic observations and state-of-the-art
processing methods
x Advance processing methods to increase consistency
between observational datasets
x Improve thermosphere models through providing
accurate and consistent space geodetic observations
x Study the impact of improved observational datasets andadvanced processing methods on orbit determinationand prediction
x Use of improved thermosphere models andobservational data sets to forward the investigation ofthermosphere variations in the context of climate change
Members:
1. Michael Schmidt (Technical University of Munich,Germany, mg.schmidt@tum.de)
2. Armin Corbin (University of Bonn, Germany,
corbin@geod.uni-bonn.de)
3. Ehsan Forootan (Cardiff University, UK, ForootanE@cardiff.ac.uk)
4. Mona Kosary (University of Tehran, Iran,mona.kosary@ut.ac.ir)
5. Lea Zeitler (Technical University of Munich, Germany,lea.zeitler@tum.de)
6. Christopher Mccullough (JPL, US, christopher.mccullough@jpl.nasa.gov)
7. Sandro Kraus (TU Graz, Austria,
sandro.kraus@tugraz.at)
8. Saniya Behzadpour (TU Graz, Austria,
behzadpour@tugraz.at)
9. Aleš Bezděk (Astronomical Institute of the Czech Academy of Sciences, Czech Republic,
ales.bezdek@asu.cas.cz)

Joint with IAG Commission 4, Sub-Commission 4.3

Terms of Reference (ToR) / Description:
Space weather events cause ionospheric disturbances thatcan be detected and monitored thanks to estimates of thevertical total electron content (VTEC) and the electron density (Ne) of the ionosphere. Various space geodetic observation techniques, in particular GNSS, satellite altimetry,
DORIS, radio occultations (RO) and VLBI are capable ofdetermining such ionospheric key parameters. For the monitoring of space weather events, low latency data availability
is of great importance, ideally real time, to enable triggering
alerts. At present, however, only GNSS is suited for thistask. The use of the other techniques is still limited due latencies of hours (altimetry) or even days (RO, DORIS,
VLBI).
The JWG 3 will investigate different approaches to monitor space weather events using the data from different space
geodetic techniques and, in particular, combinations thereof.
Simulations will be beneficial to identify the contribution ofdifferent techniques and prepare for the analysis of real data.
Different strategies for the combination of data will be investigated.
Furthermore, the geodetic measurements of the ionospheric parameters will be complemented by direct observations of the solar corona, where solar storms originate, as
well as of the interplanetary medium. Spacecrafts like
SOHO or ACE have monitored the solar corona and the solar wind for decades and will be beneficial, together withdata from other spacecrafts like SDO, in assessing the performance of geodetic observations of space weather events.
Data from Parker Solar Probe, which will allow even greater
insights, has just recently been made publicly available.
Geodetic VLBI is also capable of measuring the electron
density of the solar corona when observing targets angularly
close to the Sun and will be useful for comparisons. Other
solar-related satellite missions such as Stereo, DSCOVR,
GOES, etc. provide valuable information such as solar radiation, particle precipitation and magnetic field variations.
Other indications for solar activity - such as the F10.7 index
on solar radio flux, SOLERA as EUV proxy or rate of
Global Electron Content (dGEC), will also be investigated.
The combination and joint evaluation of these data sets withthe measurements of space geodetic observation techniques

220

is still a great challenge. Through these investigations, wewill gain a better understanding of space weather events andtheir effect on Earth’s atmosphere and near-Earth environment.
Objectives
x Selection of a set of historical representative space
weather events to be analysed.
x Determination of key parameters and products affectedby the selected space weather events.
x Identification of the main parameters to improve realtime
determination andtheprediction ofionospheric/plasmaspheric VTEC and Ne estimates aswell as ionospheric perturbations in case of extreme
solar weather conditions.

The Geodesist’s Handbook 2020

x Improving the (near) real time determination of theelectron density within the ionosphere and plasmasphereto detect space weather events.
x Combination of measurements and estimates derived
from space geodetic observation techniques byconducting extensive simulations, combining different
data sets and testing different algorithms.
x Comparison and validation using external data, inparticular data from spacecraft dedicated to monitoring
the solar corona.
x Interpretation of the results. Correlate acquired
data/products with space weather events’ impact on
geodetic applications (e.g. GNSS positioning, EGNOS
performance degradation).
Members:
TBD

Inventory of Standards and Conventions

221

GGOS Bureau of Products and Standards
Inventory of Standards and Conventions
used for the Generation of IAG Products
D. Angermann1 · T. Gruber2 · M. Gerstl1 · R. Heinkelmann3 ·U. Hugentobler2 · L. Sánchez1 · P. Steigenberger4

c International Association of Geodesy 2020
Revision August 2020 / Contents

Preface and scope of the document

Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 221
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 223

The GGOS Bureau of Products and Standards (BPS), formerly known as Bureau for Standards and Conventions(BSC), has been established as a component of the Global Geodetic Observing System (GGOS) of the International Association of Geodesy (IAG) in 2009. The BPS supports GGOS
in its goal to obtain geodetic products of highest accuracy
and consistency. In order to fully benefit from the ongoing
technological improvements of the observing systems, it isessential that the analysis of the precise space geodetic observations is based on the definition and application of common
standards and conventions and a consistent representationand parameterisation of the relevant quantities. This is of
crucial importance for the establishment of highly accurate
and consistent geodetic reference frames, as the basis for areliable monitoring of the time-varying shape, rotation andgravity field of the Earth. The BPS also concentrates on the
integration of geometric and gravimetric parameters and thedevelopment of new products, required to address importantgeophysical questions and societal needs.
A key objective of the BPS is to keep track and to foster homogenisation of adopted geodetic standards and conventions
across all components of the IAG as a fundamental basis
for the generation of consistent geometric and gravimetricproducts. The work is primarily build on the IAG Service
activities in the field of data analysis and combinations. The
BPS acts as contact and coordinating point regarding homogenisation of standards and IAG products. Towards reachingthese goals, the BPS has compiled an inventory of standards
and conventions currently adopted and used by the IAG and
its components for the processing of geometric and gravimetric observations as the basis for the generation of IAG
products. The first version of such an inventory has been

1

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . 224
1.1 GGOS: Mission, goals and structure . . . . . . . . . . 224
1.2 Standards and conventions . . . . . . . . . . . . . . . 226

2

GGOS Bureau of Products and Standards . . . . . . . . . . 233
2.1 Mission and objectives . . . . . . . . . . . . . . . . . 233
2.2 Tasks . . . . . . . . . . . . . . . . . . . . . . . . . . 234
2.3 Staff and representatives . . . . . . . . . . . . . . . . 234

3

Evaluation of numerical standards . . . . . . . . . . . . . . 236
3.1 Defining parameters . . . . . . . . . . . . . . . . . . . 236
3.2 Solid Earth tide systems . . . . . . . . . . . . . . . . . 236
3.3 Open problems and recommendations . . . . . . . . . 237

4

Product-based review . . . . . . . . . . . . . . . . . . . . . 239
4.1 Celestial reference systems and frames . . . . . . . . . 239
4.2 Terrestrial reference systems and frames . . . . . . . . 243
4.3 Earth Orientation Parameters (EOP) . . . . . . . . . . 250
4.4 GNSS satellite orbits . . . . . . . . . . . . . . . . . . 256
4.5 Gravity and geoid . . . . . . . . . . . . . . . . . . . . 260
4.6 Height systems and their realisations . . . . . . . . . . 267

5

Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . 279

Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 280
Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . 282
detlef.angermann@tum.de
1

Deutsches Geodätisches Forschungsinstitut, Technische Universität
München (DGFI-TUM), Germany
2 Ingenieurinstitut für Astronomische und Physikalische Geodäsie,Technische Universität München (IAPG), Germany
3 Helmholtz Centre Potsdam, German Research Centre forGeosciences (GFZ), Germany
4 Deutsches Zentrum für Luft- und Raumfahrt (DLR), Germany

222

Prefacereleased in January 15, 2016 and published in the Geodesists
Handbook 2016 (Angermann et al. 2016; Drewes et al. 2016).
Since 2016, a remarkable progress has been achieved in thefield of standards and conventions as well as concerning thedata analysis and generation of geodetic products, which will
be reported in an updated version of this document. During
the last four years, new realisations of the terrestrial and celestial reference systems, the ITRF2014 and ICRF3, as well as
an updated series for the Earth Orientation Parameters (EOP
14 C04) were generated by the Product Centers of the International Earth Rotation and Reference Systems Service (IERS).
In this time period also the modelling and data analysis of
the contributing space techniques Very Long Baseline Interferometry (VLBI), Satellite Laser Ranging (SLR), Global
Navigation Satellite Systems (GNSS), Doppler Orbit Determination and Radiopositioning Integrated by Satellite (DORIS)
have been significantly enhanced due to the efforts of thetechnique-specific IAG Services. Furthermore, a significant
progress has been achieved in the field of gravity-related
products provided by the gravimetric IAG Services as well

as regarding the realisation of the International Height Reference Frame (IHRF). Data analysis issues that are common to
all the space geodetic techniques are discussed at the Unified
Analysis Workshops, which are co-organised by GGOS andthe IERS. This updated version of the inventory also reflects
the outcome of the two latest Workshops held in Paris in2017 and 2019.
In this updated version of the inventory the general structureof the original document is largely kept, whereas the contentsof the individual sections has been updated to take into account the latest developments. Some (unchanged) parts of theoriginal version are also part of this updated version to ensure
the readability as a “stand-alone” document. A summary of
the updates is provided in the Document Change Record (seeTable 1). This second version of the BPS inventory reflects
the status of January 31, 2020.
The scope of this document is summarised as follows: Chapter 1 provides in the first section some general information
about GGOS including its mission, goals and the organisational structure. The second part of this introductory chap-

Table 1: Document change record summarizing the major changes of the document.
Version/Date Comments / Summary of Changes
1.0
2016-01-15

First version of the document
Angermann D., Gruber T., Gerstl M., Heinkelmann R., Hugentobler U., Sánchez L., Steigenberger P.: GGOS Bureau of Products and Standards: Inventory of standards and conventions used for the generation of IAG products. In: Drewes H., KuglitschF., Adám J. (Eds.) The Geodesist’s Handbook 2016. Journal of Geodesy, 90(10), 1095–1156, 10.1007/s00190-016-0948-z,
2016

2.0
2020-01-31

Updated Version, prepared for publication in The Geodesist’s Handbook 2020
Preface updated.
Chapter 1.1 : IAG/GGOS structure updated, Fig. 1.2 updated.
Chapter 1.2 : Update of Standards and Conventions (e.g., ISO, CODATA, IUGG, IAG and IAU Resolutions), issues on
IERS Conventions (e.g., re-writing/revising IERS Conventions) updated.
Chapter 2 : Update of BPS description and organisational structure.
Chapter 3 : Updates on numerical standards, outcome of GGOS/IERS Unified Analysis Workshops 2017 and 2019 incorporated, recommendations on numerical standards updated.
Chapter 4 : Updates of product-based review (see below).
Chapter 4.1 : Summary on ICRF2 (sect. 4.1.2) moved to section 4.1.3.1 “History of ICRS realisations”, new section 4.1.3.2
on ICRF3 included, other sections of 4.1 updated, recommendations updated.
Chapter 4.2 : New section 4.2.2 “History of ITRS realisations” included, former chapter on ITRF2008 shortened and moved
to 4.2.2, new section on ITRF2014 (4.2.3) included, other sections of 4.2 updated, outcome of Unified Analysis Workshops
incorporated, recommendations updated.
Chapter 4.3 : Section 4.3.2 updated (e.g., IERS EOP 08 C04 replaced by IERS EOP 14 C04), other sections of 4.3 updated,outcome of Unified Analysis Workshops incorporated, recommendations updated.
Chapter 4.4 : Updates on GNSS satellite orbits (e.g., satellite property information, satellite orbit models) and recommendations.
Chapter 4.5 : The chapter on gravity and geoid has been revised to incorporate the developments and the progress with the
IGFS during the last four years, in this updated version also new and more specific recommendations are provided.
Chapter 4.6 : This chapter has been revised to incorporate the developments and the progress in the field of height systems
and their realisations during the last four years, the recommendations have been revised.
Chapter 5 : A few minor updates have been performed in the summary.
Bibliography : The references have been updated.

Acknowledgements

223

ter deals with standards and conventions from a generalview along with some relevant nomenclature, and it presents
current standards, standardised units, fundamental physicalstandards, resolutions and conventions that are relevant forgeodesy. In the second chapter the mission and goals of the
BPS are summarised, along with a description of its major tasks. It also presents the BPS staff and the associatedmembers, representing the IAG Services, the International
Astronomical Union (IAU) and other entities involved instandards and conventions. Chapter 3 focusses on numericalstandards, including time and tide systems and it gives recommendations for future improvements. Chapter 4 is the key
element of this document and it contains the product-based
review, addressing the following topics: Celestial reference
systems and frames, terrestrial reference systems and frames,
EOP, GNSS satellite orbits, gravity and geoid, as well asheight systems and their realisations. In this product-based
inventory, the BPS presents the current status, identifies gaps
and inconsistencies as well as interactions between different
products. In this context also open problems and recommendations regarding standards and conventions for the generationof IAG products are provided. Finally, a summary and an
outlook towards future developments is provided.

first step an (internal) review initiated by the BPS has been
performed, followed by a second review cycle which was
conducted under the responsibilty of the IAG Bureau (Chris
Rizos, Hermann Drewes and Harald Schuh). The valuable
contributions of the reviewers are acknowledged in the 2016
document (Angermann et al. 2016).
It was proposed by the IAG Bureau (Zuheir Altamimi, Markku Poutanen and Richard Gross) that the review of this updated version should be conducted in the same way as forthe first version. Thus, it has been suggested that each chapter/product of the inventory should be reviewed by experts inthese fields. The list of rewiewers is provided in Table 2. The
contributions by all reviewers and the suppport of the IAG
Bureau are gratefully acknowledged by the authors.

Acknowledgements
The original version of this BPS inventory (published in2016) has been reviewed in a two step procedure. In the

Table 2: Reviewers designated by IAG to evaluate this document.
Chapter

Reviewers

Chapter 1.1
Chapter 1.2
Chapter 2
Chapter 3
Chapter 4.1
Chapter 4.2
Chapter 4.3
Chapter 4.4
Chapter 4.5
Chapter 4.6

Markku Poutanen (Finland), Martin Sehnal (Austria)
Michael Craymer (Canada), Markku Poutanen (Finland), Chris Rizos (Australia)
Markku Poutanen (Finland), Martin Sehnal (Austria)
Pavel Novák (Czech Republic), Nico Sneeuw (Germany)
John Gipson (USA), Axel Nothnagel (Germany)
Zuheir Altamimi (France), Thomas Herring (USA)
Aleksander Brzezinski (Poland), Richard Gross (USA)
Rolf Dach (Switzerland)
Riccardo Barzaghi (Italy), Adrian Jäggi (Switzerland)
Matt Amos (New Zealand), Dru Smith (USA)224

1 Introduction

1 Introduction
1.1 Global Geodetic Observing System(GGOS): Mission, goals and structure
The GGOS was initially created as an IAG Project during
the International Union of Geodesy and Geophysics (IUGG)
meeting in 2003 in Sapporo, Japan, in response to developments in geodesy, the increasing requirements of Earthobservations, and growing societal needs. Since 2004, GGOS
represents IAG in the Group on Earth Observation (GEO)
and contributes to the Global Earth Observation System of
Systems (GEOSS) (GEO 2005). After a preliminary development phase, the Executive Committee of the IAG decided tocontinue the Project at its meeting in August 2015 in Cairns,
Australia. From 2005 to 2007, the GGOS Steering Committee, Executive Committee, Science Panel, Working Groups,
and web pages were established. Finally, at the IUGG meeting in 2007 in Perugia, Italy, IAG evaluated GGOS to thestatus of a full component of IAG – as the permanent observing system of the IAG.
The IAG Services and Commissions provide the geodetic
infrastructure and products, as well as the expertise andsupport for scientific developments, which are the basis formonitoring the Earth system and for global change research.
GGOS relies on the observing systems and analysis capabilities already in place in the IAG Services and envisions thecontinued development of innovative technologies, methods
and models to improve our understanding of global change
processes. IAG and GGOS provide a framework that ranges
from the acquisition, transfer and processing of a tremendous
amount of observational data to its consistent integration.
Consistency among the data sets from the different (geometric and gravimetric) observation techniques is of crucial
importance for the generation of IAG products, such as geodetic reference frames which are the basis for the integrationof geometry, Earth rotation and the gravity field (see Figure
1.1).
GGOS as an organisation is built upon the existing IAG
Services as a unifying umbrella, and will continue to be developed for this purpose. Under this “unifying umbrella”,
all the products provided by the different IAG Services are
considered GGOS products – as ratified at the IAG General
Assembly in 2009 in Buenos Aires, Argentina.
The mission and the overarching strategic focus areas of
GGOS are specified in its Terms of Reference (see www.gg
os.org). They were officially adopted by the IAG Executive
Committee (EC) at the IUGG XXV General Assembly, Melbourne, Australia, 2011. Its first revision was approved by the
IAG EC during the IUGG XXVI General Assembly, Prague,
Czech Republic, 2015, and has been slightly revised in 2018.

Earth
rotation

ReferenceframesGravityfield

Geometry

Fig. 1.1: Integration of the “three pillars” geometry, Earthrotation and gravity field (Rummel 2000), modified by (Plagand Pearlman 2009).

The mission of GGOS is:
1. To provide the observations needed to monitor, map andunderstand changes in the Earth’s shape, rotation, and mass
distribution.
2. To provide the global geodetic frame of reference that is
the fundamental backbone for measuring and consistently
interpreting key global change processes and for manyother scientific and societal applications.
3. To benefit science and society by providing the foundation upon which advances in Earth and planetary systemscience and applications are built.
The overarching strategic focus areas of GGOS goals andobjectives are:1. Geodetic Information and Expertise: GGOS outcomes
will support the development and maintenance of organisational intangible assests, including geodetic informationand expertise. The development of this strategic focus area
will benefit all other goals and objectives.
2. Global Geodetic Infrastructure: Development of, advocacy for, and maintenance of existing global geodetic
infrastructure is a direct support of each GGOS goal.
3. Services, Standardisation, and Support: Optimal coordination, support, and utilisation of IAG Services, aswell as leveraging existing IAG resources, are critical tothe progress of all GGOS goals and objectives.

1.1 GGOS: Mission, goals and structure

225

GGOS Consortium (1)(Steering and Election Committee)

GGOS Science Panel

GGOS Coordinating Board (1)GGOS Affiliates

GGOS Executive Committee(Decision-Making Body)

External Stakeholders(Management Board)

GGOS Japan

ReportingDirection

GGOS Coordinating Office
•
•
•
•
•
•
•

Director
Secretariat
Outreach and User Linkage
Web and Social Media
Focus Area Coordination
Manager of External Relations
Working Group on DOIs for Geodetic Data

GGOS Bureau of Products & Standards

GGOS Bureau of Networks & Observations••••

IAG Service Network Representatives (1)Committee on Satellite Missions
Committee on Data and Information Systems
Committee on Performance Simulations andArchitectural Trade-Offs

•
•
•
•

Reporting

IAG Service Analysis Coordinators & Representatives (1)Committee on Earth System Modeling
Committee on Essential Geodetic Variables
Working Group on Towards a consistent set ofparameters for the definition of a new GRS
Reporting

GGOS Focus Areas(formerly Themes)

IERS Working Group
Site Survey and Co-location• Unified Height System• Geohazards• Geodetic Space Weather Research

IERS Conventions Centre
Standards and Conventions(1) GGOS is built upon the foundation provided by the IAG Services, Commissions, and Inter-Commission Committees

Fig. 1.2: Organisation structure of GGOS as adopted in December 2019.

4. Communication, Education, Outreach: Marketing, outreach, and engagement are critical elements for sustaining
the organisational fabric of GGOS.
The organisational structure of GGOS is comprised of thefollowing key components (see Figure 1.2):
GGOS Consortium – is the collective voice for all GGOS
matters.
GGOS Coordinating Board – is the central oversight anddecision-making body of GGOS, and represents the IAG
Services, Commissions, Inter-Commission Committees, andother entities.
GGOS Executive Committee – serves at the direction of
the Coordinating Board to accomplish day-to-day activities
of GGOS tasks.
GGOS Science Panel – advises and provides recommendations relating to the scientific content of the GGOS 2020
to the Coordinating Board; and represents the geoscientificcommunity at GGOS meetings.
GGOS Coordinating Office – coordinates the work within
GGOS and supports the Chairs, the Executive Committee andthe Coordinating Board; and coordinates GGOS external relations. Newly established components within the Coordinating

Office are the position of the Manager of External Relations
and the GGOS Working Group on “DOIs for Geodetic Data
Sets”.
Bureau of Products and Standards (former Bureau forStandards and Conventions) – tracks, reviews, examines,
evaluates the standards, constants, resolutions and conventions adopted by IAG or its components and recommends
their continued use or proposes necessary updates; works
towards the developement of new products derived from a
combination of geometric and gravimetric observations.
Bureau of Networks and Observations (former Bureau for
Networks and Communications) – develops strategies andplans to design, integrate and maintain the fundamental geodetic infrastructure, including communications and dataflows; monitors the networks and advovates for implementation of core and co-located network sites and improved
network performance.
GGOS Affiliates – are national or regional organisations
that coordinate geodetic activities in that country or region.
GGOS Affiliates allow increased participation in GGOS, especially by organisations in under-represented areas of Africa,
Asia-Pacific, and South and Central America.

226

GGOS Committees, Working Groups and Focus Areas(formerly known as Themes) – address overarching issues
common to several or all IAG components, and are a mechanism to bring the various activities of the Services, Commissions and Inter-Commission Committees together, or tolink GGOS to external organisations. Focus areas are crossdisciplinary and address specific areas where GGOS contributors work together to address broader and critical issues.
IAG – promotes scientific cooperation and research in geodesy on a global scale and contributes to it through its various
research bodies.
IAG Services, Commissions and relevant Inter-Commission Committees – are the fundamental supporting elementsof GGOS.
GGOS Inter Agency Committee (GIAC) – was a forum
that sought to generate a unified voice to communicate with
Governments and Intergovernmental organisations (GEO,
CEOS, UN bodies) in all matters of global and regional spatial reference frames and geodetic research and applications.
GIAC was dissolved when the United Nations Committee ofExperts on Global Geospatial Information Management (UNGGIM) Working Group on the Global Geodetic Reference
Frame (GGRF) was elevated to the permanent Subcommittee
on Geodesy of the UN-GGIM.
UN Committee of Experts on Global Geospatial Information Management (UN-GGIM) – led by United Nations
Member States, UN- GGIM aims to address global challenges regarding the use of geospatial information and toserve as a body for global policymaking in the field of geospatial information management.
Subcommittee on Geodesy (UN-GGIM) (SCoG) – provides an intergovernmental forum for cooperation and exchange of dialogue on issues relating to the maintenance,sustainability and enhancement of the Global Geodetic Reference Frame (GGRF).

1.2 Standards and conventions
Standards and conventions are used in a broad sense anda variety of international organisations and entities are involved. This section gives an overview of the standards andconventions that are currently in use within the geodetic community. According to Drewes (2008) and Angermann (2012)
one can distinguish between standards, standardised units,fundamental physical standards, resolutions and conventions.
In addition, the background models used for the data analysis
are introduced in this section.
1.2.1 Standards

Standards are generally accepted specifications and measures
for quantitative or qualitative values that define or represent
under specific conditions the magnitude of a unit. A technicalstandard is an established norm or requirement, which is usu-

1 Introduction

ally a formal document that provides uniform engineering or
technical criteria, methods and processes or procedures.
Various international, regional and national organisations are
involved in the development, coordination, revision, maintenance, etc. of standards that address the interests of a wide
area of users. Important for geodesy is the International Organization for Standardization (ISO), an international standard-setting body composed of representatives from a network of national standards institutes of more than 150 countries. Many standards related to geographic information, including geodetic reference systems, have been or are being
developed by ISO Technical Committee 211. ISO/TC211(committee.iso.org/home/tc211) was established to cover theareas of digital geographic information and geomatics. It
aims to establish a set of standards information concerning
objects or phenomena that are directly or indirectly associated with a location relative to the Earth. These standards
are linked to other appropriate ISO standards for information
technology and data where possible, to provide a framework
for the development of specific applications using geographic
data. Some of the ISO standards related to geodetic reference
systems include:
ISO 6709: Standard representation of geographic point
location by coordinates(www.iso.org/standard/75147.html).
ISO 19111: Geographic information – Referencing by
coordinates (www.iso.org/standard/74039.html).
ISO 19115-1: Geographic information – Metadata – Part 1
Fundamentals (www.iso.org/standard/53798.html).
ISO 19127: Geodetic Register(www.iso.org/standard/41784.html).
ISO 19135-1: Geographic information – Procedures foritem registration (www.iso.org/standard/54721.html).
ISO 19161-1: Geographic information – The International
Terrestrial Reference System (ITRS):
definition, realisations and dissemination.
Also relevant for geodesy is the Open Geospatial Consortium(OGC), an international voluntary standards organisation, established in 1994. In the OGC, more than 400 governmental,
commercial, nonprofit and research organisations worldwide
collaborate in a consensus process encouraging the development and implementation of open standards for geospatial
content and location-based services, Geographic Information
System (GIS) data processing and data sharing.
The ISO and OGC standards are applied in geo-referencing,spatial analysis, and communication (service specification).
There is a close cooperation between OGC, ISO/TC211 andIAG components. The chair and vice-chair of the Control
Body for the ISO Geodetic Registry (geodetic.isotc211.org)
are nominated by the IAG and the director of the BPS acts as
the IAG liaison to ISO/TC211.

1.2 Standards and conventions

In February 2015, the UN General Assembly adopted its
first geospatial resolution “A Global Geodetic Reference
Frame for Sustainable Development”. The UN Committeeof Experts on Global Geospatial Information Management(UN-GGIM) endorsed the GGRF Road Map and establisheda GGRF Working Group which became the UN-GGIM Subcommittee on Geodesy (SCoG) in 2017 (see www.un.org/en/ga/search/view_doc.asp?symbol=A/RES/69/266
and www.unggrf.org/). Within this SCoG five Working
Groups (former Focus Groups) have been established, addressing the areas of Geodetic Infrastructure; Policies, Standards, and Conventions; Education, Training and Capacity
Building; Outreach and Communications; and Governance.
Implementation Plans have been developed by these Working
Groups that were detailed in the GGRF Road Map. Recommendations of the Working Group on Policies, Standards andConventions are:
• Member States support the efforts already undertaken by
IAG and standards organisations, including ISO, towards
geodetic standards and to make these standards openly
available.
• Member States more openly share their data, standard
operating procedures and conventions, expertise, and technology.
• Member States resolve their concerns that currently limit
data sharing, as a valuable contribution to the enhancementof the GGRF.
The standards and conventions that are relevant for geodesy are based primarily on decisions made by internationalorganisations or bodies involved in this topic, such as• the Bureau International de Poids et Mesures (BIPM),• the Committee on Data for Science and Technology(CODATA),and by resolutions related to standards and conventions adopted by the Councils of• the International Union of Geodesy and Geophysics(IUGG),• the International Astronomical Union (IAU), and• the International Association of Geodesy (IAG).
Within the IAU, Commission A3 “Fundamental Standards”(www.iau.org/science/scientific_bodies/commissions/A3)
and the IAU’s Standards of Fundamental Astronomy (SOFA)
service (www.iausofa.org) are directly involved in standards.
1.2.2 Standardised units

In the International Vocabulary of Basic and General Terms
in Metrology (BIPM 2006; ISO/IEC 2007) the terms quantities and units are defined. The value of a quantity is expressedas the combination of a number and a unit. In order to set
up a system of units, it is necessary first to establish a system of quantities, including a set of equations relating thosequantities. Binding for geodesy is the International System

227

of Units (SI), which was adopted by the 11th General Conference on Weights and Measures (CGPM, 1960), and revised
at its 26th meeting in 2018 (effective from 20 May 2019), seewww.bipm.org/utils/common/pdf/CGPM-2018/26th-CGP
M-Resolutions.pdf.
According to these CGPM Resolutions the SI is maintainedby the BIPM. The units are divided into two classes – baseunits and derived units. In a similar way the corresponding
quantities are described as base quantities and derived quantities. In the SI there are seven base units representing different
kinds of physical quantities. Three of them are applied ingeodesy:• The second, symbol [s], is the SI unit of time. It isdefined by taking the fixed numerical value of the caesium frequency ∆vCS , the unperturbed ground-state hyperfine transition frequency of the caesium 133 atom, tobe 9 192 631 770 when expressed in the unit Hz, which isequal to s−1 .
• The metre, symbol [m], is the SI unit of length. It is definedby taking the fixed numerical value of the speed of light invacuum c to be 1/299 792 458 when expressed in the unit
m/s, where the second is defined in terms of ∆vCS .
• The kilogram, symbol [kg], is the SI unit of mass. It isdefined by taking the fixed numerical value of the Planck
constant h to be 6.626 070 15 · 10−34 when expressed in
the unit J s, which is equal to kg m−2 s−1 , where the metre
and the second are defined in terms of c and ∆vCS .
The number of derived units and derived quantities of interestin geosciences can be extended without limit. For example,
the derived unit of speed is metre per second [m/s], or centimetre per second [cm/s] in the SI. Whereas the kilometre perhour [km/h] is a unit outside the SI but accepted for use with
the SI. The same holds for the gal [cm/s2 ] which is a special
non-SI unit of acceleration due to gravity.
The realisation of the SI at the BIPM constitutes a fundamental contribution to the tasks of the IAG. One of the fivescientific departments of the BIPM, the “Time Department”
has been a service of the IAG until the end of 2019. The activities of this department are focused on the maintenance of
the SI second and the formation of the international referencetime scales.
1.2.3 Fundamental physical constants

The formulations of the basic theories of physics and theirapplications are based on fundamental physical constants.
These quantities, which have specific and universally used
symbols, are of such importance that they must be known
as accurately as possible. A physical constant is generally
believed to be both universal in nature and constant in time.
In contrast, a mathematical constant is a fixed numericalvalue, which does not directly involve any physical measurement. A complete list of all fundamental physical constants is228

given by the National Institute of Standards and Technology(NIST). NIST publishes regularly a list of the constants.
The CODATA is an interdisciplinary Scientific Committeeof the International Science Council (ISC). IUGG and IAU
are member unions of CODATA. The Committee works to
improve the quality, reliability, management and accessibility of data. CODATA is concerned with all types of data
resulting from measurements and calculations in all fields ofscience and technology, including physical sciences, biology,
geology, astronomy, engineering, environmental science, ecology and others.
The CODATA Committee (former Task Group) on Fundamental Physical Constants was established in 1969. Its purpose is to periodically provide the international scientific andtechnological communities with an internationally accepted
set of values for the fundamental physical constants. The
first such CODATA set was published in 1973, and later in
1986, 1998, 2002, 2006, 2010 and 2014 (see, Mohr et al.
2016). The latest version, the 2018 least-squares adjustmentof the values of the set of fundamental physical constants
was released in 2019. The 2018 set replaces the previously
recommended 2014 CODATA set and may also be found atwww.physics.nist.gov/Constants. The fundamental physicalconstants are classified as universal, electromagnetic, atomic
and nuclear, or physico-chemical constants as well as adopted
values. The set of values provided by CODATA do not aim
to cover all scientific fields. Only a few of these fundamental
constants are relevant for geodesy, primarily two universal
constants and two adopted values:a) Universal constants• Newtonian constant of gravitation (G):(6.674 30 ± 0.00015) · 10−11 m3 kg−1 s−2• Speed of light in vacuum (c, c0 ):299 792 458 m/s (exact)b) Adopted values (as mean values at sea level)• Standard acceleration of gravity (gn ):9.806 65 m/s2 (exact)• Standard atmosphere (atm): 101 325 Pa (exact).
The astrogeodetic community needs, in addition to these fundamental physical constants, a set of suitable fundamental
parameters as a basis for the definition and realisation ofreference systems as well as for the generation of geodetic
products. The geodetic activities in this field are addressedby the IERS Conventions Center (see Section 1.2.5) in cooperation with international organisations such as CODATA,IUGG and IAU. The present status of numerical standards
used within IAG is discussed in Section 3.1.
1.2.4 Resolutions

A resolution is a written motion adopted by a deliberating
body. The substance of the resolution can be anything that cannormally be composed as a motion. In this context we refer to

1 Introduction

the motion for adopting standards, constants or any parameters to be used by institutions and persons affiliated with the
adopting body. Most important resolutions for geodesy arethose adopted by IUGG, IAG, and IAU. The IUGG and IAG
resolutions are adopted at the IUGG General Assemblies andpublished every four years in the IAG Geodesist’s Handbook(www.iag-aig.org/geodesists-handbook). They are alsoavailable at office.iag-aig.org/iag-and-iugg-resolutions.
The IAU resolutions are adopted by General Assemblies
held every 3 years. They are published regularly in the IERS
Conventions along with detailed information for their implementation (e.g., Petit and Luzum 2010). An electronic
version can be obtained from www.iau.org/administration/
resolutions.
Resolutions are non-binding laws of a legislature, but morebinding than recommendations. In non-legal bodies, such as
IUGG, IAG and IAU, which cannot pass laws, they represent
the highest level of commitment. Resolutions shall be respected by all institutions and persons affiliated with the adopting
body.
The resolutions, which are relevant with respect to standards
and conventions for geodesy, are summarised below in chronological order. Please note that only some major information
is extracted from the original resolutions. For the full version
follow the links above.
IUGG Resolution No. 7 (1979) and IAG Resolution No. 1(1980) on the Geodetic Reference System 1980 (GRS80)(Moritz 2000). It is recommended that the Geodetic Reference System 1967 shall be replaced by a new Geodetic
Reference System 1980, also based on the theory of the geocentric equipotential ellipsoid.
IAG Resolution No. 16 (1983) on Tide Systems, recognising
the need for the uniform treatment of tidal corrections to various geodetic quantities such as gravity and station positions.
It is recommended that the indirect effect due to the permanent yielding of the Earth shall not be removed (IAG 1984).
IUGG Resolution No. 2 (1991) on the Conventional Terrestrial Reference System (CTRS) recommends that (1) CTRS
to be defined from a geocentric non-rotating system by aspatial rotation leading to a quasi-Cartesian system; (2) the
geocentric non-rotating system to be identical to the Geodetic
Reference System (GRS) as defined in the IAU resolutions;(3) the coordinate-time of the CTRS as well as the GRS to be
the Geocentric Coordinate Time (TCG); (4) the origin of thesystem to be the geocentre of the Earth’s masses including
oceans and atmosphere; and (5) the system to have no global
residual rotation with respect to horizontal motions at the
Earth’s surface.
IAU Resolution A4 (1991) has set up a General Relativistic Framework to define reference systems centred at thebarycentre of the solar system and at the geocentre.
IAU Resolution B2 (1997) on the International Celestial
Reference System (ICRS). From January 1, 1998, the IAU

1.2 Standards and conventions

celestial reference system shall be the ICRS. The corresponding fundamental reference frame shall be the International
Celestial Reference Frame (ICRF) constructed by the IAU
Working Group on Reference Frames. The IERS should takeappropriate measures, in conjunction with the IAU Working
Group on Reference Frames, to maintain the ICRF and its
ties to the reference frames at other wavelengths.
IAU Resolution (2000) contains several specific resolutions(RES):RES B1.1 Maintenance and Establishment of Reference
Frames and Systems
RES B1.2 Hipparcos Celestial Reference FrameRES B1.3 Definition of the Barycentric Celestial Reference
System (BCRS) and Geocentric Celestial Reference System (GCRS)RES B1.4 Post-Newtonian Potential Coefficients
RES B1.5 Extended Relativistic Framework for Time Transformations and Realisation of Coordinate Timesin the Solar System
RES B1.6 IAU Precession-Nutation Model
RES B1.7 Definition of the Celestial Intermediate PoleRES B1.8 Definition and Use of Celestial and Terrestrial
Ephemeris Origins
RES B1.9 Re-definition of the Terrestrial Time (TT)RES B2 Coordinated Universal Time (UTC).
The Resolutions B1.1 through B1.8 of the IAU General Assembly 2000 have been adopted by IUGG at its General
Assembly in 2003 (see Resolution No. 4). More informationon these resolutions may be found in the “Proceedings ofthe IERS Workshop on the Implementation of the New IAU
Resolutions” published in the IERS Technical Note No. 29(Capitaine et al. 2002).
IUGG Resolution 3 (2003) strongly supports the establishment of the GGOS (former IGGOS) Project within the new
IAG structure as geodesy’s contribution to the wider fieldof geosciences and as the metrological basis for the Earthobservation programs within IUGG.
IAU Resolution B1 (2006) on adopting the P03 Precession
Theory and Definition of the Ecliptic. It accepts the conclusions of the IAU Division I Working Group on Precession and
Ecliptic (Hilton et al. 2006), and recommends that the terms
lunisolar precession and planetary precession be replacedby precession of the equator and precession of the ecliptic,
respectively, and that, beginning on 1 January 2009, the precession component of the IAU 2000A precession-nutation
model be replaced by the P03 precession theory (Capitaine
et al. 2003) in order to be consistent with both dynamical
theories and the IAU 2000 nutation.
IAU Resolution B2 (2006) is a supplement to the IAU 2000
resolutions on reference systems, containing primarily two
recommendations, the first to harmonise the name of the poleand origin to “intermediate” and a second recommendation
fixing the default orientation of the BCRS and GCRS, which229

are assumed to be oriented according to the ICRS axes (formore information see the IERS Conventions 2010, Petit andLuzum 2010).
IAU Resolution B3 (2006) is on the re-definition of Barycentric Dynamical Time (TDB) (for more information see
the IERS Conventions 2010, Petit and Luzum 2010). This
resolution has also been adopted by the IUGG in 2007 as
written in Resolution 1.
IUGG Resolution No. 2 (2007) on the Geocentric and International Terrestrial Reference System (GTRS and ITRS)
endorses the ITRS as the specific GTRS for which the orientation is operationally maintained in continuity with past international agreements (BIH orientation), and adopts the ITRS
as the preferred GTRS for scientific and technical applications, and urges other communities, such as the geo-spatial
information and navigation communities, to do the same.
IUGG Resolution No. 3 (2007) on the Global Geodetic Observing System (GGOS) of the IAG. The new structure of
IAG reflected by the designation of GGOS as a permanent
component, urges sponsoring organisations and institutions
to continue their support of the elements of GGOS, which is
crucial for sustaining long-term monitoring and understanding of the Earth system.
IAU Resolution B2 (2009) on IAU 2009 AstronomicalStandards. It recommends that the list of previously published constants compiled in the report of the IAU Division
A Working Group Numerical Standards for Fundamental Astronomy (NSFA) (Luzum et al. 2011) be adopted as the IAU(2009) System of Astronomical Constants, that Current Best
Estimates (CBE) of astronomical constants be permanently
maintained as an electronic document, and that the IAU establish a permanent body to maintain the CBEs for fundamental
astronomy.
IAU Resolution B3 (2009) resolves that from 01 January2010 the fundamental astronomic realisation of the International Celestial Reference System (ICRS) shall be the Second
Realization of the International Celestial Reference Frame(ICRF2) as constructed by the IERS/International VLBI Service for Geodesy and Astrometry (IVS) Working Group on
the ICRF in conjunction with the IAU Division I Working
Group on the International Celestial Reference Frame (Feyet al. 2009).
IUGG Resolution No. 3 (2011) on the ICRF2. This resolution urges that the ICRF2 shall be used as the standard for
all future applications in geodesy and astrometry, and thatthe highest consistency between the ICRF, the ITRF, and theEarth Orientation Parameters (EOP) as observed and realisedby the IAG and its components such as the IERS should be a
primary goal in all future realisations of the ICRS.
IAU Resolution B2 (2012) on the re-definition of the Astronomical Unit of Length. It is recommended that the astronomical unit be re-defined to be a conventional unit of length
equal to 149 597 870 700 m exactly, in agreement with the230value adopted in IAU 2009 Resolution B2.
IAG Resolution No. 1 (2015) for the Definition and Realisation of an International Height Reference System (IHRS). It
outlines five fundamental conventions for the definition of
the IHRS, including a conventional value for the reference
potential W0 = 62 636 853.4 m2 s−2 , and stating the mean
tidal system/mean crust as the standard for the generation of
IHRS-related products.
IAG Resolution No. 2 (2015) for the Establishment of a
Global Absolute Gravity Reference System. It resolves,
among other issues, to initiate the replacement of the International Gravity Standardization Net 1971 (IGSN71) by
the new Global Absolute Gravity Reference System.
IUGG Resolution No. 3 (2015) on the Global Geodetic Reference Frame (GGRF) recognising the adoption in February
2015 by the General Assembly of the United Nations (UN)of a resolution entitled “A Global Geodetic Reference Framefor Sustainable Development”. It urges the UN Global Geospatial Information Management (GGIM) GGRF Working
Group to engage with IUGG and other concerned organisations such as the Committee of Earth Observation Satellites(CEOS) and the Group on Earth Observation (GEO), in orderto promote the implementation of the UN GGIM GGRG
RoadMap.
UN Resolution (2015) on a Global Geodetic Reference
Frame (GGRF). The United Nations General Assembly
adopted the resolution on a Global Geodetic Reference
Frame for Sustainable Development (A/RES/69/266) on
February 26, 2015.
IAU Resolution A1 (2018) on the IAU Strategic Plan 2020–
2030.
IAU Resolution B1 (2018) on Geocentric and International Terrestrial Reference Systems and Frames. It recommends that the ITRS be adopted as the preferred GTRS for
scientific and technical applications; and that the IAU engage, together with other concerned organisations such as
the IUGG and IAG, with the United Nations (UN) Global
Geospatial Information Management (GGIM) Subcommittee
on Geodesy in order to promote the implementation of the
UN-GGIM Road Map for the Global Geodetic Reference
Frame.
IAU Resolution B2 (2018) on the Third Realisation of theInternational Celestial Reference Frame. It resolves that, asfrom 1 January 2019, the fundamental realisation of the International Celestial Reference System (ICRS) shall be theThird Realisation of the International Celestial Reference
Frame (ICRF3), as constructed by the IAU Working Groupon the Third Realisation of the International Celestial Reference Frame.
IAG Resolution No. 1 (2019) on the International Terrestrial
Reference Frame (ITRF). It recommends to the user community that the ITRF be the standard terrestrial reference
frame for positioning, satellite navigation and Earth science

1 Introduction

applications, as well as for the definition and alignment of
national and regional reference frames.
IAG Resolution No. 2 (2019) on the Third Realisation of
the International Celestial Reference Frame. It recommends(1) that the ICRF3 should be used as a standard for all futureapplications in geodesy and astrometry; (2) that the organisations responsible for geodetic VLBI observing programs
take appropriate measures to continue existing and develop
improved observing and analysis programs to both maintainand improve ICRF3, and (3) that highest consistency between
the ICRF, the ITRF, and the EOP should be a primary goal in
all future realisations.
IAG Resolution No. 3 (2019) on the Establishment of theInternational Height Reference Frame (IHRF). It urges all
countries to engage with the IAG and concerned components,
in particular the International Gravity Field Service (IGFS),
in order to promote and support the implementation of the
IHRF by (1) installing IHRF reference stations at national
level; (2) conducting the necessary gravimetric surveys toguarantee the precise determination of potential values; (3)making data available open access; (4) contributing to thedevelopment of analysis strategies to improve the estimationof reference coordinates and modelling of the Earth’s gravity
field; and (5) describing, archiving and providing geodetic
products associated to the IHRF.
IAG Resolution No. 4 (2019) on the Establishment of theInfrastructure for the International Gravity Reference Frame.
It urges international and national institutions, agencies andgovernmental bodies in charge of geodetic infrastructure to(1) establish a set of absolute gravity reference stations on
the national level; (2) perform regular absolute gravity observations at these stations; (3) participate in comparisons ofabsolute gravimeters to ensure their compatibility; and (4)make the results available open access.
IAG Resolution No. 5 (2019) on the Improvement of the
Earth’s Rotation Theories and Models. It resolves (1) to encourage a prompt improvement of the Earth rotation theory
regarding its accuracy, consistency, and ability to model andpredict the essential EOP; (2) that the definition of all the
EOP, and related theories, equations, and ancillary models
governing their time evolution, must be consistent with thereference frames and the resolutions, conventional models,
products, and standards adopted by the IAG and its components; and (3) that the new models should be closer tothe dynamically time-varying, actual Earth, and adaptable asmuch as possible to future updating of the reference frames
and standards.
IUUG Resolution No. 2 (2019) on the International Terrestrial Reference Frame (ITRF). It resolves to recommend to
the user community that the ITRF be the standard terrestrial reference frame for positioning, satellite navigation andEarth Science applications, as well as for the definition andalignment of national and regional reference frames.

1.2 Standards and conventions

1.2.5 Conventions

A convention is a set of agreed, stipulated or generally accepted norms, standards or criteria. In the Physical Sciences,
numerical values such as constants or quantities are called
conventional if they do not represent a measured property ofnature, but originate from a convention. A conventional value
for a constant or a specific quantity (e.g., the potential of thegeoid W0 ) can be, for example, an average of measurements
agreed between the scientists working with these values.
In geodesy, conventions may be adopted by the IAG and
its components (Services, Commissions, Inter-Commission
Committees, and GGOS). Most established and common are
the conventions of the IERS, which are provided by the IERS
Conventions Center. These IERS Conventions are regularly
updated and they serve as the basis for the analysis of the geometric observations and for the generation of IERS products.
The IERS Conventions are based on the resolutions of theinternational scientific unions, namely the IUGG, IAU and
IAG and they provide those constants, models, procedures,and software that have the most significance to IERS products (e.g., celestial and terrestrial reference frames, Earthorientation parameters, etc). Since these reference frames
are based on the geometric measurement techniques GNSS,
SLR/LLR, VLBI and DORIS, the IERS Conventions provide
the basis for the work of the geometric services of the IAG:
the International GNSS Service (IGS) (Dow et al. 2009),
the International Laser Ranging Service (ILRS) (Pearlman
et al. 2002), the International VLBI Service for Geodesy
and Astrometry (IVS) (Schuh and Behrend 2012), and theInternational DORIS Service (IDS) (Willis et al. 2010).
The latest printed version are the IERS Conventions 2010
(Petit and Luzum 2010). They consist of eleven chapters that
focus on topics, such as general definitions and numericalstandards, the definition and realisation of the celestial andterrestrial reference systems, transformations between both
systems, the geopotential, displacement of reference points,
tidal variations in the Earth’s rotation, models for atmosphericpropagation delays, general relativistic models for space-timecoordinates and equations of motion and general relativistic
models for propagation. The official release of the IERS Conventions 2010 was on December 15, 2010. Updates are available at iers-conventions.obspm.fr/conventions_versions.php.
In 2018, the IERS Conventions Center released a Call to
Participate in the IERS Conventions seeking volunteer participants as Chapter Editor-in-Chief, Chapter/Assistant Experts, and Software Editor to contribute to the revision ofthese conventions. The IERS Conventions Center intends topublish a new edition by 2022. Meanwhile, a team of experts
for the revision of the IERS Conventions has been established and a work plan (including time schedule) has been
defined by the IERS Conventions Center. The director of the
BPS has been nominated as Chapter Expert for Chapter 1

231“General definitions and numerical standards” and two representatives of the International Gravity Field Service (IGFS)
accepted the invitation of the IERS Conventions Center tocontribute to the rewriting of this chapter. Hence, for the firsttime, the gravity field community is directly involved in thedevelopment of definitions and numerical standards.
Although the IERS Conventions primarily serve as reference
for the geometric observation techniques and products of
the IERS, several parts of them also provide the basis forgravity-related data and products. However, for satellite gravity field missions (e.g., CHAMP, GRACE, GOCE), specificstandards and conventions have to be used for the data analysis and product generation such as, e.g., EIGEN (Förste
et al. 2012), GOCE (European GOCE Gravity Consortium2014), EGM2008 (Pavlis et al. 2012). These gravity-related
standards are not always fully consistent with the IERS Conventions, since also mission constraints (e.g., consistency
with respect to former missions) have to be adhered to. Other
satellite missions (e.g., altimetry, SAR, remote sensing, . . . )are also often based on standards and conventions issued by
the operating agencies such as ESA, CNES or NASA, which
may also be different to the IERS Conventions.
In summary, there are currently different conventions in use
for the analysis of geometric and gravimetric observations,which need to be carefully considered when different observation types are combined. This situation is not ideal for
ensuring a consistent integration of the geometry, rotationand gravity field of the Earth, which is a key goal of GGOS.
Thus, the development of a consistent set of conventions is
an important requirement that the BPS will address.

1.2.6 Physical and empirical background models

The background models play an important role for the processing of the different space geodetic measurements andfor the generation of geodetic products. This is a very broad
topic since a large number of background models need to be
applied to account for various geophysical phenomena andtechnique-specific effects. In this section we will address this
topic only very shortly to give a brief overview and we referto the IERS Conventions, which serve as the primary reference for the background models to be used for the analysisof the space geodetic measurements and the product generation. In addition to the IERS Conventions, the techniquespecific IAG Services provide specific information for thecorresponding space techniques.
Two types of correction models can be distinguished:• Models to correct for the effect of geophysical phenomenathat affect the station positions, quasar positions and/or
satellite orbits (e.g., solid Earth tides, ocean tides, poletides, etc).

232

1 Introduction

A-priori values (e.g., station positions,
quasar coordinates for VLBI, orbits forsatellite techniques, etc.)

Original observations (e.g., VLBI,SLR, GNSS, DORIS)

Geophysical and empirical models tocorrect a-priori values (e.g., Earth tides,pole tide and ocean tides, etc.)

Computed models that affect theobservation (e.g., troposphere, ionosphere, instrumental calibrations, . . . )Computation of theoretical value andits partial derivatives for the observation at the measurement epoch

Corrected observations (e.g., VLBI,SLR, GNSS, DORIS)

Computation of “o-c”(observed minus computed)

Adjustment and computationof geodetic products• Models to account for effects that directly influence thespace geodetic observations such as signal propagation(atmosphere) and technique-specific effects (e.g. GNSS
antenna phase centre variations, thermal deformation of
VLBI telescopes, SLR range biases, etc).
The first type of models are applied to the a-priori values forstation coordinates, satellite orbits and quasar positions (inthe case of VLBI), whereas the second type are generally
computed in the observation space, but could also be applied
to the a-priori values. The corrected a-priori values are thenused to compute the theoretical geometry at the observation
epoch. Finally, the values “o-c” (observed minus computed)
are derived, and used as input for the adjustment procedureand the computation of geodetic products (see Figure 1.3).
Concerning the background models, a further type of discrimination may be mentioned. While some models refer
to a-priori fixed, fully determined values, some others use
parameterised expressions; the parameter values are estimated within the least squares adjustment process related tothe adjustment of the observations. Examples of the second
type are, for example, parameters in the solar radiation pressure model or harmonic coefficients in the description of the
Earth’s gravitational potential.
Clearly these background models need to be developed witha specific level of accuracy and that these models have to beconsistently applied according to well-defined standards andFig. 1.3: Procedure for applying geophysical and empirical background models in the processing of space
geodetic observations. Please note that in some software packages the second type of models (that affect theobservations) are applied to the a-priori values, whichshould nevertheless lead to identical results.

conventions. This is essential for the processing of the different space geodetic observations and a strong requirement
for the generation of consistent geodetic products. The IAG
Services are responsible for the definiton of the processing
standards for their particular space gedetic technique, but thisshould be done in a coordinated way to ensure consistencyof the derived products. Hence it is necessary to address this
topic and a perfect forum for this are the Unified Analysis
Workshops which take place every two years.
The evolution of the scope and accuracy of the space geodetic observations also requires a continuous improvementof the background models which should be used for the data
analysis and which must be implemented in the various software packages. This is a continuous process involving manygroups and institutions. A challenge is to ensure that the generation of the geodetic products is based on homogeneously
processed observations. This holds in particular for the ITRF
generation (see section 4.2), since it requires a unificationof the models and processing standards among all the contributing analysis and combination centres of the geometricservices as basis for a consistent reprocessing of the VLBI,SLR, GNSS, and DORIS data over the entire observation
time spans for these space geodetic techniques. The Unified
Analysis Workshops, the workshops of the geometric services and the IERS Directing Board meetings provide forums
to discuss the relevant issues in detail.

233

2 GGOS Bureau of Products and Standards
The GGOS Bureau of Products and Standards (BPS) isa redefinition of the former GGOS Bureau for Standards
and Conventions (BSC), which was established as a GGOS
component in 2009. The BPS is operated by the Deutsches
Geodätisches Forschungsinstitut, Technische Universität
München (DGFI-TUM) and the Ingenieurinstitut für Astronomische und Physikalische Geodäsie of the Technische
Universität München (IAPG) within the Forschungsgruppe
Satellitengeodäsie (FGS) (Angermann et al. 2016, 2018;
Hugentobler et al. 2012).

2.1 Mission and objectives
The Bureau of Products and Standards (BPS) supports GGOS
in its goal to obtain consistent products describing the geometry, rotation and gravity field of the Earth. This is an
important requirement for reliably monitoring global change
phenomena (e.g., global sea level rise) and for providing themetrological basis for Earth system sciences. Figure 2.1 illustrates the integration of the “three pillars” geometry, Earthrotation and gravity field to obtain consistent geodetic products as the basis for studying the Earth system and the interactions between its sub-components and the outer space (e.g.,
Rummel, 2000; Drewes, 2007; Plag and Pearlman, 2009).
A key objective of the BPS is to keep track of adopted geodetic standards and conventions across all IAG components as a fundamental basis for the generation of consistentgeometric and gravimetric products. The work is primarily
build on the IAG Service activities in the field of data analysis and combinations. The BPS shall act as contact andcoordinating point regarding homogenisation of standards
and IAG products. Moreover, the BPS interacts with external
stakeholders that are involved in standards and conventions,such as the International Organisation for Standardisation(ISO), the Committee on Data for Science and Technology(CODATA), the International Astronomical Union (IAU) andthe UN GGIM Subcommittee on Geodesy (SCoG).
The objectives of the BPS may be divided into two major
topics/activities:• Standards: A key objective is the compilation of an inventory regarding standards, constants, resolutions andconventions adopted by IAG and its components. This
includes an assessment of the present status, the identification of gaps and shortcomings concerning geodetic
standards and the generation of the IAG products, as wellas the provision of recommendations. It is obvious thatsuch an inventory needs to be regularly updated since the
IAG standards and products are continuously evolving.
The BPS shall propagate standards and conventions to thewider scientific community and promote their use. Where
necessary, the BPS should propose new standards. In thiscontext, the BPS recommends the development of a newgeodetic reference system, GRS20XX, based on the best
estimates of the major parameters related to a geocentric
level ellipsoid.
• Products: The BPS shall take over a coordinating role
regarding the homogenisation of standards and geodetic
products. The present status regarding IAG Service products shall be evaluated, including analysis and combination procedures, accuracy assessment with respect toFig. 2.1: The key role of standards and conventions for consistent geodetic products as the basis for Earth system research, for studying
interactions between its sub-components and for precisely quantifying global change phenomena.

234

GGOS requirements, documentation and metadata information for IAG products. The Bureau shall initiate steps to
identify user needs and requirements for geodetic products
and shall contribute to develop new and integrated products. The BPS shall also contribute to the developmentof the GGOS Portal (as central access point for geodetic
products), to ensure interoperability with IAG Service data
products and external portals (e.g., GEO, EOSDIS, EPOS,GFZ Data Services).

2.2 Tasks
The tasks of the Bureau of Products and Standards are to:• act as contact and coordinating point for homogenisationof IAG standards and products;• keep track of adopted geodetic standards and conventions
across all IAG components, and initiate steps to close gaps
and deficiencies;• interact with external stakeholders in the field of standards and conventions (e.g., IAU, ISO, BIPM, CODATA,
UN-GGIM, . . . );• act as IAG representative to ISO/TC 211 and to the UNGGIM GGRF Working Group “Data Sharing and Development of Geodetic Standards”;• contribute to the UN GGIM Subcommittee on Geodesy(SCoG), mainly to the Working Group “Data Sharing andDevelopment of Geodetic Standards”;• regularly update the inventory on standards and conventions used for the generation of IAG products to incorporate the latest developments in these fields;• contribute to the re-writing/revising of the IERS Conventions, mainly in the function as Chapter Expert for Chapter
1 “General definitions and numerical standards“;• focus on the integration of geometric and gravimetric observations, and to support the development of integrated
products (e.g., GGRF, IHRF, atmosphere products);• contribute to the Committee on Essential Geodetic Variables (EGV), such EGVs could then serve as a basis fora gap analysis to identify requirements concerning observational properties and networks, accuracy, spatial andtemporal resolution and latency;• contribute to the newly established Working Group "Towards a consistent set of parameters for the definition of a
new GRS";• contribute to the GGOS Working Group on “DOIs for Geodetic Data Sets”, focusing on Digital Object Identifier(DOI) for geodetic data and products to improve discoverability of data sets and to ensure that data providers receive
proper credit for their published data;

2 GGOS Bureau of Products and Standards• organisational and coordination issues as well as representation and outreach activities, including internal BPS
meetings (every two months), external Bureau meetings(twice per year), representing the BPS within IAG and atconferences and workshops, presentation and publicationof BPS activities.

2.3 Staff and representation of IAG
components and other entities
The present BPS staff members are Detlef Angermann (director), Thomas Gruber (deputy director), Michael Gerstl,
Urs Hugentobler and Laura Sánchez (all from Technical
University Munich), as well as Robert Heinkelmann (GFZ
German Research Centre for Geosciences Potsdam) andPeter Steigenberger (German Aerospace Centre (DLR), Oberpfaffenhofen).
In its current structure, the following GGOS entities are associated with the BPS:
• Committee “Contributions to Earth System Modelling”,
Chair: M. Thomas (Germany);• Committee “Definition of Essential Geodetic Variables(EGVs)”, Chair: R. Gross (USA);• Working Group “Towards a consistent set of parameters
for the definition of a new GRS”,
Chair: U. Marti (Switzerland).
According to its charter, the work of the BPS requires a closeinteraction with the IAG Analysis and Combination Centersregarding the homogenisation of standards and products. The
IAG Services and the other entities involved in standards
and geodetic products have chosen their representatives asassociated members of the BPS. The Bureau comprises thestaff members, the chairs of the associated GGOS components, the two committees and the working group as listed
above, as well as representatives of the IAG Services andother entities. The status of December 2019 is summarisedin Table 2.1. Regarding the development of standards, there
is a direct link with the IERS Conventions Center, the IAU,
BIPM, CODATA, ISO, and the UN-GGIM Subcommittee on
Geodesy.
This configuration of the BPS ensures a close interaction with
the IAG Services and the other entities involved in standards.
A communication plan has been setup for a regular exchange
of information, in particular regarding the homogenisationof standards and IAG products. Regular meetings of the BPS
staff members take place in Munich every two months toperform the operational business. In addition regular telecons and face-to-face meetings (e.g., twice per year) with the
BPS staff and the representatives (and invitees) take place tocoordinate and manage the BPS work, to monitor progressagainst schedule, and to redefine tasks and responsibilites incase of need.

2.3 Staff and representatives

235

Table 2.1: Associated members of the BPS, representing the IAG Services, IAU andother entities (status: December 2019).
T. Herring, N. Stamatakos, USA
U. Hugentobler, Germany
E. Pavlis, USA
J. Gipson, USA
F. Lemoine, J. Ries, USA
J.-M. Lemoine, H. Capdeville, France
R. Barzaghi, Italy
S. Bonvalot, France
M. Reguzzoni, Italy
E. S. Ince, Germany
K. M. Kelly, USA
H. Wziontek, Germany
J. L. Hilton, USA
M. Craymer, Canada
L. Hothem, USA
J. Ádám, Hungary
D. Angermann, Germany
J. Kusche, Germany

International Earth Rotation and Reference Systems Service (IERS)
International GNSS Service (IGS)International Laser Ranging Service (ILRS)International VLBI Service for Geodesy and Astrometry (IVS)International DORIS Service (IDS)
International DORIS Service (IDS)
International Gravity Field Service (IGFS)
Bureau Gravimétrique International (BGI)International Service for the Geoid (ISG)
International Centre for Global Earth Models (ICGEM)International Digital Elevation Model Service (IDEMS)
International Geodynamics and Earth Tide Service (IGETS)
IAU Commission A3 Representative
Chair of Control Body for ISO Geodetic Registry Network
Vice-Chair of Control Body for ISO Geodetic Registry Network
IAG Communication and Outreach Branch
IAG representative to ISO/TC211
Representative of gravity community

236

3 Evaluation of numerical standards

3 Evaluation of numerical standards
3.1 Defining parameters of geodetic
reference systems, time and tidesystems
The IUGG resolution No. 7 (1979) and the IAG resolution
No. 1 (1980) recommend that the Geodetic Reference System
1980 (GRS80) (Moritz 2000) shall be used as the conventional reference for geodetic work. The GRS80 is defined byfour constants GM, a, J2 and ω, see Table 3.1. The GRS80 is
now about 40 years old and thus these conventional constants
do not represent anymore good estimates of parameters defining geometric and gravity field models best fitting to theshape and gravity field of the current Earth. In the conceptof GRS80, the tidal systems and relativistic theories are notconsidered (Ihde et al. 2017). However, the IAG recommends
the GRS80 parameters as a conventional ellipsoid, i.e., to convert Cartesian coordinates into ellipsoidal coordinates. The
GRS80 ellipsoid is used worldwide for many map projections
and millions of coordinates are related to it.
The numerical standards and adopted constants may alsochange with time, and so we should better speak about fundamental parameters instead of constants (Groten 2004).
Since a substantial progress has been achieved in the estimation of these fundamental parameters and their temporalchanges, the introduction of a new geodetic reference system(i.e., GRS2000) was a key topic within the geodetic community, in particular in Special Commission 3 “Fundamental
Constants” (Groten 2004) of the IAG (in its old structure).
However, after lengthy discussion and consideration, it was
decided not to propose a new GRS at that time. Nevertheless,some progress was made and a consistent set of fundamental parameters and their current (2004) best estimates havebeen compiled (Groten 2004). The paper lists several possible values for the parameters. The set of constants definedin Section III of that paper is included in the IERS Conventions 2010 (Petit and Luzum 2010). Table 3.1 summarises
the numerical standards given in different sources, namely
the conventional GRS80 constants (Moritz 2000), the Earth
Gravitational Model 2008 (EGM 2008), (Pavlis et al. 2012),
the fundamental parameters of (Groten 2004), the IERS Conventions 2010, and the updated version (2017) of the IERS
Conventions 2010 which contains the new conventional geopotential value W0 issued in the IAG (2015) Resolution No. 1(Drewes et al. 2016).
Various factors have to be considered for a comparison andinterpretation of the values displayed in Table 3.1. The values are obtained from different sources aiming at different
purposes. The GRS80 is still used to define a reference level

ellipsoid and its normal gravity field (e.g., the IERS Conventions 2010, Chapter 4, recommend to use the GRS80
ellipsoid to compute geographical coordinates). Except for
the angular rotation velocity ω, all other GRS80 parameters differ from the consistent set of fundamental parameters
published by Groten about 25 years later (Groten 2004). For
example, the difference for the equatorial radius a is about
0.4 m. The adopted standards for EGM 2008 were defined in
the same geodetic reference system as adopted for EGM 96(Lemoine et al. 1998) to ensure consistency between bothgravitational field models. For a comparison of the values
displayed in Table 3.1 it has also to be considered, that they
are partly expressed in different time and tide systems.
In 2017, in cooperation between the IERS Conventions Center and the BPS, the IAG 2015 conventional value W0 =62 636 853.4 m2 s−2 has been updated in Chapter 1 of the
IERS Conventions (Stamatakos 2017, pers. communication).
Thus, the former difference beween the IERS Conventions
2010 value and the new IAG 2015 value of about −2.6 m2 s−2(equivalent to a level difference of about 27 cm) has been
resolved.
Without going into detail on time systems, it should be mentioned that the IUGG Resolution No. 2 (1991) recommends
that the Geocentric Coordinate Time (TCG) shall be used forthe geodetic reference system. In practice, however, analysis
centres of all IAG geometric services use a time standard
consistent with the Terrestrial Time (TT). As described in the
IERS Conventions the relation between both time standards
is given by the equation
LG = 1 − d(TT)/d(TCG) = 6.969290134 · 10−10(3.1)

Thus, the difference between both time standards and the corresponding length scales is about 0.7 ppb (parts per billion).
Hence the value for the gravitational constant GM depends
on the metric (see Table 3.1),
GMTT = GMTCG (1 − LG ) .

(3.2)

It follows that the TT-compatible value of GM given for the
EGM2008 standards is consistent with the TCG-compatible
value given for the IERS Conventions 2010, see Table 1.1 ofthe IERS Conventions (Petit and Luzum 2010).

3.2 Solid Earth tide systems
Concerning the tide system, the IAG resolution No. 16 (1983)
states that for the uniform treatment of tidal corrections tovarious geodetic quantities such as gravity and station positions, the indirect effect due to the permanent yielding of

3.3 Open problems and recommendations

237

Table 3.1: Comparison of numerical standards used within IAG.
semi-major axis
a
[m]
GRS80
EGM2008
IERS Conv. 2010
. . . (update 2017)

Geocentric Grav. Dyn. form factor Earth’s rotation
Constant GM
J2
ω
[10−6 ]
[1012 m3 s−2 ][rad s−1 ]6 378 137
398.600 5
6 378 136.3
398.600 4415(2)(3)
6 378 136.6
398.600 4418(4)1 082.63
1 082.635 9
1 082.635 9

7.292 115
7.292 115
7.292 115

Reference
potential W0[m2 s−2 ](1)

62 636 856.0
62 636 856.0
62 636 853.4(5)(1) The reference potential U of the GRS80 is 62 636 860.850 m2 s−2 ;0(2) TT-compatible value; (3) value given in zero-tide system; (4) TCG-compatible value;(5) value updated in the IERS Conv. 2010 in agreement with the conventional W
0adopted by the IAG Resolution No. 1, 2015.

the Earth shall not be removed (IAG 1984). In the geodetic
community the following different tidal systems are in use
and have to be distinguished (Denker 2013; Mäkinen and
Ihde 2009; Petit and Luzum 2010):• In the mean-tide system only the periodic tidal effects are
removed from the positions, but the permanent parts (bothdirect and indirect) are retained.
• The zero-tide system is the one recommended by IAG. In
this system, the periodic tidal effects and direct permanent
effects are removed completely, but the indirect deformation effects associated with the permanent tide deformation
are retained.
• In the tide free system (or non-tidal system), the total tidal
effects (periodic and permanent, direct and indirect) areremoved with a model. In this case, the required (unobservable) fluid Love numbers have to be adopted by conventional values.
• The conventional routine for the evaluation of solid Earthtides computes tidal displacements as a sum of a frequencyindependent closed form and a series of frequency-dependent corrections. The closed form includes a permanent tidewhich is wrongly multiplied with the nominal elastic Love
number. Since for a long time the reduction of the wrong
permanent part was disregarded, a separate tidal system
was created which is now called conventional tide freesystem.
For geodetic products different tidal systems are being used.
While the gravimetric services of IAG provide their products
mostly in the zero-tide system, in agreement with the IAG
resolution No. 16 of the 18th IUGG General Assembly 1983,
the geometric services supply their products, e.g., ITRF, inthe conventional tide-free system. However, the ITRF has
adopted, by convention, the same tide system as the analysis
centres of IAG services. If the users need another tide systemrepresentation, the IERS Conventions provide the necessary
conversion formulas in Chapter 7. In applications involving
satellite altimetry, the mean-tide system is commonly used.

3.3 Open problems and recommendations
There are currently different numerical standards in use within the geodetic community. The parameters of the GRS80 are
still used to define a reference level ellipsoid and normal gravity field of the Earth, although it represents the state-of-the-artof the 1970s (methods and data) and it also does not consider
tidal effects and relativistic theories. The IERS Conventions
2010 (and its updates) are widely used within geodesy andthey form the basis for processing of geometric observations
and for generation of the IERS products. In addition to the
IERS Conventions, various mission-dependent standards andconventions are used for gravity-related products and in satellite altimetry, which are often not fully consistent with the
IERS Conventions. Another shortcoming of the current situation is that the conventional parameters are partly given indifferent time and tide systems, being a potential source oferrors when combining different products.
The foundations of the IAG Resolution No. 16 (1983) arestill valid concerning the tide systems. The recommended
zero-tide system is the most adequate tide system for the gravity acceleration and potential of the rotating and deforming
Earth. However, for the terrestrial reference system parameters the conventional tide free concept is used for decades,
although the tide-free crust is far away from the real Earth’s
shape and it is unobservable. In the past, there have been
several discussions on the tide system for the terrestrial reference frame. Due to practical reasons it was decided thatit should not be changed. The current practice is to use the“conventional” tide-free system for geometry (ITRF), zerotide system for gravity, mixed (mostly mean-tide system) for
physical heights (derived from levelling), and mostly meantide system for satellite altimetry. This situation makes theuse of geodetic products rather complicated and the inconsistent treatment of the permanent tide should be resolved
within IAG.
Another issue concerns the time-tagging: at present, different
space techniques and sometimes also different groups work-

238

ing within the same technique use different time standards,
for example GPS time vs. UTC. The offset between different
time standards does not affect the comparison of most geodetic parameters. However, if a particular parameter varies
rapidly, such as ∆UT1, then it is important that the comparisons are done at the same epoch. Thus, it is recommended
at a minimum that all scientists are clear and explicit about
what time tags they are using. In a perfect world the sametime tags would be used by everyone.
The IAG resolution No. 1 (2015) provides the basic conventions for the definition of an International Height Reference
System (IHRS), being the IAG conventional W0 value its
fundamental parameter. In 2017, this value has been updated
in the IERS Conventions 2010, so that W0 is now uniquely
defined in the geodetic standards. However, the current set offundamental parameters do not fulfil the Somigliana-Pizzetti
theory of the level ellipsoid. Thus, the definition of a new
GRS is also needed from this point (see at the end of thissection).
Another issue is the impact of the new W0 value on the definition of time standards. Since LG was declared as a defining
constant by IAU in 1999, the relationship between TCG andTT does not depend anymore on the geoid realisation. The
main implication for the IAU timescales is related to the accuracy in the realisation of the International Atomic Time
(TAI). It presently corresponds to a coordinate timescale
defined in a geocentric reference frame with the SI second
as realised on the rotating geoid as the scale unit. Therefore,
TAI still has a reference to the geoid (W0 ), while TT does nothave it anymore. This is a potential source of inconsistency
because it is usually considered that TAI is a realisation of
TT. However, this issue should not be further discussed here,
since the TAI definition is under the responsibility of theGeneral Conference of Weights and Measures through theConsultative Committee on Time and Frequency.
The current situation concerning the definition of numerical standards and the use of different time and tide systems
within geodesy is a potential source for inconsistencies andeven errors of geodetic products. Thus, it is essential fora correct interpretation and use of geodetic products thatthe underlying numerical standards are clearly documented.
Moreover, if geodetic results expressed in different time ortide systems are combined, respective transformations haveto be performed to get consistent results. As an ultimate goal
all existing inconsistencies should be removed and a consistent set of standards and conventions should be developed.
As outlined in Ihde et al. (2017), IAG is considering the necessity and usefulness for replacing GRS80 by a new geodetic
reference system. Towards this aim a new GGOS Working
Group “Towards a consistent set of parameters for the definition of a new GRS” has been established as a component

3 Evaluation of numerical standardsof the BPS at the end of 2019. This WG works together
with representatives of IAG Commissions 1 and 2, the InterCommission-Committee on Theory (ICCT), the International
Gravity Field Service (IGFS) and the Committee on Essential
Geodetic Variables (EGV). The activities will focus on estimation of a new set of defining parameters for a modern GRS
based on current methods and data, and on calculating allderived parameters in a consistent way. First results of such aconsistent set of geodetic fundamental parameters have been
derived and presented by Oshchepkov (2019). This set ofdefining parameters for a new GRS was derived in the zerotide system and TT standard based on the Somiliana-Pizzetti
theory of the level ellipsoid, comprising GM, U0 , J2 , and ω.
Hence, the semi-major axis a would become a derived parameter. The BPS strongly recommends to work towards a new
GRS as the basis for a consistent set of numerical standards
to be used within IAG.
Summary of recommendations on the numerical standards,
which have also been endorsed as recommendations of the
Unified Analysis Workshops 2019 (Gross et al. 2019):
Recommendation 0.1 : The used numerical standards including time and tide systems must be clearly documented for
all geodetic products.
Recommendation 0.2 : The inconsistency concerning thetreatment of the permanent tide must be resolved within
IAG to support the GGRF requirements and user needs.
Recommendation 0.3 : Astronomical, geodetic or geophysical standards including or requiring a W0 reference value
should adopt the IAG conventional W0 value issued by the
IAG Resolution No. 1 (2015), i.e.,
W0 = 62 636 853.4 m2 s−2 .
Recommendation 0.4 : A new Geodetic Reference System
GRS20XX based on a consistent estimation of best estimates of the major parameters related to a geocentric level
ellipsoid should be developed.

239

4 Product-based review
This chapter focuses on the assessment of the standards andconventions currently adopted and used by IAG and its components for the generation of IAG products. With the compilation of such a product-based inventory, the BPS supports
GGOS in its goal to obtain consistent geodetic products andit provides also a fundamental basis for the integration of geometric and gravimetric parameters, and for the developmentof new products.
GGOS as an organisation is built on the existing IAG Services, and under this “unifying umbrella”, all the products
provided by the different IAG Services are considered GGOS
products. This declaration and also Section 7.5 “Products
available through GGOS” from the GGOS publication (Plagand Pearlman 2009) serve as the basis to specify the major
products of IAG and GGOS, addressing the following topics:
Section 4.1 Celestial reference systems and frames,
Section 4.2 Terrestrial reference systems and frames,
Section 4.3 Earth orientation parameters,
Section 4.4 GNSS satellite orbits,
Section 4.5 Gravity and geoid,
Section 4.6 Height systems and their realisations.
The sections for each of these products (or topics) were organised in a similar structure. The first part gives a brief overview, followed by a description and discussion of the present
status, and finally open problems are identified and recommendations are provided. Despite of this similar structure,
the character of these sections is partly different as a consequence of the current situation regarding the availability of
IAG products in the different fields and due to organisational
issues of the IAG Services. Although the celestial reference
frame is a product of IAU, it is addressed in this inventory,
since IAG is directly involved through the IVS and the consistency between the celestial and terrestrial reference frameis also an important reseach topic of IAG (Section 4.1). Pure
IAG products exist for the terrestrial reference frame (Section 4.2) and for the EOP (Section 4.3) which are provided
by the responsible Product Centers of the IERS. This updated
version of the inventory includes the latest version of theseproducts, the ICRF3, the ITRF2014 and the EOP 14CO4
series. The GNSS satellite orbits addressed in Section 4.4
are provided by the IGS. This technique-specific product was
included in the inventory, since the GNSS orbits are used fora wide range of applications. Also for the gravity field andgeoid (Section 4.5) as well as for the height systems and theirrealisations (Section 4.6) a lot of progess has been achieved
during the last four years, but on the other hand official IAG
products still need to be defined and implemented. Due tothis fact the character of these two corresponding sections
differs from the four others.

The BPS gives credit to the efforts and contributions of the
IAG Services, their contributing Analysis and Combinations
Centers, and the Product Centers of the IERS and IGFS,
which provide the foundation for the generation of the IAG
Products. Without their significant work and valuable support
the progress achieved during the past years would not havebeen possible.
Finally, it should also be noted that the list of topics and IAG
products is by far not complete and it should be extended
by adding other products in an updated version of this document, to incorporate the ongoing GGOS activities towards
the development of integrated geodetic products.

4.1 Celestial reference systems and frames
4.1.1 Overview

By the nature of this topic, the IAU has always been responsible for celestial reference systems and celestial reference
frames. However, in the course of technological development
many more organisations and working groups have been involved in the more recent past where observations in the radio
frequency regime have superseded optical observations. Dueto its dominating volume of observations, the International
VLBI Service for Geodesy and Astrometry (IVS) (Nothnagel
et al. 2017) was the key supplier of observations and analysis capability in the recent past. The IVS was establishedin 1999 as an international collaboration of organisations operating or supporting VLBI components to support geodetic
and astrometric work on reference systems and Earth science
research by operational activities. Due to the basics of its
technique, the IVS is a joint service of IAG and IAU. On the
IAG side, the IVS represents the VLBI technique in GGOS
and interacts closely with the IERS, which is tasked by IAU
and IUGG with maintaining the ICRF and ITRF, respectively.
As a result of this organisational structure and technical infrastructure, the IAG, through IVS, has an indirect responsibility for the provision of the celestial reference frame at radio
frequencies. The VLBI technique provides the direct link
between the celestial and the terrestrial reference frames, and,at the same time, determines the Earth orientation parameters.
Since the consistency between both frames is an important
issue that should be addressed by the scientific community(see IUGG Resolution No. 3, 2011 and IAG Resolution No. 2,2019), the topic is subject of this inventory.
The IAU resolution No. B2 from the IAU General Assemblyin 1997 resolved (a) that as from 1 January 1998, the IAU
celestial reference system shall be the International Celestial Reference System (ICRS) as specified in the 1991 IAU

240

Resolution on reference frames and as defined by the IERS
(Arias et al. 1995); (b) that the corresponding fundamental
reference frame shall be the International Celestial Reference
Frame (ICRF) constructed by the IAU Working Group onreference frames; (c) that the Hipparcos Catalogue shall be
the primary realisation of the ICRS at optical wavelengths;and (d) that the IERS shall take appropriate measures, in conjunction with the IAU Working Group on reference frames,
to maintain the ICRF and its ties to the reference frames
at other wavelengths. According to this IAU resolution, the
ICRS has been realised by the ICRF since January 1, 1998,
which is based on the radio wavelength astrometric positionsof compact extragalactic objects determined by VLBI.
The IERS is responsible for monitoring the ICRS, maintaining its realisation, the ICRF, and improving the links withother celestial reference frames. Since 2001, these activities
have been run jointly by the ICRS Centre (at the Observatoirede Paris and the US Naval Observatory) of the IERS and the
IVS, in conjunction with IAU.
4.1.2 International Celestial Reference System

Following the IAU Resolution B2 (1997), the ICRS replaced
the Fifth Catalogue of Fundamental Stars (FK5) as the fundamental celestial reference system for astronomical applications. According to IAU Resolution A4 (1991), the ICRS isa specific Barycentric Celestial Reference System (BCRS),
with its axes kinematically non-rotating with respect to the
distant objects in the universe (Petit and Luzum 2010). Theseaxes are defined implicitly through a set of coordinates of extragalactic objects, mostly quasars, BL Lac sources and radiogalaxies, all of which are Active Galactic Nuclei (AGN), as
determined in the most precise realisation of the ICRS, theICRF (for more information see (Petit and Luzum 2010)).
The celestial reference system has its principal plane as close
as possible to the mean equator at J2000.0 and the origin ofright ascension on this principal plane as close as possible tothe dynamic equinox of J2000.0.
4.1.3 International Celestial Reference Frames

History of ICRS realisations
The initial test realisation of the IERS Celestial Reference
System, RSC(IERS) 88 C01 (Arias et al. 1988) contained
228 extragalactic radio sources in total. This first catalogue
was computed by combining the VLBI solutions of three
US agencies (Goddard Space Flight Center (GSFC) and Jet
Propulsion Laboratory (JPL), both belonging to the National
Aeronautics and Space Administration (NASA), and National
Geodetic Survey (NGS)). In the adjustment process the rightascension of the source 3C273B was fixed to its conventional FK5 value (Hazard et al. 1971). 23 out of the 228

4 Product-based review

radio sources were chosen to define the axis directions of
this first frame. This initial realisation can be considered as
the intangible basis of the radio celestial frame, since all
subsequent realisations directly or indirectly refer to this initial set of coordinate axes. Between 1988 and 1994, several
celestial reference frames were determined on a regular basis
following the first one, all of which were referred to the respective previous realisation of ICRS by No-Net-Rotation(NNR) constraints.
As specified in the IAU Resolution No. 2 (1997), the ICRF,
i.e. the first conventional realisation of the ICRS, is basedon the positions of extragalactic objects provided by VLBI.
Adopted by the IAU Working Group on Reference Frames(WGRF), it was determined by the VLBI solution of the
GSFC (Ma et al. 1998; Ma and Feissel 1997). The catalogue
provides the positions and uncertainties of 608 radio sources,
including 212 defining sources used for the global NNR
condition, to realise the axes of the ICRF (Arias and Feissel 1990) with respect to previous IERS celestial reference
frames (Arias et al. 1991; Ma and Feissel 1997).
There were two extensions of ICRF: ICRF-Ext. 1 (Gambis
1999) and ICRF-Ext. 2 (Fey et al. 2004). For both extensions
the original ICRF positions of the defining sources remained
unchanged, thus preserving the initial ICRF orientation fixed.
Within the common IAU/IVS Working Group entitled “The
Second Realisation of the International Celestial Reference
Frame – ICRF2” a new version of ICRF was computed (Feyet al. 2009, 2015), which was accepted by the IAU at its
General Assembly in Rio de Janeiro, Brazil, in August 2009(see IAU Resolution No. B3, 2009) and by IUGG Resolution
No. 3 (2011). It contains the positions of 3414 compact radiosources, including a selected set of 295 defining sources. The
stability of the axes is specified to be 10 µas, making ICRF2
nearly twice as stable as its predecessor, also accompanied
by an improved noise level of about 40 µas and a more uniform sky distribution including more defining sources on thesouthern hemisphere.
The overall characteristics of the ICRF2 solution are described in (Fey et al. 2009, 2015). The a-priori models forgeophysical effects and precession/nutation used for the computations generally followed the IERS Conventions 2003
(McCarthy and Petit 2003). Specifically, corrections for solid
Earth tides, the pole tide, ocean loading, and high frequency
EOP variations were made using the IERS Conventions 2003.
Other important effects were modelled using• atmosphere pressure loading corrections according to Petrov and Boy (2004),• troposphere delays based on the Vienna Mapping Functions 1 (VMF1) of Böhm et al. (2006),• the antenna thermal deformation models of Nothnagel(2009), and4.1 Celestial reference systems and frames• the a-priori gradient model according to MacMillan and
Ma (1997).
The current realisation, the ICRF3Within the IAU Division A Working Group entitled “Third
Realisation of the International Celestial Reference Frame(ICRF3)” a new version of ICRF was computed (Charlot
et al. 2020), which was accepted by the IAU at its General
Assembly in Vienna, Austria, in August 2018 (see IAU Resolution No. B2, 2018). The developments were supported by
the IAG Sub-Commission 1.4 “Interaction of Celestial andTerrestrial Reference Frames”. The reliability of the ICRF3
could be improved through comparisons with observations
obtained at higher radio frequencies and at optical wavelength provided by European Space Agency (ESA)’s opticalastrometry mission Gaia.
The ICRF3 contains the positions of 4536 compact radiosources, including a selected set of 303 defining sources. The
stability of the axes betters the one of the previous reference
frame, ICRF2. Individual coordinates show a noise floor of
about 30 µas. For the first time, the effects of galactic rotation
on celestial coordinates is considered in the ICRF3 in termsof a correction on the observation level. Therefore, the reported celestial coordinates refer to the epoch 2015.0. Besides
the S-/X-band coordinates, ICRF3 contains several hundredsof objects in K- and/or X-/Ka-bands as well. A comparisonof ICRF3 with data release 2 (DR2) of the ESA Gaia mission
in optical wavelengths shows no deformations above about
30 µas. Mainly due to the revisiting of ICRF2 survey radiosources, the source coordinate errors have a more uniform
sky distribution. Accordingly, the ICRF3 only contains theradio source categories “defining” and “candidates”. A comparison with Gaia and ICRF2 revealed that the ICRF2 hassmall systematic deformations of up to 80 µas.
The a-priori models for geophysical effects and precession/
nutation used for the ICRF3 computations generally followed
the IERS Conventions 2010 (Petit and Luzum 2010). Specifically, corrections for solid Earth tides, the pole tide, ocean
loading, and high frequency EOP variations comply with thatconventions. Besides the conventional models mentioned
above, other important effects were modelled using tidal andnon-tidal atmosphere pressure loading corrections according
to Petrov and Boy (2004) instead of the tidal-only atmospherepressure loading model mentioned in the IERS Conventions
2010.
4.1.4 Discussion of the present status

241

Quite a large number of organisations, services and otherentities are involved. Although the responsibilities for thedefinition of the ICRS and the maintenance of the ICRF are
resolved in the IAU resolutions (see Sections 1.2.4 and 4.1.1),
the complex structure in this field requires an efficient andregular exchange of information to ensure effectiveness of
the work.
ICRS definition and its realisation
The definition and realisation of the ICRS are given in the
IERS Conventions (Petit and Luzum 2010) on the basis ofseveral IAU resolutions. The IAU Resolution A4 (recommendation VII, 1991) recommends under (1) “that the prinicipal plane of the new conventional celestial reference frame
be as near as possible to the mean equator at J2000.0 andthat the origin of the principal plane be as near as possible
to the dynamical equinox of J2000.0”. These rather imprecise
definitions result from the fact that old realisations were usually not as precise as the subsequent conventional realisations.
A series of ICRS realisations has been computed so far, andin each of those the datum has been defined with respect tothe previous realisation by applying NNR conditions. But thisis depending on the quality, number and distribution of thedefining radio sources used in the NNR condition. When applying this procedure, inconsistencies of the predecessor canaffect the reference frame definition (mainly the orientation)of new (more precise) frames.
ICRF computations
All ICRS realisations including the latest one, the ICRF3,
have been computed by only one IVS Analysis Center using
a single software package. Although the final product is controlled through a comparison with individual IVS solutions,the procedure differs from the generation of the ITRF andEOP products, which are generated from a combination ofindividual contributions (see Section 4.2 and 4.3). Currently,
formal errors of the ICRF determined by VLBI are certainly
too optimistic since they do not account for uncertainties of anumber of technique-specific models and auxiliary observations such as atmospheric pressure and air temperature. Other
examples of neglect are antenna axis offsets, thermal expansion modelling, uncertain technique-specific model components and source structure effects. Although, the imbalanceof VLBI observatories on the northern and southern hemispheres has been improved for the ICRF3, the impact of suchan effect has to be investigated in more detail.

General issues

Consistent estimation of the ICRF, ITRF and EOP

The organisational structure regarding the definition and realisation of the celestial reference system is rather complex.

The IUGG Resolution No. 3 (2011) urges that the highest
consistency between the ICRF, the ITRF and the EOP as242

observed and realised by IAG and its components such as
the IERS should be a primary goal in all future realisations of the ICRS. The newly adopted IAG Resolution No. 2(2019) recommends that highest consistency between the
ICRF, the ITRF, and the EOP should be a primary goal in
all future realisations. At present, both frames (the ICRF and
ITRF) and the EOP solutions are not fully consistent witheach other as they are computed independently by separate
IERS Product Centers. Although the recommendations of the
IUGG and IAG resolutions have not been fulfilled yet, related studies are being performed by several research groups(e.g., at JPL and Deutsches Geodätisches Forschungsinstitut, Technische Universität München (DGFI-TUM)), see forexample, Seitz et al. (2014), Kwak et al. (2018), and Soja
et al. (2019). On the international level, this topic has beenaddressed by the IAU Working Group “ICRF 3” and it isan ongoing research topic of the IAG Sub-Commission 1.4“Interaction of celestial and terrestrial reference frames”. The
topic of the consistency between the ICRF, ITRF, and EOP
is addressed at Sections 4.2 and 4.3 as well.
4.1.5 Interaction with other products

Through the VLBI observations there is a direct link of thecelestial reference frame with• terrestrial reference frames and• the Earth orientation parameters.
The interactions of the ICRF with the ITRF and EOP also
provide indirect links to the dynamic reference frames ofsatellite orbits and to other parameters derived from the mentioned products.

4 Product-based review

centre solutions computed with different software packages,
as done by the other Product Centres of the IERS. The precision of the coordinates of radio sources forming the ICRF
steadily gets better due to more accurate observations and improved analysis methods. Therefore, it shall be investigated if
source position instabilities must be included. Recent studies
on source structure effects were performed by Anderson et al.
(2019).
Consistency of ICRF, ITRF and EOPThis topic was already addressed at the IERS Retreat in Paris
2013 (see www.iers.org/IERS/EN/Organization/Workshops/Retreat2003.html).
In the above mentioned IERS Retreat 2013, it was recommended that the following questions should be addressed:(1) How consistent is the ICRF with the ITRF and EOP ?
(2) Is the ICRF decoupled enough from the ITRF so thatradio sources do not need to be included in the ITRF computations and vice versa? (3) What is the gain if ICRF, ITRF and
EOP are estimated in a common adjustment? Although thestudies mentioned in Section 4.1.4 show already some quality
improvements due to the combined adjustment of the celestial and terrestrial reference frame and the EOP, the questions
above still need to be addressed in more detail. Thus, researchgroups that can do the required combinations are encouraged
to perform such studies. On the international level the IAG
Sub-Commission 1.4 “Interaction of celestial and terrestrialreference frames” and the proposed IAG/IERS/IAU JWG on
the Consistency of CRF, TRF, and EOP should also focus on
this important topic.
Summary of recommendations on ICRS/ICRF

4.1.6 Open problems and recommendations

General issue on ICRS/ICRF
As a consequence of the interactions between IAU and various IAG components, the celestial reference system andframe is part of this inventory, although the latest ICRF3
realisation is labeled as IAU product. It helps to address
important scientific questions, like the consistency between
the celestial and terrestrial frame. Moreover, the objectivesof GGOS require not only an Earth-fixed frame, but also
the link to an inertial frame and the interactions between
both described by the EOP, which is also relevant for the
implementation of the GGRF.
ICRF computations
It remains to be considered whether the next ICRS realisation
shall be estimated from a combination of different analysis

Recommendation 1.1 : The organisations involved in thedefinition and realisation of the ICRS are asked to clarify
the structure and responsibilities. This is also important in
the framework of the implementation of the GGRF, which
includes the ICRF.
Recommendation 1.2 : It should be considered by the organisations and their responsible working groups, whether the
next ICRS realisation, should be estimated from a combination of different analysis centre solutions.
Recommendation 1.3 : Research groups are encouraged toperform further investigations on source structure effects
and to evaluate the impact on the realisation of the celestialreference system.
Recommendation 1.4 : Following IUGG Resolution No. 3(2011) and IAG Resolution No. 2 (2019), research groups
are encouraged to perform the previously mentioned studies regarding the consistency of ICRF, ITRF and EOP.
Please note that this recommendation also concerns theSections 4.2 and 4.3.

4.2 Terrestrial reference systems and frames

4.2 Terrestrial reference systems andframes
4.2.1 Overview

A Terrestrial Reference System (TRS) is a spatial reference
system co-rotating with the Earth. Its realisation is called areference frame. The nomenclature and basic concepts of aterrestrial reference system and the frame are well describedin Chapter 4 of the IERS Conventions 2010 (Petit and Luzum2010). The most recent update of Chapter 4 (v1.3.0 of April2019) is available at iers-conventions.obspm.fr/content/chap
ter4/icc4.pdf.
Terrestrial reference frames (TRF) are needed to refer thegeodetic observations and estimated parameters to a unified
global basis. High accuracy, consistency and long-term stability are required for precisely monitoring global change
phenomena as well as for precise positioning applications on
and near the Earth’s surface. The importance of geodetic reference frames for many societal and economic benefit areas
has been recognised by the United Nations too. In Feburary
2015, the UN General Assembly adopted its first geospatial
resolution “A Global Geodetic Reference Frame for Sustainable Development” (see www.un.org/en/ga/search/view_doc.
asp?symbol=A/RES/69/266 and www.unggrf.org/).
The International Terrestrial Reference System (ITRS) has
been formally adopted and recommended for Earth science
applications (IUGG 2007). The IAG Resolution No. 1 (2019)
recommends to the user community that the ITRF shouldbe the standard terrestrial reference frame for positioning,satellite navigation and Earth science applications, as well
as for the definition and alignment of national and regionalreference frames. The IERS is in charge of defining, realisingand promoting the ITRS. The IERS Conventions provide thebasis for the general definitions and numerical standards aswell as for the mathematical representation of the relevant
quantities and for the modelling of the contributing geometricspace techniques.
The International Terrestrial Reference Frame (ITRF) is arealisation of the ITRS, consisting of 3-dimensional positions
and time variations of IERS network stations observed by
space geodetic techniques. Currently, the contributing spacetechniques are VLBI, SLR, GNSS, and DORIS. According
to the Terms of Reference of the IERS, the ITRS Center hosted at the Institut National de l’Information Géographiqueet Forestiere, France (IGN), is responsible for the maintenance of the ITRS/ITRF, including network coordination, forproviding the ITRS Combination Centers with specifications,and for evaluating their respective results. The ITRS Combination Centers are responsible to provide ITRF products
by combining ITRF inputs from the Technique Centers and243

others. ITRS Combination Centres are currently maintainedby IGN (Paris, France), DGFI-TUM (Munich, Germany) andJPL (Pasadena, USA).
4.2.2 History of ITRS realisations

Until now, thirteen releases of the ITRF were published by
the IERS, starting with ITRF 88 and ending with ITRF 2014,
each of which superseded its predecessor (see Chapter 4of the IERS Conventions 2010, (Petit and Luzum 2010)).
An updating of ITRS realisations is performed every few
years, since the tracking networks of space techniques are
evolving, the period of data extends, and also the modelling and data analysis strategies as well as the combination
methods improve with time. Furthermore, several large earthquakes might have affected station positions and velocities
over large regions. Up to ITRF 2000, long-term global solutions (comprising station positions and velocities) from thefour techniques (VLBI, SLR, GNSS, and DORIS) were used
as input for the ITRF generation, which have been used by
the ITRS Centre at IGN in France to compute the ITRS
realisations.
In 2001, when the IERS was restructured, the newly established ITRS Center (former ITRS Terrestrial Reference
Frame Section) has been supplemented by ITRS Combination Centers, to enable intercomparisons of the ITRF results.
Additionally, the combination strategy for the ITRF computations has been refined. Starting with ITRF 2005, the ITRF
computations were based on time series of station positions
and EOP, including variance-covariance information fromeach of the techniques’ combination centres. The ITRF 2005
and 2008 solutions were computed at the ITRS Combination Centers operated by IGN and DGFI. A comparison anddiscussion of the ITRF2008 (Altamimi et al. 2011) and theDTRF2008 (Seitz et al. 2012) is provided in the 2016 versionof this inventory (Angermann et al. 2016). The current ITRS
realisation, the ITRF2014, is summarised in Section 4.2.3.
In January 2019, the IERS disseminated a call for participation for a new ITRF2020 solution to be released by the ITRS
Center at the end of 2021. This new ITRS realisation willcontain six years of additional observations until the endof 2020. New sites have been added to the ITRF networkand new colocation sites as well as new local ties are now
available. Moreover, the geometric IAG Services have further improved their processing strategies, new models havebeen implemented and the ITRS Combination Centers haverefined their combination methodologies.
4.2.3 The current ITRS realisation, the ITRF 2014

The ITRF 2014 is the current realisation of the ITRS (Altamimi et al. 2016). It is based on reprocessed solutions or
normal equations of the four space techniques VLBI, SLR,

244

4 Product-based review

GNSS, and DORIS comprising time series of station positions and EOP. They are generated by individual analysis
centres of the technique-specific IAG Services, namely the
IGS, ILRS, IVS and IDS. In the ITRF 2014 call for participation it was specified that the input data shall conform to
the IERS Conventions 2010 (Petit and Luzum 2010). Moreover, guidelines for the ITRS Combination Centers were
provided in this call. The time series cover the entire observation history for each of the four techniques and the individual
contributions were combined per-technique by the responsible technique-specific combination centres of the IGS, ILRS,
IVS, and IDS. The major characteristics of the input data for
the ITRF 2014 are given in Table 4.1.
The ITRF2014 is generated with an enhanced modelling of
nonlinear station motions, including seasonal (annual andsemi-annual) signals of station positions and post-seismic
deformation (PSD) for sites that were subject to major earthquakes. In case of ITRF2014 and for stations subject to PSD,
the user should add the sum of all PSD corrections to thelinearly propagated position, using equation 4.16 of the mostrecent update of Chapter 4 of the IERS Conventions (iersconventions.obspm.fr/content/chapter4/icc4.pdf):
X(t) = X(t0 ) + (t − t0 )X˙ + δ XPSD (t)The ITRF2014 PSD parametric models, together with all
equations allowing users to compute the PSD corrections andFortran subroutines are available at the ITRF2014 website
itrf.ign.fr/ITRF_solutions/ITRF2014.
Compared to the ITRF2008, the input data for the ITRF2014
were significantly improved. Besides six more years of observations, also technical upgrades of satellite and stationequipment as well as a higher number of stations and satellites allows for a more robust realisation of the ITRS. Moreover, the entire observation time series for all techniques
were reprocessed by using the latest technique-specific andgeophysical background models (as specified in the IERS
Conventions 2010 and its updates) and, if appropriate, by implementing new parameterisations. Table 4.2 summarises themost important changes in modelling and parameterisationfrom ITRF2008 to ITRF2014.Detailed information for eachof the four techniques is provided in the references given in
Table 4.2.
In addition to the local ties used in the ITRF2008 computation, a certain number of new local ties from new colocationsites and/or from new surveys were used for the ITRF2014(Altamimi et al. 2016).
These input data were used by the three ITRS Combination
Centers at IGN (France), DGFI-TUM (Germany) and JPL(USA) to compute the ITRS realisations, i.e., the ITRF 2014
(Altamimi et al. 2016), the DTRF 2014 (Seitz et al. 2020,2016) and the JTRF 2014 (Abbondanza et al. 2017). While
DTRF 2014 and ITRF 2014 are secular frames providing station positions at a reference epoch and constant velocities
according to the conventional ITRS definition, the JTRF 2014is based on a KALMAN filter approach delivering time seriesof station positions. Thus, the two conventional multi-year
solutions computed at IGN and DGFI-TUM are not directlycomparable with the JTRF 2014 time series of weekly station
position and EOP solutions. The characteristics of these threesolutions are summarised in Table 4.3.
The ITRS combination strategies have been substantially
improved compared to the ITRF2008 computations. The
ITRF2014 involves two main innovations dealing with themodelling of non-linear station motions, namely seasonal
signals present in the time series and post-seismic deformation (PSD) for stations subject to major earthquakes. Also the
DTRF2014 is characterised by two main innovations: For the
first time, it considers non-tidal loading corrections derived
from geophysical models. Secondly, it provides as additional
DTRF2014 products the time series of the station position
residuals, the weekly SLR translation parameters and thenon-tidal loading (NT-L) corrections, which were provided
by the GGFC (Tonie van Dam). The ITRS Combination Center at JPL provided its first ITRS realisation, the JTRF2014,
in the form of time series of weekly solutions comprisingstation positions and EOP.
The IERS Technical Note on the ITRF2014 (Altamimi et al.
2017) is supplemented by an additional IERS Technical Note

Table 4.1: Input data sets for ITRF 2014 (TC: Techniques’ Combination Center, AC:
Analysis Center, NEQs: Normal Equations). In addition, also geodetic local tie information is used as input for the ITRF computations.
TC

# ACs
per techniqueTime period

Sampling

Data

Constraints

IGS
IVS
ILRS
ILRS
IDS

9
9
7
8
6

1994.0 – 2015.1
1980.0 – 2015.0
1983.0 – 1993.0
1993.0 – 2015.0
1993.0 – 2015.0

Daily
Daily
Fortnightly
WeeklyWeeklySolutions
NEQs
Solutions
Solutions
Solutions

Minimum
None
Loose
Loose
Minimum

4.2 Terrestrial reference systems and frames

245

Table 4.2: New models and parameterisations applied by the geometric technique services for thegeneration of the ITRF2014 input data; the table has been taken from (Seitz et al. 2020) and has beenslightly modified.
TechniqueServiceModel changes and new parameterisation

DORIS

IDS

IDS input data for ITRF2014 (Moreaux et al. 2016)- models improvements of some satellites (Envisat, Cryosat-2, Jason-2)- parameterisation of antenna frequency offsets- most recent time-variable gravity field EIGEN-6S2 (Förste et al. 2012)- improved modelling of radiation pressure accelaration- refined modelling of atmospheric drag- satellite attitude laws in POD software has been re-verified by some ACs- timetagging for Envisat solved- SAA effects on SPOT-5 oscillator solved

GNSS

IGS

IGS input data for ITRF2014 (Rebischung et al. 2016)- switch from weekly to daily resolutions- implementation of IGb08/igs08.atx reference frame- implementation (partly) of new attitude models for ecclipsing satellites- modelling of Earth radiation pressure, and (mostly) of antenna thrust

SLR

ILRS

ILRS input data for ITRF2014 (Luceri and Pavlis 2016)- four satellites: Lageos 1/2 and Etalon 1/2- daily mean pole values derived from IERS series- centre-of-mass correction for each satellite in specific tables- modelling or estimation of range corrections for a number of sites

VLBI

IVS

IVS input data for ITRF2014 (Bachmann et al. 2016)- provision of celestial pole offsets- fixing of source positions to ICRF2 (Fey et al. 2015)- new axis offsets and eccentricities

generalmodelsIERS

General models according to IERS Conventions 2010 (Petit and Luzum 2010)- mean pole model (all, except ILRS as given above)- Earth’s gravity field model- tidal station displacements- tidal variations in Earth rotation- Nutation model- relativistic effects- tropospheric and ionospheric propagation delays(Altamimi and Dick 2020). It includes the two other ITRS
solutions, the DTRF2014 and JTRF2014, a comparision of
the three solutions performed at IGN and DGFI-TUM aswell as evaluations of the three ITRS solutions done by the
IERS Technique Centers, which provide the input data for the
ITRF generation. Such Technique Center contributions havebeen provided by the IDS, ILRS and IVS. These evaluations
confirm the high quality of the three ITRS solutions as wellas the improvement compared to the ITRF2008.
This IERS Technical Note 40 (Altamimi and Dick 2020)
gives credit to the various contributions to the ITRF2014,
which yield an excellent basis for the ITRF2014 evaluation.
However, concerning the ITRF accuracy, it should be notedthat the cross-validations of the three ITRS solutions (which
are based on the same input data) are mainly a measure for
their consistency, and they do not fully reflect the various im-

pact factors that need be considered to quantify the accuracyof the terrestrial reference frame (see Section 4.2.4).
4.2.4 Discussion of the present status

ITRS definition vs. its realisation
According to the IERS Conventions (Petit and Luzum 2010),
the ITRS definition is based on the following principles:• It is geocentric, the centre of mass being defined for thewhole Earth, including oceans and atmosphere;• The unit length is the meter (SI). This scale is consistent
with the TCG time coordinate for a geocentric local frame,in agreement with IAU and IUGG (1991) resolutions;• Its orientation was initially given by the Bureau International de l’Heure (BIH) orientation of the BIH Terrestrial
System (BTS) at epoch 1984.0;

246

4 Product-based review

Table 4.3: Summary of combination strategies for the ITRF2014, DTRF2014 and JTRF2014 (PSD: Post-seismic deformation,
NT-L: Non-tidal loading). More details on the combination strategies are found in the references for the ITRF2014 (Altamimi
et al. 2016), the DTRF2014 (Seitz et al. 2020) and JTRF2014 (Abbondanza et al. 2017).
Solution

ITRF2014

DTRF2014

JTRF2014

Institute

IGN (Paris, France)

DGFI-TUM (Munich,Germany)

JPL (Pasadena, USA)

Software

CATREF

DOGS-CSCATREF + KALMAN

Combination
approach

Solution (parameter) level

Normal equation level

Solution (parameter) level

Station position

Position XITRF (t0 )+ velocity ẊITRF (t0 )+ PSD models (selected
stations)+ periodic signals(on request)

Position XDTRF (t0 )+ velocity ẊDTRF (t0 )+ NT-L models+ SLR origin+ residual station motions

Weekly positions X̃ITRF (ti )Earth orientation
parameters

Combined:− Terrestrial pole (PM),− PM rates from GNSS and
VLBI
Separate VLBI-only:− dUT1,− LOD,− Celestial pole

Combined:− Terrestrial pole (PM),− PM rates from GNSS and
VLBI,− LOD from GNSS + SLR +VLBI
Separate VLBI-only:− dUT1,− Celestial pole

Combined:− Terrestrial pole (PM),− PM rates from GNSS and
VLBI
Separate VLBI-only:− dUT1− Celestial pole

• The time evolution of the orientation is realised by using ano-net-rotation (NNR) condition with regard to horizontal
tectonic motions over the whole Earth.
In the following, we compare the ITRS definition with its
realisation:
Origin: The ITRF origin is realised by SLR observations.
Through the orbit dynamics, SLR determines the Centre ofMass (CM). According to the IERS Conventions 2010 (Petit
and Luzum 2010), the ITRF2014 and DTRF2014 origin follows the mean Earth centre of mass, averaged over the timespan of SLR observations used and modelled as a secular(linear) function in time. It can be regarded as a crust-based
TRF with the origin realised as a mean CM (Blewitt 2003;
Dong et al. 2003; Petit and Luzum 2010; X. Wu et al. 2015).
However, various geophysical applications and precise orbit
determination require station coordinates to be referred tothe instanteneous CM. To obtain such an instantaneous geocentric position, it is recommended in the IERS Conventions(Petit and Luzum 2010) to substract the so-called geocentre
motion (i.e. the vector from the crust-based ITRF origin to
the instanteneous centre of mass) from the ITRF position.
However, the expression “geocentre motion” is defined differently in the geodetic literature (e.g., Dong et al. 2003), andmoreover, a commonly accepted model to account for thiseffect is not available yet. The ITRF2014 provides an annual
geocentre motion model derived from the same SLR data thatdefine the ITRF2014 long-term origin (Altamimi et al. 2016).
The DTRF2014 delivers the time series of the SLR translation
parameters as an additional product (Seitz et al. 2016), andthe JTRF2014 realises the origin at the quasi-instanteneous
CM as sensed by SLR (Abbondanza et al. 2017). Although
SLR is the most precise observation technique to realise the
ITRS origin, it has to be considered that the SLR results may
be affected by the so-called network effect due to a relatively
sparse network and due to the blue-sky effect if atmosphericloading is not considered (Collilieux et al. 2009).
Scale: The ITRS scale is specified to be consistent with the
TCG coordinate time (IAU and IUGG resolutions, 1991),
whereas its realisation is consistent with the terrestrial time(TT). The difference between both time scales dTT/dTCG isabout 1 - 0.7 · 10−9 (see Section 3.1), equivalent to a height
difference of 4.5 mm at the surface of the Earth. The ITRS
scale is realised by SLR and VLBI observations and, similar as for the origin, the results are affected by relatively
sparse networks. In the ITRF2014 computations, IGN estimated a scale difference between VLBI and SLR of 1.37 ppb at
epoch 2010.0 (Altamimi et al. 2016), whereas the DTRF2014
did not exhibit such a scale discrepancy. Based on the scale
tests performed at DGFI-TUM, which did not show a significant scale offset between VLBI and SLR, the DTRF2014
scale was realised as a weighted mean of the SLR and VLBI
scale (Seitz et al. 2020). In contrast to DTRF and JTRF, theITRF2014 includes a scale factor between SLR and VLBI

4.2 Terrestrial reference systems and frames

as unknown parameter in the combination model. The scaleissue is an ongoing topic mainly of the ILRS, the IVS andthe ITRS Combination Centres.
Orientation and its time evolution: The orientation of thecoordinate axes of the reference frame could, theoretically,
also be defined by the Earth’s gravity field, namely the second
degree spherical harmonic coefficients which are related tothe orientation of the principal axes of inertia. This definitionof the orientation is not used in practice because its determination is not as precise as for the origin, and the satellite orbits
are not so sensitive with respect to its variations. Instead,these reference frame parameters are realised by external
NNR conditions. This is done by successive transformations
with respect to the previous ITRF realisation. Thus, its realisation depends on the network geometries and the stations
used for the definition, including the weighting. The orientation rate of the ITRF2000 was aligned to that of thegeophysical model NNR-NUVEL-1A (Argus and Gordon
1991; DeMets et al. 1990, 1994). The succeeding realisations,
i.e., the ITRF2005, ITRF2008 and ITRF2014, were conventionally realigned to its predecessor. As deformation zones
are neglected in the geophysical model and plate motions
are averaged over long time periods (up to 1 Myr), there aredifferences with respect to present-day motions (Altamimi
et al. 2012; Argus et al. 2011; DeMets et al. 2010; Drewes
2009; Kreemer et al. 2006). According to Drewes (2012),
the resulting station velocity differences are of 1.1 mm/yr
around a rotation pole with a latitude of about −60◦ and alongitude of about 120◦ . The first version of this inventory
also provides an alternative concept by defining “absolute”
plate motions with respect to the Earth’s mantle by moving
hot spots. Such a “hot-spot” model might be useful for geophysical considerations, but it is not compliant with the ITRS
definition.
Input data for ITRF computations
For a particular ITRS realisation, the specifications for the
input data, i.e. solutions and/or normal equations in SINEX
format, are given in the call for participation of the IERS,
which is released by the ITRS Center. Such a call specifies
which parts of the IERS conventions should be obeyed, including updates. It is also stated that, whenever deviations
from the recommendations of the IERS Conventions are preferred, it is requested that the effects of those deviations are
documented.
Each intra-technique solution is a combination of several
Analysis Centre (AC) solutions as shown in Table 4.1 (theseare 9 individual solutions for GNSS and VLBI, 8 for SLR,
and 6 for DORIS). Moreover, different software packages arein use by the ACs for processing space geodetic observations.
Although much care is taken by the ACs to provide data thatare fully consistent with these definitions, the current status

247

is that this information is not always clearly (or fully) documented and, in some cases, the corresponding AC log-files
are not up to date. Thus, it is difficult to assess the impact ofpossible deviations, if some of the input data are not fully inaccordance with the adopted standards and conventions.
Furthermore, different subsets of the available data are usedby the services for generating the ITRF input data, e.g., incase of GNSS, different station networks are selected by theACs. In addition, some ACs only use GPS and some use
GPS and GLONASS, but other GNSS are not consideredby the IGS up to ITRF2014. Thus, the IGS input data for
the ITRF2014 are different in terms of network geometries
and the included GNSS data. In case of SLR, low sphericalsatellites and tracking data to GNSS satellites are not usedin ILRS computations. The ILRS is performing various tests
on the inclusion of additional satellites in order to enhance
future SLR contributions to the ITRF.
Modelling of station positions and displacements
The instantaneous position of a station X(t), which is fixed
to the Earth’s crust, is defined in Chapter 4 of the IERS
Conventions 2010 (Petit and Luzum 2010) as the sum of aregularised station position XR (t) and conventional corrections ∑n ∆Xn (t),X (t) = XR (t) + ∑ ∆Xn (t) .

(4.1)

n

In the conventional secular approach, the regularised station
position itself is parameterised by a linear model describing
the position at any epoch ti by the position at the reference
epoch t0 plus a constant velocity multiplied by the time difference (ti − t0 )XR (ti ) = XR (t0 ) + Ẋ(t0 ) · (ti − t0 ).

(4.2)

According to the IERS Conventions 2010 (Petit and Luzum2010), the displacements of reference markers on the crust
are modelled by conventional correction models, considering the effects on stations due to solid Earth tides, ocean
loading, rotational deformation caused by polar motion andocean pole tide loading. Even if these various effects areconventionally modelled, one has to keep in mind that model
uncertainties, and possible model errors could affect the corrections of the instantaneous station positions. Such errors
and also other effects (that are not considered in the conventional corrections) will become visible as residuals in theposition time series.
The updated version of Chapter 4 of the IERS Conventions(iers-conventions.obspm.fr/content/chapter4/icc4.pdf)
specifies the regularised coordinates of ITRF stations as parametric functions of time. They are composed of:• Station positions at a reference epoch and station velocities
until ITRF2008. Note that station velocities were takenfrom geophysical models before ITRF91.

248• Station positions at a reference epoch, station velocities
and post-seismic deformation (PSD) functions for somestations in ITRF2014.
The time series analysis reveals non-linear motions of several
millimeters or even more (up to a few centimeters) for somestations. These motions are caused by various effects that are
not properly modelled or for which accurate models are notavailable (e.g., Bevis and Brown 2014; Blossfeld et al. 2014;
X. Wu et al. 2015). Various investigations (e.g., van Dam et al.
2012; Davis et al. 2012) have shown that periodic variationsin the time series of station positions with amplitudes up toa few centimeters are caused by neglected surface loading
and other (unmodelled) effects. In the study of Ray et al.
(2013), it was found that non-tidal loading deformation does
not explain more than half of the vertical annual variationsin GNSS station position time series and much less in thehorizontal components. Roggenbuck et al. (2015) comparedloading models for atmosphere, ocean and hydrology andstudied the impact on global SLR, VLBI and GNSS solutions.
Männel et al. (2019) studied the surface loading corrections
for VLBI and GNSS networks at the observation level. The
DTRF2014 applied non-tidal loading corrections for atmosphere and hydrosphere by using models provided by Tonie
van Dam (personal communication). The results show thatthe seasonal variations in the residual time series for station
positions and datum parameters (origin and scale) could besignificantly reduced (compared to the standard DTRF2014
solution without applying loading corrections).
Furthermore, some stations are located in deformation zones
and are affected by post-seismic behaviour after strong earthquakes (e.g., Freymueller 2010; Sánchez et al. 2013). These
effects are modelled by exponential post-seismic correction
models in ITRF2014 and by a piecewise linear function representation in DTRF2014, whereas the post-seismic behavior
is directly captured by the time series-based JTRF2014. A
few stations are also affected by anthropogenic effects like,e.g., yearly groundwater withdrawal (Bawden et al. 2001). A
dominant source for producing non-linear station motions are
systematic errors and technique-specific effects. Examples
are modelling discrepancies of the technique-dependent internal reference points, such as GNSS phase centre offsets
and variation models for satellites and stations (Schmid et al.
2016) and corrections for radio antenna thermal deformations(Nothnagel 2009) as well as draconitic variations in GNSS
positions (Amiri-Simkooei 2013).
Integration of space techniques at colocation sites
A major limiting factor for the integration of the different
space geodetic techniques, the inter-technique combination,is the rather inhomogeneous and relatively sparse distribution of colocation sites. In total, 139 local tie SINEX files

4 Product-based review

available for 91 colocation sites (with two or more technique
instruments which were or are currently operating) were usedin the ITRF2014 (Altamimi et al. 2016). There are not somany colocations between VLBI, SLR and DORIS, and thus,
GNSS plays a major role in linking together these three techniques. In total, there are 212 tie vectors between GNSS
and the reference points of the three other techniques: 62 to
VLBI, 50 to SLR, and 67 to DORIS (Altamimi et al. 2016).
On the other hand, the large number of GNSS discontinuities
is critical for the combination of GNSS with the other threetechniques. The discrepancies between the terrestrial local tie
vectors and the space geodetic solutions are a good quality
measure for the accuracy of the terrestrial reference frame.
According to Altamimi et al. (2016), more than half of thecolocations show tie discrepancies larger than 5 mm. The fulllist of local tie discrepancies is available at the ITRF2014
website. The interpretation of these discrepancies is a challenge, since various impact factors have to be considered suchas systematic errors of the space techniques, uncertainties forthe definition of the reference points, local site instabilities,
outdated local surveys, largely different observation epochs
for “old” instruments as well as uncertainties of the terrestrial
local tie measurements.
4.2.5 Interaction with other products

The ITRF is a key geodetic product, that provides the basis
for precise positioning on the Earth’s surface and for Earthorbiters as well as for many practical applications (e.g., navigation, surveying, mapping) and for Earth sciences. How
well the reference frame can be realised has important implications for Earth system studies and for monitoring globalchange phenomena such as sea level rise. There is an interaction between the terrestrial reference frame and all otherproducts addressed in this inventory, such as• Celestial reference frames• Earth orientation parameters• Satellite orbits• Gravity field models• Heights
4.2.6 Open problems and recommendations

Reference frame definition
The ITRF origin follows the average CM, realised (linearlywith time) by SLR data (Altamimi et al. 2016). However,satellite precise orbit determination and various demanding
applications require station coordinates refering to the instantaneous CM. Although the ITRF2014 provides an annual
geocentre motion, which allows the computation of such an
instantenous CM, the sparseness of the ILRS network alongwith its temporal variations hinders the highly precise determination of the SLR-derived geocentre motion (X. Wu
et al. 2012). Thus, this topic needs to be further studied and4.2 Terrestrial reference systems and frames

it is recommended to include other methods and data for theestimation of the geocentre motion.
The scale of the ITRS is defined in TCG time scale (consistent with IAU and IUGG (1991) resolutions), whereas its
realisation refers to TT. To avoid inconsistencies, the relation
between both time scales (see equation 3.1) must always be
considered correctly if observations and/or products referto different time systems. Concerning the realisation of thescale, in the ITRF2014 a significant scale offset between
VLBI and SLR was estimated (Altamimi et al. 2016). Although the recent estimation of range biases by the ILRS
seems to largely explain the scale offset, this issue needs tobe further investigated by the ILRS and IVS together with
the ITRS Combination Centres and it should be studied in
the framework of the upcoming ITRF2020 computations.
The orientation of the ITRS is realised by external NNR conditions, whereas for each particular realisation successive
transformations with respect to the previous ITRF realisation
have been performed. Consequently, this procedure depends
on the network geometries and the stations used for the transformations. The orientation rate of ITRF2014 as well was
successively transformed to that of ITRF2000, which wasaligned to that of the geological model NNR-NUVEL-1A, as
outlined in Section 4.2.4.
Input data for ITRF computations
In practice, it is questionable, whether all partial solutions
for the ITRF are based on exactly the same standards andconventions. To get an overview about the present situation
it is recommended that the Services (IGS, ILRS, IVS, IDS)
together with all contributing ACs compile documentationof the standards and conventions currently applied in thesoftware packages used for the data processing. Such a compilation of the processing standards has been performed already by the IDS, which is given as an example. A tablesummarizing the standards that are used by the IDS Analysis
Centers with respect to their ITRF2014 submissions is available at ids-doris.org/combination/contribution-itrf2014.html.
The efforts of the IGS to tabulate models used by its Analysis Centers should also be mentioned. For this purpose, thecorresponding information is summarised on a Google docs
spreadsheat and can be updated by the IGS Analysis Centersto reflect model updates. These efforts should be continued(and strengthened) by the IAG Services to ensure that theprocessing standards are consistently applied by all Analysis
Centers as a prerequisite for consistent products.
Handling of non-linear station motions
Although a significant progress concerning the handling of
non-linear station motions has been achieved in the framework of the ITRF2014, this topic is subject of further research.

249

The fact that the three ITRS Combination Centres applied different approaches to account for non-linear station motions
is beneficial to do comparisons between them and to perform
detailed studies on this issue. Moreover, a comparison of thedifferent observation time series at colocation sites provides
valuable information to separate geophysical effects fromtechnique-specific effects. Following the recommendationsof the ITRF2020 call for participation and the Unified Analysis Workshop 2019 (Gross et al. 2019), the GGFC should be
invited to provide a unified loading model including all contributions (atmosphere, hydrology, and ocean) for all ITRF2020
sites.

Integration of space techniques
The observed discrepancies at colocation sites (which exceed
5 mm for more than half of the colocations) are a major limiting factor for the integration of the different geodetic spacetechniques. A challenge is the separation of the different impact factors that need to be considered (see Section 4.2.4).
A problem in this context is the sparse distribution of highquality colocation sites. Colocation with GNSS plays a dominant role for the integration of the different techniques, but
the large number of GNSS discontinuities is critical. Thus,
it is an overall goal to improve the spatial distribution ofcolocation sites and the availability of precisely measured
local ties. However, the required maintenance, sustainability
and enhancement of the geodetic infrastructure goes beyond
the responsibilities of IAG, and it involves activities on thepolitical level, such as those of the UN-GGIM Subcommittee
on Geodesy, which provides an intergovernmental forum forcooperation and exchange of dialogue on these issues. In
addition to the classical colocation on Earth, a challenge forthe future would be the colocation of sensors in space.
Taking into account the current deficiencies and open problems mentioned above, it is obvious that the ITRF accuracy
requirements (formulated by IAG/GGOS) at a level of 1 mm
and the stability of 0.1 mm/yr are not achieved yet, and probably exceeded by a factor of about 5 to 10.
The following recommendations on the ITRS/ITRF are provided:
Recommendation 2.1 : ITRF defining parameters: The realisation of the ITRF origin, scale, orientation and their time
evolution should be consistent with the ITRS definition.
Concerning geocentre models, it is recommended to supplement the ITRF2014 geocentre model by other methods
and data and to compare the results between different geocentre models. The SLR and VLBI scale issue should befurther studied.

250

Recommendation 2.2 : ITRF input data: In order to get consistent ITRF results, the input data should be based on
unified standards and conventions, such as the latest version of the IERS Conventions. The Services (IGS, ILRS,
IVS and IDS) and their contributing ACs should provide
the relevant information on the status of the standards andconventions currently applied in the data processing.
Recommendation 2.3 : Non-linear station motions: The
handling of non-linear station motions should be further
studied. The GGFC should be invited to provide a unified
loading model including all contributions (atmosphere,hydrogolgy, and ocean) for all ITRF2020 sites (see recommendations of the ITRF2020 CfP and the Unified Analysis
Workshop 2019).
Recommendation 2.4 : Integration of space techniques: The
station networks and the spatial distribution of high quality
colocation sites should be further improved to achieve amore stable integration of the different space techniques.
This overall recommendation goes beyond IAG responsibilities, as an improvement of the geodetic infrastructure
involves the political level and funding issues. In addition
to the colocation on Earth, the benefits of the colocation in
space should be studied. This recommendation is fundamental to achieve the IAG/GGOS accuracy requirements
for the terrestrial reference frame and to ensure its longterm stability.
Recommendation 2.5 : ITRF evaluation: The availability of
three ITRF solutions ensures an evaluation of the quality of
the final product. The IERS Technical Note 40, comprising
the individual contributions and the product evaluation is
gratefully acknowledged and it is recommended that also
for upcoming ITRS realisations such a Technical Note iscompiled.

4.3 Earth Orientation Parameters (EOP)
4.3.1 Overview

Earth orientation and Earth rotation are two aspects of thesame physical effect. Earth rotation describes the change ofthe orientation of the Earth’s body with respect to a space
fixed reference frame. Astronomy, satellite geodesy, or precise navigation require an accurate knowledge of the orientation of the Earth in a quasi inertial reference frame. Various
disciplines of geosciences depend on the gravitational andgeodynamic impact of rotation. Earth rotation is one of theimpulses of the dynamics of the Earth system and the interactions between individual components, such as the exchangeof angular momentum between atmosphere, ocean and solid
Earth, or the coupling mechanism between the Earth’s coreand mantle (Plag and Pearlman 2009; Seitz and Schuh 2010).
Both requirements, orientation and rotation, will be fulfilled

4 Product-based review

if the Earth Orientation Parameters (EOP) are given as functions of time, usually as a combination of diurnal time series
with analytic models.
Practically, the EOP are the parameters representing the rotational part of the transformation between two reference
frames, a terrestrial and a celestial frame. According to thedefinition by the IERS, these two frames are actual realisations of the geocentric International Terrestrial Reference
System (ITRS) and the Geocentric Celestial Reference System (GCRS) or the Barycentric Celestial Reference System(BCRS):
rotationtranslation
ITRS −−−−−−−−→ GCRS −−−−−−−−→ BCRS.
The ITRS orientation is given by the IUGG Resolution 2(2007). It is operationally maintained in continuity with pastinternational agreements (BIH orientation). The initial orientation at 1984.0 is the orientation given by the Bureau
International de l’Heure (BIH) Terrestrial System (BTS84).
The GCRS specification (IAU Resolution A4, 1991, andupdate: IAU Resolution B1.3, 2000) follows a geocentric
relativistic metric. The orientation of the GCRS is derived
from the BCRS (IAU Resolution B2, 2006). The different
metrics of GCRS and BCRS imply a slight difference of therespective orientations, which are called geodesic precession
and geodesic nutation (Fukushima 1991).
The BCRS is assumed to be oriented according to the ICRS(IAU Resolution B2, 2006). The latter is recommended toshow no global rotation with respect to a set of distant extragalactic objects. According to IAU Resolution B2 (1997)
the initial orientation of the ICRS is given through the IERS
celestial reference frame of the year 1995 (IERS95) as described by the ICRS Product Center (Arias et al. 1995) within
the IERS.
Since the EOP depend on the actual realisations of the conventional terrestrial and celestial reference systems, the EOP
system should be readjusted as soon as a new release of ITRF
or ICRF is adopted.
Concerning its numerical realisation, the transformation of
Cartesian coordinates from ITRS to GCRS at date t is split
into three segments
GCRS

ITRS
polar
motion

W (t)
TIRS

Q(t)
R(t)

CIRS

precessionnutation

Earth rotation

where Q(t), R(t), and W (t) are rotation matrices and R(t)fits to the mean physical rotation of the Earth. The meaningof “mean” still has to be specified. The choice of the intermediate systems Terrestrial Intermediate Reference System(TIRS) and Celestial Intermediate Reference System (CIRS)

4.3 Earth Orientation Parameters (EOP)

is delaminated by the convention on R(t) being an elementary rotation around the z-axis. Hence TIRS and CIRS have acommon z-axis, refering to the celestial pole, which approximates a mean rotation axis of the Earth. Q(t) and W (t)−1represent the motion of that celestial pole in the GCRS andITRS respectively. If the celestial pole is choosen according
to the IAU 2000/2006 resolutions, it will be called Celestial
Intermediate Pole (CIP).
According to IAU 2000 Resolution B1.7, the CIP separates
the motion of the rotation axis of the ITRS in the GCRS intoa celestial and a terrestrial part. The convention is such that
(Capitaine 2013; Petit and Luzum 2010):• The celestial motion of the Celestial Intermediate Pole
(CIP) (precession-nutation) includes all the terms withperiods greater than 2 days in the Geocentric Celestial
Reference System (GCRS). According to this definition,
precession-nutation of the CIP includes the Free Core Free
Core Nutation (FCN) signal, but does not include the socalled subdiurnal nutations.
• The terrestrial motion of the CIP (polar motion) includes
all the terms outside the retrograde diurnal band in the
ITRS (i.e. frequencies lower than -1.5 cycles per siderealday (cpsd) or greater than -0.5 cpsd).
As outlined in the IERS Conventions 2010 (Petit and Luzum2010), the motion Q(t) of the CIP in the GCRS is realisedby the IAU 2006/2000A precession-nutation model (Wallace
and Capitaine 2006) plus additional time-dependent corrections derived by the IERS from space geodetic techniques.
The motion W (t)−1 of the CIP in the ITRS is provided by
the IERS through time series derived from space geodetic observations and models including variations with frequencies
outside the retrograde diurnal band. The implementation of
the IAU 2000 and IAU 2006 resolutions for the transformation is detailed in the IERS Conventions 2010 (Petit andLuzum 2010).
Concerning the realisation of EOP products, the EOP are
represented by the five following quantities (as specified thelatest IAU 2000/2006 version of the terrestrial-celestial transformation):• δX = X −Xmodel , δY = Y− Ymodel : corrections to the xand y-coordinates of the CIP unit vector in the celestial
system GCRS using the model IAU 2000/2006,• ∆UT1 = UT1 − UTC : difference of mean solar time (Universal Time UT1) and Coordinated Universal Time (UTC)
vice the averaged atomic time,• xp , yp : Cardan angles W (t) = R3 (−s′ )R2 (xp )R1 (yp ), called“pole coordinates”.

251

The IERS is responsible for providing the time series of xp ,
yp , ∆UT1, δ X, δY on an operational basis derived from thevarious space geodetic techniques (VLBI, SLR, GNSS, and
DORIS). The EOP products are available from the databaseof the IERS (see www.iers.org). Two Product Centers are
responsible for the EOP generation, namely the IERS Earth
Orientation Center and the IERS Rapid Service/Prediction
Center (see IERS 2020). The IERS EOP series result froma combination of different input data provided by different
space-geodetic techniques and the corresponding IAG Services, i.e., IDS, IGS, ILRS, and IVS.
In the IERS Conventions 2010, a conventional model for themean pole is given. It consists of a third order polynomial
until 2010.0, and a linear model later on. This model was
replaced by a purely linear model (secular pole) in the February 2018 update of the conventions (IERS 2018). This update
affects the modelling of displacements of reference points aswell as the geopotential due to pole tide and ocean pole tide.
It should also be noted that besides the IERS EOP products,
other combined Earth orientation series (e.g., SPACE 2018,
COMB 2018, POLE 2018) are generated annually at JPL’s
Geodynamics and Space Geodesy Group in support of tracking and navigation of interplanetary spacecraft (Gross 2000;
Ratcliff and Gross 2019).

4.3.2 IERS Earth Orientation Center

The IERS Earth Orientation Center is responsible for monitoring of long-term EOP, publications for time disseminationand leap second announcements. It is located at the Observatoire de Paris in France (see hpiers.obspm.fr/eop-pc). The
general procedure for the generation of the EOP series is
described in various publications (e.g., Bizouard and Gambis
2009; Bizouard et al. 2019; Gambis 2004; Gambis and Luzum 2011).
The Earth Orientation Center provides the following main
products:
Bulletin B contains final daily Earth orientation data for one
month(see ftp://hpiers.obspm.fr/iers/bul/bulb_new/bulletinb.pdf)
Bulletin C contains announcements of leap seconds in UTC(see ftp://hpiers.obspm.fr/eoppc/bul/bulc/BULLETINC.
GUIDE)
Bulletin D contains an announcement of the value ∆UT1 =
UT1 − UTC (see ftp://hpiers.obspm.fr/eoppc/bul/buld/
BULLETIND.GUIDE)EOP 14C04 contains long term Earth orientation data
(see ftp://hpiers.obspm.fr/iers/eop/eopc04/C04.guide.pdf)

252

Realisation of EOP time series
The Earth Orientation Center of the IERS, located at Paris
Observatory, SYRTE, has the task to provide the internationalreference time series for the EOPs, referred as “IERS C04”,
resulting from a combination of EOP series derived fromthe four space geodetic techniques VLBI, SLR, GNSS, and
DORIS. The IERS EOP 14C04 (abbreviated 14C04) solution
became the international reference EOP series on February
1, 2017 (Bizouard et al. 2019). It replaced the former IERS
EOP 08C04 series (Bizouard and Gambis 2009). The 14C04
series is available from 1962 on and it provides updates until
about 30 days in the past. It contains smoothed values of xp ,
yp , UT1–UTC, LOD, δ X, δY at 1-day intervals w.r.t. IAU
2006/2000A precession-nutation model and it is aligned on
the ITRF2014 and ICRF2. The 14C04 series is updated on adaily basis with a latency of 30 days and the data are accessible as yearly files since 1962 and as one file 1962–now. A
documentation for this EOP series is given by Bizouard et al.
(2019).
The generation of the 14C04 solutions is based on the combination of operational series as provided by the techniquecentres of IVS, ILRS, IGS, and IDS, as well as operational
solutions maintained by several IVS analysis centres (including VLBI intensives) and one IGS analysis centre (Bizouard
et al. 2019). Thus, in case of VLBI and GNSS, in addition
to the intra-technique combined series also solutions of individual analysis centres are used for the 14C04 combination.
While the three satellite techniques deliver continuous input
data for estimating pole coordinates and LOD, VLBI provides the full set of all five EOP, but with non-continuous
observations organised in VLBI sessions. In addition, also
the EOP solution associated with the ITRF2014 is used as
reference series to align the 14C04 solution with the latest
realisation of the terrestrial reference frame.
The computation of the C04 series is split into two parts(Bizouard et al. 2019):• In the initial part, the data preparation is performed once
per year. This data preparation comprises the selectionof input series, the rescaling of the formal uncertainties
provided with the EOP values, and the characterisation of
their eventual inconsistency with respect to the ICRF and
ITRF.
• The second part is the combination procedure itself which
is done on a daily basis. This procedure comprises several
steps which are described in Bizouard et al. (2019).
The IERS Earth Orientation Center has upgraded the processing to align the 14C04 results with the ITRF2014 (Bizouard et al. 2017). By estimating and removing continuous
piece wise linear functions from the intra-technique solutions over a period of 31 years (1984–2015) with respect to

4 Product-based review

the guide series, namely the EOP solution associated with
the ITRF2014 and the IVS combined series, the 14C04 results get rid of the so-called “network effect”. This leads toan improved consistency and stronger long-term stability ofthe solution, which has been confirmed by Allan deviation
analysis (Bizouard et al. 2017).
To assess the accuracy of the 14C04 solution various comparisons have been performed (Bizouard et al. 2019). A comparison with the former 08C04 series indicates a significant improvement of the EOP results. The y-pole component of the
08C04 series shows a jump of about 30 µas in 2011, which
is not visible in the new 14C04 series. Also the noise levelof the x- and y-pole components obtained from 14C04 could
be reduced significantly compared to the previous 08C04
series. This is evidenced by the standard deviations of thedifferences between the C04 (both 08C04 and 14C04) andthe intra-technique and guide series (see Table 6 in Bizouard
et al. (2019)). The 14C04 differences to the IVS combination
exhibit standard deviations of less than 30 µas for nutationand 3.4 µs for UT1 over the period 2010–2015. The differences to the pole coordinates of the IGS solution reveal astandard deviation of 30 µas for polar motion.
4.3.3 IERS Rapid Service/Prediction Center

The IERS Rapid Service/Prediction Center is responsible
for providing predicted EOP and measured EOP on a rapid
turnaround basis, primarily for real-time users and othersneeding EOP information sooner than that available in the
final series published by the IERS Earth Orientation Center.
It is located at the United States Naval Observatory (USNO)
in Washington, D.C., USA (see www.usno.navy.mil/USNO/earth-orientation). The general procedure for the generationof the real-time EOP and predictions is described in various
publications (e.g., Luzum et al. 2014; McCarthy and Luzum
1991; Stamatakos et al. 2020, 2007).
The IERS Rapid Service/Prediction Center provides the following main products:
Bulletin A contains xp , yp and UT1–UTC including their errors at daily intervals and predictions for one year into the
future (see ftp://cddis.gsfc.nasa.gov/pub/products/iers/
readme.bulla).
Standard Rapid EOP Data contain quick-look weekly estimates of the EOP since 1973-01-02 (finals.all) or
since 1992-01-01 (finals.data) and predictions for the
next 365 days (see ftp://cddis.gsfc.nasa.gov/pub/products/iers/readme.finals).
Daily Rapid EOP Data contain quick-look daily estimatesof the EOP (file finals.daily) for the last 90 days andpredictions for the next 90 days (see ftp://cddis.gsfc.nasa.gov/pub/products/iers/readme.finals).

4.3 Earth Orientation Parameters (EOP)GPS Daily Rapid EOP Data contain quick-look daily estimates of the EOP (file gpsrapid.daily) for the last 90
days and predictions for the next 15 days (see ftp://cddis.gsfc.nasa.gov/pub/products/iers/readme.gpsrapid).
Realisation of real-time EOP and predictions
The input data series for the IERS Rapid Service and Prediction Center along with estimated accuracies for each of thesecontributions to the EOP combination solutions are given in
Table 1 of Stamatakos et al. (2020). These series include combined intra-technique solutions of the IVS, IGS and ILRS
as well as VLBI, SLR and GNSS solutions of individual
analysis centres. All the VLBI contributions provide direct
measurements of UT1. The IGS ultra-rapid solutions (IGS
Ultra) provide LOD as input parameter, and the solutions
labelled as USNO GPS UT contain UT1-like estimates basedon GPS orbit modelling. The IGS Final and IGS Rapid aswell as the solutions of the ILRS only provide pole coordinates as input parameters. Due to orbit modelling issues of thesatellite techniques and correlations between orbit parameters
and the EOP, the VLBI solutions have been used to correct
for an LOD bias and to minimise drifts in UT estimates in
the IGS Ultra and the USNO GPS UT solutions.
The algorithm used for the determination of the quick-look
EOP results is based on a smoothing cubic spline interpolation. Each of the input data is weighted according to theirreported errors. The procedure is referred to as a “weighted
smoothing cubic spline” (Luzum et al. 2014; McCarthy andLuzum 1991). The input series are corrected for possible
systematic differences in the form of offsets and rates withrespect to the long-term 14C04 series of the IERS Earth
Orientation Centre by using a robust linear estimator. The
statistical weights used in the spline are proportional to theinverse square of the estimated accuracy of the individual
techniques computed over the past several years. Minimalsmoothing is applied, consistent with the estimated accuracy of the input data. More information on the combination
approach is provided in the literature (Luzum et al. 2014;
Stamatakos et al. 2020).
The accuracy of the combined EOP solutions of Bulletin A
is shown in Table 2 of Stamatakos et al. (2020). The meanand standard deviations are derived from a comparison of therunning, weekly, and daily products compared to the longterm 14C04 series of the IERS Earth Orientation Center. The
obtained standard deviations are in the range of about 40 to80 µas for the pole coordinates and between 50 and 75 µs
for UT1–UTC.
Concerning the prediction techniques, the algorithm for polar
motion predictions was changed in 2017 to incorporate aleast-squares, autoregressive (LS+AR) method as describedin (Stamatakos et al. 2020). The UT1–UTC prediction makes

253

use of UT1-like data product derived from a combinationof the operational National Centers for Environment Prediction (NCEP) and US Navy’s Global Environmental Model(NAVGEM) Atmospheric Angular Momentum (AAM) analysis and forecast. AAM-based predictions are used to determine the UT1 predictions for a prediction length up to 7.5
days (Johnson et al. 2005). For longer predictions, the LOD
excitations are combined smoothly with the longer-term UT1
predictions as described by McCarthy and Luzum (1991).
Table 4.4 summarises the quality of the predictions of thepole coordinates and UT1–UTC until 90 days in the future(Stamatakos et al. 2020). The RMS values of the differences
between the EOP time series predictions produced by the
17:00 UTC daily EOP solutions and the 14C04 solution
demonstrate that the accuracy of the predictions could besignificantly improved due to the implementation of refinedprocedures.
Table 4.4: Root mean square of the differences between the EOP time series predictions produced by
the 17:00 UTC daily EOP solutions and the 14C04
combination solutions for 2017 (the values are extracted from Table 3a of Stamatakos et al. (2020)).
Days infuture

xp
mas

xp
mas

UT1–UTC
ms

0
1
5
10
20
40
90

0.07
0.31
1.75
3.29
5.89
10.24
17.25

0.04
0.23
1.32
2.29
3.80
5.78
9.28

0.074
0.087
0.198
0.537
2.347
5.118
9.748

4.3.4 Discussion of the present status

Theoretical aspects of precession-nutation models
In 2015, IAU and IAG established a Joint Working Group(JWG) “Theory of Earth rotation and validation” that continued the former IAU/IAG JWG “Theory of Earth Rotation”(Ferrándiz and Gross 2015). During the current term, theJWG is continuing under the name “Improving Theories
and Models of the Earth’s Rotation”. The purpose of thisJWG is to promote the development of theories of Earthrotation that are fully consistent and that agree with observations, useful for providing predictions of the EOP withthe accuracy required to meet future needs as recommended by GGOS. From the findings of this JWG, it can beconcluded that various issues are affecting the accuracy andconsistency of the presently available precession-nutation
models. The work provided the basis for the formulation of

254

IAG resolution No. 5 (2019) “Improvement of the Earth’s Rotation Theories and Models” (see Section 1.2.4). The issuesof precession-nutation models have been discussed during
the Unified Analysis Workshop 2019 in Paris, and several
recommendations have been provided (Ferrandiz and Escapa
2019; Gross et al. 2019). A summary of these recommendations is given at the end of this section. More information on
this JWG is available at the website hosted by the University
Alicante at web.ua.es/en/wgterv/.
Input data for EOP generation
The EOP products provided by the Earth Orientation Centerand the Rapid Service/Prediction Center of the IERS are generated from VLBI, SLR, GNSS data. For the latest 14C04
series also DORIS data have been included for the first time.
The input data comprise intra-technique combined solutions
provided by the technique centres of the IVS, ILRS, IGS, and
IDS, as well as individual analysis centre solutions and the
EOP solution associated with the ITRF2014 for the alignment
with the ITRS. As a consequence, several measurements ofthe same space geodetic technique are included more thanonce in the EOP combination. At the same time, the corresponding stochastic model does not account for the multiple
usage of identical input data leading to over-optimistic formal
errors.
Although the standards and conventions used by all the contributing AC should follow the IERS Conventions as closely
as possible, the current status is that they are not always fully(or clearly) documented, and that in some cases the corresponding AC log files are not up to date. Thus, it is difficult toassess the impact of inconsistencies on the EOP products.

4 Product-based review

The procedure applied at the IERS Rapid Service/Prediction
Center for the generation of the real-time EOP and predictions cannot be considered as a rigorous combination, since it
is also based on various processing steps on the solution (parameter) level. Although the general procedure is describedin the literature, a detailed documentation of the analyticaland mathematical foundations is partly missing. It was reported by Stamatakos et al. (2017), that beginning in 2016,a UT1–UTC convergence solution problem was occurring
more often than in previous years. It was found that a probable cause could be the UT GPS inputs or the pre-processingof these input data before using it in the combination.
As described in Bizouard et al. (2019), the 14C04 solution
has been tied to the two guide series, the IVS combinationand the EOP solution associated with the ITRF2014, to ensure the consistency with the conventional reference frames,
the ICRF2 and ITRF2014. However, this procedure does notinclude all relevant parameters of the contributing space techniques, and thus, it does not ensure full consistency between
the EOP and the terrestrial and celestial reference frame.
4.3.5 Interaction with other products

The Earth Orientation Parameter are directly linked with
• Celestial reference frames• Terrestrial reference frames• Second degree gravity field coefficients (C20 , C21 , S21 )• Satellite orbits• Parameters of geophysical fluids, particularly atmospheric,oceanic and hydrologic angular momentum (AAM, OAM,
HAM).
4.3.6 Open problems and recommendations

Combination methods and consistency of EOP products

Theoretical aspects of precession-nutation models

The combination procedure for the generation of the 14C04
series comprises several processing steps, which are performed on the solution (parameter) level. Regarding the contributing input solutions, only VLBI contains the full set
of EOP, whereas the satellite techniques provide the pole
coordinates and LOD. By using these data sets, not all correlations among the EOP can be considered in the combination, and in addition the parametrisations of the EOP are
not fully consistent across the different techniques. Thus, theprocedure of the IERS Earth Orientation Centre cannot be
considered as a rigorous combination approach. Moreover,the literature gives a rather general description of the various
data preparation and processing steps for the generation of
the 14C04 series, whereas the analytical/mathematical combination model (including the alignment and extrapolation of
the series) is not fully described. Thus, it is difficult to judge
the present combination procedure comprehensively and forassessing their impact on the combination results.

Issues affecting the accuracy and consistency of the presently
available precession-nutation models were addressed by thejoint IAU/IAG Working Group (JWG) “Theory of Earth rotation and validation” that continued the former JWG “Theoryof Earth Rotation” (Ferrándiz and Gross 2015). Some of the
major findings of this JWG was presented at the Unified Analysis Workshop (Ferrandiz and Escapa 2019). The following
recommendations were provided at this Workshop (Grosset al. 2019): (1) the amplitudes of the leading nutations of
the IAU2000 theory be updated and a shortened series forcertain operational purposes be tested; (2) the inconsistencies
found in the precession-nutation models be corrected; (3) theavailable FCN models be tested (for fitting Celestial Pole
Offset (CPO)) and consideration be given to the question ofwhether or not the IERS should recommend the FCN models to use; and (4) the tasks of the joint IAU/IAG Working
Group on Improving Earth Rotation Theories and Models beprioritised to get outcomes in two years.

4.3 Earth Orientation Parameters (EOP)

Input data for EOP generation
In order to get consistent EOP products, it is a fundamental requirement that the input data must be based on unified
standards, conventions and models. This objective is the basis
for the following recommendations:(1) Although the contributions used for the generation of
the EOP products should be based on the latest version of
the IERS Conventions, it is not clear if there are any deviations. Thus, all the geometric services (IGS, ILRS, IVS,
and IDS) together with their contributing analysis centres
should provide the relevant information on the present statusof the standards and conventions currently applied in the dataprocessing.
(2) The subsequent change of the mathematical representation of EOP functions in solutions or normal equations caninvolve a considerable loss of approximation accuracy. Thus,
the parameterisation of the EOP functions should be identical
for the contributions of all individual space geodetic techniques.
(3) Though VLBI only allows to solve for the full set of EOP,
the satellite techniques should provide solutions or equations
containing all five EOP regardless of whether some of themwere fixed or constrained. That makes the full information
contained in the different space techniques available for the
combination, which is necessary to derive realistic correlations between the parameters.
(4) Moreover, the measurements of a single space geodetic
technique should only be included once in the EOP combination in agreement with the associated stochastic model.
(5) It is also recommended to investigate all the contributing
input data in detail to avoid any data problems or inconsistencies in the EOP combinations.
(6) At the Unified Analysis Workshop 2019 (Gross et al.
2019), it was recommended that also LLR data should beconsidered for the EOP combinations.
Combination methods and consistency of EOP products
A reference paper for the generation of the 14C04 has been
provided by Bizouard et al. (2019). The procedures for thedetermination of the near-real time and predicted EOP aremainly described in the IERS Annual Reports (Stamatakos
et al. 2020). It is recommended that the analytical and mathematical foundations of the EOP combination proceduresare described in full detail. This holds also for the alignmentof the long-term series with the terrestrial and celestial reference frame as well as for the extrapolation of the EOP
beyond the ITRF2014 data period. The IERS Earth Orientation Center and the IERS Rapid Service/Prediction Center
should consider a detailed description of the procedures including the full mathematical and analytical background in
IERS Technical Notes (in the same way as for the ITRF).

255

Although the accuracy of both, the 14C04 series and the nearreal-time and predicted EOP has been improved due to advanced procedures, it is recommended that the EOP ProductCenters should consider the implementation of rigorous combination methods. Concerning EOP predictions, it should be
investigated how the results could be further improved by
reducing the latency of the last data point and by more frequently updating the AAM and Oceanic Angular Momentum(OAM) data.
Concerning the accuracy of the 14C04 series, the estimatespublished in the literature (Bizouard et al. 2019) are derived
from an internal comparison, and are certainly too optimistic. Thus, it is recommended to use also external data andgeophysical models for an accuracy assessment of the EOP
products. Another topic is the consistency of the ICRF, the
ITRF and the EOP (see IUGG resolution No. 3 (2011) and
IAG resolution No. 2 (2019)) which has been addressed in
Section 4.1 (see Recommendation 1.4).
Summary of recommendations on EOP
Recommendation 3.1 : Review of precession-nutation models: As outcome of the Unified Analysis Workshop 2019,the following recommendations were provided (Ferrandiz
and Escapa 2019): (1) update the amplitudes of the leading
nutations of the IAU2000 theory and test shortened series
for certain operational purposes; (2) correct the inconsistencies found in the precession-nutation models; (3) test
the available FCN models and consider whether the IERS
should recommend FCN models or not. (4) The IAU/IAG
JWG on Improving Earth rotation theories and models
should prioritise these tasks to get outcomes in two years.
Recommendation 3.2 : Input data for EOP products: complete and up-to-date documentations of the standards andconventions for the contributing input solutions are necessary. Remaining inconsistencies need to be resolved toensure consistent EOP products. The weighting should beproperly performed if measurements of the same space geodetic technique are included more than once in the EOP
combination.
Recommendation 3.3 : EOP combination procedure: The
general procedures for the EOP combinations are described in the literature. It is recommended that also theanalytical and mathematical foundations are describedin full detail, which probably could be done in an IERS
Technical Note. Furthermore, the development of rigorous
combination methods should be considered by the EOP
Product Centers.
Recommendation 3.4 : EOP Prediction: Although the accuracy has been improved significantly by implementing
refined procedures it should be investigated how the results
can be further improved by reducing the latency of the last
data point and by more frequently updating the AAM andOAM data.

256

4 Product-based review

4.4 GNSS satellite orbits
Global Navigation Satellite Systems (GNSS) like the US
American GPS, the Russian GLONASS, the European Galileo, and the Chinese BeiDou are the most popular space
geodetic techniques with a wide range of applications. Precise GNSS satellite orbits and clocks provide the basis for
mm-level positioning for realising global and regional reference systems, geophysical studies, surveying, deformation
monitoring, and cadastre.
The Analysis Centres (ACs) of the IGS process observationsof global GNSS tracking networks on a regular basis in orderto provide a variety of products. One of the IGS core products are the final orbits. GPS and GLONASS final orbits are
generated by the IGS Analysis Centre Coordinator (ACC) asa weighted mean of the individual AC orbits (Beutler et al.
1995; Griffiths and Ray 2009). They are provided with alatency of 12 – 18 days.
For the two new global navigation systems, Galileo and BeiDou, and the regional Quasi-Zenith Satellite System (QZSS),
satellite orbits are computed by the ACs of the Multi-GNSS
Pilot Project (Montenbruck et al. 2017b) of the IGS. The
Indian Regional Navigation Satellite System (IRNSS) is currently not covered by the MGEX ACs due to lack of dualfrequency tracking data. An experimental multi-GNSS orbit product is generated by the IGS ACC since April 2019
covering GPS, GLONASS, Galileo, BeiDou, and QZSS
(acc.igs.org/mgex_experimental.html).
Due to advances in observation modelling and processing
strategies since the establishment of the IGS in 1994, theorbit quality has steadily improved. In order to achieve thehighest product quality also for the orbits of the early years
and to achieve consistency with current operational orbits,
the IGS conducted two reprocessing campaigns up to now.
The second reprocessing covers 1994 – 2014 (Griffiths 2018)
and provided the input for ITRF2014 (Altamimi et al. 2016).
The third reprocessing campaign is currently in progress andwill provide input for ITRF2020. Users are advised to use
the latest generation of reprocessed products to achieve thehighest level of accuracy as well as consistency with the operational products for time periods where the reprocessed
products are not available.
The individual analysis centres contributing to the IGS final
orbit combination are:
COD Center for Orbit Determination in Europe,
Switzerland
EMR Natural Resources Canada, Canada
ESA European Space Agency, Germany
GFZ Deutsches GeoForschungsZentrum, Germany
GRG GRGS-CNES/CLS, France
JPL Jet Propulsion Laboratory, USA
MIT Massachusetts Institute of Technology, USA
NGS National Geodetic Survey, USA
SIO Scripps Institution of Oceanography, USA
4.4.1 Summary of standards

The standards listed in Table 4.5 are based on the recommendations for the second and third IGS reprocessing campaign (acc.igs.org/reprocess2.html and acc.igs.org/repro3/

Table 4.5: Selected standards of the third IGS reprocessing campaign.

General Standards
Reference Frame
Antenna Model
P1C1 Code Biases
Phase Wind-Up
Gravity Field
Ocean tide model
Pole tide
Subdaily ERP Model
Earth radiation pressure
Antenna thrust
Non-Tidal Loading
Higher-order Ionosphere
A Priori Troposphere Delay
Troposphere Mapping

IERS 2010 Conventions (Petit and Luzum 2010)
ftp://igs-rf.ign.fr/pub/IGSR3/IGSR3_2077.snx
http://ftp.aiub.unibe.ch/users/villiger/igsR3_2077.atx
ftp://ftp.unibe.ch/aiub/bcwg/cc2noncc
according to J. Wu et al. (1993)
e.g., GGM05C (Ries et al. 2016)
FES2014b (Carrere et al. 2015)
linear mean pole (IERS 2018)
Desai and Sibois (2016)
applied, http://acc.igs.org/orbits/ERPFBOXW.F
applied (Steigenberger et al. 2018, 2019)not applied
2nd and 3rd order applied(Fritsche et al. 2005; Hernández-Pajares et al. 2011)
GPT2 model (Lagler et al. 2013) to compute hydrostatic delays according to Davis et al. (1985)
GPT2 (Lagler et al. 2013) or more modern

4.4 GNSS satellite orbits

257

repro3.html) as well as the recommendations of the IGS
Analysis Center Workshop 2019 and the Unified Analysis
Workshop 2019 (acc.igs.org/workshop2019.html and www.
ggos.org/en/unified-analysis-workshop-2019/general-uaw/).
For the third IGS reprocessing, the IGS Reference Frame
Working Group and the Antenna Working Group prepared
dedicated reference frame and antenna calibration files, see
Table 4.5. Due to mostly outdated analysis log files, thecompliance of the ACs with these standards could not be
verified.

surface areas are available for BeiDou-2 (CSNO 2019b) and
BeiDou-3 (CSNO 2019a). However, no public informationon the detailed geometry of any GNSS satellites is currently
available.

4.4.2 Discussion and deficiencies

Table 4.6 lists orbit models recommended for different satellite types included in the third IGS reprocessing. Depending on the satellite type, different versions of the Empirical
CODE Orbit Model (ECOM, Arnold et al. 2015; Beutler et al.
1994) or the GPS Solar Pressure Model (GSPM, Bar-Severand Kuang 2005) are recommended as a minimum modelling standard. However, applying a bow-wing model together
with additional empirical parameters is preferred.

Solar radiation pressure modelling

Earth radiation pressure

Modeling of the Solar Radiation Pressure (SRP) is probably
the largest error source of today’s GNSS orbits. Deficiencies in the SRP modelling are visible as harmonics of thedraconitic year in orbital (Griffiths and Ray 2013) and otherparameters: station positions (Amiri-Simkooei 2013; Rayet al. 2008), geocentre (Hugentobler et al. 2005), and Earth
Rotation Parameters (ERP) (Steigenberger 2009). A comparison of different SRP models can be found in Sibthorpe et al.
(2011).

Earth radiation pressure due to visible and infrared emissions of the Earth in particular affects the scale of the orbits(Bury et al. 2020; Rodriguez-Solano et al. 2011; Ziebart et al.
2007). Starting with the switch to IGS14/igs14.atx, Earth radiation pressure is considered by most ACs. Whereas opticalproperties of satellite surfaces for visible light are available
for several satellites as mentioned in the previous section,coefficients for infrared radiation are not yet available.

A partly reduction of these systematic errors was achievedby recent developments including an adjustable box-wingmodel (Rodriguez-Solano et al. 2014), the extended Empirical CODE Orbit Model (Arnold et al. 2015), a cuboid
box model for the Galileo IOV satellites (Montenbruck et al.
2015b), a box-plate model for GIOVE-B (Steigenberger et al.
2015), and box-wing models for Galileo (Bury et al. 2019),
BeiDou (X. Yan et al. 2019), and QZS-1 (Montenbruck et al.
2017a; Zhao et al. 2018a). The ray-tracing approach is themost sophisticated SRP modelling technique (Bhattarai et al.
2019; Darugna et al. 2018; Z. Li et al. 2018) but requires
detailed knowledge about geometry and optical properties.
Optical properties and surface areas are currently available
for GPS Block II (Fliegel et al. 1992), Block IIR (Fliegel andGallini 1996), Galileo IOV and FOC satellites (GSA 2019),
and the QZS-1 – 4 satellites (Cabinet Office 2019a,b,c,d). Incomplete optical properties (only absorption coefficients) andAntenna thrust
When transmitting navigation signals, GNSS satellites experience an acceleration in radial direction depending on the
power of the emitted signals called antenna thrust. RodriguezSolano et al. (2012) report a 5 mm radial orbit change when
considering antenna thrust in GPS orbit determination.
Steigenberger et al. (2018) measured the transmit power of
selected GPS, GLONASS, Galileo, and BeiDou-2 satellites
with a high-gain antenna. They report transmit power values between 20 and 265 W resulting in radial orbit shifts
between 1 and 27 mm. Manufacturer values for the transmit power of the QZSS satellites are published in (Cabinet Office 2019a,b,c,d). Recent transmit power measurements of newly launched GLONASS satellites are given
in Steigenberger et al. (2019). Due to the lack of transmit antenna gain pattern, the BeiDou-2 gain pattern wereTable 4.6: Orbit modelling recommendations for the third IGS reprocessing campaign according to Moore (2019).

Satellite type

Minimum modelling

Preferred modelling

GPS Block IIA
GPS Block IIR
GPS Block IIF
GPS Block III
GLONASS
Galileo

ECOM-2, GSPM
ECOM-2, GSPM
ECOM-1, GSPM
ECOM-2, GSPM
ECOM-1, GSPM(GLONASS)
ECOM-2

Box-wing + empirical
Box-wing + empirical
Box-wing + empirical
Box-wing + empirical
Box-wing + empirical
Box-wing + empirical258

used for estimation of the BeiDou-3 MEO satellite transmit
power included in the IGS satellite metadata file available
at mgex.igs.org/IGS_MGEX_Metadata.php. The transmit
power of the BeiDou-3 IGSO and GEO as well as all IRNSS
satellites is currently unknown.
Attitude
The basic attitude condition of a GNSS satellite is that thenavigation antenna points to the centre of the Earth and thesolar panels are oriented perpendicular to the Sun (Montenbruck et al. 2015a). To fulfill these conditions, the satellite
has to rotate around its z-axis. The speed of this rotation
depends on the elevation of the Sun above the orbital plane.
Due to technical restrictions, the implementation of the attitude control deviates from this ideal case. Several models
for the attitude of dedicated GNSS satellites are available butthese models are not used by all ACs at the moment.
• GPS Block II, IIA, IIR: Kouba (2009a)• GPS Block IIA: Rodriguez-Solano et al. (2013)• GPS Block IIF: Dilssner (2010)• GLONASS-M: Dilssner et al. (2010)• BeiDou-2 IGSO-1, IGSO-6, MEO-6: Dilssner (2017)• BeiDou-3S: X. Li et al. (2018)• BeiDou-3: CSNO (2019c) and Shanghai Engineering Center for Microsatellites (2018)• Galileo IOV and FOC satellites: GSA (2019)• QZSS: Cabinet Office (2019a,b,c,d).
Satellite antenna model
GNSS measurements refer to the electrical phase centre of
the transmission and receiving antennas. The mean differences between the mechanically well-defined antenna reference point of the receiver antennas and the centre of mass
for the satellite antennas are called Phase Centre Offsets(PCOs). Variations of the actual phase centre depending on
azimuth and elevation of the transmitted/received signal arecalled Phase Centre Variations (PCVs). As no ground calibrations are available for the transmitting antennas of GPS
and GLONASS except for the first GPS III satellite (G074),
satellite antenna phase centre offsets and variations were estimated from global GNSS data to derive antenna models forthese systems.
For GPS and GLONASS, the current model igs14.atx(Rebischung et al. 2016) contains only block-specific PCVs
and satellite-specific PCOs for the ionosphere-free linear
combination of L1 and L2. Azimuthal variations of the satellite antennas (Schmid et al. 2005) are not yet considered forthese GNSS. Furthermore, satellite-specific antenna PCVs
could account for deviations of the individual transmitting

4 Product-based review

antennas from the block-specific mean values. Such satellitespecific PCVs are published for each transmit frequency ofGalileo IOV and FOC (GSA 2019) as well as QZS-2 – 4(Cabinet Office 2019b,c,d).
Lockheed Martin published L1, L2, and L5 PCO values forthe first GPS III satellite (Lockheed Martin 2019). L5 satellite
antenna calibrations for the other GPS satellites as well as
GLONASS L3 calibrations are currently not available. Manufacturer PCO values for the BeiDou-3S satellites are givenin (Zhao et al. 2018b). Frequency-specific satellite antennaphase centre offsets of the active BeiDou-2 and BeiDou-3
satellites for B1, B2, and B3 were published by the China
Satellite Navigation Office (CSNO) in December 2019.
The availability of pre-flight calibrations for the Galileo satellite antennas makes it possible to derive the terrestrial scalefrom GNSS observations. The inclusion of Galileo in thethird IGS reprocessing might even enable a contribution of
GNSS to the scale definition of ITRF2020 (Villiger et al.
2019).
Receiver antenna model
The IGS receiver antenna model is mainly composed of absolute robot calibrations for L1 and L2. Only for a few antennas,
converted relative calibrations are included. For the third IGS
reprocessing campaign, a dedicated file IGSR3_2077.atx
was compiled by the Antenna Working Group including 36
robot calibrations by Geo++ and one chamber calibration by
University of Bonn for the following additional frequencies:
1176.45 MHz: GPS L5, Galileo E5a, BeiDou B2a
1191.795 MHz: Galileo AltBOC and BeiDou ACE-BOC
1207.14 MHz: Galileo E5b, BeiDou B2b1268.52 MHz: BeiDou B31278.75 MHz: Galileo E6, QZSS L62
However, not all frequencies are available for all calibrations.
In addition, calibrations for GLONASS L3 (1202.025 MHz)and the IRNSS S-band frequency of 2492.028 MHz are still
missing. The latter fact is insignificant at the moment as noneof the antennas currently used within the IGS has a dedicated S-band capability and only one receiver type supports
tracking of this signal.
Non-tidal loading
It is currently not recommended to apply non-tidal loading
corrections at the observation level. However, aliasing effects
can be introduced by this procedure (Dach et al. 2011). In
addition, one should be aware that atmospheric loading ispartly compensated when using GMF/GPT (Kouba 2009b;
Steigenberger et al. 2009).

4.4 GNSS satellite orbits

259

Subdaily ERP modeldraft release of the IGS satellite metadata file available at
mgex.igs.org/igs_metadata.snx. More details on the importance and availability of satellite metadata are given in a white
paper of the MGWG (Montenbruck and Steigenberger 2020).

Griffiths and Ray (2013) found subdaily alias errors in IGS
orbit, coordinate, geocentre, and ERP products. They attributed these errors to deficiencies of the IERS subdaily ERP
model and concluded that an improved model is needed tomitigate these errors. As a consequence, an IERS Working
Group on Diurnal and Semi-diurnal EOP Variations was established. In July 2019, this working group recommended themodel of Desai and Sibois (2016) based on hydrodynamic
ocean models obtained from altimetry.
Thermal modelling of monuments
Temperature changes induce thermal expansions of the bedrock and the monuments, where the GNSS antennas aremounted on, as well as tilts of the monuments. Romagnoli
et al. (2003), H. Yan et al. (2009), Hiroshi (2013), Wanget al. (2018) report vertical displacements in the order of afew millimeters. However, as additional information about
the thermal properties of the bedrock and the monument aswell as temperature data are required, these corrections are
currently not applied by the IGS ACs.
Operational information
The knowledge about selected operational information, inparticular orbit maneuvers and attitude mode switches, is essential for precise orbit determination. Most GNSS providers
issue so-called notice advisories announcing, e.g., planned
outage periods of individual satellites:
Notice Advisory to NAVSTAR Users (NANU)GPSGLONASS Notice Advisory to GLONASS Users (NAGU)
Galileo Notice Advisory to Galileo Users (NAGU)
QZSSNotice Advisory to QZSS Users (NAQU)
However, these advisories do not contain information about
the exact maneuver epoch(s). Such information is currently
only provided for QZSS by Cabinet Office, Government ofJapan (CAO) in the form of detailed Operational History
Information (OHI), i.e., time, duration, and magnitude oforbit maintenance maneuvers, changes of attitude modes,
and time of reaction wheel unloading (Cabinet Office 2019e,
2020a,b,c).
Satellite metadata
Many of the effects and models described in the paragraphs
above require knowledge about the corresponding GNSS
satellites, e.g., satellite mass, sensor offsets, transmit power,
etc. The IGS Multi-GNSS Working Group (MGWG) prepared an extension of the SINEX format in order to store
and exchange these GNSS metadata (mgex.igs.org/IGS_MGEX_Metadata.php). The MGWG also maintains a

4.4.3 Links to other products

Changes in the orbit modelling directly affect the following
geodetic products:• Terrestrial Reference Frame (TRF)• TRF densification, e.g., regional reference frame of the
IAG Reference Frame Sub-Commission for Europe(EUREF), or Sistema de Referencia Geocéntrico para las
Américas (Geocentric Reference Frame for the Americas)(SIRGAS)• GNSS satellite orbits and clocks• Earth Orientation Parameters (EOP)• Time-dependent Total Electron Content (TEC) maps
• Troposphere Zenith Total Delay (ZTD) time series
Changes in the orbit modelling affect the following products
utilizing GNSS satellite orbits:• Low Earth Orbiter (LEO) satellite orbits• Static gravity field• Time-dependent gravity field• Time series of sea surface heights• Time series of ice sheet and glacier elevations
4.4.4 Open problems and recommendations

The BPS has identified open problems in the field of GNSS
orbit modelling and recommendations for further studies.
These include:• The consistency of the orbit solutions submitted by the
IGS Analysis Centers has to be assured.
• Radiation pressure modelling and aliasing of orbital errors
into geodetic parameters needs to be further studied.
• The impact of different arc lengths (1-day vs. 30 hours
vs. 3-day) on geodetic parameters needs to be assessed.
Selected aspects are already published in (Lutz et al. 2016)• Receiver antenna calibrations beyond L1/L2 are required
for all antennas and all frequencies used in the IGS.
• Satellite antenna offsets are required for IRNSS and SBAS
satellites.
• Satellite antenna phase centre variations are required for
BeiDou, IRNSS, QZS-1, and SBAS.
• Attitude models are required for GPS III, IRNSS, andSBAS satellites.
• Transmit power levels are required for GPS III, IRNSS,
and SBAS satellites.
• No combined clock product is available for GLONASS,
BeiDou, Galileo, and QZSS.
• No orbit products are available for IRNSS and SBAS.

260

Summary of recommendations on GNSS orbits
Recommendation 4.1 : Up-to-date analysis strategy summary files should be provided by all ACs for their operational, MGEX, and reprocessed products.
Recommendation 4.2 : The impact of analysis strategies
such as radiation pressure modelling and orbit arc length
on derived geodetic parameters should be investigated indetail.
Recommendation 4.3 : The contribution of Galileo antenna
calibrations to a GNSS-derived realisation of the terrestrial
scale should be studied.
Recommendation 4.4 : Satellite operators should be urged
to provide missing detailed information about satellite
dimensions, optical and infrared surface properties, attitude models, antenna offsets, antenna phase patterns, radio
emission power, transmit antenna gain pattern, and operational information such as maneuvers.
Recommendation 4.5 : A multi-GNSS-capable orbit andclock combination software shall be developed.

4.5 Gravity and geoid
Gravity and geoid related data and products are collected
and prepared by several IAG services, which all together areorganized under the umbrella of the International Gravity
Field Service (IGFS). The overall goal of IGFS is to coordinate the collection, validation, archiving and disseminationof gravity field related data and to coordinate courses, information materials and general public outreach relating to
the Earth’s gravity field. One of the overarching goals of the
IGFS is to unify gravity field related products for the needsof the Global Geodetic Observing System (GGOS). IGFS
coordinates the servicing of the geodetic and geophysicalcommunities with gravity field-related data, software andinformation. The combined data of the IGFS entities include
global models of the static (mean) Earth gravity field and its
time-variable component, terrestrial, airborne, satellite andmarine gravity observations, Earth tide data, Global Positioning System (GPS) levelling data, digital models of terrain
and bathymetry as well as the oceanic gravity field and geoidfrom satellite altimetry.
Under the umbrella of the IGFS the following services andcentres are available. They represent the “operating arms” of
the IGFS and are independently organized. Nevertheless the
IGFS coordinates their activities specifically regarding joint
standards and conventions in order to ensure inter-operabilityof their products. In addition the IGFS Central Bureau (IGFS
CB) develops and provides online applications for the creation of metadata for gravity and geoid data. This shall ensurethat all metadata required to fully describe a numerical dataset are available.

4 Product-based review

BGI Bureau Gravimétrique International, Toulouse,
France : The overall task of BGI is to collect, on aworldwide basis, all measurements and pertinent information about the Earth gravity field, to compile
them and store them in a computerized data base inorder to redistribute them on request to a large variety
of users for scientific purposes.
ISG International Service for the Geoid, Milano, Italy : The
main tasks of ISG are to collect geoid data on a worldwide scale, to collect and distribute software for geoid
determination, to conduct research on procedure forgeoid determination, to organize geoid schools, and toedit and distribute the Newton’s Bulletin.
ICGEM International Center for Global Earth Models, Potsdam, Germany : The main tasks of ICGEM are to collect and archive all existing global gravity field models,
web interface for getting access to global gravity fieldmodels, web based visualization of the gravity fieldmodels, their differences and their time variation, web
based service for calculating different functionals of thegravity field models, web site for tutorials on sphericalharmonics and the theory of the calculation service.
COST-G International Combination Service for Time-variable Gravity Fields, Bern, Switzerland :COST-G is the Product Center of the IGFS for timevariable gravity fields. COST-G provides consolidated
monthly global gravity models in terms of sphericalharmonic coefficients and thereof derived grids by combining solutions from individual analysis centres (ACs).
The COST-G ACs adopt different analysis methods but
apply agreed-upon consistent processing standards todeliver time-variable gravity field models, e.g. fromGRACE/GRACE-FO,
low-low satellite-to-satellite tracking (ll-SST),
high-low satellite-to-satellite tracking (hl-SST),
Satellite Laser Ranging (SLR).
IDEMS International Digital Elevation Model Service,
ESRI, Los Angeles, USA :The main tasks of IDEMS are the distribution of dataand information about Digital Elevation Models, relevant software and related datasets (including representation of Inland Water within Digital Elevation Models)
which are available in the public domain.
IGETS International Geodynamics and Earth Tide Service,
Strasbourg, France : The primary objective of IGETS is
to provide a service to monitor temporal variations of
the Earth gravity field through long-term records fromground gravimeters, tiltmeters, strainmeters and othergeodynamic sensors. IGETS continues the activitiesof the GGP to provide support to geodetic and geophysical research activities those of ICET in collecting,archiving and distributing Earth tide records.

4.5 Gravity and geoid

The general character of the products offered by the IGFS
services is slightly different to products of other IAG services.
While for example the ITRF is generated by a combinationof products or observations provided by various other IAG
services, IGFS products are mostly singular products either
representing observations or geophysical models. Geophysical models usually are based on various data or observations,which are taken from a number of sources (e.g. satellite mission data, terrestrial observations). This implies that products
from the IGFS as a minimum shall indicate the standards
applied for their generation. In many cases this can be guaranteed, but there are also other products for which this hardly
is possible. Often huge software packages, following specificstandards and conventions implemented at some point form
the basis for generating the products. These standards andconventions often are unknown or not specified together withthe products.
In the following sections the products offered by the IGFS
centres are shortly described and references for these products are provided. In the subsequent table for each identified
product an inventory of the standards needed to describe theseproducts is given (on a best knowledge basis). This information is extracted from the available information provided on
the services web sites or the related documentation.
4.5.1 IGFS – Central Bureau

The IGFS Central Bureau (IGFS CB) acts as the central coordination and communication centre of the IGFS. The IGFS
CB high level tasks include• The provision of the link between the IGFS entities, IAG,
and external projects, networks or organisations (oceanic,
atmospheric, hydrology and others).
• The provision of the link to the GGOS bureau and communicate their requirements and recommendations to the
IGFS.
• The implementation of standards and recommendations
related to gravity field observations, securing consistency
with geometric standards, and promotion of their use within the geoscientific community.
Within these activities the IGFS CB is developing online applications for the creation of metadata for gravity and geoid
data, which shall be established as a service for searching
the metadata database in order to locate dataset sources. In
addition the metadata description secures that for a numerical
dataset all needed information is available in order to correctly interpret it. So far draft versions for a geoid metadata
editor and for a gravity data editor have been developed as
Web applications. These metadata editors ask for the following information classes :261

Geoid Metadata Editor (v0.1.3) and Gravity Metadata
Editor (v0.2.6).
Section 1: Metadata Reference Information• Responsible Organisation and Contact• Metadata Creation and Review Dates• Metadata Prototype Information:

Section 2: Identification Information• Resource Coordinate Reference System• Resource Citation• Resource Description• Resource Status• Resource Point of Contact• Spatial Extent Geographic Bounding Box Coordinates• Resource Maintenance and Updates• Keywords• Resource Constraints and Security Information

Section 3: Distribution Information• Distributor• Standard Order Process• Metadata Constraints

Section 4 – Alternative Geoid Data: Standard and Conventions• General Standards and Conventions (GM, a, f)• Tide System• Reference Ellipsoid• Standard Density of the Earth

Page 4 – Alternative Gravity Data: Standard and Conventions• General Standards and Conventions (GM, a, f, normal
gravity reference ellipsoid)• Earth’s Gravity Field Permanent Tide System• Earth Orientation Parameters Specifications• Tidal Conventions• Station Coordinates and Corrections

Section 5 – Alternative Geoid Data: Data and Data Quality
Information• Attribute Accuracy• Logical Consistency Report• Completeness Report• Data Distribution• Geoid Data / Gravity Data
• Position Accuracy / Position and Height Accuracy

Section 5 – Alternative Gravity Data: Data and Data Quality
Information• Attribute Accuracy• Logical Consistency Report262• Completeness Report• Data Distribution• Gravity Data
• Position and Height Accuracy• Time Period of Content
4.5.2 BGI – Bureau Gravimétric International

The overall task of the Bureau Gravimétrique International(BGI) is to collect, on a worldwide basis, all measurements
and pertinent information about the Earth gravity field, tocompile them and store them in a computerized data basein order to redistribute them on request to a large variety
of users for scientific purposes. BGI central office is located in Toulouse, France, in the premises of the Observatoire
Midi-Pyrénées (OMP).
The products of the BGI are
Gravity Databases:• Collection of land and marine gravity data.
• Gravity data at reference stations.
• Data from absolute gravity stations(see mirror site: agrav.bkg.bund.de).
Grids and Models:• High resolution grids and maps of the Earth’s gravity anomalies (Bouguer, isostatic and surface free-air), computed
at global scale in spherical geometry (World Gravity Map(WGM)2012).
• Regional gravity anomaly grids computed from the Earth
Gravitation Model 2008 (EGM 2008).
• Gridded estimates of (i) gravity accelerations, (ii) gravity
disturbances, (iii) quasigeoid undulations, and (iv) deflection of the vertical components from the ultra high resolution GGMplus global gravity field model (Hirt et al.
2013).
More details about tasks and products can be found at theservice web site bgi.omp.obs-mip.fr/ and in the following
documents offered via the web site:• Land gravity data format (EOL) / Sea gravity data format(EOS):
bgi.omp.obs-mip.fr/content/download/720/4949/file/
BGI_EOL_EOS_Data_format.pdf• Fortran routine to extract [Longitude/Latitude/Bouguer]
fields from EOL data file:
bgi.omp.obs-mip.fr/content/download/721/4952/file/conveol2xyz.pdf• Determination of normal gravity (BGI document):
bgi.omp.obs-mip.fr/content/download/723/9056/file/
BGI_Normal_gravity_determination.pdf

4 Product-based review• Définition des anomalies gravimétriques (in French):
bgi.omp.obs-mip.fr/content/download/724/4972/file/
FORMUL00.pdf• Gravity definitions & anomaly computations (NGA document):
bgi.omp.obs-mip.fr/content/download/725/4975/file/computations.pdf• Description of the International Database for Absolute
Gravity Measurements:
bgi.omp.obs-mip.fr/content/download/727/4992/file/
AGrav_Wziontek_etal2.pdf
See also: (Wilmes et al. 2009).
Apart from the product descriptions a number of tutorials
are offered in English and French language providing thefundamentals of gravity theory and satellite geodesy.
See: bgi.omp.obs-mip.fr/data-products/Documentation/tut
orials.
4.5.3 ISG – International Service for the Geoid

ISG activities are on educational, research, and data distribution sides : principal purposes of ISG are the collection anddistribution of geoid models, the collection and distributionof software for geoid computation, and the organisation oftechnical schools on geoid determinations. The tasks of the
ISG are• to collect geoid data on a worldwide scale (geoid repository)• to collect and distribute software for geoid determination(software download)• to conduct researches on procedure for geoid determination (projects)• to organize Geoid schools• to edit and distribute the Newton’s Bulletin
The products of the International Service for the Geoid (ISG)are• Grids of local and regional geoid estimates, collectedworldwide (geoid repository).
• Geoid Software (local geoid estimation; spherical harmonics manipulation; global models handling, evaluation ofdifferent functionals of the gravity field). As this is specific software and not a data product no standards andconventions are identified.
• International schools on geoid determination and thematic
schools. As this is not a data product no standards andconventions are identified.
More details about tasks and products can be found at theservice web site www.isgeoid.polimi.it/index.html and in thefollowing documents offered by the web site:4.5 Gravity and geoid• Geoid model specifications:
www.isgeoid.polimi.it/Geoid/ISG_format_20160121.pdf• Software is provided via this web link:
www.isgeoid.polimi.it/Software/software.html
4.5.4 ICGEM – International Center for Global EarthModelsThe International Center for Global Earth Models collects
and distributes historical and actual global gravity field models of the Earth and offers calculation service for derived
quantities. In particular this includes: Collecting and archiving of all existing global gravity field models, maintaining
an online archive for getting access to global gravity fieldmodels, providing web based visualization of the gravity fieldmodels, their differences and their time variation, offeringa service for calculating different functionals of the gravity
field models, and providing tutorials on spherical harmonics
and the theory used by the calculation service.
The products of International Centre for Global Earth Models(ICGEM) are• Static gravity field models as spherical harmonic series.
• Gravity field solutions for dedicated time periods (timevariable model series) as spherical harmonic series.
Monthly, weekly and daily solutions with or without applying non-isotropic filtering.
• Topographic gravity field models model . . . spherical harmonic series in ICGEM format (topography heights andgravitational potential).
• Calculation of gravity functionals on freely selectable grids
or on user defined points. The following functionals are
implemented so far: height anomaly, geoid height, gravity disturbance, gravity anomaly, Bouguer anomaly, gravity, gravitation, radial gravity gradient, equivalent waterheight.
• Visualization service for static and temporal gravity fieldmodel functionals, trends and amplitudes for temporalfields and spherical harmonics.
• Evaluation of gravity field models by degree variances andby GNSS-levelling comparisons.
• Additionally ICGEM offers also gravity field models ofother celestial bodies (Moon and Mars) including the calculation and visualization service.
More details about tasks and products can be found at theservice web site icgem.gfz-potsdam.de/home and in the following documents offered via the web site:• The theory and formulas used by the calculation serviceof the ICGEM are described in the Scientific Technical
Report STR09/02:
icgem.gfz-potsdam.de/str-0902-revised.pdf

263• Article about global models:
icgem.gfz-potsdam.de/GlobalModelsEncyclopedia.pdf• Description of the ICGEM format:
icgem.gfz-potsdam.de/ICGEM-Format-2011.pdf• Information on the topographic gravity field models:
icgem.gfz-potsdam.de/Topomodels_description_ICGEM.pdf
4.5.5 COST-G – International Combination Service
for Time-variable Gravity Fields

COST-G is the product centre of IGFS for standardization ofgravity derived mass transport products in order to improve
the quality, robustness and reliability of individual solutions
and in order to enable hydrologists, glaciologists, oceanographers, geodesists and geophysicists to take full advantage of one well-defined, consolidated time variable gravity
product. COST-G tasks are: (1) Developing the synergy between international teams working on gravity field modelling;(2) Improving and homogenizing the modelling adopted by
the Analysis Centers (AC); (3) Providing combined reference
solutions by the Combination Center (CC); (4) Assessing thereference solutions by a Validation Center (VC); (5) Organizing dissemination by a dedicated webmaster (WM). The
combination service infrastructure will improve the actual
standards and turn it into an operational mode that will enable the use of Gravity Recovery And Climate Experiment(GRACE) and Gravity Recovery And Climate Experiment –Follow On (GRACE-FO) mass redistribution data for monitoring hydrological events such as floods or droughts for
instance. COST-G will provide consolidated time-variableglobal gravity models in terms of spherical harmonic coefficients and thereof derived grids by combining solutions fromindividual analysis centres as well as validation criteria which
will be made available through dedicated web-interfaces.
The main products of COST-G are monthly global gravity field models derived from the combination of solutions from the COST-G analysis centres and partner analysis centres. In particular products at different processing
levels are provided: Monthly global gravity field models interms of spherical harmonic coefficients (Level-2 products).
Post-processed Level-2 products in terms of spherical harmonic coefficients with various corrections applied (Level2B products). User-friendly grids based on Level-2B products (Level-3 products) for various scientific applications
as described at GFZ’s Gravity Information Service (GravIS,
gravis.gfz-potsdam.de/home).
Apart from these main products COST-G is also offering
additional products helping to process the main products:
Monthly means of background models that are generated bya weighted combination of the corresponding products of
the individual analysis centres (applying the same weights as264

used for the generation of the combined gravity field models) Monthly means of combined atmosphere and ocean dealiasing products.

4 Product-based review

The COST-G products are disseminated via ICGEM and
GFZ’s ISDC at icgem.gfz-potsdam.de/series/02_COST-G/
and ftp://isdcftp.gfz-potsdam.de/grace/GravIS/COST-G
respectively. The COST-G Processing Standards and Release
Notes are available at cost-g.org/download/COST_G_STA
NDARDS.pdf and cost-g.org/download/COST_G_RL01.pdf,
respectively. Visualizations of the COST-G products areprovided by GFZ’s Gravity Information Service (GravIS,
gravis.gfz-potsdam.de) and the COST-G Plotter (cost-g.org/).

The service does hardly provide data products via its web
site, but mostly links to other institutional, project related orsatellite mission web sites, where digital elevation models
are made available. Standards and conventions for IDEMS
products are not specified and no documentation about themost important digital elevation products is provided. Only ashort tutorial “Getting started with IDEMS” an introduction
to DEMs, and a bibliography is provided via the web site.
The tutorial about the IDEMS in the present form is a mix ofa general user manual and some kind of ArcGIS advertisement. From the information available at the web site it is not
immediately obvious which models are freely accessible tothe public.

4.5.6 IDEMS – International Digital Elevation Model
Service

4.5.7 IGETS – International Geodynamics and Earth
Tide Service

The website of the IAG International Digital Elevation Model
Service (IDEMS) provides a focus for distribution of dataand information about digital elevation models, sphericalharmonic models of Earth’s global topography, lunar andplanetary Digital Elevation Model (DEM), relevant softwareand related datasets. All information is provided via the service web site www.cse.dmu.ac.uk/EAPRS/iag/.

The International Geodynamics and Earth Tide Service (IGETS) provides a service to monitor temporal variations of the
Earth gravity field through long-term records from groundgravimeters, tiltmeters, strainmeters and other geodynamic
sensors. IGETS is composed by two analysis centres hosted
by University of French Polynesia in Tahiti and by University of Strasbourg and by a main data centre hosted GFZ
Potsdam. Additionally, University of Strasbourg is hosting
the central bureau and a secondary data centre. More details about IGETS can be found on the following web site:
igets.u-strasbg.fr/index.php.

Currently, this site hosts different categories about products
and information about DEMs, namely:• Bathymetry and Ice Data,• Earth Models,• Geodesy relevant DEM and Bathymetric Terrain Model(BTM) Studies• Global DEMs
• Planetary Terrain Data
• Regional DEMs
• Software and Apps
• Using DEMs and Esri Products.
The products of IDEMS are:• Compilation, tutorial-style provision and maintenance of
information on global gridded DEMs;• Compilation of available national elevation data sets withinformation on data resolution, methods used for DEM
generation and links to providers;• Generation and dissemination of spherical-harmonic models of Earth’s global topography and bathymetry;• Compilation of geodesy-relevant DEM-studies;• Extension of the focus from Earth to Moon and terrestrial
planets through compilation of information on available
planetary topography models.

The main products of IGETS are the raw and processed datafrom worldwide superconducting gravimeters. In particular
data at different processing levels are provided. These are :• Raw gravity and local pressure records sampled at 1 or
2 seconds, in addition to the same records decimated at
1-minute samples (Level 1 products).
• Gravity and pressure data corrected for instrumental perturbations, ready for tidal analysis (Level 2 products).
• Gravity residuals after particular geophysical corrections(including solid Earth tides, polar motion, tidal and nontidal loading effects) (Level 3 products).
Apart from these main products IGETS is also offering additional products helping to process the main products (vialinks to other web sites). These are :• Superconducting gravimeter data for major Earthquakes(minute and second sampling);• Atmospheric attraction computation service;• mGlobe Matlab/Octave toolbox for computation of globalhydrological, atmospheric and non-tidal ocean loading
effects;• Loading service (displacements, gravity, tilts).

4.5 Gravity and geoid

Details about the main IGETS products can be found at
the ISDC Web site of GFZ at isdc.gfz-potsdam.de/iget
s-data-base/documentation/. In particular there is available a report providing documentation and conventions for
the IGETS products. See gfzpublic.gfz- potsdam.de/p
ubman/item/escidoc:1870888:7/component/escidoc:
1948897/STR-1608_voigt.pdf.
4.5.8 IGFS Products Inventory of Standards

From the descriptions provided in the previous chapters thefollowing product categories of the IGFS can be summarized.
For these product categories certain standards and conventions need to be identified such that they are compatible(product identifier: product description):
Land and marine gravity data and gravity data at
reference stations
BGI2
Absolute gravity station data
BGI3
Grids of gravity anomalies
ISG1
Grids of regional geoid solutions
ICGEM1 Global gravity field model as spherical harmonicseries (static, time variable)
ICGEM2 Gravity field functionals on a grid
IDEM1 Grids of digital elevation models
IGETS1 Superconducting gravimeter data

BGI1

Products which are not mentioned above either shall not be
regarded as a data product (e.g. geoid software, schools) orare not specified in sufficient detail in order to identify ifstandards and conventions play a role at all. So far metadatadefinitions have only been generated for geoid and gravity
data either on grids or point-wise. Metadata for spherical harmonic series still need to be defined, but are overlapping toa large extent with metadata elements as defined for gravity
and geoid products. The following list summarizes metadata,
which are related to standards and conventions (metadata
code and metadata description). The numbers are indicating
the metadata field number, while letters indicate if a metadata entry is either specified for the geoid (N), for gravity
observations (G) or both (A).
Metadata related to product standards and conventions:A4.1.1 Gravitation constant of the Earth (GM)A4.1.2 Equatorial radius of the Earth
A4.1.3 Flattening of the Earth
G4.1.4 Reference ellipsoid for normal gravity computation
A4.2.1 Permanent tide system
G4.2.2 Permanent tide system Earth orientation parameters
N4.3 Reference ellipsoid for geoid heights
G4.3 Earth orientation parameters specifications
N4.4 Standard density of the Earth value
G4.4.1 Solid Earth tides
G4.4.2 Solid Earth pole tide model

265

G4.4.3 Oceanic pole tide modelG4.4.4 Tidal ocean loading
G4.4.5 Non-tidal ocean loading modelG4.4.6 Non-tidal atmospheric loading modelG4.5.1 Horizontal and vertical coordinates
G4.5.2 Standard density of the Earth value
G4.5.3 Vertical gravity gradientG4.5.4 Air pressure correction
A5.4 Data distribution: points or grid and grid specifications
N5.5.1 Geoid model type (gravimetric, hybrid, etc.)
N5.5.2 Fitting or integration methodology
G5.5 Gravity data type (absolute, type of anomaly, etc.)
N5.6 Geoid height data type (undulation or height anomaly)
G5.8 Time period and time reference
The following Table 4.7 provides a summary of the identified
standards and conventions for the above mentioned IGFS
products and specifically if they are addressed by the metadata descriptions (= metadata description available; N/A =not applicable for this product). Each line in the table represents one of the above mentioned metadata. In case additional
metadata are needed for specific products they are indicatedby additional lines in the table. So far the following additional metadata were identified: Degree = Maximum degreeof spherical harmonic series applied to determine the product;
Filter = Indication if a filter has been applied and what filter
parameters were used.
4.5.9 Recommendations

The updated IGFS web-site acts as an umbrella for all its
services and provides basic information about their tasks andproducts. The services of the IGFS shall ensure that all metadata required to make use of their products are delivered
together with the products. In order to make product conversions to different representations or reference systems therequired algorithms shall be described in the IGFS services
documentation. For this purpose it is recommended to create a unique document per service (or even better for theIGFS), where these algorithms are described in detail. Some
services of the IGFS could provide information about theirproducts in a more concise way. Further remark on BGI andIDEMS: Many of the products collected by these services
are not publicly available. Although they appear as IAG Services, this data is not available for research within the IAG.
From the analysis of the services and their products somerecommendations can be drawn.
Recommendation 5.1 : For all IGFS products (i.e. from theaffiliated services and centres) metadata as specified by
the IGFS-CB shall be provided. If needed, further metadata categories in addition to geoid and gravity shall be
developed by the IGFS-CB.

266

Table 4.7: Summary of theidentified standards and conventions for IGFS products.

4 Product-based review

A4.1.1
A4.1.2A4.1.3G4.1.4A4.2.1G4.2.2
N4.3
G4.3
N4.4
G4.4.1G4.4.2G4.4.3G4.4.4G4.4.5G4.4.6G4.5.1
G4.5.2G4.5.3G4.5.4A5.4
N5.5.1
N5.5.2
G5.5
N5.6
G5.8
DegreeFilter

BGI1

BGI2

BGI3

ISG1







N/A

N/A











N/A
N/A

N/A

N/A
N/A

N/A
N/A
N/A
N/A


N/A

N/A







N/A
N/A


N/A
N/A

N/A

N/A
N/A







N/A

N/A











N/A
N/A

N/A

N/A
N/A




N/A

N/A

N/A

N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A



N/A

N/A
N/A
N/A

Recommendation 5.2 : BGI shall collect and distribute gridsof altimetric gravity anomalies. So far these data are notyet offered by the IGFS.
Recommendation 5.3 : BGI and IGETS partially areproviding similar products, i.e. observations fromground gravimeters. It is recommended that both services
implement joint standards for these products in order toensure compatibility.
Recommendation 5.4 : The ISG Software has some overlap
with the on-line tools available at the ICGEM. It is strongly
recommended to make sure that both Software systems arecompatible, i.e., that the same standards and conventions
are used.
Recommendation 5.5 : COST-G products shall be disseminated via the ICGEM. It is recommended not to establish aseparate service for provision of combined time variablegravity field series. Same standards as used by ICGEM(e.g. format) shall be applied. What concerns mass transport grids, it shall be made sure that these are as wellcompatible to the ICGEM calculation service. In addition

ICGEM1 ICGEM2



N/A

N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A

N/A
N/A






N/A

N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A

N/A
N/A
N/A









IGETS1






N/A

N/A











N/A
N/A

N/A

N/A
N/A

the relationship to the GFZ driven GravIS system shall bedefined and ideally both shall be combined.
Recommendation 5.6 : The IDEMS in the present form cannot be regarded as a product repository as it hardly provides access to real digital elevation data grids. At various
places on the IDEMS web pages links to ArcGIS are set.
In order to make full use of the web site an ArcGIS software license seems to be needed. So IDEMS shall not be
regarded as an open access scientific service, but a mixof service and public relation for ESRI who is maintaining the IDEMS web site. It is strongly recommended toseparate the web site content to a product service part,which should point towards accessible DEM’s (the real
IDEMS) and another section which might be more related
to ArcGIS applications.
Recommendation 5.7 : All products to be delivered under
the umbrella of IGFS shall be publicly available for research applications. Otherwise these products shall not be
advertised anymore as IGFS supported products.

4.6 Height systems and their realisations

267

4.6 Height systems and their realisations

case, information about the mass density (either by digitaldensity models or density hypotheses) is also necessary.

In the first version of this inventory, published in 2016 (Angermann et al. 2016), the section “Height Systems and theirrealisations” concentrated on the discrepancies of the local
height systems and their combination with geometric (ellipsoidal) heights and (quasi-)geoid models. Special care wasgiven to the inventory of corrections or reductions applied
to the different vertical coordinates to remove or retain geophysical effects influencing the vertical positioning. In thisupdated version of the inventory, we add a description of thestandards that are being discussed (as of December 2019)
for the implementation of the International Height Reference
System (IHRS) and its realisation, the International Height
Reference Frame (IHRF), as stated by the IAG Resolution
No. 1, 2015 released in the IUGG2015 General Assembly(Drewes et al. 2016).

For the treatment of the surface gravity, the standards published with the International Gravity Standardization Net
1971 (IGSN71) (Morelli et al. 1974) and the International
Absolute Gravity Basestation Network (IAGBN) (Boedecker1988) are available. Nevertheless, there are still large databases referring to the old gravity reference called Potsdam
system (Borrass 1911). Gravity surveys with geophysical purposes (e.g., oil exploration) are in general not freely available
and the standards applied to their processing are not clear.

4.6.1 Overview

Currently, a formal GGOS height systems product or an
IAG Height Systems Service does not exist. However, theavailability of geodetic space techniques, especially GNSS
and dedicated-gravity field missions (i.e., CHAMP, GRACE,
GOCE), motivates the combination of current geodetic products to determine gravity field-related heights. This combination is normally performed according to the relationh − H − N = 0. The ellipsoidal heights (h) are derived from
GNSS positioning while the geoid or quasi-geoid models (N)are computed combining satellite and terrestrial (aerial, marine) gravity data. The orthometric or normal heights (H) areusually obtained from spirit levelling (+ gravity reductions)referring to local vertical datums.
The determination of ellipsoidal heights is expected to conform to the IERS and IGS standards, since these heights
depend on the geocentric Cartesian coordinates and on thesize, orientation, and position of the reference ellipsoid used
for their transformation into ellipsoidal coordinates. For thecomputation of the (quasi-)geoid, a compilation of standards(like the IERS conventions) is not available. The processingof CHAMP, GRACE and GOCE data is well-documented
in the specific guidelines (Dahle et al. 2013; Gruber et al.
2010; Lühr et al. 2002). However, the computation of thelong-wavelength constituents of the (quasi-)geoid (degreen ≤ 200 . . . 250 in a spherical harmonic expansion) produces
different results depending on the combination of satellitebased gravity data and the processing strategy used for theestimation of the spherical harmonic coefficients. The medium to short-wavelength components (n > 250) of the (quasi)geoid are usually estimated by combining surface (terrestrial,
airborne, marine) gravity data and the gravitational effects ofthe topography derived from digital terrain models. In thisHistorically, the determination of the physical heights initially followed two basic conventions: (1) the geoid coincides
with the mean sea level and (2) the corresponding verticalcoordinate must be the orthometric height. The realisation ofthese conditions was carried out by estimating the local meansea level at selected tide gauges and by means of geodeticlevelling in combination with gravity reductions. It should be
stressed that orthometric heights depend on the mass density
distribution in the Earth’s interior which is not known at a
sufficient degree. Any hypothesis about the density distribution creates a different realisation of the orthometric heightsystem, but also of the geoid as a level surface running in
the Earth’s interior over the continents. Alternatively, andsince about the middle of the 20th century, some height systems are based on normal heights and the quasi-geoid as thereference surface. The geoid and the quasi-geoid are practically identical in marine areas, and the realisation of thequasi-geoid can also be set equivalent to the local mean sea
level at the reference tide gauges. In general, the existing
physical heights not only refer to local (unconnected) levels
but are also static (without considering variations in time)and contain large uncertainties caused primary by systematic
errors in levelling, omission or different approximations in
the gravity reductions, and non-modelled effects in the height
determination (more details in Table 4.8).
Considering these characteristics, it is clear that the state-ofthe-art allows the combination of ellipsoidal and physicalheights with (quasi-)geoid models with an accuracy varying
from some cm up to 2 m. This may satisfy some practicalapplications, but measuring, understanding and modelling
global change effects with magnitudes at cm- or mm-levelis not possible. The solution of these deficiencies requires
the establishment of a gravity field-related global verticalreference system, capable of supporting the standardisation(unification) of the existing height systems and the precise
combination of physical and geometric heights globally. The
implementation of such a vertical reference system is a main
objective of GGOS (see GGOS Focus Area Unified Height
System in GGOS 2020 Action Plans 2011–2015, unpublished) and the success of this initiative has to be necessarily
supported by a clear statement of standards and conventions.

268

4 Product-based review

Table 4.8: Characteristics and present status of the existing physical height systems.

Characteristics

Present status
Reference level and vertical datum– Definition: the geoid according to Gauss (1876) and Listing(1873).
– Basic convention: the geoid coincides with the undisturbed
mean sea level.
– Realisation: mean sea level averaged over a certain periodof time at an arbitrarily selected tide gauge.
– Remark: The interpretation of this convention has changed
over the years depending on the type and quality of geodetic
observations and analysis strategies available for modellingboth the mean sea surface and the geoid, e.g., (Ekman 1995;
Heck 2004; Heck and Rummel 1990; Mather 1978; Sánchez2012).

– There are as many vertical datums as reference tide gauges(at present more than 100 worldwide) and the reference levels
relate to different determination epochs.
– Height systems based on the quasi-geoid realise the reference level and the vertical datum in the same manner because
geoid and quasi-geoid are practically identical in ocean areas
and at the coast lines (where the tide gauges are established).

Vertical coordinates– Definition: orthometric heights (as tacit consequence ofintroducing the geoid as the reference surface).
– Realisation: levelling with gravity reductions (in samecases using normal gravity instead of observed surface gravity).
– No convention about the gravity reduction (sometimes no
reduction).
– Remark: Normal heights and quasi-geoid are preferred insome countries/regions.

– Vertical coordinates realise different orthometric heighttypes depending on the applied orthometric hypothesis.
– There is no unique relation between reference surface andvertical coordinates if the geoid is not computed using thesame orthometric hypothesis as applied for the orthometricheights.
– The determination of normal heights does not depend on
any orthometric hypothesis, but only on the parameters of
the reference ellipsoid. The same holds for the quasi-geoid.

Reference frames– The vertical control over continental areas has been extended by means of spirit levelling along vertical networks.
– Drawbacks: levelling is very time-consuming and the systematic errors significantly grow with the distance from thereference tide gauge.

– Most of the vertical networks have been measured
piece-wise over very long time periods and the verticalcoordinates refer to different epochs.
– The estimation of vertical displacements at levelling points
by spirit levelling is very difficult (expensive) and in mostcases they are neglected.
– The accuracy of the heights is limited regionally by theerror propagation of spirit levelling to dm-level in remoteareas and globally by the datum realisation to m-level.

4.6 Height systems and their realisations269

4.6.2 Summary of standards

The tide-generating potential is modelled according to :As a first attempt, the inventory of the standards used inheight systems concentrates on the effects removed or retained in the different coordinates associated with vertical
positioning; i.e., those corrections (or reductions) applied tothe instantaneous station positions to generate regularisedor quasi-static coordinates. The coordinates considered are:geometry on land (station positions derived from GNSS positioning), terrestrial gravity (relative and absolute gravity
values measured on or near the Earth’s surface), geopotential numbers (derived from levelling in combination withgravity reductions), and (quasi-)geoid models. To identify
which standards have to be taken into account in this inventory, Table 4.9 summarises the magnitude of the main effects
currently considered.

• for the geometric coordinates (following IERS Conventions): Cartwright and Edden (1973) and Cartwright andTayler (1971). Transformation parameters to the modelsof Doodson (1921) and Hartmann and Wenzel (1995) arealso provided;• for the CHAMP, GRACE, and GOCE data: the same as
the IERS Conventions;• for the terrestrial gravity: beside the Cartwright model(Cartwright and Edden 1973; Cartwright and Tayler 1971),
the Longman (1959) formulation was also widely applied
before IGSN71. In recent years, the model of Hartmann
and Wenzel (1995) is also used.

Apart from the effects caused by secular changes (represented by the so-called station velocities), the largest magnitudes
are related to the treatment of the permanent tide (see Section 3.2). In the case of the geometrical coordinates (i.e.,
ITRS/ITRF), the realisation of the tide-free system is basedon the elastic response of the Earth to the semidiurnal components of the tidal potential (cf. nominal Love numbers(Petit and Luzum 2010, Chapters 6 and 7)). This approximation is called the conventional tide-free system. In theterrestrial gravity and spirit levelling processing, the tide-freesystem assumes the Earth in a hydrostatic equilibrium (cf.
secular or fluid limit Love numbers (Munk and MacDonald 1960)). This approximation is called the tide-free system.
These two different approximations cause discrepancies up
to 0.16 m in the tide-free vertical coordinates. The computation of the (quasi-)geoid is done in the tide-free or zero-tidesystem. However, some models apply the elastic response
approximation and others apply the hydrostatic equilibrium
condition. In this way:
• the geometric coordinates are given in the conventional
tide-free system;• the terrestrial gravity data are given in general in the zerotide system (following the IAG Resolution No. 16, 1983),
but some values determined before 1983 refer to the tidefree system;• the geopotential numbers are given in the tide-free, zerotide or mean-tide system. This depends on the applicationof the so-called astronomical reduction to levelling. This
reduction produces coordinates in the tide-free system. If
the indirect effect of the permanent tide is restored, they
are given in the zero-tide system. If the astronomical reduction is not taken into account, the geopotential numbers
are assumed to be in the mean-tide system;• the global gravity models and the derived (quasi-)geoid
models are published in the conventional tide-free or zerotide system. The mean-tide system is also used especiallyfor oceanographic applications.

The changes induced by the solid Earth tides (estimated bymeans of Love numbers) in the IERS Conventions are computed following the models of Wahr (1981) and Mathews
et al. (1995) in combination with the model Preliminary Reference Earth Model (PREM) (Dziewonski and Anderson
1981). Further corrections for the anelasticity of the mantle
and resonance effects caused by oceanic currents and tides,
and the Chandler wobble, the retrograde Free Core Nutation(FCN) and the prograde Free Inner Core Nutation (FICN) arealso included. The estimation of the pole tide and ocean poletide effects is based on (Wahr 1985), but using the so-called
fluid Love numbers (Munk and MacDonald 1960), i.e., thedeformation for an Earth in hydrostatic equilibrium. Hereit should be mentioned again that the direct deformation of
the Earth’s surface caused by the tide-generating potential
is estimated applying (frequency-dependent) Love numbers
for an elastic Earth. The ocean pole tide loading is computed
using the model of equilibrium of Desai (2002). The pole tideand ocean pole tide loading effects in GRACE and GOCE
and in terrestrial gravity data of high-precision (absolute andsuperconducting gravimetry) are computed as in the IERS
Conventions.
The ocean loading effects in the geometric coordinates aremodelled according to Farrell (1972) and using the conventional computation routine of Scherneck (1991) described in
the IERS Conventions. The ocean tide models preferred by
the IERS are TPXO 7.2 (Egbert et al. 1994) and FES2004(Letellier and Lyard 2005), while in the analysis of GRACE
and GOCE data the model FES2004 is used.
Non-tidal effects (from ocean, atmosphere and hydrology)
are not removed from the geometrical coordinates; i.e., theseeffects are included in the station positions. In the IERS Conventions, the atmospheric tidal effects caused by the solar diurnal and semidiurnal components are modelled according to(Ray and Ponte 2003), while in the GRACE data processing
the model of Biancale and Bode (2006) is used. GOCE dataprocessing does not reduce this effect directly; it is modelled
together with non-tidal effects.

270

4 Product-based review

Table 4.9: Summary of geophysical effects and their magnitudes.
EffectGeometry on land

Terrestrial gravity

Geopotential numbers

Solid Earthpermanent tideelastic response of theEarth−0.12 m at pole,+0.06 m at equator, orhydrostatic equilibrium−0.28 m at pole,+0.14 m at equator

at pole :+0.61 µm s−2
at equator :−0.30 µm s−2

Periodic components of
the Solid Earth tide (modelled as elastic responseof the Earth)at pole :−0.18 m (Moon),−0.08 m (Sun),at equator :+0.36 m (Moon),+0.16 m (Sun)Moon :µm−1.1 to +0.5 2 ,
s
Sun :
µm
−0.5 to +0.3 2sMoon :±0.056 mm per km oflevelling,Sun :±0.026 mm per km oflevelling

Solid Earth pole tide(modelled as hydrostatic
equilibrium)±0.0270 m (vert),±0.0070 m (hz)

< +0.082 µm s−2 (at latitude 45◦ )±3 cm in 430 days

Oceanic pole tide (modelled as hydrostatic
equilibrium)±0.0018 m (vert),±0.0005 m (hz)hydrostatic equilibrium
equipotential surfaces
move as the geoid, but
simultaneously

unknown

Geoidanelastic response of theEarth−0.19 m at pole,+0.10 m at equator

as undisturbed sea level−0.26 m at pole,+0.52 cm at equator±0.0270 m

negligible±0.0018 m

LOD variations (modelled as hydrostatic
equilibrium)

up to 1 m

0.0007 to 0.007µm
s2

negligible

negligible

Tidal ocean loading±0.10 m±(0.01 to 0.02)µm
s2

negligible

unknown

Non-tidal ocean loading

unknown

unknown

unknown

Tidal atmospheric loading±0.0015 m< 0.003 µm s−2

negligible−0.003 to − 0.004µm s−2 /hPa

unknown

Non-tidal atmosphericloading

unknown

Tidal hydrologic loading(groundwater)±0.050 m

Non-tidal hydrologic
loading (groundwater,snow, ice)

±0.050 m

Secular changes (like tectonics, GIA, subsidence,etc.)

up to 0.1 m/yr

unknown

0.05 to 0.1 µm s−2

unknown

The non-tidal effects in the case of GRACE and GOCE are
understood as short-term mass variations of the atmosphereocean system. The corresponding effects are reduced fromthe spherical harmonic coefficients directly to get a quasistationary representation of the Earth’s gravity field. The
estimation of this reduction is based on the Ocean Model
for Circulation and Tides (OMCT) (Thomas 2002) combined with the numerical weather models produced by theEuropean Centre for Medium-Range Weather Forecasts(ECMWF). Hydrological effects are assumed to be containedin the epoch-gravity models computed from GRACE.
In the computation of terrestrial gravity anomalies, the at-

10 mm in 100 to 1000 km
unknown
15 mm in 20 to 2000 km

negligible

unknown

unknown

10 to 12 mm
in 10 to 8000 km

up to 0.1 m/yr

unknownmospheric effects are modelled by means of a standard atmosphere, i.e., a spherical model considering radial densitychanges only. In some cases, this approximation is refined bytaking into account the perturbations caused by the terrain
irregularities in the atmosphere-Earth surface coupling. The
estimation of this reduction is based on an inverse Bouguer
plate with the mean density of the atmosphere.
Regarding the level differences measured by geodetic levelling, the only applied reduction is the astronomical correction;
the other effects (like pole tide, ocean pole tide, non-tidal
loading, etc.) are considered insignificant (Heck 1984).

4.6 Height systems and their realisations

4.6.3 Discussion and deficiencies

According to the summary presented in the previous sections,the largest discrepancies of the existing height systems andtheir combination with geometrical heights and (quasi-)geoid
models are caused by:• different reference levels (i.e., zero-height surfaces) in thelocal height systems;• datum inconsistencies associated with the individual vertical coordinates, e.g., no coincidence between the zeroheight level of the vertical networks and the level of the(quasi-)geoid models;• omission or different approximations in the computationof gravity reductions in the levelling data; i.e., different
types of physical heights (orthometric, normal, normalorthometric, etc.);• vertical coordinates associated with different reference
epochs (in general, dH/dt is unknown and therefore omitted);• systematic effects and distortions, e.g., long-wavelength(quasi-)geoid errors, poorly modelled radial effects in
GNSS positioning, over-constrained levelling network adjustments, systematic errors in levelling, etc.;• assumptions and theoretical approximations taken into account for the data processing; e.g., hypotheses in geoid
and orthometric height computation, atmospheric delay
in GNSS, neglecting ocean dynamic topography at tidegauges, etc.;• dissimilar approaches to reduce the same effect in the
different height types, in particular, the treatment of theluni-solar permanent tide;• systematic and random errors in the different height types
h, H, and N.
To overcome these deficiencies, it is necessary, among othertasks,• to unify (standardise) the existing height systems; i.e., torefer all physical heights to one and the same reference
level (defined and realised globally);• to introduce geopotential numbers as the primary verticalcoordinate in order to avoid inconsistencies caused bydifferent gravity reductions in the height determination;• to guarantee that geometrical and physical heights represent the same Earth’s surface geometry; i.e., the so-called
regularised station positions should include consistent reductions, especially the treatment of the permanent tide.
In the same way, the secular changes should be included
in both representations: geometrical (dh/dt) and physical(dH/dt) heights;• to adopt a conventional global gravity model to be usedas the long-wavelength component in the estimation of(quasi-)geoid models of high resolution.

271

Table 4.10 shows some examples about the requirements andpresent limitations concerning the combination of physicaland geometric heights.
4.6.4 The IAG resolution for the definition andrealisation of an International Height Reference
System (IHRS)

A first concrete step oriented to the establishment of a worldwide unified (standardised) vertical reference system is therelease of an IAG resolution for the definition and realisationof an International Height Reference System (IHRS). This
resolution outlines five basic conventions for the definitionof the IHRS. The definition is given in terms of potential
parameters: the vertical coordinates are geopotential numbers (−∆WP = CP = W0 −WP ) referring to an equipotential
surface of the Earth’s gravity field realised by the IAG conventional value W0 = 62 636 853.4 m2 s−2 . The spatial referenceof the position P for the potential WP = W (X) is given bycoordinates X of the ITRF. The units of length and time are
the meter (m) and the second (s) as expressed by the International System of Units (SI). This resolution also states thatparameters, observations, and data should be related to themean tidal system/mean crust. This is in contradiction with
the IAG resolution No. 16 (1983); however, the mean tidal
system is necessary to support oceanographic applications,especially in coastal areas. More details about the foundations of this IAG resolution can be found in (Ihde et al. 2017)
and (Sánchez et al. 2016).
4.6.5 Towards an standardisation for the IHRS
realisation

The convention WP = W (X), with X = [X,Y, Z]ITRF makes
evident that the IHRS is based on the combination of a geometric component given by X and a physical component
given by the determination of W at X. X is to be determined in the ITRS/ITRF and consequently, it follows the IERS
standards and conventions (see details in Section 4.2). The
potential values W may be in general determined from geopotential numbers CP or by solving the geodetic boundary
value problem (GBVP). Geopotential numbers CP are known
from levelling with gravity reductions and the potential values W would be given by WP = W0 −CP . However, as theyrefer to local vertical datums (different reference levels),
this approach requires the vertical datum unification of thelevelling-based height systems into the IHRS and its reliability is limited by the drawbacks of the existing height systems(see Table 4.8). Therefore, this approach is useful for thetransformation of the existing height systems to the IHRS,
but it is unsuitable for the precise realisation of the IHRS
(Sánchez and Sideris 2017).
The determination of absolute potential values WP from observational data is only possible after introducing adequate

272

4 Product-based review

Table 4.10: Requirements and present limitations concerning the combination of physical and geometric heights (taken from (Sánchez2012)).

Requirement

Present status

Ellipsoidal heights h and (quasi-)geoid heights N must be
given with respect to the same ellipsoid; i.e., the same ellipsoidal parameters have to be used
• for the transformation of geocentric Cartesian coordinates
into ellipsoidal coordinates,• as reference field for the solution of the geodetic boundary
value problem,• for scaling global gravity models, etc.

• Different ellipsoidal parameters (a, GM) are applied ingeometry and gravity.
• h and N given in different tide systems; e.g,
– the mean-tide system in oceanography, satellite altimetry, levelling,– the conventional tide-free system in ITRF positions,
GRS80, some (quasi-)geoid models,– the zero-tide system in some (quasi-)geoid models, terrestrial gravity data.

P

hy

hy

P
p
ra
g
o
Top

H
h

id
Geo

p
ra
g
o
Top

H
h

id
Geo

N

N

d
Ellipsoid(N)E l l i p s oi)oid(hEll i p s

Physical heights H and (quasi-)geoid undulations N mustreflect the same reference surface; i.e., the height reference
surface H0 obtained by subtracting the physical height Hfrom the ellipsoidal height h shall be consistent with the(quasi-)geoid derived from gravity (solution of the boundary
value problem).

• Orthometric heights H and geoid models N obtained fromthe solution of the boundary value problem are based on
different hypotheses.
• H and N refer to different tide systems.
• Systematic errors over long distances in levelling reduce
the reliability of H0 .

y

gr
o
p
To

d=
i
o
Ge
Ellipsoi

H

H p-

d

h

H0

N

P

ap
h

ap
h

P
y

gr
o
p
To
H0
Hpid
Geo

Ellipsoi

Hp
h

N

d

4.6 Height systems and their realisations

273

Table 4.10 continued

Requirement

Present status

Physical heights H and ellipsoidal heights h must represent
the same Earth’s surface• H and h refer to different epochs and, in the most cases,
dH/dt is unknown.
• Different reductions (for Earth-, ocean-, atmospheric tides,
ocean and atmospheric loading, post-glacial rebound, etc.)
are applied.

gro
Top o gr
p
To
id
Geo

P

)

h)
(
y

P

ap
h

ap
ap h
h

y

(H

H
h
N

d
Ellipsoiconstraints. The main constraint is that the gravitational potential V must vanish at infinity; i.e., V∞ = 0. Consequently,
this constraint is the primary convention for the realisationof the physical component of the IHRS. In this context, thepotential values WP may be obtained using a global gravity
model of high degree (GGM-HD) or by estimating the anomalous potential TP after solving the GBVP. The potential
values are given by WP = UP + TP , where U is the potentialof an appropriately selected reference ellipsoid.
The availability of GGM-HD, like the EGM2008 model(Pavlis et al. 2013, 2012) or the EIGEN-C series (e.g., Förste
et al. 2015), makes it possible to carry out a direct computation of WP by introducing the ITRF coordinates X of any point
into the spherical harmonic expansion equation representing
a GGM-HD. However, in areas with few terrestrial gravity
data, the higher degrees of the GGM-HD do not containthe full signal of the Earth’s gravity field and the so-calledomission error increases strongly. According to Rummel etal. (n.d.), the expected accuracy after applying one of thesemodels is ±40 cm2 s−2 to ±60 cm2 s−2 (equivalent to ±4 cm
to ±6 cm) in well surveyed regions, and about ±200 cm2 s−2
to ±400 cm2 s−2 (±20 cm to ±40 cm) with extreme cases of±10 m2 s−2 (±1 m) in sparsely surveyed regions. In addition, different GGM-HD deliver different potential values
for the same position X. This is probably a combined effectof including different gravity data of high-resolution (terres-

y

gr
o
Top

h

H0
Hpid
Geo

Ellipsoi

HpNdtrial, airborne and marine gravity data) and applying different
standards, models and procedures in the estimation of the harmonic coefficients. As the realisation of the IHRS demands
the best possible accuracy of the potential values (target is the
sub-centimetre level ≈ ±10 cm2 s−2 ), the direct applicationof GGM-HD for the IHRS realisation is still considered to
be inappropriate.
Regarding the solution of the GBVP, there is a long list ofdifferent approaches depending on the observables available
for the formulation of the GVBP (e.g., Heck and Seitz 1993):
fixed GBVP (boundary surface known, 3D position of theobservables available), scalar-free GBVP (boundary surface
unknown, horizontal position of the observables available),or a vector-free GBVP (boundary surface unknown, positionof the observables unavailable). As the existing gravity databanks mainly contain gravity anomalies with latitude and longitude values, the scalar-free GBVP is the most used formulation presently. Its solution is faced applying different methodologies, for instance, the Stokes integral or the Molodensky
series with unmodified or modified kernel functions, leastsquares collocation, radial basis functions, spectral modifications, etc. A common strategy in these different methodologies is a remove-compute-restore procedure (Schwarz
et al. 1990; Tscherning 1986). It allows the combination of
the long-wavelength component provided by a satellite-only
GGM with gravity observables of high-resolution (terrestrial,274

airborne and marine gravity data, deflections of the vertical,
terrain gravity effects, etc.).
A rigorous standardisation of the method to solve the GBVP
seems to be not suitable because (1) it exists different data
availability and different data quality around the world (e.g.
terrestrial gravity data, terrain models, GPS/levelling, etc.),and (2) regions with different characteristics require particular approaches (e.g. modification of kernel functions andsize of integration caps depending on the terrestrial gravity data availability, or geophysical reductions like glacialisostatic adjustment effects, which are very much larger inpolar regions than in equatorial zones). One possibility toovercome this issue would be a centralised computation of
the potential values WP in a similar way as the IERS combination centres determine the ITRF. However, this option isstill unviable due to the restricted accessibility to terrestrial
gravity data. To exploit at maximum the existing data to get
as accurate as possible potential values, national/regional
experts in the gravity field (or geoid) modelling should be
involved in the determination of the IHRS/IHRF coordinates.
They have access not only to terrestrial gravity data but also
to terrain models of high-resolution, GNSS/levelling data,etc. The idea is that they utilise all the data they have available to determine the potential values using the computation
approaches they have implemented for their regions. However, to minimise discrepancies and to obtain as similar andcompatible results as possible with the different methods, abasic set of standards should be set up.
To advance in this purpose, during the Joint Scientific Assembly of the International Association of Geodesy (IAG)
and the International Association of Seismology and Physics
of the Earth’s Interior (IASPEI) (Kobe, Japan, Aug 2017),
it was agreed to initiate an empirical experiment (Sánchez2019) towards:• the computation of IHRF coordinates, geoid heights andheight anomalies using exactly the same input data and theown methodologies (software) of colleagues involved in
the gravity field modelling, and• the comparison of the results, to highlight the differences
caused by disparities in the computation methodologies
and to identify a set of standards that allow to get as similarand compatible results as possible.
The input data for this experiment were provided by the US
National Geodetic Survey (NGS) and contain terrestrial gravity data (59,303 points), airborne gravity data (41 lines in
E-W direction and 7 lines in N-S direction), GNSS/levelling
data (510 points) and a digital terrain model for an area of
about 500 km x 800 km in Colorado, USA. The experimentis conducted under the cooperation of

4 Product-based review• GGOS-JWG: Strategy for the Realisation of the IHRS
(chair: L. Sánchez, Germany)• IAG JWG 2.2.2: The 1 cm geoid experiment (chair: Y. M.
Wang, USA)
• IAG SC 2.2: Methodology for geoid and physical heightsystems (chair: J. Ågren, Sweden)• ICCT JSG 0.15: Regional geoid/quasi-geoid modelling– Theoretical framework for the sub-centimetre accuracy(chair: J. Huang, Canada)
The Colorado data were distributed in Feb. 2018, together
with a document summarizing a minimum set of basic requirements (standards) for the computations (see section
4.6.6). Ten different groups delivered solutions and the results were discussed during the Gravity, Geoid and Height
Systems (GGHS2018) Symposium (Copenhagen, Denmark,Sep 2018). Main conclusions are (Sánchez et al. 2018b; Wanget al. 2018):• Two solutions were declared as outliers. They present large
discrepancies (at the 1.5 m level) in (quasi-)geoid heights
as well in the potential numbers with respect to the othersolutions.
• In the geoid comparison, six solutions agree within 3 cm
to 10 cm in terms of standard deviation with respect to themean value.
• In the quasi-geoid comparison, the same six solutions
agree within 1 cm to 4 cm in terms of standard deviation
with respect to the mean value.
• In the comparison of the potential values, four solutions
agree within 1 cm to 2 cm in terms of standard deviation
with respect to the mean value.
• The discrepancies present a high correlation with the topography.
Possible sources of discrepancy are:• Different handling of terrain corrections/reductions.
• Inconsistent use of the zero-degree term.

• Precision degradation due to the conversion of height anomalies to geoid heights and vice versa.
• Uncertainties in the processing of the airborne gravity data.
To refine the results, a second computation for the Colorado
experiment was completed in Apr 2019. In total, 14 solutions
were delivered. At present, the comparison of geoid heights,
height anomalies and potential values is going on.

4.6 Height systems and their realisations

4.6.6 Preliminary standards for the IHRS realisation

This section summarises the basic agreements outlined for thecomputation of station potential values as IHRS coordinates,
geoid undulations and height anomalies within the Colorado
experiment.
They have been prepared by L. Sánchez (Deutsches Geodätisches Forschungsinstitut, Technical University Munich, Germany), J. Ågren (Lantmäteriet, Swedish mapping, cadastraland land registration authority, Sweden), J. Huang (Natural
Resources Canada, Canada), Y. M. Wang (NOAA’s National
Geodetic Survey, USA), and R. Forsberg (National Space
Institute, Denmark), see (Sánchez et al. 2018a).
Basics• The determination of station potential values WP as IHRS
coordinates is straightforward if the disturbing potential
TP is known: WP = UP + TP .
• The potential values realising the IHRS coordinates must
be determined at the reference stations; i.e., at the Earth’s
surface and not at the geoid.
• According to the IHRS definition, the station coordinateshave to be given in the mean-tide system. To be consistent
with the GBVP definition, it is recommended to performthe computations in the zero-tide system and afterwards,
to transfer the coordinates to the mean-tide system at thevery end, using simplified formulas. This keeps the computations consistent with the gravity/geoid work in zero-tide
without introducing many transformations and corrections.
• For these first experiments, we assume the Earth’s gravity
field to be stationary; i.e., time changes are disregarded sofar.
Standards
General constants (numerical values needed for the solutionof several equations):• Constant of gravitation (G)6.674 28 × 10−11 m3 kg−1 s−2• Geocentric gravitational constant (GM)
3.986 004 415 × 1014 m3 s−2 (including the Mass of the
Earth’s Atmosphere)• Nominal mean angular velocity of the Earth (ω)
7.292 115 × 10−5 rad s−1• Conventional reference potential value (W0 )62 636 853.4 m2 s−2• Average density of topographic masses (ρ)
2670 kg m−3 . This topographic density shall be assumed
when computing the geoid height.
Reference ellipsoid (to be used for the computation of gravity anomalies, disturbing potential, ellipsoidal coordinates,
geoid heights, height anomalies, etc.):

275• GRS80 parameters published by Moritz (2000). Previous
publications contain some typos in the normal gravity formulae.
• Atmospheric reduction has to be applied on the (terrestrial
and airborne) gravity data.
Global Gravity Model (GGM):• Since the disturbing potential should be estimated withhigh-precision, it is proposed to compute (a) the long wavelength component (about d/o < 200. . . 250) using a satelliteonly GGM and (b) the short wavelength component (d/o> 200. . . 250) by the combination of terrestrial (airborne,
marine and land) gravity data and detailed terrain models.
• The GGM should be at least based on the combinationof SLR (satellite laser ranging), GRACE and GOCE data,
due to the improvement offered by these data to the longwavelengths of the Earth’s gravity field modelling. Suggested models are the latest GOCO releases, i.e.,
GOCO05s, d/o=280 (Mayer-Gürr and GOCO Team 2015);
GOCO06s, d/o=300 (Kvas et al. 2019).
• Although, the use of a satellite-only GGM is preferred, thepossibility of using a combined GGM is open (combinedmeans including terrestrial gravity data). It is importantthat the satellite-only component of the combined modelis based on the combination of SLR, GRACE and GOCE
data.
• If required, the conversion between the zero-tide systemand the tide-free system should be made using:
√
TF
ZT
C̄20
− C̄20= 3.11080·10−8 × 0.3/ 5First-degree terms: The first-degree coefficients (C10 = C11 =S11 = 0) are assumed to be zero to align the Earth’s centre ofmasses with the origin of the geometric coordinate system(ITRS/ITRF). In this way, the disturbing potential T is givenby (cf. Eq. 2-170 Heiskanen and Moritz 1967):∞

T (ϑ , λ ) = T0 + T1 (ϑ , λ ) + ∑ Tn (ϑ , λ )
n=2

with

(4.3)

T1 (ϑ , λ ) = 0

Zero-degree term: The zero-degree term should be dealt with
as follows:• For the disturbing potential (T ): The zero-degree term T0
has to include the difference between the GGM and reference ellipsoid’s GM constants (cf. Eq. 2-172 Heiskanen
and Moritz 1967):
T0 = GMGGM − GMGRS80 /rP == 3.986 004 415 × 1014 m3 s−2(4.4)

14 3 −2− 3.986 00 × 10 m s /rPwith rP beeing the geocentric radial distance of the computation point P.

276

4 Product-based review• For the quasi-geoid (ζ ) or the geoid (N): In addition to
the difference between the two GM values, the difference
between the reference potential W0 value adopted by the
IHRS and the potential U0 on the reference ellipsoid has tobe considered (cf. the generalised Brun’s formula in Eq. 2178, and also Eq. 2-182 Heiskanen and Moritz 1967):

GMGGM − GMGRS80
∆W0
ζ0 =
−
rP · γQ
γQGMGGM − GMGRS80
∆W0
N0 =
−
rP0 · γQ0
γQ0

(4.5)
(4.6)

with
∆W0 = W0 −U0 == 62 636 853.4 m2 s−2 − 62 636 860.850 m2 s−2= − 7.45 m2 s−2n=2

Level surface

(4.8)

e

W (P) = U(P) + γ ζ (P) + ∆W0 .

e

m

b lin

onst.

P
W=W

TelluroidPg z

U = UQ= WPQ
acevel surf

Ea
O

H
H

e

Quasi-geoid

Potential values WP as IHRS/IHRF coordinates:To determine
the potential value WP at the stations located on the Earth’s
surface, consistency with the approach used for the estimation of the disturbing potential should be ensured. If thequasi-geoid is computed, the disturbing potential is determined at the point P on the Earth’s surface (see Fig. 4.1) andthe estimation of WP is straightforward:


∞
(4.7)
W (P) = U(P) + T (P) = U(P) + T0 + ∑ Tn (P)PlumNormal plumb line

W¹c

Geoid
Co-geoid1) To compute the quasi-geoid: compute starting with n = 2
and then add Eq. (4.5).
2) To compute the geoid: compute N starting with n = 2 andthen add Eq. (4.6).

orFigure 4.1 shows the positions of P, Q, P0 and Q0 .

leNormalAs it was stated above that the geoid/quasi-geoid should beconsistent with the IHRS reference level W0 and that GRS80
is to be used as normal gravity field/ellipsoid, it is concluded:

rth

gQ
HN
h

‘s s

urf

W

ace

¹c
on

st.

PO

W=W

gO

0

z

N
Ellipsoid

Q’O

gO

QO

W ¹ const.

W ¹ const.

U = U0Fig. 4.1: Heights and reference surfaces

4.6 Height systems and their realisations

When the geoid is computed, the disturbing potential is determined at the point P0 on the geoid (inside the Earth’s topographic masses, see Fig. 4.1) and an upward continuation
would be necessary to estimate WP on the Earth’s surface.
This upward continuation must be consistent with the hypotheses applied to reduce the gravity values from the Earth’s
surface to the geoid. Therefore, it is strongly recommended
to start from the quasi-geoid or disturbing potential at surface and then to infer the potential values WP using Eq. (4.7)
or (4.8). If the geoid computation is preferred, it would benecessary to transform N to ζ and then to infer the potential values WP with (4.7) or (4.8). The transformation fromN to ζ must be consistent with the hypotheses applied forthe geoid computation. As this transformation produces aprecision degradation, it is not desired for the computationof the potential values WP .
As mentioned in Section 4.6.5, these standards will be refined in agreement with the results of the on-going Colorado
experiment.
4.6.7 Links to other products

To best exploit the advantages offered by space geodetic
techniques, especially in the combination of GNSS positioning and satellite-based (quasi-)geoid models, modern heightsystems should support with high precision the integrationof physical and geometrical coordinates. For that purposethe interaction of the following IAG/GGOS components andproducts is necessary
GGOS Focus Area Unified Height System: to assess its
requirements for the definition and realisation of a unified
global vertical reference system.
IAG Commission 1 (Reference Frames): to identify strategies, standards and conventions needed to increase theaccuracy of the geometrical heights.
IAG Commission 2 (Gravity Field) and ISG (International Service for the Geoid): to identify strategies, standards and conventions needed to increase the accuracy ofthe (quasi-)geoid modelling.
IAG Sub-commissions 1.3 (Regional Reference Frames),
2.1 (Gravimetry and Gravity Networks) and 2.4 (Regional Geoid Determination): to assess the detailed characteristics of the existing height systems in order to extent
the global vertical reference frame activities to nationaland regional level.
IERS and IGS: to recognise the standards applied for thecomputation of the geometric vertical coordinates and toalign (if necessary) these standards with those outlined/
applied by the gravity community.
IGS Working Group Tide Gauge Benchmark Monitoring (TIGA) and Permanent Service for Mean Sea Level(PSMSL): to connect the local height-zero levels to the277

terrestrial reference frame and to model the sea surface
topography at the reference tide gauges.
IGFS and ICGEM: to identify the most appropriate global
gravity model to compute the long-wavelength components of the global reference surface.
BGI and IAG Sub-commissions 2.1 (Gravimetry andGravity Networks) and 2.4 (Regional Geoid Determination): to improve the availability of terrestrial (shipborne and airborne) gravity data for the computation of themedium-wavelength components of the global reference
surface.
IDEMS: to identify the most appropriate elevation models
to estimate the terrain effects in the (quasi-)geoid modelling (short-wavelength components of the global reference
surface).
This list is far from being complete and it includes expected products, which currently do not exist or have not been
considered by some IAG/GGOS components.
4.6.8 Open problems and recommendations

A main result of the Colorado experiment should be a document similar to the IERS conventions; i.e., a sequence ofchapters describing the different components to be considered for the realisation of the IHRS and its practical utilisation. Based on these conventions, a first solution for the
IHRF should be computed. The aim of this first solution isto evaluate the achievable accuracy under the present conditions (data availability, computation methods, etc.) andto identify key actions to improve the determination of the
IHRS/IHRF coordinates. These key actions include an investigation about the best way to establish an IHRS/IHRF
element within the IGFS to ensure the maintenance and availability of the IHRF. This implies regular updates of the IHRFyy to take account for new stations, coordinate changes withtime, improvements in the estimation of coordinates (moreobservations, better standards, better models, better computation algorithms, etc.), geodetic products associated to the
IHRF (description and metadata), and the organisational andoperational infrastructure to ensure the IHRF sustainability.
To improve the standardisation of the existing height systems,
it is necessary, among other issues, that meta-data describing
the characteristics of the existing height systems be implemented. These meta-data should include for instance:• epoch and time span applied for the mean sea level introduced as a zero-height;• changes of the mean sea level and vertical position of thereference tide gauges;• information about the levelling techniques applied to extend the vertical control through the countries;• gravity reductions applied to the measured level differences;• precision of levelling and gravity data;278• epoch and tide system to which the vertical coordinates
refer, etc.
When this information is available, it would be possible totransform the existing physical heights in such a way that they
can be combined with GNSS positioning and (quasi-)geoid
models consistently. For that purpose, it is necessary to involve the national agencies responsible for the maintenanceof vertical networks.
Since the vertical datum unification is based on the combination of levelling data (+ gravity reductions), GNSS positioning and (quasi-)geoid modelling, it is convenient tooutline the minimal requirements to be satisfied by thosestations used for this purpose. For instance, it is well-known
that the vertical coordinates derived from GNSS positioning are strongly influenced by systematic errors and physical phenomena that reduce their accuracy considerably. The
determination of the level discrepancies between different
height systems should be determined including the mostprecise ellipsoidal heights only; i.e., at ITRF stations andregional densification stations like EPN, SIRGAS, NAREF,
etc. These stations must also be connected by spirit levellingto the reference tide gauges; and gravity measurements along
the levelling lines must be available for the computation of
the corresponding geopotential numbers. Complementarily,
the geoid models of high resolution should be estimated in aconsistent manner. Currently, the geoid computation is not aunified or standardised procedure, and it is possible to finddifferent geoid models over the same region although they arebased on the same input data, i.e., there are as many geoids
as computations. In addition, it is usual to compute improved
geoid models, if new gravity data and new analysis strategies are available; however, it is not clear how frequently thegeoid should be updated.
From the organisational point of view, it is necessary that
the IAG/GGOS components named in the previous section
precisely outline which products are under their responsibility and how they are generated. As a first step, a description
similar to the IERS Conventions should be implemented foreach product. The standards outlined by each IAG/GGOS
component must be classified into a hierarchical structure,
showing which of them have to be followed by everyone,
which of them are applicable in geometry or gravity only,
which of them are technique-specific, etc. Missing products
must be identified and the necessary actions taken for theirgeneration. This procedure has to be extended also to themarine and fluvial areas. At present, the discussion concentrates on the height systems on land areas; but the verticalcoordinates on water and ice areas should also refer to thesame global unified height system.

4 Product-based review

Summary of recommendations on height systems
Recommendation 6.1: It is necessary that the IAG/GGOS
components involved in the vertical coordinate determination should outline precisely which products are under
their responsibility and how they are generated.
Recommendation 6.2 : To achieve the standardisation of
the existing height systems, it is necessary, among others,
that meta-data describing the characteristics of the existingheight systems be implemented.
Recommendation 6.3 : Since the vertical datum unification
is based on the combination of levelling data (+ gravity reductions), GNSS positioning, and (quasi-)geoid modelling,
the minimal requirements to be used for stations should beoutlined.
Recommendation 6.4 : The GGOS Focus Area Unified
Height System, the IAG Commission 2 (Gravity Field)
and the IGFS should investigate the best way to establish
an IHRS/IHRF element within the IGFS to ensure themaintenance and availability of the IHRF and its products.

279

5 Summary
The GGOS Bureau of Products and Standards (BPS) has
compiled an inventory of standards and conventions used forthe generation of IAG products. The first version of this document has been published in the Geodesists Handbook 2016.
During the last four years, the inventory has been updated toincorporate the changes and new developments concerning
standards, conventions and the generation of IAG products.
This second version of the document has been prepared forthe publication in the Geodesists Handbook 2020.
According to its Terms of Reference, a key activity of the
BPS is to assess the standards and conventions adopted andused by IAG and its components for the processing of geometric and gravimetric observations as basis for the generationof IAG products. The work has been performed in cooperation with the IAG Services and the other entities involvedin standards and conventions, such as IAU, ISO, CODATA
and the UN-GGIM Subcommittee on Geodesy. The overall
objective of this inventory is to evaluate the present statusconcerning standards and geodetic products, to identify gaps
and shortcomings, and to provide recommendations for improvements. In this way, the BPS supports IAG in its goal toobtain geodetic products of highest accuracy and consistency.
This second version of the inventory includes an update of
the GGOS structure and the BPS activities. It also comprises
various updates in the field of standards and conventions,such as the newly released ISO standards by ISO/TC211 covering geographic information and geomatics, the activities of
the GGRF Working Group “Data Sharing and Developmentof Geodetic Standards” within the UN-GGIM Subcommittee
on Geodesy, the re-writing/revising of the IERS Conventions
initiated by the IERS Conventions Centers, and the recently
adopted resolutions by IAG, IUGG and IAU that are relevantfor geodetic standards and products. An open problem is thecurrent situation concerning numerical standards includingtime and tide systems. The fact that various definitions are in
use within the geodetic community is a potential source for inconsistencies and even errors of geodetic products. The BPS
recommends that these inconsistencies need be resolved andthat a new Geodetic Reference System should be developed.
Since 2016, new IERS products have been released for thecelestial and terrestrial reference frame as well as for the
EOP, namely ICRF3, ITRF2014 and EOP 14C04. Althougha significant progress has been achieved compared to the previous realisations, there are still some deficiencies and open
problems that are addressed in this inventory, and recommendations are provided to further improve the accuracy andconsistency of these products. Concerning GNSS satellite
orbits the modelling has been improved and some missing
information has been provided by the satellite operators, butthere are still some remaining deficiencies. A remarkableprogress has been achieved in the field of gravity and geoid
related data and products, including the establishment of the
IGFS Central Bureau and the development of a dedicateddata and products portal based on online applications for thecreation of metadata for gravity and geoid data. Finally, thelatest developments in the field of height systems and theirrealisations are reported, open problems are discussed andrecommendations towards the realisation of the IHRS areprovided.
This inventory will be updated on a regular basis to incorporate the latest developments regarding standards and geodetic
products. Thereby, also the ongoing activities of IAG towards
the development of new products need to be incorporated in
the updates of this inventory.

280

Glossary

Glossary
AAM
AC
ACC
AGN

Atmospheric Angular Momentum.
Analysis Centre.
Analysis Centre Coordinator.
Active Galactic Nuclei.

FGS
FICN
FK5
FOC

BCRS
BGI
BIH
BIPM
BPS
BSC
BTM

Barycentric Celestial Reference System.
Bureau Gravimétrique International.
Bureau International de l’Heure.
Bureau International de Poids et Mesures.
GGOS Bureau of Products and Standards.
GGOS Bureau for Standards and Conventions.
Bathymetric Terrain Model.

GCRS
GEO
GEOSS
GFZ

CAO
Cabinet Office, Government of Japan.
CBE
Current Best Estimates.
CEOS
Committee of Earth Observation Satellites.
CIP
Celestial Intermediate Pole.
CIRS
Celestial Intermediate Reference System.
CMCentre of Mass.
CODATA Committee on Data for Science and Technology.
CODE
Center for Orbit Determination in Europe.
COST-G International Combination Service forTime-variable Gravity Fields.
CPO
Celestial Pole Offset.
CSNO
China Satellite Navigation Office.
CTRS
Conventional Terrestrial Reference System.
DEM
Digital Elevation Model.
DGFI-TUM Deutsches Geodätisches Forschungsinstitut,
Technische Universität München.
DLR
Deutsches Zentrum für Luft- und Raumfahrt.
DOI
Digital Object Identifier.
DORIS Doppler Orbit Determination andRadiopositioning Integrated by Satellite.
ECMWF European Centre for Medium-Range Weather
Forecasts.
ECOM Empirical CODE Orbit Model.
EGM 2008 Earth Gravitation Model 2008.
EGV
Essential Geodetic Variables.
EOP
Earth Orientation Parameters.
EOSDIS NASA’s Earth Observing System Data andInformation System.
EPN
EUREF Permanent GNSS Network.
EPOS
European Plate Observing System.
ERP
Earth Rotation Parameters.
ESA
European Space Agency.
EUREF IAG Reference Frame Sub-Commission for
Europe.
FCNFree Core Nutation.

Forschungsgruppe Satellitengeodäsie.
Free Inner Core Nutation.
Fifth Catalogue of Fundamental Stars.
Full Operational Capability.

Geocentric Celestial Reference System.
Group on Earth Observation.
Global Earth Observation System of Systems.
Helmholtz Centre Potsdam, German ResearchCentre for Geosciences.
GGIM
Global Geospatial Information Management.
GGOS
Global Geodetic Observing System.
GGRF
Global Geodetic Reference Frame.
GIAC
GGOS Inter Agency Committee.
GIS
Geographic Information System.
GLONASS Globalnaja nawigazionnaja sputnikowaja
sistema.
GMF
Global Mapping Function.
GNSS
Global Navigation Satellite System.
GPS
Global Positioning System.
GPT
Global Pressure and Temperature.
GPT2
Global Pressure and Temperature 2.
GRACE Gravity Recovery And Climate Experiment.
GRACE-FO Gravity Recovery And Climate Experiment –Follow On.
GRS
Geodetic Reference System.
GRS80 Geodetic Reference System 1980.
GSFC
Goddard Space Flight Center.
GSPM
GPS Solar Pressure Model.
International Association of Geodesy.
International Absolute Gravity Basestation
Network.
IAPG
Ingenieurinstitut für Astronomische und
Physikalische Geodäsie, Technische Universität
München.
IAU
International Astronomical Union.
ICGEM International Centre for Global Earth Models.
ICRF
International Celestial Reference Frame.
ICRF2
Second Realization of the International Celestial
Reference Frame.
ICRSInternational Celestial Reference System.
IDEMS International Digital Elevation Model Service.
IDS
International DORIS Service.
IERS
International Earth Rotation and Reference
Systems Service.
IGETS International Geodynamics and Earth Tide
Service.
IGFS
International Gravity Field Service.
IGFS CB IGFS Central Bureau.
IAG
IAGBN

Glossary

IGN
IGS
IGSN71
IGSO
IHRF
IHRS
ILRS
IOV
IRNSS
ISC
ISG
ISO
ITRF
ITRS
IUGG
IVS

281

Institut National de l’Information Géographiqueet Forestiere, France.
International GNSS Service.
International Gravity Standardization Net 1971.
Inclined Geo-Synchronous Earth Orbit.
International Height Reference Frame.
International Height Reference System.
International Laser Ranging Service.
In-Orbit Validation.
Indian Regional Navigation Satellite System.
International Science Council.
International Service for the Geoid.
International Organization for Standardization.
International Terrestrial Reference Frame.
International Terrestrial Reference System.
International Union of Geodesy and Geophysics.
International VLBI Service for Geodesy andAstrometry.

JPL

Jet Propulsion Laboratory.

LEO
LLR
LOD

Low Earth Orbiter.
Lunar Laser Ranging.
Length of Day.

MEO
Medium Earth Orbit.
MGEX Multi-GNSS Pilot Project.
MGWG Multi-GNSS Working Group.
NAGU
Notice Advisory to Galileo Users.
NAGU
Notice Advisory to GLONASS Users.
NANU
Notice Advisory to NAVSTAR Users.
NAQU
Notice Advisory to QZSS Users.
NAREF North American Reference Frame.
NASA
National Aeronautics and Space Administration.
NAVGEM US Navy’s Global Environmental Model.
NCEP
National Centers for Environment Prediction.
NGS
National Geodetic Survey.
NIST
National Institute of Standards and Technology.
NNR
No-Net-Rotation.
NSFA
IAU Division A Working Group NumericalStandards for Fundamental Astronomy.
OAM
OGC
OHI
OMCT

Oceanic Angular Momentum.
Open Geospatial Consortium.
Operational History Information.
Ocean Model for Circulation and Tides.

PCO
PCV
PREM
PSMSL

Phase Centre Offset.
Phase Centre Variation.
Preliminary Reference Earth Model.
Permanent Service for Mean Sea Level.

QZSS

Quasi-Zenith Satellite System.

SLR
SOFA
SRP

Space Based Augmentation System.
Subcommittee on Geodesy (UN-GGIM).
International System of Units.
Solution INdependent EXchange format.
Sistema de Referencia Geocéntrico para las
Américas (Geocentric Reference Frame for theAmericas).
Satellite Laser Ranging.
Standards of Fundamental Astronomy.
Solar Radiation Pressure.

TCG
TDB
TEC
TIGA
TIRS
TRF
TRS
TT

Geocentric Coordinate Time.
Barycentric Dynamical Time.
Total Electron Content.
Tide Gauge Benchmark Monitoring.
Terrestrial Intermediate Reference System.
Terrestrial Reference Frame.
Terrestrial Reference System.
Terrestrial Time.

SBAS
SCoG
SI
SINEX
SIRGAS

UN
United Nations.
UN-GGIM UN Committee of Experts on Global
Geospatial Information Management.
USNO
United States Naval Observatory.
UTC
Coordinated Universal Time.
VLBI

Very Long Baseline Interferometry.

WGM
WGRF

World Gravity Map.
IAU Working Group on Reference Frames.

ZTD

Zenith Total Delay.

282

Bibliography

Bibliography
Abbondanza, C., T. M. Chin, R. S. Gross, M. Heflin, J. Parker,
B. Soja, T. van Dam and X. Wu (2017): ‘JTRF2014,
the JPL Kalman filter and smoother realization of theInternational Terrestrial Reference System’. In: Journal of Geophysical Research: Solid Earth 122.8. DOI:
10.1022/2017JB014360.
Altamimi, Z., X. Collilieux and L. Métivier (2011): ‘ITRF
2008: an improved solution of the International Terrestrial Reference Frame’. In: Journal of Geodesy 85.8,
pp. 457–473. DOI: 10.1007/s00190-011-0444-4.
Altamimi, Z. and W. Dick (2020): ‘Description and evaluation of DTRF2014, JTRF2014 and ITRF2014’. In:
IERS Technical Note No. 40. Bundesamt für Kartographie und Geodäsie, Frankfurt am Main.
Altamimi, Z., L. Métivier and X. Collilieux (2012): ‘ITRF
2008 plate motion model’. In: Journal of GeophysicalResearch 117.B7. DOI: 10.1029/2011JB008930.
Altamimi, Z., P. Rebischung, L. Metivier and X. Collilieux(2017): ‘Analysis and Results of ITRF2014’. In: IERS
Technical Note No. 38. Bundesamt für Kartographie
und Geodäsie, Frankfurt am Main.
Altamimi, Z., P. Rebischung, L. Métivier and X. Collilieux(2016): ‘ITRF2014: A new release of the International
Terrestrial Reference Frame modeling nonlinear station
motions’. In: Journal of Geophysical Research: Solid
Earth 121.8, pp. 6109–6131. DOI: 10.1002/2016JB013
098.

Angermann, D., T. Gruber, M. Gerstl, R. Heinkelmann, U.
Hugentobler, L. Sánchez and P. Steigenberger (2018):‘GGOS Bureau of Products and Standards: Recent Activites and Future Plans.’ In: International Symposium on
Advancing Geodesy in a Changing World. Ed. by J.
Freymueller and L. Sánchez. International Associationof Geodesy Symposia 149, pp. 153–159. Springer,
Cham. DOI: 10.1007/1345_2018_28.
Argus, D. F. and R. G. Gordon (1991): ‘No-net-rotation
model of current plate velocities incorporation platemotion model NUVEL-1’. In: Geophysical Research
Letters 18.8, pp. 2038–2042. DOI: 10.1029/91GL01532.
Argus, D. F., R. G. Gordon and C. DeMets (2011): ‘Geologically current motion of 56 plates relative to the nonet-rotation model reference frame’. In: Geochemistry,
Geophysics, Geosystems 12.11. DOI: 10.1029/2011GC003751.
Arias, E. F., P. Charlot, M. Feissel and J.-F. Lestrade (1995):‘The extragalactic reference system of the International
Earth Rotation Service, ICRS’. In: Astronomy and Astrophysics 303, pp. 604–608.
Arias, E. F. and M. Feissel (1990): ‘The celestial system of
the International Earth Rotation Service’. In: Proceedings of the Symposium of the International Astronomical
Union. Ed. by J. H. Lieske and V. K. Abalakin. Vol. 141,
pp. 119–128. Springer.

Amiri-Simkooei, A. R. (2013): ‘On the nature of GPS draconitic year periodic pattern in multivariate position
time series’. In: Journal of Geophysical Research 118.5.
DOI : 10.1002/jgrb.50199.

Arias, E. F., M. Feissel and J.-F. Lestrade (1988): An extragalactic reference frame consistent with the BIH Terrestrial System (1987). BIH Annual Report, pp. D-113–
D-121.

Anderson, J., M. Xu, R. Heinkelmann, S. Lunz and H. Schuh(2019): ‘Source Structure Effects’. In: Unified Analysis
Workshop 2019. URL: http://www.ggos.org/en/unifiedanalysis-workshop-2019/presentations/.

—

Angermann, D. (2012): ‘Standards and Conventions for Geodesy’. In: Journal of Geodesy 86.10: The Geodesist’s
Handbook 2012. Ed. by H. Drewes, H. Hornik, J. Ádámand S. Rózsa, pp. 961–963. DOI: 10.1007/s00190-0120584-1.
Angermann, D., T. Gruber, M. Gerstl, R. Heinkelmann, U.
Hugentobler, L. Sánchez and P. Steigenberger (2016):‘GGOS Bureau of Products and Standards: Inventoryof standards and conventions used for the generationof IAG products’. In: Journal of Geodesy 90.10: The
Geodesist’s Handbook 2016. Ed. by H. Drewes, F. Kuglitsch, J. Ádám and S. Rózsa, pp. 1095–1156. DOI:
10.1007/s00190-016-0948-z.

(1991): The IERS extragalactic Celestial Reference
Frame and its tie with HIPPARCOS. IERS Technical
Note 7. Observatoire de Paris.

Arnold, D., M. Meindl, G. Beutler, R. Dach, S. Schaer, S.
Lutz, L. Prange, K. Sośnica, L. Mervart and A. Jäggi(2015): ‘CODE’s new empirical orbit model for the
IGS’. In: Journal of Geodesy 89.8, pp. 775–791. DOI:
10.1007/s00190-015-0814-4.
Bachmann, S., D. Thaller, O. Roggenbuck, M. Lösler and L.
Messerschmidt (2016): ‘IVS contribution to ITRF2014’.
In: Journal of Geodesy 90.7, pp. 631–654. DOI: 10.100
7/s00190-016-0899-4.
Bar-Sever, Y. and D. Kuang (2005): New Empirical Derived
Solar Radiation Pressure Model for Global Positioning
System Satellites During Eclipse Seasons. Tech. rep.
IPN Progress Report.

Bibliography

Bawden, G. W., W. Thatcher, R. S. Stein, K. W. Hudnut
and G. Peltzer (2001): ‘Tectonic contraction across
Los Angeles after removal of groundwater pumping effects’. In: Letters to Nature 412, pp. 812–815. DOI:
10.1038/35090558.
Beutler, G., E. Brockmann, W. Gurtner, U. Hugentobler, L.
Mervart, M. Rothacher and A. Verdun (1994): ‘Extended orbit modeling techniques at the CODE processing
center of the international GPS service for geodynamics (IGS): theory and initial results’. In: Manuscripta
Geodaetica 19, pp. 367–386.
Beutler, G., J. Kouba and T. Springer (1995): ‘Combining
the orbits of the IGS Analysis Centers’. In: Bulletin
Geodesique 69, pp. 200–222.
Bevis, M. and A. Brown (2014): ‘Trajectory models and reference frames for crustal motion geodesy’. In: Journalof Geodesy 88.3, pp. 283–311. DOI: 10.1007/s00190-0
13-0685-5.
Bhattarai, S., M. Ziebart, S. Allgeier, S. Grey, T. Springer,
D. Harrison and Z. Li (2019): ‘Demonstrating developments in high-fidelity analytical radiation force modelling methods for spacecraft with a new model for GPS
IIR/IIR-M’. In: Journal of Geodesy 93.9, pp. 1515–
1528. DOI: 10.1007/s00190-019-01265-7.
Biancale, R. and A. Bode (2006): Mean annual and seasonal atmospheric tide models based on 3-hourly and6-hourly ECMWF surface pressure data. ScientificTechnical Report STR06/01. Deutsches GeoForschungsZentrum, Potsdam.
Bizouard, C. and D. Gambis (2009): ‘The combined Solution
C04 for Earth Orientation Parameters, Recent Improvements’. In: Geodetic Reference Frames. Ed. by H.
Drewes. International Association of Geodesy Symposia 134, pp. 265–270. Springer, Berlin, Heidelberg.
DOI : 10.1007/978-3-642-00860-3.
Bizouard, C., C. Lambert, O. Becker and J.-Y. Richard(2017): combined solution C04 for Earth Orientation
Parameters consistent with the International Terrestrial
Reference Frame 2014. Tech. rep. URL: ftp://hpiers.obs
pm.fr/iers/eop/eopc04/C04.guide.pdf.
Bizouard, C., S. Lambert, C. Gattano, O. Becker and J.-Y.
Richard (2019) : ‘The IERS EOP 14C04 solution
for Earth orientation parameters consistent with ITRF
2014’. In: Journal of Geodesy 93.5, pp. 621–633. DOI:
10.1007/s00190-018-1186-3.
Blewitt, G. (2003): ‘Self-consistency in reference frames,
geocenter definition, and surface loading of the solid
Earth’. In: Journal Geophysical Research 108.B2. DOI:
10.1029/2002JB002082.

283

Blossfeld, M., M. Seitz and D. Angermann (2014): ‘Nonlinear station motions in epoch and multi-year reference
frames’. In: Journal of Geodesy 88.1, pp. 45–63. DOI:
10.1007/s00190-012-1547-6.
Boedecker, G. (1988): International Absolute Gravity Basestation Network (IAGBN). Absolute gravity observations data processing standards and station documentation. Bull. Inf. 63, pp. 51–57. Bureau GravimétriqueInternational.
Böhm, J., B. Werl and H. Schuh (2006): ‘Troposphere mapping functions for GPS and Very Long Baseline Interferometry from European Centre for Medium-Range
Weather Forecasts operational analysis data’. In: Journal of Geophysical Research 111, B02406. DOI: 10.102
9/2005JB003629.
Borrass, E. (1911): ‘Bericht über die relativen Messungender Schwerkraft mit Pendelapparaten in der Zeit von1808 bis 1909 und über ihre Darstellung im Potsdamer
Schweresystem’. German. In: Teil 3: Spezialberichtüber die relativen Schweremessungen. Verhandlungender 16. allgemeinen Konferenz der internationalen Erdmessung.
Bureau International des Poids et Mesures (2006): The International System of Units (SI). 8th ed. URL: www.bipm.org/en/si/si_brochure.
Bury, G., K. Sośnica, R. Zajdel and D. Strugarek (2020):‘Toward the 1-cm Galileo orbits: challenges in modelingof perturbing forces’. In: Journal of Geodesy 94.2. DOI:
10.1007/s00190-020-01342-2.
Bury, G., R. Zajdel and K. Sośnica (2019): ‘Accounting for
perturbing forces acting on Galileo using a box-wingmodel’. In: GPS Solutions 23.3. DOI: 10.1007/s10291019-0860-0.
Cabinet Office (2019a): QZS-1 Satellite Information. Tech.
rep. SPI_QZS1_A. Government of Japan, National
Space Policy Secretariat. URL: https://qzss.go.jp/en/tec
hnical/qzssinfo/khp0mf0000000wuf-att/spi-qzs1_a.pd
f (visited on 11/12/2019).
—(2019b): QZS-2 Satellite Information. Tech. rep. SPIQZS2_C. Government of Japan, National Space Policy
Secretariat. URL: https://qzss.go.jp/en/technical/qzssin
fo/khp0mf0000000wuf-att/spi-qzs2_c.pdf (visited on
11/12/2019).

—(2019c): QZS-3 Satellite Information. Tech. rep. SPIQZS3_B. Government of Japan, National Space Policy
Secretariat. URL: https://qzss.go.jp/en/technical/qzssin
fo/khp0mf0000000wuf-att/spi-qzs3_b.pdf (visited on
11/12/2019).

284

Cabinet Office (2019d): QZS-4 Satellite Information. Tech.
rep. SPI-QZS4_C. Government of Japan, National
Space Policy Secretariat. URL: https://qzss.go.jp/en/technical/qzssinfo/khp0mf0000000wuf-att/spi-qzs4_c.pdf (visited on 11/12/2019).
— (2019e): The history information of QZS-1 operation.
Tech. rep. OHI-QZS1. Government of Japan, National
Space Policy Secretariat. URL: https://qzss.go.jp/en/tec
hnical/qzssinfo/khp0mf0000000wuf-att/ohi-qzs1_201
91002.pdf (visited on 13/02/2020).
— (2020a): The history information of QZS-2 operation.
Tech. rep. OHI-QZS2. Government of Japan, National
Space Policy Secretariat. URL: https://qzss.go.jp/en/tec
hnical/qzssinfo/khp0mf0000000wuf-att/ohi-qzs2.pdf(visited on 13/02/2020).
— (2020b): The history information of QZS-3 operation.
Tech. rep. OHI-QZS3. Government of Japan, National
Space Policy Secretariat. URL: https://qzss.go.jp/en/tec
hnical/qzssinfo/khp0mf0000000wuf-att/ohi-qzs3_202
00203.pdf.
— (2020c): The history information of QZS-4 operation.
Tech. rep. OHI-QZS4. Government of Japan, National
Space Policy Secretariat. URL: https://qzss.go.jp/en/tec
hnical/qzssinfo/khp0mf0000000wuf-att/ohi-qzs4_202
00203.pdf (visited on 25/04/2019).
Capitaine, N. (2013): ‘New concepts and models for Earthorientation transformation’. Tutorial. In: Journées 2013
Systèmes de référence spatio-temporels. Observatoirede Paris. URL: https://syrte.obspm.fr/jsr/journees2013/p
owerpoint/Tutorial-EOP-Capitaine-jsr13.pdf.
Capitaine, N., D. Gambis, D. D. McCarthy, G. Petit, J. Ray,B. Richter, M. Rothacher, E. M. Standish and J. Vondrak (2002): Proceedings of the IERS Workshop on
the Implementation of the New IAU Resolutions. IERS
Technical Note 29. Bundesamt für Kartographie undGeodäsie, Frankfurt am Main.
Capitaine, N., P. T. Wallace and J. Chapront (2003): ‘Expression for IAU 2000 precession quantities’. In: Astronomy
and Astrophysics 412.2, pp. 567–586. DOI: 10.1051/00
05-6361:20031539.
Carrere, L., F. Lyard, M. Cancet and A. Guillot (2015): ‘FES
2014, a new tidal model on the global ocean with enhanced accuracy in shallow seas and in the Arctic region’. In: Geophysical Research Abstracts. Vol. 17.
EGU2015-5481-1. URL: https://meetingorganizer.copernicus.org/EGU2015/EGU2015-5481-1.pdf.
Cartwright, D. E. and A. C. Edden (1973): ‘Corrected Tablesof Tidal Harmonics’. In: Geophysical Journal of theRoyal Astronomical Society 33.3, pp. 253–264. DOI:
10.1111/j.1365-246X.1973.tb03420.x.

Bibliography

Cartwright, D. E. and R. J. Tayler (1971): ‘New Computations of the Tide-generating Potential’. In: GeophysicalJournal of the Royal Astronomical Society 23.1, pp. 45–
73. DOI: 10.1111/j.1365-246X.1971.tb01803.x.
Charlot, P. et al. (2020): ‘The Third Realization of the International Celestial Reference Frame by Very Long
Baseline Interferometry’. In: Astronomy & Astrophysics. in review.
Collilieux, X., Z. Altamimi, J. Ray, T. van Dam and X. Wu(2009): ‘Effect of the satellite laser ranging network
distribution on geocenter motion estimates’. In: Journalof Geophysical Research 114.B4. DOI: 10.1029/2008.JB005727.
CSNO (2019a): Announcement on the release of Beidou satellite related parameters. in Chinese. URL: http://www.beidou.gov.cn/yw/gfgg/201912/t20191209_19613.html.
— (2019b): Announcement: Release of the BDS-2 Satellite
Related Parameters. URL: http : / / en . beidou . gov . cn
/WHATSNEWS/201912/t20191209_19641.html.
— (2019c): Definitions and descriptions of BDS/GNSS
satellite parameters for high precision applications.
Tech. rep. BD 420025-2019. in Chinese. URL: http://www.beidou.gov.cn/yw/gfgg/201911/W020191126
317485269344.pdf.
Dach, R., J. Böhm, S. Lutz, P. Steigenberger and G. Beutler (2011): ‘Evaluation of the impact of atmosphericpressure loading modeling on GNSS data analysis’. In:
Journal of Geodesy 85.2, pp. 75–91. DOI: 10.1007/s001
90-010-0417-z.
Dahle, C., F. Flechtner, C. Gruber, D. König, R. König,G. Michalak and K.-H. Neumayer (2013) : GFZ
GRACE Level-2 Processing Standards Document forLevel-2 Product Release 0005: revised edition, January 2013. Scientific Technical Report STR 12/02 rev.
ed. Deutsches GeoForschungsZentrum, Potsdam. DOI:
10.2312/GFZ.b103-1202-25.
van Dam, T., X. Collilieux, J. Wuite, Z. Altamimi and J. Ray(2012): ‘Nontidal ocean loading: amplitudes and potential effects in GPS height time series’. In: Journal of
Geodesy 88.11, pp. 1043–1057. DOI: 10.1007/s00190012-0564-5.
Darugna, F., P. Steigenberger, O. Montenbruck and C. S.
(2018): ‘Ray-tracing solar radiation pressure modelingfor QZS-1’. In: Advances in Space Research 62.4, pp.
935–943. DOI: 10.1016/j.asr.2018.05.036.
Davis, J. L., T. A. Herring, I. I. Shapiro, A. E. E. Rogers and
G. Elgered (1985): ‘Geodesy by radio interferometry:
Effects of atmospheric modeling errors on estimates ofbaseline length’. In: Radio Science 20.6, pp. 1593–1607.
DOI : 10.1029/RS020i006p01593.

Bibliography

Davis, J. L., B. P. Wernicke and M. E. Tamisiea (2012): ‘Onseasonal signals in geodetic time series’. In: Journal ofGeophysical Research 117.B1. DOI: 10.1029/2011JB00
8690.
DeMets, C., R. G. Gordon and D. F. Argus (2010): ‘Geologically current plate motions’. In: Geophysical JournalInternational 181.1, pp. 1–80. DOI: 10.1111/j.1365-24
6X.2010.04491.x.
DeMets, C., R. G. Gordon, D. F. Argus and S. Stein (1990):‘Current plate motions’. In: Geophysical Journal International 101.2, pp. 425–478.
—(1994): ‘Effect of recent revisions of the geomagnetic
reversal timescale on estimates of current plate motions’.
In: Geophysical Research Letters 21.20, pp. 2191–2194.
DOI : 10.1029/94GL02118.

Denker, H. (2013): ‘Regional gravity field modelling: Theory and practical results’. In: Sciences of Geodesy – II.
Ed. by G. Xu. Springer, pp. 185–291. DOI: 10.1007/97
8-3-642-28000-9.
Desai, S. D. (2002): ‘Observing the pole tide with satellite altimetry’. In: Journal of Geophysical Research: Oceans
107.C11, pp. 1–13. DOI: 10.1029/2001JC001224.
Desai, S. D. and A. E. Sibois (2016): ‘Evaluating predicted
diurnal and semidiurnal tidal variations in polar motion
with GPS-based observations’. In: Journal of Geophysical Research: Solid Earth 121.7, pp. 5237–5256. DOI:
10.1002/2016JB013125.
Dilssner, F. (2010): ‘GPS IIF-1 satellite: Antenna Phase
Center and Attitude Modeling’. In: Inside GNSS 5.6,
pp. 59–64.
—(2017): A note on the yaw attitude modeling of BeiDou
IGSO-6. Tech. rep. ESA/ESOC. URL: http://navigat
ion-office.esa.int/attachments_24576369_1_BeiDou_IGSO-6_Yaw_Modeling.pdf.

Dilssner, F., T. Springer, G. Gienger and J. M. Dow (2010):‘The GLONASS-M satellite yaw-attitude model’. In:
Advances in Space Research 47.1, pp. 160–171. DOI:
10.1016/j.asr.2010.09.007.
Dong, D., T. Yunck and M. Heflin (2003): ‘Origin of theInternational Terrestrial Reference Frame’. In: Journal
Geophysical Research 108.B4. DOI: 10/1029/2002JB00
22035.
Doodson, A. T. (1921): ‘The Harmonic Development of
the Tide-Generating Potential’. In: Proceedings of theRoyal Society of London. Series A 100.704, pp. 305–329.
DOI : 10.1098/rspa.1921.0088.
Dow, J. M., R. E. Neilan and C. Rizos (2009): ‘The International GNSS Service in a changing landscape of Global
Navigation Satellite Systems’. In: Journal of Geodesy
83.3-4, pp. 379–387. DOI: 10.1007/S00190-008-03003.

285

Drewes, H. (2008): ‘Standards and conventions relevant forgeodesy’. In: Journal of Geodesy 82.11: The Geodesist’s
Handbook 2008. Ed. by H. Drewes, H. Hornik, J. Ádámand S. Rózsa, pp. 833–835. DOI: 10.1007/s00190-0080259-0.
—(2009): ‘The actual plate kinematic and crustal deformation model APKIM2005 as basis for a non-rotating
ITRF’. In: Geodetic Reference Frames. Ed. by H.
Drewes. International Association of Geodesy Symposia 134, pp. 95–99. Springer, Berlin Heidelberg. DOI:
10.1007/978-3-642-00860-3.

— (2012): ‘How to fix the geodetic datum for reference
frames in geosciences applications?’ In: Geodesy for
Planet Earth. Ed. by S. Kenyon, M. Pacino and U.
Marti. International Association of Geodesy Symposia
136, pp. 67–76. Springer, Berlin, Heidelberg. DOI:
10.1007/978-3-642-20338-1.
Drewes, H., F. Kuglitsch, J. Ádám and S. Rózsa (2016): ‘The
Geodesist’s Handbook 2016’. In: vol. 90. 10, pp. 981–
982. DOI: 10.1007/s00190-016-0948-z.
Dziewonski, A. M. and D. L. Anderson (1981): ‘Preliminaryreference Earth model’. In: Physics of the Earth andPlanetary Interiors 25.4, pp. 297–356. DOI: 10.1016/00
31-9201(81)90046-7.
Egbert, G. D., A. F. Bennett and M. G. G. Foreman (1994):‘TOPEX/POSEIDON tides estimated using a global inverse model’. In: Journal of Geophysical Research:
Oceans 99.C12, pp. 24821–24852. DOI: 10.1029/94JC0
1894.
Ekman, M. (1995): ‘What is the geoid?’ In: vol. 95. Reportsof the Finnish Geodetic Institute 4. Finnish Geodetic
Institute, pp. 49–51.
European GOCE Gravity Consortium (2014): GOCE HighLevel Processing Facility – GOCE Standards. Ed. by
T. Gruber, O. Abrikosov and U. Hugentobler. Technical
Note GO-TN-HPF-GS-011. ESA. 81 pp.
Farrell, W. E. (1972): ‘Deformation of the Earth by surface
loads’. In: Reviews of Geophysics 10.3, pp. 761–797.
DOI : 10.1029/RG010i003p00761.
Ferrándiz, J. M. and R. S. Gross (2015): ‘Report on the activies of the IAG/IAU Joint Working Group on Theoryof Earth Rotation’. In: IAG 150 Years. Ed. by C. Rizos and P. Willis. International Association of Geodesy
Symposia 143, pp. 533–538. Springer, Cham. DOI:
10.1007/1345-2015-166.
Ferrandiz, J. and A. Escapa (2019): ‘Review of Nutation
Issues’. In: Unified Analysis Workshop 2019.

286

Fey, A. L., D. Gordon and C. S. Jacobs, eds. (2009): The
Second Realization of the International Celestial Reference Frame by Very Long Baseline Interferometry.
IERS Technical Note 35. Bundesamt für Kartographie
und Geodäsie, Frankfurt am Main. URL: www.iers.org/IERS/EN/Publications/TechnicalNotes/tn35.html.
Fey, A. L., C. Ma, E. F. Arias, P. Charlot, M. Feissel-Vernier,A.-M. Gontier, C. S. Jacobs, J. Li and D. S. MacMillan (2004): ‘The second extension of the International
Celestial Reference Frame: ICRF-Ext.1.’ In: The Astronomical Journal 127.12, pp. 3587–3608.
Fey, A. L. et al. (2015): ‘The second Realization of theInternational Celestial Reference Frame by Very Long
Baseline Interferometry’. In: The Astronomical Journal
150.58, pp. 3587–3608. DOI: 10.1088/0004-6256/150/2/58.
Fliegel, H. F. and T. E. Gallini (1996): ‘Solar Force Modelingof Block IIR Global Positioning System Satellites’. In:
Journal of Spacecraft and Rockets 33.6, pp. 863–866.
DOI : 10.2514/3.26851.
Fliegel, H. F., T. E. Gallini and E. R. Swift (1992): ‘Global
Positioning System Radiation Force Model for Geodetic
Applications’. In: Journal of Geophysical Research
97.B1, pp. 559–568. DOI: 10.1029/91JB02564.
Förste, C., S. L. Bruinsma, O. Abrikosov, J.-M. Lemoine,
M. J. C., F. Flechtner, G. Balmino, F. Barthelmes and
R. Biancale (2015): EIGEN-6C4 The latest combined
global gravity field model including GOCE data up todegree and order 2190 of GFZ Potsdam and GRGS Toulouse. GFZ Data Services: Gravity field. ICGEM. DOI:
10.5880/icgem.2015.1.
Förste, C., S. L. Bruinsma, R. Shako, O. Abrikosov, F. Flechtner, J.-C. Marty, J.-M. Lemoine, C. Dahle, K.-H. Neumeyer, F. Barthelmes, R. Biancale, G. Balmino and
R. König (2012): ‘A new release of EIGEN-6, thelatest combined gravity field model including LAGEOS,GRACE and GOCE data from the collaboration of GFZPotsdam and GRGS Toulouse’. In: Geophysical Research Abstracts 14. EGU2012-2821-2.
Freymueller, J. T. (2010): ‘Active tectonics of plate boundary
zones and the continuity of plate boundary deformationfrom Asia to North America’. In: Current Science 99.12,
pp. 1719–1732.
Fritsche, M., R. Dietrich, C. Knöfel, A. Rülke, S. Vey, M.
Rothacher and P. Steigenberger (2005): ‘Impact ofhigher-order ionospheric terms on GPS estimates’. In:
Geophysical Research Letters 32.23. DOI: 10.1029/200
5GL024342.
Fukushima, T. (1991): ‘Geodesic nutation’. In: Astronomy
and Astrophysics 244.1, pp. L11–L12.

Bibliography

Gambis, D. (1999): First extension of the ICRF, ICRF-Ext.1.
IERS Annual Report 1998, chapter VI. Observatoire deParis.
—(2004): ‘Monitoring Earth Orientation using space-geodetic techniques: state-of-the-art and prospective’. In:
Journal of Geodesy 78.4, pp. 295–303. DOI: 10.1007/s0
0190-004-0394-1.

Gambis, D. and B. Luzum (2011): ‘Earth rotation monitoring,
UT1 determination and prediction’. In: Metrologia 48,
S165–S170.
Gauss, C. F. (1876): ‘Trigonometrische und polygonometrische Rechnungen in der Feldmesskunst’. German.
In: Bestimmung des Breitenunterschiedes zwischen den
Sternwarten von Göttingen und Altona durch Beobachtungen am ramsdenschen Zenithsektor. Ed. by K. G.
der Wissenschaften zu Göttingen. Carl Friedrich Gauss
Werke, neunter Band. Verlag von Eugen Strien.
GEO (2005): The Global Earth Observing System of Systems (GEOSS) – 10-Year Implementation Plan. URL:
earthobservations.org.
Griffiths, J. (2018): ‘Combined orbits and clocks from IGS
second reprocessing’. In: Journal of Geodesy. DOI:
10.1007/s00190-018-1149-8.
Griffiths, J. and J. Ray (2009): ‘On the precision and accuracy of IGS orbits’. In: Journal of Geodesy 83.3-4,
pp. 277–287. DOI: 10.1007/s00190-008-0237-6.
— (2013): ‘Sub-daily alias and draconitic errors in the
IGS orbits’. In: GPS Solutions 17.3, pp. 413–422. DOI:
10.1007/s10291-012-0289-1.
Gross, R. S. (2000): ‘Combination of Earth orientation measurements: SPACE97, COMB97, and POLE97’. In: Journal of Geodesy 73.12, pp. 627–637. DOI: 10.1007/s001
900050001.
Gross, R. S., R. Heinkelmann and Z. Altamimi (2019): Report of Unified Analysis Workshop. Tech. rep. URL: htt
p://ggos.org/media/filer_public/8a/95/8a95e490-33c54942-a291-369790cf320c/uaw2019_report_v2.pdf.
Groten, E. (2004): ‘Fundamental parameters and current(2004) best estimates of the parameters of common relevance to astronomy, geodesy, and geodynamics’. In:
Journal of Geodesy 77, pp. 724–731. DOI: 10.1007/s00
190-003-0373-y.
Gruber, T., O. Abrikosov and U. Hugentobler (2010): GOCE
standards. Document GP-TN-HPF-GS-0111, Issue 3.2.
Prepared by the European GOCE Gravity Consortium
EGG-C. URL: earth.esa.int/pub/ESA_DOC/GOCE/.
GSA (2019): Galileo Satellite Metadata. European Global
Navigation Satellite Systems Agency. URL: https://www.gsc-europa.eu/support-to-developers/galileo-satellit
e-metadata (visited on 13/02/2020).

Bibliography

Hartmann, T. and H. G. Wenzel (1995): ‘The HW95 tidal
potential catalogue’. In: Geophysical Research Letters22.24, pp. 3553–3556. DOI: 10.1029/95GL03324.
Hazard, C., J. Sutton, A. N. Argue, C. M. Kenworthy, L. V.
Morrison and C. A. Murray (1971): ‘Accurate radio andoptical positions of 3G273B’. In: Nature 233, pp. 89–91.
DOI : 10.1038/physci233089a0.
Heck, B. (1984): Zur Bestimmung vertikaler rezenter Erdkrustbewegungen und zeitlicher Änderungen des Schwerefeldes aus wiederholten Schweremessungen und Nivellements. German. DGK Reihe C 302. Deutsche
Geodätische Kommission (DGK), Munich.
—(2004): ‘Problems in the Definition of Vertical Reference Frames’. In: V Hotine-Marussi Symposium on
Mathematical Geodesy. Ed. by F. Sanso. International
Association of Geodesy Symposia 127, pp. 164–173.
Springer, Berlin Heidelberg. DOI: 10.1007/978-3-66210735-5_22.

Heck, B. and R. Rummel (1990): ‘Strategies for Solving the
Vertical Datum Problem Using Terrestrial and Satellite
Geodetic Data’. In: Sea Surface Topography and the
Geoid. Ed. by H. Sünkel and T. Baker. International
Association of Geodesy Symposia 104, pp. 116–128.
Springer, New York. DOI: 10.1007/978-1-4684-7098-7.
Heck, B. and K. Seitz (1993): Effects of non-linearity inthe geodetic boundary problems. German. DGK Reihe A 109. Deutsche Geodätische Kommission (DGK),
Munich.
Heiskanen, W. A. and H. Moritz (1967): Physical Geodesy.
W. H. Freeman and Company, San Francisco London.
Hernández-Pajares, M., J. Miguel, J. Sanz, À. Aragón-Àngel,
A. García-Rigo, D. Salazar and M. Escudero (2011):‘The ionosphere: effects, GPS modeling and the benefits
for space geodetic techniques’. In: Journal of Geodesy
85.12, pp. 887–907. DOI: 10.1007/s00190-011-0508-5.
Hilton, J. L., N. Capitaine, J. Chapront, J. M. Ferrandiz,
A. Fienga, T. Fukushima, J. Getino, P. Mathews, J.-L.
Simon, M. Soffel, J. Vondrak, P. T. Wallace and J. William (2006): ‘Report of the International Astronomical
Union Division I Working Group on Precession andthe Ecliptic’. In: Celestial Mechanics and Dynamical
Astronomy 94.3, pp. 351–367. DOI: 10.1007/s10569-00
6-0001-2.
Hiroshi, M. (2013): ‘Sub-daily noise in horizontal GPS
kinematic time series due to thermal tilt of GPS monuments’. In: Journal of Geodesy 87.4, pp. 393–401. DOI:
10.1007/s00190-013-0613-8.
Hirt, C., S. J. Claessens, T. Fecher, M. Kuhn, R. Pail and
M. Rexer (2013): ‘New ultrahigh-resolution picture ofEarth’s gravity field’. In: Geophysical Research Letters40.16, pp. 4279–4283. DOI: 10.1002/grl.50838.

287

Hugentobler, U., T. Gruber, P. Steigenberger, D. Angermann,
J. Bouman, M. Gerstl and B. Richter (2012): ‘GGOS
Bureau for Standards and Conventions: Integrated standards and conventions for geodesy.’ In: Geodesy for
Planet Earth. Ed. by S. Kenyon, M. Pacino and U.
Marti. International Association of Geodesy Symposia
136, pp. 995–998. Springer, Berlin, Heidelberg. DOI:
10.1007/978-3-642-20338-1.
Hugentobler, U., S. Schaer, R. Dach, M. Meindl, C. Urschl
and G. Beutler (2005): ‘GNSS Geocenter for Precise
Point Positioning’. In: Geophysical Research Abstracts
7. SRef-ID: 1607-7962/gra/EGU05-A-09651.
IAG (1984): ‘Resolutions of the XVIII general assembly of
the International Association of Geodesy’. In: Journalof Geodesy 58, pp. 309–323.
IERS (2018): IERS Conventions (2010) Chapter 7 (Updated):
Displacement of the reference point. Tech. rep. URL:
http://iers-conventions.obspm.fr/content/chapter7/icc7.pdf.
—(2020): IERS Annual Report 2018. URL: www.iers.org/AR2018.

Ihde, J., L. Sánchez, R. Barzaghi, H. Drewes, C. Foerste, T.
Gruber, G. Liebsch, U. Marti, R. Pail and M. Sideris(2017): ‘Definition and proposed realization of the International Height Reference System (IHRS)’. In: Surveys
in Geophysics 38.3, pp. 549–570. DOI: 10.1007/s10712-017-9409-3.
International Union of Geodesy and Geophysics (IUGG)(2007): Resolutions of the XXIV IUGG General Assembly in Perugia. Resolution No. 2. URL: iugg.org.res
olutions/perugia07.pdf.
ISO/IEC (2007): International Vocabulary of Metrology– Basic and General Concepts and Associated Terms(VIM). Guide 99:2007. International Organization forStandardization (ISO/IEC). URL: www.iso.org.
Johnson, T. J., B. J. Luzum and J. R. Ray (2005): ‘Improved Near-Term Earth Rotation Predictions Using Atmospheric Angular Momentum Analysis and Forecasts’.
In: Journal of Geodynamics 39.3, pp. 209–221.
Kouba, J. (2009a): ‘A simplified yaw-attitude model for
eclipsing GPS satellites’. In: GPS Solutions 13.1, pp. 1–
12. DOI: 10.1007/s10291-008-0092-1.
— (2009b): ‘Testing of global pressure/temperature (GPT)model and global mapping function (GMF) in GPS analyses’. In: Journal of Geodesy 83.3, pp. 199–208. DOI:
10.1007/s00190-008-0229-6.
Kreemer, C. W., D. A. Lavallée, G. Blewitt and W. E. Holt(2006): ‘On the stability of a geodetic no-net-rotation
frame and its application for the International Terrestrial
Reference Frame’. In: Geophysical Research Letters
133.17. DOI: 10.1029/2006GL027058.

288

Bibliography

Kvas, A., T. Mayer-Gürr, S. Krauss, J. M. Brockmann, T.
Schubert, W.-D. Schuh, R. Pail, T. Gruber, A. Jäggi
and U. Meyer (2019): The satellite-only gravity fieldmodel GOCO06s. Tech. rep. GFZ Data Services. URL:
http://doi.org/10.5880/ICGEM.2019.002.

Lühr, H., L. Grunwaldt and C. Förste (2002): CHAMP reference systems, transformations and standards. Doc.
CH-GFZ-RS-002. Deutsches GeoForschungsZentrum,
Potsdam. URL: op.gfz-potsdam.de/champ/more/docs_CHAMP.html.

Kwak, Y., M. Bloßfeld, R. Schmid, D. Angermann, M. Gerstl
and M. Seitz (2018): ‘Consistent realization of celestial
and terrestrial reference frames’. In: Journal of Geodesy
92.8, pp. 1047–1061. DOI: 10.1007/s00190-018-11306.

Lutz, S., M. Meindl, P. Steigenberger, G. Beutler, K. Sosnica,
S. Schaer, R. Dach, D. Arnold, D. Thaller and A. Jäggi(2016): ‘Impact of the arc length on GNSS analysis results’. In: Journal of Geodesy 90.4, pp. 365–378. ISSN:
0949-7714. DOI: 10.1007/s00190-015-0878-1.

Lagler, K., M. Schindelegger, J. Böhm, H. Krásná and T.
Nilsson (2013): ‘GPT2: Empirical slant delay model
for radio space geodetic techniques’. In: GeophysicalResearch Letters 40.6, pp. 1069–1073. DOI: 10.1002/gr
l.50288.

Luzum, B., N. Capitaine, A. Fienga, W. Folkner, T.
Fukushima, J. Hilton, C. Hohenkerk, G. Krasinski, G.
Petit, E. Pitjeva, M. Soffel and P. Wallace (2011): ‘The
IAU 2009 system of astronomical constants: Reportof the IAU working group on numerical standards for
Fundamental Astronomy’. In: Celestial Mechanics andDynamical Astronomy 110.4, pp. 293–304. DOI: 10.100
7/s10569-011-9352-4.

Lemoine, F. G., S. Kenyon, J. Factor, R. Trimmer, N. K.
Pavlis, D. Chinn, C. M. Cox, S. Klosko, S. Luthke, M.
Torrence, Y. Wang, R. G. Williamson, E. C. Pavlis, R.
Rapp and T. R. Olson (1998): The Development of
the Joint NASA GSFC and the National Imagery and
Mapping Agency NIMA Geopotential Model EGM96.
NASA Technical Publication TP-1998-206861. NASA
Goddard Space Flight Center, Washington, D.C.
Letellier, T. and F. Lyard (2005): ‘Etude des ondes de marée
sur les plateaux continentaux’. Université Paul Sabatier,Toulouse. URL: books.google.com.ar/books?id=%5C_3
UEOgAACAAJ.
Li, X., X. Hu, R. Guo, C. Tang, S. Zhou, S. Liu and J. Chen
(2018): ‘Orbit and Positioning Accuracy for New Generation Beidou Satellites during the Earth Eclipsing
Period’. In: Journal of Navigation 71.05, pp. 1069–
1087. DOI: 10.1017/s0373463318000103.
Li, Z., M. Ziebart, S. Bhattarai, D. Harrison and S. Grey
(2018): ‘Fast solar radiation pressure modelling withray tracing and multiple reflections’. In: Advances inSpace Research 61.9, pp. 2352–2365. ISSN: 0273-1177.
DOI : 10.1016/j.asr.2018.02.019.
Listing, J. B. (1873): Ueber unsere jetzige Kenntnis derGestalt und Groesse der Erde. German. Gesellschaft
der Wissenschaften und der Georg-August-Universität,
pp. 33–98.
Lockheed Martin (2019): SVN74 APC & ISC data release,
January 2019.

Luzum, B., N. Stamatakos, M. S. Carter, B. Stetzler and N.
Shumate (2014): ‘Rapid Service/Prediction Centre’. In:
IERS Annual Report 2013, pp. 65–82. Bundesamt für
Kartographie und Geodäsie, Frankfurt am Main. URL:
www.iers.org/AR2013.
Ma, C., E. F. Arias, T. M. Eubanks, A. L. Fey, A.-M. Gontier,
C. S. Jacobs, O. J. Sovers, B. A. Archinal and P. Charlot(1998): ‘The International Celestial Reference Frame
as realized by Very Long Baseline Interferometry’. In:
The Astronomical Journal 116.1, pp. 516–546. DOI:
10.1086/300408.
Ma, C. and M. Feissel, eds. (1997): Definition and Realization of the International Celestial Reference System by
VLBI astrometry of extragalactic objects. IERS Technical Note 23. Observatoire de Paris. URL: www.iers.or
g/IERS/EN/Publications/TechnicalNotes/tn23.html.
MacMillan, D. S. and C. Ma (1997): ‘Atmospheric Gradients and the VLBI Terrestrial and Celestial Reference
Frames’. In: Geophysical Research Letters 24.4, pp.
453–456. DOI: 10.1029/97GL00143.
Mäkinen, J. and J. Ihde (2009): ‘The permanent tide in heightsystems’. In: Observing our changing earth. Ed. by
M. G. Sideris. International Association of Geodesy
Symposia 133, pp. 81–87. Springer, Berlin, Heidelberg.
DOI : 10.1007/978-3-540-85426-5_10.

Longman, I. M. (1959): ‘Formulas for computing the tidal
accelerations due to the moon and the sun’. In: Journalof Geophysical Research 64.12, pp. 2351–2355. DOI:
10.1029/JZ064i012p02351.

Männel, B., H. Dobslaw, R. Dill, S. Glaser, K. Balidakis, M.
Thomas and H. Schuh (2019): ‘Correcting surface loading at the observation level: impact on global GNSS andVLBI station networks’. In: Journal of Geodesy 93.10,
pp. 2003–2017. DOI: 10.1007/s00190-019-01298-y.

Luceri, C. and E. C. Pavlis (2016): The ILRS contribution to
ITRF2014. Tech. rep. URL: http://itrf.ign.fr/ITRF_solut
ions/2014/doc/ILRS-ITRF2014-description.pdf.

Mather, R. S. (1978): ‘The role of the geoid in four dimensional Geodesy’. In: Marine Geodesy 1.3, pp. 217–252.
DOI : 10.1080/01490417809387968.

Bibliography

Mathews, P., B. A. Buffett and I. I. Shapiro (1995): ‘Love
numbers for diurnal tides: Relation to wobble admittances and resonance expansions’. In: Journal of Geophysical Research: Solid Earth 100.B6, pp. 9935–9948.
DOI : 10.1029/95JB00670.
Mayer-Gürr, T. and the GOCO Team (2015): ‘The combined
satellite gravity field model GOCO05s’. In: GeophysicalResearch Abstracts 17: EGU2015-12364, EGU General
Assembly, Vienna, Austria.
McCarthy, D. D. and B. Luzum (1991): ‘Combination of
precise observations of the orientation of the Earth’. In:
Bulletin Geodesique 65, pp. 22–27.
McCarthy, D. D. and G. Petit, eds. (2003): IERS Conventions (2003). IERS Technical Note 32. Bundesamt für
Kartographie und Geodäsie, Frankfurt am Main.
Mohr, P. J., D. B. Newell and B. N. Taylor (2016): ‘CODATA
recommended values of the fundamental physical constants: 2014’. In: Reviews of modern physics 88. DOI:
10.1103/RevModPhys.88.035009.
Montenbruck, O., R. Schmid, F. Mercier, P. Steigenberger,
C. Noll, R. Fatkulin, S. Kogure and A. S. Ganeshan(2015a): ‘GNSS satellite geometry and attitude models’.
In: Advances in Space Research 56.6, pp. 1015–1029.
DOI : 10.1016/j.asr.2015.06.019.
Montenbruck, O. and P. Steigenberger (2020): IGS White Paper on Satellite and Operations Information for Generation of Precise GNSS Orbit and Clock Products. Tech.
rep. Version 2020/02/04. IGS Multi-GNSS Working
Group. URL: https://kb.igs.org/hc/en-us/article_attachments/360049470472/Whitepaper_SatelliteMetaData_IGS_200204.pdf.
Montenbruck, O., P. Steigenberger and F. Darugna (2017a):‘Semi-analytical solar radiation pressure modeling for
QZS-1 orbit-normal and yaw-steering attitude’. In: Advances in Space Research 59.8, pp. 2088–2100. ISSN:
0273-1177. DOI: 10.1016/j.asr.2017.01.036.
Montenbruck, O., P. Steigenberger and U. Hugentobler(2015b): ‘Enhanced Solar Radiation Pressure Modeling for Galileo Satellites’. In: Journal of Geodesy
89.3, pp. 283–297. DOI: 10.1007/s00190-014-0774-0.
Montenbruck, O., P. Steigenberger, L. Prange, Z. Deng, Q.
Zhao, F. Perosanz, I. Romero, C. Noll, A. Stürze, G.
Weber, R. Schmid, K. MacLeod and S. Schaer (2017b):‘The Multi-GNSS Experiment (MGEX) of the International GNSS Service (IGS) – Achievements, Prospects
and Challenges’. In: Advances in Space Research 59.7,
pp. 1671–1697. ISSN: 0273-1177. DOI: 10.1016/j.asr.2
017.01.011.

289

Moore, M. (2019): IGS Analysis Centre Workshop Potsdam
2019: Summary and Recommendations. URL: https://s3-ap-southeast-2.amazonaws.com/igs-acc-web/igs-accwebsite/workshop2019/Workshop_Findings.pdf.
Moreaux, G., F. G. Lemoine, H. Capdeville, S. Kuzin, M. Otten, P. Štěpánek, P. Willis and P. Ferrage (2016): ‘Contribution of the International DORIS Service to the 2014
realization of the International Terrestrial Reference
Frame’. In: Advances in Space Research 58.12: Scientific Applications of DORIS in Space Geodesy, pp.
2479–2504. DOI: 10.1016/j.asr.2015.12.021.
Morelli, C., C. Gantar, T. Honkasalo, K. McConnell, J. Tanner, B. Szabo, U. Uotila and C. Wahlen (1974): The International Standardization Net 1971 (IGSN71). IUGGIAG, Publ. Spec. No. 4.
Moritz, H. (2000): ‘Geodetic Reference System 1980’. In:
Journal of Geodesy 74(1), pp. 128–162. DOI: 10.1007/s
001900050278.
Munk, W. H. and G. J. MacDonald (1960): The Rotationof the Earth: A Geophysical Discussion. Cambridge
monographs on mechanics and applied mathematics.
University Press.
Nothnagel, A. (2009): ‘Conventions on thermal expansion
modelling of radio telescopes for geodetic and astrometric VLBI’. In: Journal of Geodesy 83.8, pp. 787–792.
DOI : 10.1007/s00190-008-0284-z.
Nothnagel, A., T. Artz, D. Behrend and Z. Malkin (2017): ‘International VLBI Service for Geodesy and Astrometry-– Delivering high-quality products and embarking on
observations of the next generation’. In: Journal of Geodesy 91.7, pp. 711–721. DOI: 10.1007/s00190-016-09
50-5.
Oshchepkov, I. (2019): ‘40 Years of GRS80: Do We Need a
New Ellipsoid?’ In: IUGG 2019 Abstract.
Pavlis, N. K., S. A. Holmes, S. C. Kenyon and F. J. K. (2013):‘Correction to “The development of the Earth Gravitational Model 2008 (EGM2008)”’. In: Journal of Geophysical Research 118, p. 2633. DOI: 10.1002/jgrb.501
67.
Pavlis, N. K., S. A. Holmes, S. C. Kenyon and J. K. Factor(2012): ‘The development and evaluation of the Earth
Gravitational Model 2008 (EGM2008)’. In: Journal ofGeophysical Research 117, B04406. DOI: 10.1029/201
1JB008916.
Pearlman, M., J. J. Degnan and J. M. Bosworth (2002): ‘The
International Laser Ranging Service’. In: Advances inSpace Research 30.2, pp. 135–143. DOI: 10.1016/S027
3-1177(02)00277-6.

290

Bibliography

Petit, G. and B. Luzum, eds. (2010): IERS Conventions(2010). IERS Technical Note 36. Bundesamt für Kartographie und Geodäsie, Frankfurt am Main. URL: www.iers.org/IERS/EN/Publications/TechnicalNotes/tn36.html.

Rodriguez-Solano, C. J., U. Hugentobler, P. Steigenberger,
M. Blossfeld and M. Fritsche (2014): ‘Reducing thedraconitic errors in GNSS geodetic products’. In: Journal of Geodesy 88.6, pp. 559–574. DOI: 10.1007/s0019
0-014-0704-1.

Petrov, L. and J.-P. Boy (2004): ‘Study of the atmosphericpressure loading signal in Very Long Baseline Interferometry Observations’. In: Journal of GeophysicalResearch 109.B03405. DOI: 10.1029/2003JB002500.

Rodriguez-Solano, C. J., U. Hugentobler, P. Steigenberger
and S. Lutz (2011): ‘Impact of Earth radiation pressure
on GPS position estimates’. In: Journal of Geodesy
86.5, pp. 309–317. DOI: 10.1007/s00190-011-0517-4.

Plag, H.-P. and M. Pearlman, eds. (2009): Global Geodetic
Observing System – Meeting requirements of a global
society on a changing planet in 2020. Springer. DOI:
10.1007/978-3-642-02687-4.

Roggenbuck, O., D. Thaller, G. Engelhardt, S. Franke, R.
Dach and P. Steigenberger (2015): ‘Loading-Induced
Deformation Due to Atmosphere, Ocean and Hydrology: Model Comparisons and the Impact on Global
SLR, VLBI and GNSS Solutions’. In: REFAG 2014. Ed.
by T. van Dam. International Association of Geodesy
Symposia 146, pp. 71–77. Springer. DOI: 10.1007/134
5_2015_214.

Ratcliff, J. T. and R. S. Gross (2019): Combinations of Earth
Orientation measurements : SPACE 2018, COMB 2018,
and POLE 2018. JPL Publication 19-7. NASA. URL:
https://keof.jpl.nasa.gov/combinations/SpaceCombPol
e_latest.pdf.
Ray, J., Z. Altamimi, X. Collilieux and T. van Dam (2008):‘Anomalous harmonics in the spectra of GPS position
estimates’. In: GPS Solutions 12.1, pp. 55–64. DOI:
10.1007/s10291-007-0067-7.
Ray, J., J. Griffiths, X. Collilieux and P. Rebischung (2013):‘Subseasonal GNSS positioning errors’. In: GeophysicalResearch Letters 40, pp. 5854–5860. DOI: 10.1002/201
3/2013GL058160.
Ray, R. D. and R. M. Ponte (2003): ‘Barometric tides from
ECMWF operational analyses’. In: Annales Geophysicae 21.8, pp. 1897–1910. DOI: 10.5194/angeo-21-189
7-2003.
Rebischung, P., R. Schmid and T. A. Herring (2016): IGSMAIL-7399: Upcoming switch to IGS14/igs14.atx. URL:
https://lists.igs.org/pipermail/igsmail/2016/001233.ht
ml.
Ries, J., S. Bettadpur, R. Eanes, Z. Kang, U. Ko, C. McCullough, P. Nagel, N. Pie, S. Poole, T. Richter, H. Save
and B. Tapley (2016): The Development and Evaluationof the Global Gravity Model GGM05. Tech. rep. Center
for Space Research, The University of Texas at Austin.
DOI : 10.26153/tsw/1461.
Rodriguez-Solano, C. J., U. Hugentobler and P. Steigenberger(2012): ‘Impact of Albedo Radiation on GPS Satellites’.
In: Geodesy for Planet Earth. Ed. by S. Kenyon, M.
Pacino and U. Marti. International Association of Geodesy Symposia 136, pp. 113–119. Springer, Berlin,
Heidelberg. DOI: 10.1007/978-3-642-20338-1_14.
Rodriguez-Solano, C. J., U. Hugentobler, P. Steigenberger
and G. Allende-Alba (2013): ‘Improving the orbits ofGPS block IIA satellites during eclipse seasons’. In:
Advances in Space Research 52.8, pp. 1511–1529. DOI:
10.1016/j.asr.2013.07.013.

Romagnoli, C., S. Zerbini, L. Lago, B. Richter, D. Simon,
F. Domenichini, C. Elmi and M. Ghirotti (2003): ‘Influence of soil consolidation and thermal expansion effects
on height and gravity variations’. In: Journal of Geodynamics 35.4–5, pp. 521–539. DOI: 10.1016/S0264-370
7(03)00012-7.
Rummel, R. (2000): ‘Global Integrated Geodetic and Geodynamic Observing System (GIGGOS)’. In: Towards an
Integrated Geodetic and Geodynamic Observing System(IGGOS). Ed. by R. Rummel, H. Drewes, W. Bosch andH. Hornik. International Association of Geodesy Symposia 120, pp. 253–260. Springer, Berlin Heidelberg.
DOI : 10.1007/978-3-662-04827-6_3.
Rummel, R., T. Gruber, J. Ihde, G. Liebsch, A. Rülke, U.
Schäfer, M. G. Sideris, E. Rangelova, P. Woodworth andC. Hughes: STSE-GOCE+, Height system unification
with GOCE. Doc. No. GO-HSU-PL-002. Version 1.0
2014-02-24. URL: http://www.goceplushsu.eu/ext/doc/f
in-doc/GO-HSU-RP-0020_1.0_Abstract.pdf.
Sánchez, L. (2012): ‘Towards a vertical datum standardisation under the umbrella of Global Geodetic Observing
System’. In: Journal of Geodetic Science 2.4, pp. 325–
342. DOI: 10.2478/v10156-012-0002-x.
— (2019) : ‘Report of the GGOS Focus Area Unified
Height System’. In: IAG Reports 2015–2019 (Travauxde l’AIG). Vol. 41. in press.
Sánchez, L., J. Ågren, J. Huang, Y. M. Wang and R. Forsberg (2018a): Basic agreements for the computationof station potential values as IHRS coordinates, geoid
undulations and height anomalies within the Colorado
1 cm geoid experiment. Version V0.5 2018-10-30. URL:
https://ihrs.dgfi.tum.de/fileadmin/JWG_2015/Colorad
o_Experiment_Basic_req_V0.5_Oct30_2018.pdf.

Bibliography

Sánchez, L., R. Čunderlík, N. Dayoub, K. Mikula, Z. Minarechová, Z. Šíma, V. Vatrt and M. Vojtísková (2016):‘A conventional value for the geoid reference potential
W0 ’. In: Journal of Geodesy 90.9, pp. 815–835. DOI:
10.1007/s00190-016-0913-x.
Sánchez, L., W. Seemüller, H. Drewes, L. Mateo, G.
Gonzáles, A. Silva, J. Pampillón, W. Martinez, V. Cioce,
D. Cisneros and S. Cimbaro (2013): ‘Long-term stability of the SIRGAS reference frame and episodic station movements caused by the seismic activity in the
SIRGAS region’. In: Geodetic Reference Frames forApplications in Geosciences. Ed. by Z. Altamimi and C.
Xavier. International Association of Geodesy Symposia
138, pp. 153–161. Springer, Berlin Heidelberg. DOI:
10.1007/978-3-642-32998-2-24.
Sánchez, L. and M. G. Sideris (2017): ‘Vertical datum unification for the International Height Reference System(IHRS)’. In: Geophysical Journal International 209.2,
pp. 570–586. DOI: 10.1093/gji/ggx025.
Sánchez, L. et al. (2018b): ‘Advances in the establishment of
the International Height Reference Frame (IHRF)’. In:
International Symposium on Gravity, Geoid and Height
Systems 2018 (GGHS2018). Copenhagen, Denmark.
Scherneck, H.-G. (1991): ‘A parametrized solid earth tidemodel and ocean tide loading effects for global geodetic
baseline measurements’. In: Geophysical Journal International 106.3, pp. 677–694. DOI: 10.1111/j.1365-246
X.1991.tb06339.x.
Schmid, R., R. Dach, X. Collilieux, A. Jäggi, M. Schmitz
and F. Dilsner (2016): ‘Absolute IGS antenna phasecenter model igs08.atx: status and potential improvements’. In: Journal of Geodesy 90.4, pp. 343–364. DOI:
10.1007/s00190-015-0876-3.
Schmid, R., M. Rothacher, D. Thaller and P. Steigenberger(2005): ‘Absolute phase center corrections of satellite
and receiver antennas: Impact on global GPS solutions
and estimation of azimuthal phase centervariations of
the satellite antenna’. In: GPS Solutions 9.4, pp. 283–
293. DOI: 10.1007/s10291-005-0134-x.
Schuh, H. and D. Behrend (2012): ‘VLBI: A fascinating
technique for geodesy and astrometry’. In: Journal of
Geodynamics 61, pp. 68–80. DOI: 10.1016/j.jog.2012.0
7.007.

291

Seitz, M., D. Angermann, M. Blossfeld, H. Drewes and M.
Gerstl (2012): ‘The 2008 DGFI Realization of the ITRS:DTRF2008’. In: Journal of Geodesy 86.12, pp. 1097–
1123. DOI: 10.1007/s00190-012-0567-2.
Seitz, M., M. Bloßfeld, D. Angermann, M. Gerstl and F. Seitz(2020): ‘DTRF2014: The first secular ITRS realizationconsidering non-tidal station loading’. In: Journal of
Geodesy. in review.
Seitz, M., M. Bloßfeld, D. Angermann, R. Schmid, M. Gerstl
and F. Seitz (2016): ‘The new DGFI-TUM realizationof the ITRS: DTRF2014 (data)’. In: Deutsches Geodätisches Forschungsinstitut. DOI: 10.1594/PANGAEA.86
4064.
Seitz, M., P. Steigenberger and T. Artz (2014): ‘Consistent adjustment of combined terrestrial and celestial reference
frames’. In: Earth on the Edge: Science of a Sustainable Planet. Ed. by C. Rizos and P. Willis. International
Association of Geodesy Symposia 139, pp. 215–221.
Springer, Berlin, Heidelberg. DOI: 10.1007/978-3-64237222-3.
Shanghai Engineering Center for Microsatellites (2018) :‘Satellite Geometry and Attitude Mode of MEO Satellites of BDS-3 Developed by SECM’. In: ION GNSS+
2018. ION.
Sibthorpe, A., W. Bertiger, S. D. Desai, B. Haines, N. Harvey
and J. P. Weiss (2011): ‘An evaluation of solar radiationpressure strategies for the GPS constellation’. In: Journal of Geodesy 85(8), pp. 505–517. DOI: 10.1007/s001
90-011-0450-6.
Soja, B., R. S. Gross, C. Abbondanza, T. M. Chin, M. Heflin,
J. Parker and X. Wu (2019): ‘Chasing consistency:
joint determination of terrestrial and celestial reference
frames’. In: Geophysical Research Abstracts 21.EGU
2019-10211: EGU General Assembly 2019, Vienna, Austria. URL: meetingorganizer.copernicus.org/EGU2019/EGU2019-10211.pdf.
Stamatakos, N., M. Davis, N. Shumate, M. S. Carter and C.
Hackmann (2017): ‘Rapid Service/Prediction Centre’.
In: IERS Annual Report 2016. Bundesamt für Kartographie und Geodäsie, Frankfurt am Main. URL: www.iers.org/AR2016.

Schwarz, K. P., M. G. Sideris and R. Forsberg (1990): ‘The
use of FFT techniques in physical geodesy’. In: Geophysical Journal International 100.3, pp. 485–514. DOI:
10.1111/j.1365-246X.1990.tb00701.x.

—

Seitz, F. and H. Schuh (2010): ‘Earth rotation’. In: Sciencesof Geodesy-I, Advances and Future Directions. Ed. by
G. Xu. Springer, pp. 185–227. DOI: 10.1007/978-3-64
2-11741-1.

Stamatakos, N., B. Luzum and W. Wooden (2007): ‘Recent Improvements in IERS Rapid Service / Prediction
Centre Products’. In: Journees Systemes de Reference
Spatio-Temporels, pp. 163–166.

(2020): ‘Rapid Service/Prediction Centre’. In: IERS
Annual Report 2018, pp. 102–124. Bundesamt für
Kartographie und Geodäsie, Frankfurt am Main. URL:
www.iers.org/AR2018.

292

Steigenberger, P. (2009): ‘Reprocessing of a global GPS
network’. In: Deutsche Geodätische Kommission, Reihe
C Vol. 640. ISSN: 0065-5325.
Steigenberger, P., J. Boehm and V. Tesmer (2009): ‘Comparison of GMF/GPT with VMF1/ECMWF and implications for atmospheric loading’. In: Journal of Geodesy
83.10, pp. 943–951. DOI: 10.1007/s00190-009-0311-8.
Steigenberger, P., O. Montenbruck and U. Hugentobler(2015): ‘GIOVE-B solar radiation pressure modelingfor precise orbit determination’. In: Advances in Space
Research 55.5, pp. 1422–1431. DOI: 10.1016/j.asr.2014.12.009.
Steigenberger, P., S. Thoelert and O. Montenbruck (2018):‘GNSS satellite transmit power and its impact on orbit
determination’. In: Journal of Geodesy 92.6, pp. 609–
624. ISSN: 1432-1394. DOI: 10.1007/s00190-017-1082-2.
— (2019): GPS and GLONASS Satellite Transmit Power:
Update for IGS repro3. technical report. DLR/GSOC
TN 19-01. URL: http://acc.igs.org/repro3/TX_Power_2
0190711.pdf.
Thomas, M. (2002): Ocean induced variations of Earth’s
rotation – Results from a simultaneous model of global
circulation and tides. PhD dissertation. University of
Hamburg, Germany.
Tscherning, C. C. (1986): ‘Functional methods for gravity field approximation in Mathematical and NumericalTechniques in Physical Geodesy’. In: Lecture Notes inEarth Sciences. Ed. by H. Sünkel. Vol. 7. Springer
Berlin Heidelberg, pp. 3–47.
Villiger, A., L. Prange, R. Dach, F. Zimmermann, H. Kuhlmann and A. Jäggi (2019): ‘Satellite and receiver chamber calibrated antenna pattern for TRF scale determination’. In: 7th International Colloquium on Scientificand Fundamental Aspects of GNSS.
Wahr, J. M. (1981): ‘The forced nutations of an elliptical,
rotating, elastic and oceanless earth’. In: GeophysicalJournal of the Royal Astronomical Society 64.3, pp. 705–
727. DOI: 10.1111/j.1365-246X.1981.tb02691.x.
— (1985): ‘Deformation induced by polar motion’. In:
Journal of Geophysical Research: Solid Earth 90.B11,
pp. 9363–9368. DOI: 10.1029/JB090iB11p09363.

Bibliography
URL : https://ihrs.dgfi.tum.de/fileadmin/JWG_2015/Wa

ng_report_GGHS2018ColoradoGeoidReportMod.pdf.
Willis, P., H. Fagard, P. Ferrage, F. G. Lemoine, C. E. Noll, R.
Noomen, M. Otten, J. Ries, M. Rothacher, L. Saudarin,
G. Tavernier and J. J. Valette (2010): ‘The International
DORIS Service, towards maturity’. In: Advances inSpace Research 45.12: DORIS: scientific applications
in geodesy and geodynamics. Ed. by P. Willis, pp. 1408–
1420. DOI: 10.1016/j.asr.2009.11.018.
Wilmes, H., H. Wziontek, R. Falk and S. Bonvalot (2009):‘AGrav – The New International Absolute Gravity Database of BGI and BKG and its benefit for the Global
Geodynamics Project (GGP)’. In: Journal of Geodynamics 48, pp. 305–309.
Wu, J., S. Wu, G. Hajj, W. Bertiger and S. M. Lichten (1993):‘Effects of antenna orientation on GPS carrier phase’.
In: Manuscripta Geodaetica 18, pp. 91–98.
Wu, X., C. Abbondanza, Z. Altamimi, T. M. Chin, X. Collilieux, R. S. Gross, M. B. Heflin, Y. Jiang and J. W.
Parker (2015): ‘KALREF – A Kalman filter and timeseries approach to the International Terrestrial Reference Frame realization’. In: Journal of GeophysicalResearch Solid Earth 120. DOI: 10.1002/2014JB01162
2.
Wu, X., J. Ray and T. van Dam (2012): ‘Geocenter motion
and its geodetic and geophysical implications’. In: Journal of Geodynamics 58, pp. 44–61. DOI: 10.1016/j.jog.2012.01.007.
Yan, H., W. Chen, Y. Zhu, W. Zhang and M. Zhong (2009):‘Contributions of thermal expansion of monuments andnearby bedrock to observed GPS height changes’. In:
Geophsical Research Letters 36.13, L13301. DOI: 10.1
029/2009GL038152.
Yan, X., C. Liu, G. Huang, Q. Zhang, L. Wang, Z. Qin and S.
Xie (2019): ‘A Priori Solar Radiation Pressure Modelfor BeiDou-3 MEO Satellites’. In: Remote Sensing
11.13, p. 1605. DOI: 10.3390/rs11131605.
Zhao, Q., G. Chen, J. Guo, J. Liu and X. Liu (2018a): ‘Ana priori solar radiation pressure model for the QZSSMichibiki satellite’. In: Journal of Geodesy 92.2, pp.
109–121. DOI: 10.1007/s00190-017-1048-4.

Wallace, P. T. and N. Capitaine (2006): ‘Precession-nutation
procedures consistent with IAU 2006 resolutions’. In:
Astronomy and Astrophysics 459.3, pp. 981–985. DOI:
10.1051/0004-6361:20065897.

Zhao, Q., C. Wang, J. Guo, B. Wang and J. Liu (2018b):‘Precise orbit and clock determination for BeiDou-3 experimental satellites with yaw attitude analysis’. In:
GPS Solutions 22.1. ISSN: 1521-1886. DOI: 10.1007/s1
0291-017-0673-y.

Wang, Y. M., R. Forsberg, L. Sánchez, J. Ågren and J. Huang(2018): ‘Report on Colorado geoid comparisons’. In:
International Symposium on Gravity, Geoid and Height
Systems 2018 (GGHS2018). Copenhagen, Denmark.

Ziebart, M., A. Sibthrope, P. Cross, Y. Bar-Sever and B.
Haines (2007): ‘Cracking the GPS - SLR Orbit Anomaly’. In: Proceedings of ION GNSS 2007, pp. 2033–
2038. Fort Worth, Texas.

International Earth Rotation and Reference Systems Service (IERS)

293

International Earth Rotation and Reference Systems
Service (IERS)
Chair of the Directing Board: Brian Luzum (USA)
Director of the Central Bureau: Daniela Thaller (Germany)https://www.iers.org/

Development

Products

The IERS was established as the International Earth Rotation Service in 1987 by the International Astronomical
Union and the International Union of Geodesy and Geophysics, and it began operation on 1 January 1988. Since
2001, the IERS works in a new organizational structure; in
2003, the new name of the Service, without changing its
abbreviation, was adopted. The IERS is a Regular Memberof the ICSU World Data System (WDS) and an Associate
Member of the International Committee on Global
Navigation Satellite Systems (ICG).

IERS collects, archives and distributes products to satisfy
the objectives of a wide range of applications, research andexperimentation. These products include the following:
x International Celestial Reference Frame;
x International Terrestrial Reference Frame;x Final daily earth orientation data updated monthly;x Rapid service estimates of near real-time earthorientation data and their predictions updated four times
per day;x Announcements of the differences between astronomical and civil time for time distribution by radio stations;x Leap second announcements;
x Products related to global geophysical fluids such as
mass and angular momentum distribution;
x Annual reports and technical notes on conventions andother topics;
x Long-term earth orientation information.
The accuracies of these products are sufficient to support
current scientific and technical objectives including thefollowing:
x Fundamental astronomical and geodetic reference
systems;x Monitoring and modeling earth rotation/orientation;
x Monitoring and modeling deformations of the solid
earth;x Monitoring mass variations in the geophysical fluids,
including the atmosphere and the hydrosphere;
x Artificial satellite orbit determination;x Geophysical and atmospheric research, studies of dynamical interactions between geophysical fluids and thesolid earth;x Space navigation.

Objectives
The primary objectives of the IERS are to serve the astronomical, geodetic and geophysical communities by
providing the following:x The International Celestial Reference System (ICRS)
and its realization, the International Celestial Reference
Frame (ICRF);
x The International Terrestrial Reference System (ITRS)
and its realization, the International Terrestrial
Reference Frame (ITRF);
x Earth orientation parameters required to study earthorientation variations and to transform between the
ICRF and the ITRF;
x Geophysical data to interpret time/space variations in the
ICRF, ITRF or earth orientation parameters, and modelsuch variations;x Standards, constants and models (i.e., conventions) encouraging international adherence.

294

The Geodesist’s Handbook 2020

Structure

IERS Directing Board, as of June 2020

The IERS accomplishes its mission through the following
components:
x Technique Centers: International GNSS Service, International Laser Ranging Service, International VLBI
Service, and International DORIS Service;x Product Centers: Earth Orientation Center, Rapid
Service/Prediction Center, Conventions Center, ICRSCenter, ITRS Center, and Global Geophysical Fluids
Center with Special Bureaus for the Atmosphere, for the
Oceans, for Hydrology, and for Combination;
x ITRS Combination Centers at Deutsches Geodätisches
Forschungsinstitut at TU München (DGFI-TUM),
Institut Géographique National (IGN), Jet Propulsion
Laboratory (JPL);x Analysis Coordinator;
x Central Bureau;x Directing Board;x Working Groups: WG on Site Survey and Co-location,
WG on SINEX Format, WG on the ConsistentRealization of TRF, CRF, and EOP.
Some of these components (e.g., Technique Centers) may
be autonomous operations, structurally independent from
IERS, but which cooperate with the IERS. A participatingorganization may also function as one or several of thesecomponents.

Zuheir Altamimi (France),
ITRS Center Representative
Christian Bizouard (France) Earth Orientation Center
Representative
Sigrid Böhm (Austria),
IVS Representative
Jean-Paul Boy (France),
GGFC Representative
Aleksander Brzezinski (Poland), IAU Representative
Hugues Capdeville (France) IDS Representative
Rolf Dach (Switzerland),IGS Representative
Richard Gross (USA),GGOS Representative
Rüdiger Haas (Sweden),IVS Representative
Christine Hackman (USA), Rapid Service/Prediction
Center Representative
Robert Heinkelmann (Germany), Analysis Coordinator
Thomas Herring (USA),
IAG / IUGG Representative
Brian Luzum (USA),
Chair of the IERS Directing
Board
Chuck Meertens (USA),
IGS Representative
Erricos C. Pavlis (USA),ILRS Representative
Jérôme Saunier (France),
IDS Representative
Jean Souchay (France),
ICRS Center Representative
Nick Stamatakos (USA),
Conventions Center
Representative
Daniela Thaller (Germany) Director of the Central Bureau
Jean-Marie Torre (France), ILRS Representative

International DORIS Service (IDS)

295

International DORIS Service (IDS)
Chair of the Governing Board: Frank Lemoie (U.S.A.)
Director of the Central Bureau: Laurent Soudarin (France)
https://ids-doris.org/

Terms of Reference (ToR)
Accepted by the IAG Executive Committee at the XXIIIthIUGG General Assembly, Sapporo, Japan, July 1, 2003.
Revised by the IDS ToR Working Group, and approved by
the IDS Governing Board on, June 23, 2011.
Addenda issued by the IDS Governing Board, approvedby the IAG Executive Committee at the XXVIth IUGG
General Assembly, Prague, Czech Republic, June 26, 2015

Introduction
The DORIS (Doppler Orbit determination and Radiopositioning Integrated on Satellite) system for satellite orbit
determination and precise positioning was developed by
the Centre National d’Etudes Spatiales (CNES) in conjunction
with the Institut Géographique National (IGN) and theGroupe de Recherche de Géodesie Spatiale (GRGS).
A proof of concept for the International DORIS Service(IDS) was conducted through a pilot phase prior to theestablishment of the International DORIS Experiment in1999 by the International Association of Geodesy (IAG).
The IDS formally began on July 1, 2003 after the IAG
official approval at the IUGG General Assembly in Sapporo. The IDS is an IAG Service and operates in close cooperation with the International Earth rotation and Reference
systems Service (IERS).

The IDS Mission
The primary objective of the IDS is to provide a service tosupport geodetic and geophysical research activities
through DORIS data and derived products.
The IDS collects, archives and distributes DORIS observation data sets of sufficient accuracy to satisfy theobjectives of a wide range of applications and experimentations. From these data sets the following products arederived:x Coordinates and velocities of the IDS tracking stations
x Geocenter and scale of the Terrestrial Reference Framex High accuracy ephemerides of the DORIS satellites
x Earth orientation parameters (EOPs)
The accuracies of these products are sufficient to support
current scientific objectives including:x Realization of global accessibility to and theimprovement of the International Terrestrial Reference
Frame (ITRF)
x Monitoring deformations of the solid Earthx Monitoring crustal deformation at tide gauges
x Monitoring variations in the hydrosphere (sea level,ice-sheets, etc.)x Orbit determination for scientific satellites

The IDS Organization
The IDS accomplishes its mission through the following
components:
x Satellites carrying a DORIS receiverx Network of tracking stations
x Data Centers
x Analysis Centers, Associate Analysis Centers andAnalysis Coordinatorx Combination Centerx Working Groups
x Central Bureau
x Governing Board

296

The Geodesist’s Handbook 2020

Satellites Carrying a DORIS Receiver

Data Centers

Since July 2003, the CNES and the European Space Agency (ESA) have provided DORIS data to the IDS. Data fromadditional agencies are expected and welcome. DORIS
receivers are flown on LEO satellites for precise orbit
determination as well as for geodetic applications. Satellites with DORIS receivers are listed on the IDS website athttps://ids-doris.org/.
A representative of the DORIS system serves as a voting member of the Governing Board.

The Data Centers are in direct contact with the CNES,
which provides the DORIS data. The Data Centers archive
the DORIS data, derived products, and ancillary information required to process these data.
A representative of the Data Centers serves as a voting
member of the Governing Board.

Tab. 1 DORIS data available at IDS Data Centers (Jan. 2020)

Analysis Centers, Associate Analysis
Centers and Analysis Coordinator
The Analysis Centers (ACs) are committed to provide atleast one of the above IDS products on a regular basis.
Expertise in DORIS data analysis and operational capability are essential factors in the selection of Analysis Centers. ACs adhere to IDS recommendations for the creationof high-quality products and their timely archiving anddistribution. Currently, only groups providing IDS products routinely may be considered as Analysis Centers.

Satellite

Start

End

Type

SPOT-231-MAR-90

04-JUL-90

04-NOV-92

15-JUL-09

Remotesensing

25-SEP-92

01-NOV-94

Remotesensing

SPOT-301-FEB-94

09-NOV-96

Remotesensing

SPOT-401-MAY-98

24-JUN-13

Remotesensing

SPOT-511-JUN-02

11-DEC-15

Remotesensing

Analysis Center

Country

Software

21-JUN-13

Altimetry

ESA/ESOC

Germany

NAPEOS

Geod. Observatory Pecny

Czech Rep.

Bernese13-JUN-02

08-APR-12

Altimetry,
Environment

NASA/GSFCUSAGEODYN

Jason-2

12-JUL-08

10-OCT-19

Altimetry

IGN

FranceGIPSY/OASISCryosat-2

30-MAY-10–

Altimetry

INASAN

RussiaGIPSY/OASIS

HY-2A

1-OCT-11–

Altimetry

CNES/CLSFrance

GINS/DYNAMO

SARAL

14-MAR-13–

Altimetry

Jason-3

17-JUN-16–

Altimetry

SENTINEL-3A

16-FEB-16–

Altimetry

SENTINEL-3B

25-APR-18–

Altimetry

TOPEX/
seidonPo-

Jason-1
ENVISAT

15-JAN-02

Network of Tracking Stations
The IDS network is composed of DORIS permanent tracking stations located at host institutions and maintained by
the IGN. A list of the sites (past and present) is included on
the IDS website at https://ids-doris.org/.
The network also includes additional DORIS stations
proposed by the IDS to observe during specific campaignsof scientific interest. A representative of the Network
serves as a voting member of the Governing Board.

Tab. 2 List of IDS Analysis Centers and Associate Analysis Centers (January 2020)

Associate Analysis Center
GFZ

Germany

EPOS-OC

CNES/POD

FranceZoom

TU Delft

Netherlands

DGFI-TUM

GermanyDOGS

The Analysis Coordinator assists the Analysis Centersand monitors their activities to ensure that the IDS objectives are carried out. The Analysis Coordinator, working
with the Analysis Centers, is expected to provide quality
control, performance evaluation, and continued development of appropriate analysis standards. The Analysis Coordinator, with the support of the Combination Center, isalso responsible for the appropriate combination of theAnalysis Centers products into a single set of prescribeddata products.

International DORIS Service (IDS)The Analysis Coordinator and a representative of theAnalysis Centers serve as voting members of the Governing Board.
Associate Analysis Centers provide specialized or derived products, not necessarily at regular intervals (such as
precise orbits, station positions, Earth Orientation Parameters, ionospheric products, tropospheric delays, or any
scientific data products of a mission specific nature). They
are recognized as such by the Governing Board, uponrecommendation of the Analysis Coordinator. The Associate Analysis Centers are encouraged to present their results
at IDS meetings and to submit their final results in IDS
Data Centers for dissemination to researchers and otherusers. An Associated Analysis Center (AAC) may become
an Analysis Center after demonstrating its expertise andoperational capability during a test period.

Combination Center
The IDS appoints a Combination Center (CC) to combine
individual AC solutions and to generate IDS data products
for submission to the IERS for the formulation of the periodic update of the ITRF and other geodetic products. The
CC is selected by the Governing Board every four years
through a Call for Participation initiated six months prior
to the end of the current CC term. Interested centers submit
proposals outlining their plan for operation of the CC andthe resources that they will commit.
A representative of the Combination Center serves as avoting member of the Governing Board.

Working Groups
IDS Working Groups provide expertise on particular topics
related to the IDS components and on development ofparticular IDS product(s) or service(s) relying on the IDS
infrastructure.
All Working Groups are created when needed and retired by the IDS Governing Board when their work has
been completed or they are no longer needed. Each Working Group must develop a charter that includes a mandate,a list of specific tasks, a schedule, and an identified Chairperson.
The Chairpersons of the Working Groups are nonvoting members of the IDS Governing Board (see below).

Central Bureau
The Central Bureau (CB) is the executive arm of the IDS
Governing Board and as such is responsible for the general297

management of the IDS consistent with the directives,
policies and priorities set by the Governing Board.
In this role the CB, within available resources, coordinates IDS activities, facilitates communications, maintains
documentation, and organizes reports, meetings, and workshops. The CB responds to external inquiries about the
IDS, promotes the use of IDS data and products, and coordinates interactions with other services, including the
IERS.
The CB supports the Combination Center in combining
the various Analysis Centers products and providing all
information necessary to validate the final combined products.
The CB operates the information system for the IDS andproduces the IDS Annual Reports and IDS Associates
directory. The CB coordinates the publication of otherdocuments required for the satisfactory planning and dayto-day operation of the Service, including standards andspecifications regarding the performance, functionality andconfiguration requirements of all Service elements.
Although the Chairperson of the Governing Board is theofficial representative of the IDS to external organizations,the CB, consistent with the directives established by theGoverning Board, is responsible for the day-to-day liaison
with such organizations.
The long-term function of the IDS is assured throughredundancy and emergency contingency plan for all of its
components except for the CB. The Central Bureau serves
for a term of four years. One year prior to the end of eachterm, the GB formally reviews the performance of theCentral Bureau. At the behest of the GB, the CB may be
asked to reconfirm its commitment to serve another four
years. If the CB agrees, it submits a proposal for GB approval. If the CB declines or if the GB chooses to change
CB operators, the GB announces a Call for Proposals for a
new IDS Central Bureau to take over responsibilities including a six-month transition phase with the outgoing
Central Bureau.
In summary, the Central Bureau performs primarily along-term coordination role to ensure that IDS participants
contribute to the Service in a consistent and harmonious
manner and adhere to IDS standards.
The Director of the Central Bureau serves as a voting
member of the Governing Board.

Governing Board
The principal role of the Governing Board (GB) is to set
policy and to exercise broad oversight of all IDS functions
and components. It also controls general activities of theService, including restructuring, when appropriate, tomaintain Service efficiency and reliability.

298

The Governing Board (GB) consists of eleven voting
members and a number of nonvoting members. The membership is chosen to try to strike the right balance between
project specialists and the general community. The voting
membership of the GB is distributed as follows:
Elected by IDS Associates (see below):
Analysis Centers’ representative:
1
Data Centers’ representative
1
Analysis Coordinator:
1
Members-at-Large:
2
Appointed members:
Director of the Central Bureau:
1
IERS representative to IDS:
1
IAG representative to IDS:
1
Combination Center representative:
1
DORIS System representative (CNES):
1
Network representative (IGN):
1
Total number of voting members:
11
During their mandate, the Working Group chairpersons are
GB members with voice but without vote.
The elected members have staggered four-year terms,
with elections every two years. There is no limit to thenumber of terms that a person may serve, however he or
she may serve only two terms consecutively as an elected
member. The Analysis Center representative, the Data
Center representative, and one Member-at-Large are elected during the first two-year election. The Analysis Coordinator and the other Member-at-Large are elected in thesecond two-year election. Although no formula is prescribed, efforts should be made to keep the GB membership properly balanced with regard to supporting organizations and geographic representation.
Members of the GB become IAG Fellows with the appropriate rights and privileges, as described on the IAG
website, after an initial two-year period.
Composition of the IDS Governing Board (January 2020):
Claudio Abbondanza, NASA/JPL, USA, Member at Large
Hughes Capdeville, CLS, France, Analysis Coordination
Petr Štěpánek, Geod. Observatory Pecny, Czech Rep.,
Analysis Coord.
Denise Dettmering, DGFI/TUM, Germany, Member at
Large
Pascale Ferrage, CNES, France, System Representative
Frank Lemoine(Chair) NASA/GSFC, Analysis Center
Representative
Brian Luzum,
GSFC, USA, IERS Representative
Guilhem Moreaux CLS, France, Combination Center Repr.
Patrick Michael, GSFC, USA, Data Flow Coordinator
Ernst Schrama,
TU Delft, The Netherlands, IAG Representative
Jérôme Saunier, IGN, France, Network Representative

The Geodesist’s Handbook 2020

Laurent Soudarin, CLS, Director of Central Bureau

GB Elections
The GB elects a Chairperson from its members to serve aterm of four years with the possibility of re-election for
one additional term. The Chairperson does not vote on GB
decisions, except in the case of a tie. The Chairperson is
the official representative of the IDS to external organizations.
Five members of the GB are elected by the IDS Associates. A nominating committee conducts the elections formembership on the IDS Governing Board. The nominating
committee consists of three members. The Chair of thenominating committee is appointed by the Chair of the GB,
and must be a member of the GB not currently up for reelection. The GB chooses the remaining two members of
the nominating committee from the list of IDS Associates.
The nominating committee solicits nominations fromthe IDS Associates for each position to be filled; at least
two candidates are required for each position. The Central
Bureau runs the election. All IDS Associates are eligible tovote. Election is by a simple majority of votes received foreach position. The two Member-at-Large positions arefilled by the two candidates receiving the most votes; avote by the GB will resolve any situation of a tie.

Appointed Members
The IAG and IERS representatives to the IDS Governing
Board are appointed by the IAG Executive Committee andby the IERS Directing Board, respectively, for a maximumof two four-year terms. The DORIS System representative
and the Network representative are appointed by CNES
and IGN, respectively, for four-year terms without limitation. The Director of the Central Bureau and the Combination Center representative are the two other appointed
members.
In case of a resignation from the Governing Board, theCB, after consulting with the appropriate IDS components,
nominates a replacement candidate for election by the GB.
The replacement will serve until the end of the term of theresigned Board member.

GB Decisions
Most decisions at GB meetings are to be made by consensus orby a simple majority vote of the voting members present,
provided that there is a quorum consisting of at least six voting
members of the GB. GB decisions can be made through email
or other correspondence by a majority vote of the GB voting
membership. Changes in the IDS Terms of Reference andInternational DORIS Service (IDS)

Chairperson of the GB can only be made by a 2/3 majority ofthe members of the GB, i.e., by seven or more votes.

GB Meetings
The Board shall meet at least annually and at such othertimes as shall be considered appropriate by the Chairperson or at the request of three members. The Central Bureau
provides the secretariat of the GB.

IDS representatives to the IERS and the
IAG
Through the existing reciprocity agreement between the
IDS and the IERS, the IDS Analysis Coordinator serves as
the DORIS Technique Center representative to IERS, andas such, subject to Governing Board approval, is a memberof the IERS Directing Board (together with another person
selected by the IDS Governing Board). This arrangement
ensures full cooperation between the two services.

299

IDS Associates
IDS Associates are persons representing organizations thatparticipate in any of the IDS components. A participating
institution can submit a person s name, email, and primary
IDS function in its organization to the Central Bureau for
application to become an IDS Associate, with a limit often. The Governing Board approves all memberships. The
Governing Board reserves the right to appoint additional
associates who do not participate in any IDS components
but who contribute significantly to the IDS or whose activities rely on DORIS data and products. Such names arenominated directly by the IDS GB.
The Central Bureau maintains the current list of IDS
Associates and makes the list available on the IDS website.
IDS Associates vote for the incoming Analysis Centers’representative, the Data Centers’ representative, the Analysis Coordinator, and the Members-at-Large representatives
as members of the GB.
The GB must approve the list of IDS Associates eligible
for voting in the elections at least three months prior to theelection process. For the purposes of the election, current
and former GB members are also considered IDS Associates.
IDS Associates are considered IAG Affiliates.

IDS and DORIS quick reference list
1.
2.
3.
4.
5.

6.

IDS website
https://ids-doris.org/
Contacts
Central Bureau ids.central.bureau@ids-doris.org
Governing Board ids.governing.board@ids-doris.org
Data Centers
CDDIS: ftp://cddis.gsfc.nasa.gov/doris/
IGN: ftp://doris.ensg.eu and ftp://doris.ign.fr
Tables of Data and Products
https://ids-doris.org/ids/data-products/tables-of-data-products.html
IDS web service
https://ids-doris.org/webservice
DOR-O-T for DORis Online Tools (pronounced in French like the given name Dorothée) is the IDS web service developed to promote the use of the DORIS products. The current version of the service provides tools to browse timeseries in an interactive and intuitive way, and a network viewer.
Citation
The following article is suggested for citation in papers and presentations that rely on DORIS data and results:
Willis, P.; Lemoine, F.G.; Moreaux, G.; Soudarin, L.; Ferrage, P.; Ries, J.; Otten, M.; Saunier, J.; Noll, C.; Biancale, R.; Luzum, B., 2016. The International DORIS Service (IDS), recent developments in preparation for
ITRF2013, IAG SYMPOSIA SERIES, 143, 631-639, DOI: 10.1007/1345_2015_164

300

7.

The Geodesist’s Handbook 2020

DORISmailThe DORIS mail service is used to send information of general interest to the DORIS community. To send a DORISMail, use the following address: dorismail@ids-doris.org
8. List of the documentation
It gives a table compiling links to the various pages providing documents, grouped in four categories: DORIS systemcomponents; IDS information system; Publications, presentations; Documents
https://ids-doris.org/ids/reports-mails/documentation.html
9. List of presentations given at DORIS or IDS meetings
Full list of presentations given at DORIS or IDS meetings with the corresponding access links
https://ids-doris.org/ids/reports-mails/meeting-presentations.html
10. List of documents and links to discover the DORIS system
https://ids-doris.org/analysis-coordination/documents-related-to-data-analysis.html
11. List of DORIS publications in international peer-reviewed journals
https://ids-doris.org/ids/reports-mails/doris-bibliography/peer-reviewed-journals.html
12. Overview of the DORIS system
https://www.aviso.altimetry.fr/en/techniques/doris.html
13. Overview of the DORIS satellite constellation
https://ids-doris.org/doris-system/satellites.html
14. Site logs
DORIS stations description forms and pictures from the DORIS installation and maintenance department:
https://ids-doris.org/doris-system/tracking-network/site-logs.html
15. Virtual tour of the DORIS network with Google Earth
Download the file at https://ids-doris.org/doris-system/tracking-network/network-on-google-earth.html and visit the
DORIS sites all around the world.
16. IDS video channel
Videos of the DORIS-equipped satellites in orbit
https://www.youtube.com/channel/UCiz6QkabRioCP6uEjkKtMKg
17. IDS Newsletters
Find all the issues published in color with live links on the IDS website
https://ids-doris.org/ids/reports-mails/newsletter.html
18. Photo Gallery
https://ids-doris.org/ids/gallery.html

International GNSS Service (IGS)301

International GNSS Service (IGS)
Chair of the Governing Board: Gary Johnston (Australia)
Director of the Central Bureau: Allison Craddock (USA)
http://www.igs.org/

Background
For over twenty-five years, the International Global
Navigation Satellite System (GNSS) Service (IGS) has
carried out its mission to advocate for and provide freely andopenly available high-precision GNSS data and products.
IGS was first approved by its parent organization, theInternational Association of Geodesy (IAG), at a scientificmeeting in Beijing, China, in August of 1993. A quarter
century later, the IGS community gathered for a workshop
in Wuhan, China, in October/November 2018 to blaze a pathto Multi-GNSS through global collaboration.
The Mission of the IGS is to “provide on an openly
available basis, the highest-quality GNSS data, products,
services in support of the terrestrial reference frame; Earthobservation and research; Positioning, Navigation andTiming (PNT); and other applications that benefit thescientific community and society.”
In 2019, the IGS adopted an official slogan: “Providing
openly available GNSS data and products that benefit
science and society,” as well as an official organizational
vision: “A better understanding of the Earth through theapplication of GNSS.”

Community Collaboration
At the heart of the IGS is a strong culture of sharing
expertise, infrastructure, and other resources for the purposeof encouraging global best practices for developing anddelivering GNSS data and products all over the world. The
collaborative nature of the IGS community, which as of2019 includes over 140 GNSS stakeholder organizations
from 45 countries leverages this diversity to integrate andmake full use of all available GNSS technologies while
promoting further innovation. Over 15,000 product users,

some of whom comprise the backbone of the worldwide
geodetic community, ensure that new technologies andsystems are integrated into routine IGS products.
Responsive to this innovation, the IGS develops andpublicly releases standards, guidelines, and conventions forthe collection and use of GNSS data and products. The IGS
strives to maintain an international federation withcommitted contributions from its members. To view the listof IGS Governing Board members, please visit:
http://www.igs.org/about/gb

Underpinning Observing Systems andReference Frames
The IGS is a critical component of the IAG’s Global
Geodetic Observing System (GGOS), where it facilitates
cost-effective geometrical linkages with and among otherprecise geodetic observing techniques, including: Satellite
Laser Ranging (SLR), Very Long Baseline Interferometry(VLBI), and Doppler Orbitography and Radio Positioning
Integrated by Satellite (DORIS). These linkages arefundamental to generating and accessing the International
Terrestrial Reference Frame (ITRF).

Engagement with the United Nations
IGS engages with diverse organizations that have an interestin geodetic applications of GNSS. Notably, the IGS has
supported the development of the Global Geodetic
Reference Frame (GGRF) resolution, roadmap, andimplementation plan within the United Nations (UN) Global
Geospatial Information Management (GGIM) Committeeof Experts (http://ggim.un.org). IGS also participates in the
United Nations Office for Outer Space Affairs (UNOOSA)International Committee on GNSS (ICG).

302

The Geodesist’s Handbook 2020

International GNSS Service (IGS)

Data and Analysis Centers
The IGS ensures high reliability by building redundancy
into all its components. Critical to this activity are three
categories of data center – operational, regional, and global.
At the “ground level” are operational data centers, which are
in direct contact with IGS tracking sites, and are responsible
for such efforts as station monitoring and local archiving of
GNSS data. Operational data centers also validate, format,
exchange, and compress data. Regional data centers thencollect tracking data from multiple operational data centersor stations, maintaining a local archive and providing online
access to their data.
The six global data centers (Crustal Dynamics Data
Information System, Scripps Institution of Oceanography,
European Space Agency /ESAC, Korean Astronomy andSpace Science Institute, Institut National de l’Information
Géographique et Forestière, and Wuhan University) receive,
retrieve, archive and provide online access to tracking datafrom operational and regional data centers. The Data Center
Coordinator ensures coordination among data centers, aswell as global data centers archiving and backing up IGS
data and products, and maintaining a balance of data
holdings across the IGS network.
Analysis centers then receive and process tracking datafrom one or more data centers for the purpose of generating
IGS products, including satellite ephemerides, Earthrotation parameters, station coordinates, and clock
information. These products are produced in ultra-rapid,
rapid, final, and reprocessed versions for each analysis
center.
Associate analysis centers produce specialized products,
including ionospheric information, tropospheric parameters,
or station coordinates and velocities for global and regional
subnetworks. Regional and global network associate
analysis centers complement this work as new capabilities
and products emerge within the IGS.
Products from each analysis center are then combined
into a single set of orbit and clock products by the Analysis
Center Coordinator, who monitors and assists the activities
of analysis centers to ensure IGS standards for quality
control, performance evaluation, and analysis are
successfully executed. The Analysis Center Coordinatoralso regularly collaborates with the International Earth
Rotation and Reference System Service (IERS) on behalf of
the IGS.

Growing a Multi-GNSS IGS Network
The foundation of the IGS is a global network of over 500
permanent and continuously operating stations of geodetic
quality. These stations track signals from GPS, and303

increasingly also track signals from GLONASS, Galileo,
BeiDou, QZSS, NavIC (IRNSS) as well as space-based
augmentation systems (SBAS). As of late 2019, the IGS has
506 Stations, of which 308 are Multi-GNSS stations, and
259 Real-time stations. Central Bureau collaboration with
the Infrastructure Committee ensures appropriate and timely
addition and decommissioning of stations, along withcollaboration with the Antenna Working Group for regularchanges to station antennas and rcvr_ant.tab file. The
percentage of multi-GNSS capable IGS network is expected
to grow in the coming years.
The IGS Multi-GNSS Experiment (MGEX) was
founded in 2012 to build a network of GNSS tracking
stations, characterize the space segment and user equipment,
develop theory and data-processing tools, and generate data
products for emerging satellite systems. The stations within
its network contain a diverse assortment of receiver andantenna equipment that are recognized and characterized by
the IGS in equipment description files. Other than GPS andGLONASS, no combination process has yet been
implemented within IGS for precise orbit and clock
products of the other, newer, constellations. Despite this,inter-comparison among analysis centers, as well as
utilizing Satellite Laser Ranging (SLR), has been used toassess the precision or accuracy for various products.
The growing role of multi-GNSS within the IGS
network was benchmarked by the transition of MGEX to
official IGS Project status in 2016. For the sake ofconsistency, and as a nod to its heritage, use of the acronym“MGEX” has been retained. MGEX and its associatedMulti-GNSS Working Group recently published acomprehensive paper detailing its achievements in the last
five years, future prospects, and challenges. The article,
published in Advances in Space Research, Volume 59, Issue
7, 1 April 2017, Pages 1671–1697, discusses the multiGNSS products derived from the IGS monitoring station
network as well as progress made within the MGEX Project
to include BeiDou, Galileo, and QZSS for precise point
positioning, atmospheric research, and other applications.
Further improvements are expected through bettercharacterization of spacecraft and respective refinements ofradiation pressure models, antenna phase center variations,and other effects. In response to this, the Multi-GNSS
Working Group released a White Paper, titled “Satellite andOperations Information for Generation of Precise GNSS
Orbit and Clock Products.” The paper discusses theparameters needed to ensure the highest possible
performance of IGS products for all constellations andclearly articulates the need for open provision of satellite
and certain other operations information by the GNSS
providers.

304

A Multi-GNSS Future
Though the accuracy of current IGS multi-GNSS products
lags standard IGS products for GPS and GLONASS, multiGNSS paves the way for complete exploitation of new
signals and constellations in navigation, surveying,geodesy, and remote sensing. For complete, current
information about MGEX, please visit the MGEX part of
the IGS website: http://mgex.igs.org/.
As it enters its second quarter-century, the IGS is
evolving into a truly multi-GNSS service. In response toever-growing applications for precise GNSS data as a public

The Geodesist’s Handbook 2020

utility, the IGS conducts regular reviews of its activities,
products, and services. The IGS also works with ICG todevelop common understandings of the requirements for
system monitoring through a joint pilot project with the
ICG’s International GNSS Monitoring and Assessment(IGMA) subgroup.
IGS also looks outward to other techniques through its
participation in the IAG’s GGOS, which has illuminated
how SLR observations to GNSS satellites, as well as GNSS
observation of non-GNSS satellites, has a key role to playin improving our understanding of observational errors andthus drive further improvement of IGS products.

International Laser Ranging Service (ILRS)

305

International Laser Ranging Service (ILRS)
Chairman of the Governing Board: Toshimichi Otsubo (Japan)
Director of the Central Bureau: Michael Pearlman (USA)Secretary of the Central Bureau: Carey Noll (USA)
Analysis Coordinator: Erricos C. Pavlis (USA)
http://ilrs.gsfc.nasa.gov/

Development
Satellite Laser Ranging (SLR) was established in the mid1960s, with early ground system developments by NASA,
SAO, and CNES. Early US and French satellites provided
laser targets that were used mainly for inter-comparison
with other tracking systems, refinement of orbit determination techniques, and as input to the development of groundstation fiducial networks and global gravity field models.
Early SLR brought the results of orbit determination and station positions to the meter level of accuracy. The SLR network was expanded in the 1970s and 1980s as other groups
built and deployed systems, and technological improvements began the evolution toward the decimeter and centimeter accuracy. Since 1976, the main geodetic target has
been LAGEOS (subsequently joined by LAGEOS-2 in1992), providing the backbone of the SLR technique’s contribution to the realization of the International Terrestrial
Reference Frame (ITRF). Lunar tracking activity began in1969 after the deployment of the first retro-reflector arrayon the surface of the Moon by the Apollo 11 astronauts.
Tracking campaigns were initially organized through
COSPAR and through the Satellite and Lunar Laser Ranging (SLR/LLR) Sub-commission on the Coordination ofSpace Techniques for Geodesy and Geodynamics (CSTG).
With strong encouragement from the President of the
CSTG, the Sub-commission Steering Committee undertook
the formation of the International Laser Ranging Service,
ILRS in April 1998, following a similar initiative that had
brought the GPS community together under the International GPS (now GNSS) Service, IGS, in 1993. The ILRS is

one of the space geodetic services of the International Association of Geodesy (IAG) and is a member of the IAG’s
Global Geodetic Observing System (GGOS).
The ILRS is a major component of GGOS, providing observations that contribute to the determination of the threefundamental geodetic observables and their variations, that
is, Earth's shape, Earth's gravity field and Earth's rotationalmotion. The ILRS continues as one of the fundamental inputs to the ITRF. Currently, 40 stations in the ILRS network
track over 100 satellites in LEO, MEO, GNSS, and synchronous orbits. Some stations in the ILRS network support lunar ranging, with plans to extend ranging to interplanetary
missions with optical transponders.
On the current path toward mm accuracy SLR and LLRpractitioners are now building new systems and upgrading
old ones to improve ground system performance using
higher pulse repetition rates (0.1 – 100 kHz) for faster dataacquisition; smaller, faster slewing telescopes for more
rapid target acquisition and pass interleaving; capabilities toranging from Low Earth Orbiting (LEO) satellites to the
Earth navigation satellites; more accurate pointing for
greater link efficiency; narrower laser pulse widths for
greater precision; new detection systems for greater ranging
accuracy; greater temporal, spatial, and spectral filtering for
improved signal to noise conditions; more automation for
operational economy (24/7) and greater temporal coverage;
and modular construction and more off-the-shelf components for lower fabrication/operations/ maintenance cost.
Over the next 5 years, considerable expansion to the
ILRS network is anticipated (see Table 1). However significant geographic gaps will exist in Africa, Latin America,
Oceana, and Antarctica.

306

The Geodesist’s Handbook 2020

Table. Future ILRS Network Developments
Site Name
La Plata, Argentina
San Juan, Argentina
Metsähovi, Finland
Greenbelt, MD, USA
Haleakala, HI, USA
McDonald, TX, USA
Ny Ålesund, Norway
Ensenada, Mexico
Java, Indonesia
Gran Canaria, Spain
Tahiti, French Polynesia
Mt Abu, India
Ponmundi, India
Tsukuba, Japan
Yebes, SpainType
Upgraded core site
Upgraded SLR system
New SLR system
Replacement core site
Replacement core site
Replacement core site
New core site
New SLR site
New SLR site
New SLR in core site
New SLR system
New SLR site
New SLR site
New SLR site
New SLR site

MissionThe ILRS collects, merges, analyzes, archives and distributes Satellite Laser Ranging (SLR) and Lunar Laser Ranging (LLR) observation data sets of sufficient accuracy to satisfy the GGOS objectives of a wide range of scientific, engineering, and operational applications and experimentation. The basic observable is the precise time- of-flight of an
ultra-short laser pulse to and from a retroreflector-equipped
satellite. These data sets are used by the ILRS to generate anumber of fundamental added value products, including but
not limited to:x Centimeter accuracy satellite ephemerides;
x Earth orientation parameters (polar motion and length ofday);
x Three-dimensional coordinates and velocities of the
ILRS tracking stations;x Time-varying geocenter coordinates;
x Static and time-varying coefficients of Earth's gravity
field;x Fundamental physical constants;
x Lunar ephemerides and librations;x Lunar orientation parameters.

Structure
The ILRS structure includes the following permanent components:
x Tracking Station Network;
x Operations Centers;x Global Data Centers;x Analysis, Lunar Analysis, Associate Analysis, and Combination Centers;

Agency
BKG, Germany
NAOC, China
FGI, Finland
NASA, USA
NASA, USA
NASA, USA
NMA, Norway/NASA, USA
IPIE, Russian Federation
IPIE, Russian Federation
IPIE, Russian Federation
IPIE, Russian Federation
ISRO, India
ISRO, India
JAXA, Japan
IGS, Spain

Timeframe
2020 – 2021
2020 – 2021
2020 – 2021
2022 – 2024
2024 – 2026
2022 – 2025
2022 – 2025
2022 – 2026
2022 – 2026
2022 – 2026
2022 – 2026
2020 – 2022
2020 – 2022
2022 – 2024
2022 – 2024

x Central Bureau;x Governing Boardx Specialized Standing Committees (Analysis, Missions,
Networks and Engineering, Data Formats and Procedures, and Transponders).
Information on these permanent components can be foundin the ILRS website (http://ilrs.gsfc.nasa.gov/). From time
to time, the ILRS also establishes temporary Study Groups
to address timely topics.

Governing Board (2019-2020)
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x

Michael Pearlman, Ex-officio, Director Central Bureau
Carey Noll, Ex-officio, Secretary Central Bureau
Urs Hugentobler, Ex-officio, Repr. IAG Commission 1
Daniela Thaller, Appointed, IERS Repr. to ILRS
Giuseppe Bianco, Appointed, EUROLAS Network
Repr.
Georg Kirchner, Appointed, EUROLAS Network Repr.
James Bennett, Appointed, WPLTN Network Repr.
Zhang Zhongping, Appointed, WPLTN Network Repr.
Jan McGarry, Appointed, NASA Network Repr.
Stephen Merkowitz, Appointed, NASA Network Repr.
Vincenza Luceri, Elected, Analysis Center Repr.
Erricos Pavlis, Elected, Analysis Center Representative
Christian Schwatke, Elected, Data Center Repr.
Jean-Marie Torre, Elected, LLR Representative
Toshimichi Otsubo, Elected, At Large Repr. (Chair)
Matthew Wilkinson, Elected, At Large Representative
Ulrich Schreiber, Board Appointed Member
Krzysztof Sośnica, Board Appointed Member

International Laser Ranging Service (ILRS)

Past chairs of the ILRS Governing Board
x John Degnan
x Werner Gurtner (deceased)x Graham Applebyx Giuseppe Bianco

Products
The most important aspects of the SLR and LLR observations are absolute accuracy and long, stable time histories at
a number of sites. Accuracy approaches the level of a few
mm for modern stations; time histories can be 40 years ormore on some satellites (e.g., LAGEOS, Starlette, Beacon),and now more than 50 years on the Moon. Since the inception of the service, the ILRS has put the generation of official analysis products high on its agenda. Official submissions to the IERS include weekly solutions for station coordinates and Earth Orientation Parameters (EOPs) submitted
on a daily frequency. Additionally, some of the ILRS Analysis Centers (ACs) submit estimates of GM and time-varying geocenter motion to the IERS Global Geophysical Fluids Center. Other user products include static and time-varying coefficients of Earth's gravity field, accurate satellite
ephemerides for POD and validation of altimetry, relativity,and satellite dynamics, backup POD for other missions, andLunar ephemeris for relativity studies and lunar libration forlunar interior studies.
The products of the Analysis, Lunar Analysis, and Associate Analysis Centers are made available to the scientificcommunity through the two Global Data Centers:x Crustal Dynamics Data Information System (CDDIS) at
NASA’s Goddard Space Flight Center, Greenbelt, MD,USA
x European Data Center (EDC), at DGFI - TUM, Munich,Germany
The high accuracy of SLR/LLR data products support many
scientific, engineering, and operational applications including:x Realization and maintenance of the International Terrestrial Reference Frame (ITRF)
x Access to Earth’s center of mass relative to the global
network and its time variations
x Monitoring three-dimensional deformations of the solid
Earthx Monitoring Earth rotation variations and polar motion
x Monitoring the long wavelength static and dynamic
components of Earth's gravity field.
x Supporting, via precise ranging to altimeter satellites,
the monitoring of variations in the topography of the liquid and solid Earth (ocean circulation, mean sea level,ice sheet thickness, wave heights, vegetation canopies,
etc.)

307

x Calibration and validation of microwave tracking techniques (e.g., GPS, GLONASS, Galileo, BeiDou, and
DORIS)x Picosecond global time transfer experiments
x Determination of non-conservative forces acting on satellites
x Determination of satellite attitude
x Astrodynamical observations including determination of
the dynamic equinox, obliquity of the ecliptic, and theprecession constantx Gravitational and general relativistic tests, including
Einstein's Frame-dragging, Equivalence Principle, theRobertson-Walker b parameter, and time rate of changeof the gravitational constant, G
x Lunar physics including the dissipation of rotational energy, shape of the core-mantle boundary (Love Numberk2), and free librations and stimulating mechanisms
x Solar System ties to the International Celestial Reference Frame (ICRF)
x Tracking of space debris

Contacts
Michael Pearlman, Director, ILRS Central Bureau
mpearlman@cfa.harvard.edu
Carey Noll, Secretary, ILRS Central Bureau
Carey.Noll@nasa.gov
Toshi Otsubo, Chair, ILRS Governing Boardt.otsubo@r.hit-u.ac.jp
Erricos Pavlis, ILRS Analysis Coordinator
epavlis@umbc.edu

Publications
The ILRS Central Bureau maintains a comprehensive website as the primary vehicle for the distribution of information
within the ILRS community. This site can be accessed at
http://ilrs.gsfc.nasa.gov. Many ILRS and related publications and reports can now be accessed online through the
ILRS website including:x ILRS Terms of Reference andx ILRS Standing Committee charters, members, reports
x ILRS network description and status
x ILRS satellite descriptions and tracking information
x ILRS workshop/meeting reports and presentations
x ILRS service reports
x ILRS associates directoryx ILRS organization and technical contacts
x Science and engineering references and reports

308

The Geodesist’s Handbook 2020

International VLBI Service for Geodesy andAstrometry (IVS)
Chair of Directing Board: Axel Nothnagel (Austria)
Coordinating Center Director: Dirk Behrend (USA)https://ivscc.gsfc.nasa.gov

Development
The International VLBI Service for Geodesy and Astrometry (IVS) is an international collaboration of organizations,which operate or support Very Long Baseline Interferometry (VLBI) components. IVS was established in 1999 andbecame a service of IAG that year. In 2000, IVS was recognized as a service of the International Astronomical Union(IAU). In 2013 an agreement was signed between the IVS
and the International Science Council (ISC; formerly ICSU)
accepting the service as a Network Member of ISC’s World
Data System (WDS). The IVS interacts closely with the International Earth Rotation and Reference Systems Service(IERS), which is tasked by IAU and IUGG/IAG with maintaining the international celestial and terrestrial reference
frames (ICRF and ITRF).

Mission/Objectives
The objectives of IVS are:x To provide a service to support geodetic, geophysical,
and astrometric research and operational activities.
x To promote research and development activities in all
aspects of the geodetic and astrometric VLBI technique.
x To interact with the community of users of VLBI products and to integrate VLBI into a global Earth observing
system.
To meet these objectives, IVS coordinates VLBI observing
programs, sets performance standards for VLBI stations, establishes conventions for VLBI data formats and data products, issues recommendations for VLBI data analysis software, sets standards for VLBI analysis documentation, andinstitutes appropriate VLBI product delivery methods to ensure suitable product quality and timeliness. IVS closely co-ordinates its activities with the astronomical community because of the dual use of many VLBI facilities and technologies for both astronomy and astrometry/geodesy.

Products
VLBI data products currently available arex All components of Earth orientationx Terrestrial reference frame
x Celestial reference framex Tropospheric parametersx Baseline lengths
All VLBI data products are archived in IVS Data Centers
and are publicly available.

Structure / Board / Members
IVS accomplishes its goals through Permanent Components. As of 2020 the IVS has:x 34 Network Stations, acquiring high performance VLBI
data.
x 3 Operation Centers, coordinating activities of Network
Stations.
x 8 Correlators, processing acquired data, providing feedback to stations and providing processed data to analysts.
x 5 Data Centers, distributing products to users, providing
storage and archiving functions.
x 29 Analysis Centers, analyzing the data and producing
results and products.
x 7 Technology Development Centers, developing new
VLBI technology.
x 1 Office for Outreach and Communications, promoting
knowledge of the VLBI technique and IVS activities.
x 1 Coordinating Center, coordinating daily and long-term
activities of IVS.

International VLBI Service for Geodesy and Astrometry (IVS)

All together there are 88 Permanent Components, representing 42 organizations in 21 countries, and ~315 individuals who are Associate Members. The 42 organizations that
support IVS components are IVS Member Organizations.
There are also 6 Affiliated Organizations that cooperatewith IVS on issues of common interest but do not support
an IVS component.
In addition, the IVS has a Directing Board to determine
policies, standards, and goals. The current IVS Directing
Board consists of the following members (alphabetical):
1. J. Anderson (Germany) Analysis and Data Centers Representative
2. D. Behrend (USA) Coordinating Center Director
3. P. Charlot (France) IAU Representative
4. F. Colomer (Spain) Network Stations Representative
5. A. de Witt (South Africa) At Large member
6. J. Gipson (USA) Analysis Coordinator
7. R. Haas (Sweden) IERS representative
8. D. Hall (USA) Correlators and Operation Centers Representative
9. H. Hase (Argentina) Network Stations Representative
10. E. Himwich (USA) Network Coordinator
11. N. Kotary (USA) Office for Outreach and Communications
12. J. Li (China) Member-at-Large
13. E. Nosov (Russia) At Large member
14. A. Nothnagel (Austria) Analysis and Data Centers Representative
15. C. Ruszczyk (USA) Technology Development Centers
Representative
16. O. Titov (Australia) IAG Representative
17. G. Tuccari (Italy) Technology Coordinator309

The Office for Outreach and Communications was created in 2019 to establish and maintain an outreach programthat would promote knowledge of the VLBI technique andthe activities of the IVS and foster an understanding of theimportance of its products for the scientific communities
and the general public. The outreach Web pages are being
established under the URL https://vlbi.org, and fledgling Twitter and Instagram accounts have been created. A new IVS logo
was designed, replacing the 20-year-old logo.

Committees and Working Groups
IVS currently has one active working group, one task force,and three committees:x Working Group 7 on Satellite Observations with VLBI.
x Task Force on Seamless Auxiliary Data.
x Observing Program Committee (OPC).
x Committee on Training and Education (CTE).
x VGOS Technical Committee (VTC).

Publications and Meetings
IVS publishes a Biennial Report, a thrice-annual Newsletter,and Proceedings from its biennial General Meeting. All publications are published electronically on the Web site. IVS
holds a General Meeting every two years, a Technical Operations Workshop every two years, and an Analysis Workshop every year. Information about all IVS activities isavailable at the IVS Web site under the URLs https://vlbi.org
and https://ivscc.gsfc.nasa.gov.

310

The Geodesist’s Handbook 2020

International Gravity Field Service (IGFS)
R. Barzaghi,
Politecnico di Milano, Italyriccardo.barzaghi@polimi.it
Director of Central Bureau: G. Vergos
Aristotle University of Thessaloniki, Greece
vergos@topo.auth.gr
Chair:

http://igfs.topo.auth.gr/

Objectives
IGFS is a unified "umbrella" IAG service, which will:x Coordinate collection, validation, archiving anddissemination of gravity field related datax Coordinate courses, information materials and generalpublic outreach relating to the Earth’s gravity fieldx Unify gravity products for the needs of GGOS, theGlobal Geodetic Observing System
The IGFS coordinates the following “Level-1” IAG services:x BGI (Bureau Gravimetrique International), Toulouse,
Francex ISG (International Service for the Geoid), Politecnico
di Milano, Milano, Italy
x IGETS (International Geodynamics and Earth Tides
Service), EOST, Strasbourg, Francex ICGEM (International Center for Global EarthModels), GFZ, Potsdam, Germanyx IDEMS (International Digital Elevation Model
Service), ESRI, Redlands, CA, USA
Furthermore, IGFS has one Product Center, namely
COST-G (Combination Service for Time-variable Gravity
fields) at AIUB, Berne, Switzerland.
The overall goal of IGFS is to coordinate the servicingof the geodetic and geophysical community with gravity
field related data, software and information. The combined
data of the IGFS entities will include global geopotential
models, terrestrial, airborne, satellite and marine gravity
observations, Earth tide data, GPS/leveling data, digitalmodels of terrain and bathymetry, as well as ocean gravity field and geoid from satellite altimetry. Both the staticand the temporal variations of the gravity field will becovered by the IGFS.
IGFS will – in cooperation with the Services - make aspecial effort in trying to secure release of data from nati-

onal and international institutions holding data on the spatial and temporal gravity variations, geoid and the surface
heights of the Earth, to make them widely available to thescientific community.
IGFS will coordinate regional conferences, tutorials
and schools to train young scientists and members of national institutions in the various aspects of the gravity field
science, computations, and data collection. IGFS will
maintain a publication activity related to the gravity field,
especially through “Newton’s Bulletin”.

Structure
The Service is organized by means of the following
structure:x Advisory Board
x Central Bureau
x Product Centers
x Services
The Advisory Board is composed of:x Directors (or their delegates) of each of theServices/Centers of IGFS
x Chairs of the IGFS working groups
x Presidents (or their delegates) of the IAG Commissions
related to the Service workx A representative of the IAG Executive Committee(IAG- EC)x Members appointed among the IAG affiliates.
The Advisory Board:x Coordinates the scientific strategy
x Coordinates the joint activity of the Centers
x Oversees the participation of the Service ininternational projects
x Presents to the IAG-EC proposals for associating newcenters

International Gravity Field Service (IGFS)

x Elects the IGFS affiliates upon nomination by theServices/Centers or affiliates.
The Advisory Board is appointed for four years between
IUGG General Assemblies. The existing Advisory Board
selects new members as required and nominates the Chairof the IGFS. The election is to be confirmed by the IAGEC. The Advisory Board makes decisions by majority
vote; it can also vote by email. The Advisory Board decides the Terms of Reference for IGFS.

IGFS Services and Centers
The IGFS Services and Centers are the “operating arms” of
IGFS. They are committed to produce services and products related to the gravity field of the Earth and/or theplanets and are approved by the IAG-EC. Services andCenters can include bodies of structures external to the
IAG (e.g., the BGI which is reporting to FAGS). They will
have their own governing bodies, nominated according tointernal rules, also taking into account the interests of the
supporting entities. In particular, each governing body will
have a Director, elected according to internal rules.
Services and Centers will maintain a list of data andproducts, providing them to the general public according totheir policy of dissemination. They will deliver services
in the form of data archiving, data analysis and dissemination, software, training on gravity field estimation, support to field campaigns etc. COST-G, the IGFS ProductCenter, will provide consolidated monthly global gravity
field models in terms of spherical harmonic coefficientsand derived grids by combining solutions from individual
Analysis Centers. The activities of each Service/Center
will be reviewed annually by the IAG-EC.

IGFS Central Bureau
The IGFS Central Bureau will act as the central coordination and communication center of the IGFS. The Central
Bureau will provide: a link between the IGFS entities,
IAG, and external projects, networks or organizations(oceanic, atmospheric, hydrologic…); a link to the GGOS
Bureaus in order to communicate their requirements andrecommendations to the IGFS Services. It will also implement standards and recommendations related to gravity
field observations, secure consistency with geometric standards and promote their use within the geoscience community. Furthermore, the Central Bureau will maintain the
IGFS website and arrange gravity field related meetings
and workshops.

311

Working groups
JWG GGOS 0.1.3: Implementation of the International
Height Reference Frame (IHRF) (joint with GGOS, Commission 1, Commission 2, ICCT)JWG GGOS: Towards a consistent set of parameters forthe definition of a new GRS (joint with GGOS, Commissions 1, Commission 2, ICCT, IERS Committee on EGV)JSG T26: Geoid/quasi-geoid modelling for the realizationof the geopotential height datum (joint with Commission 2,
GGOS, ICCT)JSG T.37: Theory and methods related to the combinationof high-resolution topographic/bathymetric models in geodesy (joint with ICCT, IDEMS)

IGFS Advisory Board
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x

H. Abd-Elmotaal (Egypt)
J.-P. Barriot (French Polynesia)
S. Bonvalot (France)
S. Bettadpur (USA)R. Forsberg (Denmark)Y. Fukuda (Japan)
T. Gruber (Germany)
J. Huang (Canada)
E. S. Ince (Germany)
A. Jäggi (Switzerland)
K. Kelly (USA)U. Marti (Switzerland)
T. Otsubo (Japan)
R. Pail (Germany)
M. Reguzzoni (Italy)
M. G. Sideris (Canada)
L. Sanchez (Germany/Columbia)
I. N. Tziavos (Greece)
L. Vitushkin (Russia)
Y. Wang (USA)
H. Wziontek (Germany)

312

The Geodesist’s Handbook 2020

International Centre for Global EarthModels (ICGEM)
Director: E. Sinem Ince (Germany)
http://icgem.gfz-potsdam.deTerms of Reference
The determination of Earth’s global gravity field is one of
the main tasks of geodesy: it serves as a reference forgeodesy itself and provides essential information about the
Earth, its interior and its fluid envelope for all geosciences.
Thus, it is important to model the gravity field globally andmake the state-of-the-art models available to public as
geodetic products. With accurate satellite measurements, it
is now possible to map the static gravity field as well as its
variations with much higher spatial and temporal resolutions
compared to the first of its kinds. The list of such models is
continuously growing and requires dedicated maintenance.
International Centre for Global Earth Models (ICGEM)
is one of the five services coordinated by the International
Gravity Field Service (IGFS) of the International
Association of Geodesy (IAG). The primary objective of the
ICGEM service is to collect and archive all existing staticand temporal global gravity field models and provide an
online interactive calculation service for the computation ofgravity field functionals freely available to the generalpublic. The calculation of the different functionals of thegeopotential (e.g. geoid, gravity anomaly, gravity
disturbance, equivalent water height) from a defined global
model, on a specified grid or points with respect to a definedreference system, is not trivial for science and scientists andis a responsibility of geodesy too. Additionally, it isimportant to visualize the spatial and temporal distributionof the global gravity field and therefore interactive
visualization is also provided by ICGEM.

Development
With the initiation of IGFS and the commitment for hosting
and financial support by German Research Centre forGeosciences (GFZ), the ICGEM service was established in2003 and aimed to collect and archive static gravity fieldmodels initially. Due to the increasing interest of the users
and model developers, temporal gravity field models havealso been made available on the same platform after thelaunch of GRACE mission. The service has been
extensively used and promises further developments toserve multidisciplinary research.

Objectives
ICGEM is designed as a web-based service andcomprehends:
x collecting and long-term archiving of existing static
global gravity field models, solutions from dedicatedshorter time periods (e.g. monthly GRACE/GRACE-FO
models), and topographic gravity field models,x making the above-mentioned models available on the
web in a standardized format as described in Barthelmes
and Förste (2011),
x since late 2015, the possibility of assigning DigitalObject Identifiers (DOIs) to the models,x a web interface to calculate gravity field functionals
from the spherical harmonic models on freely selectablegrids and user-defined points,x a 3-D interactive visualization of the models (geoid
undulations and gravity anomalies),
x quality checks of the static gravity field models via
comparisons with other models in the spectral domain
and w.r.t. GNSS/levelling-derived geoid undulations,x the visualization of surface spherical harmonics as tutorial,
x the theory and formulas of the calculation service
documented in GFZ’s Scientific Technical Report
STR09/02 (Barthelmes, 2013),
x manuals and tutorials for global gravity field modellingand usage of the service (Barthelmes, 2014) andInternational Centre for Global Earth Models (ICGEM)

313

scientific journal papers for educational and reference
purposes (Ince et al. 2019) and finally,
x the ICGEM web-based gravity field discussion forum
for questions on ICGEM and its products and to request
knowledge exchange.

Services
The Models
ICGEM relies on other centres and institutes who develop
static and temporal gravity field models that are madeavailable on ICGEM. By February 2020, 176 static gravity
field models are listed in ICGEM (http://icgem.gfzpotsdam.de/tom_longtime). Apart from 17 older models, allother models are available in the form of spherical harmoniccoefficients. Models from dedicated time periods (e.g.
monthly solutions from GRACE) of Science Data System
Centres CSR, JPL, and GFZ, and various other solutions
such as from CNES/GRGS and ITSG are also available.
Recently, the combined monthly models produced based on
the COST-G standards have been made available(http://icgem.gfz-potsdam.de/series). Finally, topographic
gravity field models have been made available for the firsttime in 2014 as requested by users and model developers(http://icgem.gfz-potsdam.de/tom_reltopo). Such models
can enhance the benefit from the gravity field products inhigh frequency components and in multidisciplinary studies.

Fig. 1 Visualization (geoid) of a global gravity field model.

Digital Object Identifiers (DOI)
In order to support open science and open data, ICGEM
does not only provide free access to the models but supports
the assignment of Digital Object Identifiers (DOI) to makethe models citable. Since 2016, ICGEM together with the
GFZ Library and Information Services, provides a service
to assign a DOI to the models, i.e. to the datasets of thecoefficients. Currently, over 30 models have been assigned
DOIs. ICGEM encourages the model developers to request
DOI at http://pmd.gfz-potsdam.de/panmetaworks/metaedit.
The 3D Visualization
An online interactive service for the visualization of themodels (in terms of height anomalies and gravity anomalies)
as illuminated projection on a freely rotatable sphere isavailable (http://icgem.gfz-potsdam.de/vis3d/longtime, seealso Fig. 1). Differences of two models, arbitrary degree
windows, zooming in and out, are possible. The
visualization of spherical harmonics is also possible fortutorial purposes (see Fig. 2).

Fig. 2 3D visualization of spherical harmonics as a tutorial.
The images show (a) tesseral (l = 9, m = 4), (b) sectorial (l= 9, m = 9), and (c) zonal (l = 9, m = 0) spherical harmonics(Ince et al. 2019).
The Calculation Service
A web-interface to calculate gravity field functionals fromthe spherical harmonic models on freely selectable grids or
at user-defined points with respect to a reference system of
the user’s choice is provided. The following functionals areavailable in the grid calculation (http://icgem.gfzpotsdam.de/calcgrid):
x pseudo height anomaly on the ellipsoid (or at arbitraryheight above the ellipsoid)x height anomaly (on the Earth’s surface)x geoid height (height anomaly plus spherical shell
approximation of the topography)
x gravity disturbance314

x gravity disturbance in spherical approximation (atarbitrary height above the ellipsoid)
x gravity anomaly (classical and modern definition)
x gravity anomaly (in spherical approximation, at arbitraryheight above the ellipsoid)x simple Bouguer gravity anomaly
x gravity at the Earth’s surface (including the centrifugal
acceleration)
x gravity on the ellipsoid (or at arbitrary height above theellipsoid, including the centrifugal acceleration)
x gravitation on the ellipsoid (or at arbitrary height above
the ellipsoid, without centrifugal acceleration)
x second derivative in spherical radius direction (atarbitrary height above the ellipsoid)x equivalent water height (water column)
Beside the functionals listed above, deflections ofvertical can be computed at user-defined points(http://icgem.gfz-potsdam.de/calcpoints).
In the calculation setting, filtering is possible byselecting the range of used coefficients or the filter length ofa Gaussian averaging filter. The calculated grids together
with the calculation settings included in the header part canbe downloaded once the calculation is completed. For gridcalculations, the corresponding plots created using GMT (inPostscript or Portable Network Graphics format) areavailable for download (see Fig. 3). Since 2018, calculations
on user-defined points are available (see Fig. 4) and theresults can be downloaded in ASCII format as well.

The Geodesist’s Handbook 2020

Fig. 4 User-defined point calculation interface and settings(Ince et al. 2019)

Fig. 5 Comparison of the models w.r.t. GNSS-levelling:
Root mean square (rms) about mean of GNSS / levelling
minus gravity field model derived geoid heights [m]. Notethe XGM2019 is evaluated for two different Nmax.

Fig. 3 Example of grid and plot generation by thecalculation service: gravity disturbances of the Chicxulub
crater region from the model XGM2019e_2159.

ICGEM continues to evaluate the static gravity field models
w.r.t. GNSS/levelling derived geoid undulations (see the listin Fig. 5) and in the spectral domain w.r.t. already reliable
models (see Figs. 6). Visualization of the improvement of
the satellite-only models w.r.t. EIGEN-6C4 over the years
are shown as a function of spatial resolution in Fig. 7.Apartfrom the gravity field models of the Earth, ICGEM hosts
similar models for other celestial bodies (Moon, Mars,
Venus and Ceres). A 3D visualization of the Moon’s geoid
is shown in Fig. 8

International Centre for Global Earth Models (ICGEM)

Fig. 6 Comparison of the satellite-only model
GO_CONS_GCF_2_DIR_R6 in the spectral domain with
one of the most recent models that combines satellite andterrestrial data (EIGEN-6C4).

315

Fig. 7 Visualization of the improvement of satellite-onlymodels over the past decades: Geoid differences to themodel EIGEN-6C4 as a function of spatial resolution.

FAQs and Discussion ForumIn May 2017, to support the users from different disciplines
and levels, ICGEM introduced the Frequently Asked
Questions (FAQs) and their short and detailed answers.
Such answers are expected not only to help students andresearchers for educational purposes, but also to understandthe background of the ICGEM products. Moreover, toincrease the knowledge exchange with and among the users
ICGEM’s discussion forum is expanded and it isencouraged to be used to share gravity field related
questions and information.
Fig. 8 Visualization of the “Geoid” of the Moon.

316

The Geodesist’s Handbook 2020

Outlook

Other references:

ICGEM is a unique platform to collect and provide accessto a comprehensive list of gravity field models that are ofstatic, temporal and topographic kind. Beside the calculationand visualization services, complementary documentations
about the models are made available. The ICGEM service isa worldwide service and is not aimed to a specific user
community. It continues to update its content with newmodels and additional features as requested by users, anddepending on availability. The coordination andcommunication of the ICGEM Service are made through the
ICGEM’s staff (icgem@gfz-potsdam.de) with input frominternational contributors.

Barthelmes, F.: Definition of Functionals of the
Geopotential and Their Calculation from Spherical
Harmonic Models: Theory and formulas used by thecalculation service of the International Centre for Global
Earth Models (ICGEM), Scientific Techni- cal Report
STR09/02, Revised Edition, January 2013, Deutsches
GeoForschungZentrum
GFZ,
https://doi.org/10.2312/GFZ.b103-0902-26,2013.
Barthelmes, F.: Global Models, in: Encyclopedia of
Geodesy, edited by: Grafarend, E., Springer
International
Publishing,
1–9,
https://doi.org/10.1007/978-3-319-02370-0_43-1, 2014.
Barthelmes, F. and Förste, C: The ICGEM-format. Potsdam:
GFZ German Research Centre for Geosciences,available at: http: //icgem.gfz-potsdam.de/ICGEMFormat-2011.pdf (last access: 25 February 2020), 2011.

Data Policy
Access to global gravity field models, derived products andtutorials, once offered by the center, shall be unrestricted forany external user.

Reference
Reference for ICGEM Service and its products is as follows:
Ince, E. S., Barthelmes, F., Reißland, S., Elger, K., Förste,
C., Flechtner, F., and Schuh, H.: ICGEM – 15 years ofsuccessful collection and distribution of global gravitationalmodels, associated services, and future plans, Earth Syst.
Sci. Data, 11, 647–674, https://doi.org/10.5194/essd-11647-2019, 2019.

Staff
ICGEM is hosted by GFZ Potsdam. After the long-time
director of the ICGEM service Franz Barthelmes’
retirement, current staff consists of
E. Sinem InceSven Reißland
The staff is allocated part-time and responds to queries on a
best-effort basis.

Point of Contact
E. Sinem Ince
Helmholtz Centre Potsdam
GFZ German Research Centre for Geosciences
Telegrafenberg,
D-14473 Potsdam,
Germany
E-mail: elmas.sinem.ince@gfz-potsdam.deInternational Digital Elevation Model Service (IDEMS)

317

International Digital Elevation Model Service (IDEMS)
Director: Kevin M. Kelly (USA)https://idems.maps.arcgis.com/home/

Introduction
The International Digital Elevation Model Service (IDEMS)
is one of five Servics of the International Gravity Field Service (IGFS) of the International Association of Geodesy(IAG). IDEMS provides a focus for distribution of data andinformation about digital elevation models, spherical-harmonic models of Earth’s global topography, lunar and planetary DEM, relevant software and related datasets (including representation of Inland Water within Digital Elevation
Models) which are available in the public domain. IDEMS
is hosted and operated by Environmental Systems ResearchInstitute (Esri) (http://www.esri.com/).

Products
IDEMS currently hosts 31 sources of terrestrial and planetary DEM data providers (see Table 1) and 126 referencesof DEM and bathymetry research papers relevant to geodesy
and Earth sciences. The IDEMS bibliography is updated regularly (currently two times per year) to provide the user
community with an up-to-date overview over key developments in DEM production, validation and applications. The
IDEMS bibliography includes recent and seminal papers
describing relevant data sets of Earth's topography, bathymetry, ice data and composite elevation models. Some
DEM sources appear in multiple categories to facilitate
source discovery for the researcher. IDEMS serves as a repository of links to DEM data providers rather than a DEM
data storage facility. The site also provides access to Esri’s
free ArcGIS Earth software which is fully integrated with
the ArcGIS platform for accessing, sharing, and publishingmaps and data. ArcGIS Earth is available here:(https://www.esri.com/en-us/arcgis/products/arcgisearth/overview).

Over the last 3 years, the IDEMS website has been continually updated with new DEM datasets, both terrestrial
and planetary. Table 1 lists the current content available
from the IDEMS website.

Structure
The Governing Board (GB) of IDEMS consists of fivemembers who oversee the operation and general activitiesof the service. The GB is structured as follows:
Director of IDEMS:
Deputy Director of IDEMS:
IAG/IGFS representative:
Advisory member:
Advisory member:

Mr Kevin M Kelly
Dr Fei Wang
Dr Riccardo Barzhagi
Dr Christian Hirt
Dr Michael Kuhn

Screenshot of home page of IDEMS318

The Geodesist’s Handbook 2020

Table 1. DEM and Related Data Sources Hosted on IDEMS
Bathymetry and Ice Data (12) Antarctica CryoSat-2 DEM
Bedmap2
BOEM Northern Gulf of Mexico Bathymetry
Elevation Coverage Map (Esri)
Flight MH370 Bathymetry
Global Bathymetry BTM (Esri)
Global Water Body Map (G3WBM)
Ice, Cloud, and Land Elevation (ICESat / GLAS Data)
Polar Geospatial Center
Randolph Glacier Inventory (RGI 6.0)
SRTM30_PLUS (30 arc-sec grid), 2014
Svalbard time-lapse terrain data
Global DEMs (14)

ALOS/PRISM AW3D30
ASTER GDEM v2
Elevation Coverage Map (Esri)
Esri Elevation Layers
ETOPO1 (60 arc-sec grid), 2009
Global Terrain DEM (Esri)
Global Water Body Map (G3WBM)
MERIT DEM (SRTM-based Bare-Earth model), 2017
NASADEM (reprocessed SRTM model), 2017
SRTM v3 (NASA)
SRTM v4.1 (CGIAR-CSI)
SRTM30_PLUS (30 arc-sec grid), 2014
TanDEM-X DEM
Viewfinder Panorama DEMs (2014)

Regional DEMs (7)Antarctica CryoSat-2 DEM
Arctic DEM Explorer
OpenTopography
Elevation Coverage Map (Esri)
Esri Elevation Layers
Polar Geospatial Center
Svalbard Time-Lapse Terrain Model

Planetary Terrain Data (3)NASA Planetary Data System (PDS) Geosciences Node
Planetary topography data archive
USGS Astrogeology Science Center

Earth Models (4)Earth2014 (60 arc-sec), 2014
ICE-6G GIA Model
Preliminary Reference Earth Model (PREM)
Topographic Earth Models (LMU Munich)International Geodynamics and Earth Tide Service (IGETS)

319

International Geodynamics and Earth Tide Service (IGETS)
Chair: Hartmut Wziontek (Germany)
Director of the Central Bureau: Jean-Paul Boy (France)
http://igets.u-strasbg.fr/

1 Terms of Reference
1.1 Objectives
The primary objective of the International Geodynamics andEarth Tide Service (IGETS) is to provide a Service tomonitor temporal variations of the Earth gravity field
through long-term records from ground gravimeters,
tiltmeters, strainmeters and other geodynamic sensors.
IGETS continues the activities of the Global Geodynamic
Project (GGP) to provide support to geodetic and geophysicalresearch activities using superconducting gravimeter (SG)data within the context of an international network. IGETS
continues the activities of the International Center for Earth
Tides (ICET), in particular, in collecting, archiving anddistributing Earth tide records from long series of gravimeters,
tiltmeters, strainmeters and other geodynamic sensors.
1.2 Products and Goals
IGETS is the main data center of worldwide high precision
SG records; the products hosted at the IGETS data centers are:x Raw gravity and local pressure records sampled at 1 or 2
seconds, in addition to the same records decimated at 1minute samples (Level 1 products);
x Gravity and pressure data corrected for instrumental
perturbations, ready for tidal analysis. This product isderived from the previous datasets, and is computed by
one or several Analysis Centers (Level 2 products).
x Gravity residuals after particular geophysical corrections(including solid Earth tides, polar motion, tidal and nontidal loading effects). This product is also derived fromthe previous dataset and is computed by one or several
Analysis Centers (Level 3 products).
IGETS strives to provide long-term gravity residuals
based on repeated absolute gravity measurements atparticular stations accessible through the Absolute Gravity
database.
IGETS also acts as the main data center of long-termseries recorded from other geodynamic sensors (spring
gravimeters, tiltmeters, strainmeters, etc.), including thehistorical dataset from the ICET databank.
IGETS may conduct comparison, validation anddistribution of tidal analysis software or any other software,
which can be used to process or correct gravity, tilt or strain
long time series.
IGETS may organize symposia and workshops toprovide a forum for presentation and discussion of all
aspects of IGETS activities.

2 Permanent Components
IGETS accomplishes its objectives through the following
permanent components:
x Stations
x Analysis Centersx Data Centers
2.1 Stations
The IGETS network consists of high quality and stability
measurements of gravity, tilts and strain, including
superconducting gravimeters. Stations should comply withthe performance standards for data quality and reliability,
developed since 1997 during the Global Geodynamics
Project (GGP), specified by the Directing Board.
2.2 Analysis Centers
The Analysis Centers are committed to produce data
products accordingly to the recommendations andspecifications defined by IGETS Directing Board, and send

320

their final products to the main Data Center for
dissemination to researchers and other users. They may
produce any of the IGETS products, or any of thecorrections needed to compute them.
The primary Analysis Center is responsible forcomputing SG corrected data (the Level 2 products). The
final SG residuals (the Level 3 products) are computed by
the secondary Analysis Center. The institutions currently incharge of these tasks are given in the attachment of the ToR;
the attachment is not part of the ToR and can be changed by
the Directing Board with two-third majority.
2.3 Data Centers
The IGETS Data Centers are repositories of any data
products, including station log files. Their primaryobjectives are to collect, archive and distribute these datawith efficiency and reliability. Data centers may mirror
some of the other data centers to increase the accessibilityof the IGETS datasets.
The primary Data Center hosts all SG data products(Levels 1, 2 and 3). A secondary Data Center is hosting allother datasets, including the historical products. The
institutions currently in charge of these tasks are given in theattachment of the ToR, and can be changed by the Directing
Board with a two-thirds majority of voting members.
2.4 Central Bureau
The Central Bureau is the executive arm of the IGETS
Directing Board, and is responsible for all operational
activities of the Service. The Central Bureau coordinates
IGETS activities, facilitates communications, maintains
documentations and organizes reports, meetings andworkshops.
The Central Bureau operates on a term of four years. One
year prior to the end of each term, the IGETS Directing
Board formally reviews the performances of the Central
Bureau, and may then request the Central Bureau toreconfirm its commitment to serve another four years. If theCentral Bureau agrees, it submits a proposal for approval by
the Directing Board. If the Central Bureau declines, or if the
Directing Board chooses to change the Central Bureau, theDirecting Board announces a call for proposal for a new
IGETS Central Bureau, to take the responsibility including
a six-month transition phase.
The Director of the Central Bureau serves as a memberof the Directing Board.
IGETS will accept proposals at any time from scientificindividuals, groups or institutions to become a new
permanent component of the service (this can be a newstation, or an analysis and/or data center). The Directing
Board will review such proposals for approval.

The Geodesist’s Handbook 2020

3 Directing Board
3.1 Role and responsibilities
The Directing Board sets the objectives, determines
policies, adopts standards, and sets the scientific andoperational goals for IGETS. The Directing Board exercises
general oversight of the activities of IGETS including
modifications to the organization that are deemed
appropriate and necessary to maintain efficiency andreliability. The Directing Board may determine appropriate
actions to ensure the quality of the IGETS products.
3.2 Membership
The Directing Board consists of representatives of the
IGETS components, members-at-large, appointed members
and ex officio members. Its members are:
Elected Members (5)x Raw Data Preparation representative;x Analysis Center representative;x Data Center representative;
x Network representative;x Scientific Product evaluation representative.
Appointed Members (5)x Director of the Central Bureau;x Absolute Gravity Data Base representative;x IAG representative;x BGI representative;x IGFS representative.
Members at large (2)x The members of the Directing Board elect the Members
at large in a second round after their nomination orelection, to insure a better geographical distribution.
3.3 Elections
IGETS associates are voting for the elected members.
The elected members have staggered four-year terms.
There is no limit to the number of terms that a person may
serve, however he/she may serve only two terms
consecutively as an elected member. All IGETS associates
are eligible to vote. Election is by a simple majority of votes
received for each position. A vote by the Directing Board
will resolve any situation of a tie.
3.4 IGETS Chair
The IGETS Chair is one of the Directing Board members
and is elected by the Board for a term of four years with thepossibility of reelection for one additional term. The Chairis the official representative of IGETS to externalorganizations.

International Geodynamics and Earth Tide Service (IGETS)

3.5 Decisions
Most decisions by the Directing Board are made byconsensus or by simple majority vote of the memberspresent. In case of a tie, the Chair decides how to proceed.
If a two-thirds quorum is not present, the vote shall be held
later by electronic mail. A two-thirds vote of all Board
members is required to modify the Terms of Reference, tochange the Chair, or to replace any of the members before
their normal term expires.

321

Attachment of the ToR
Analysis Centers
The primary Analysis Center, in charge of computing Level
2 products is hosted by the University of Polynesia (Tahiti,
French Polynesia).
The secondary Analysis Center, in charge of computing
the final gravity residuals is the EOST (Ecole etObservatoire des Sciences de la Terre) (Strasbourg, France).

3.6 Meetings

Data Centers

The Directing Board meets at least annually or more
frequently if meetings are called by the Chair or at therequest of at least three Board members. The Board willconduct periodic reviews of the IGETS organization and its
mandate, functions, and components.

The primary Data Center is the Information Systems andData Center (ISDC) at GFZ (Potsdam, Germany),
responsible for the collection of Levels-1, 2 and 3 data. The
other datasets, including the historical products, are hosted
at EOST (Strasbourg, France).

4 Definitions

Central Bureau

4.1 Associate Members
Individuals associated with organizations that support an
IGETS component may become IGETS Associate
Members. Associate Members take part in the election of
the incoming members of the Directing Board.
4.2 Corresponding Members
IGETS Corresponding Members are individuals who
express interest in receiving IGETS publications, wish toparticipate in workshops or scientific meetings organized by
IGETS, or generally are interested in IGETS activities.

The Central Bureau is hosted by the EOST (Strasbourg,
France).
Directing Board (2020)
Chair of IGETS:
H. Wziontek, Germany
Director of the Central Bureau:
J.-P. Boy, France
Raw Data Preparation Represent.: V. Palinkas, Czech
Analysis Center Representative: J.-P. Barriot, France
Data Center Representative:
C. Foerste, Germany
Network Representative:
H.-P. Sun, China
Scientific Product Evaluation Rep.: C. Voigt, Germany
Members at Large:
D. Crossley, USA
J. Hinderer, France
B. Meurers, Austria
Absolute Gravity Database Rep.: H. Wziontek, Germany
IAG Representative:
S. Pagiatakis, Canada
BGI Representative:
S. Bonvalot, France
IGFS Representative:
N. Sneeuw, Germany

322

The Geodesist’s Handbook 2020

International Gravimetric Bureau
Bureau Gravimétrique International (BGI)
Director: Sylvain Bonvalot (France)
http://bgi.obs-mip.fr

Terms of Reference
Overview
The Bureau Gravimétrique International (BGI) has beencreated in 1951 as a scientific service of IAG during the
IUGG (International Union in Geophysics and Geodesy)
General Assembly for ensuring the collection, validation
and archiving of all gravity measurements acquired at the
Earth’s surface and their distribution to scientific users. The
technological and scientific evolutions which occurred overthe following decades in the area of gravimetry (improvements in field, airborne and seaborne gravity meters, development of absolute gravity meters, space gravity missions,etc.) provided significant increases of the number, diversity
and accuracy of the gravity field observables. Following
these evolutions, BGI has contributed to provide original databases and services (products, documentation, tutorials,
software…) for a wide international community concernedby the studies of the Earth gravity field. The strategic planfor period 2019-2023 will maintain this objective, ensuring
a long term usability and sustainability of the highest-quality of gravity data.
BGI is an official service of the International Association of Geodesy (IAG) and is coordinated with others IAG
services (IGeS, ICGEM, IDEMS, IGETS) by the International Gravity Field Service (IGFS). It also directly contributes within IAG to the activities of Commission 2 “Gravity
Field” and Global Geodetic Observing System (GGOS). It
is recognized by the International Council for Science(ICSU) successively as one of the services of the Federationof Astronomical and Geophysical Services (FAGS) and of
the World Data System (WDS).
BGI has its central bureau in Toulouse, France(GET/OMP) and operates with the support of various
French agencies (CNES, CNRS/INSU, IGN, IRD, SHOM,

BRGM, IFREMER) and Universities (Toulouse, Paris,
Strasbourg, Montpellier, Brest, Le Mans). BGI services also
benefits from the close collaboration of other agencies from
Germany (BKG), Italy (POLIMI), Greece (AUTH), Czech
Republic (VÜGTK), Denmark (DTU) and USA (NGA).

Missions and objectives
The primary task of BGI is to improve the global knowledgeof the Earth’s gravity field through the collection, homogenization and validation of all available gravity measurements (relative or absolute) and make this information available to a large variety of users for scientific applications.
With this aim, BGI holds and maintains for IAG the fundamental global databases of relative and absolute static gravity measurements and develops services to serve the scientific community. The most current services provided by BGI
include:x The supply of gravity data, reference stations, products,
software and documentation.
x The validation and the archiving of gravity dataset andproducts provided to BGI and the attribution to data providers of a traceable international reference through a
Digital Object Identifier (DOI).
x The realization and/or evaluation of global models(Earth Geopotential Model, World Gravity Map for instance) as well as regional data compilations carried out
for gravity or geoid studies.
BGI also actively contributes to the definition of protocols,
practices and recommendations aimed at improving thegravity data acquisition and processing and the realizationof gravity surveys and networks. BGI is more specificallyinvolved in the following actions:International Gravimetric Bureau (BGI)

323

x The definition and establishment of the “International
Gravity Reference System & Frame (IGRS/IGRF)” promoted through the IAG Joint Working Group 2.1.1.
x The evaluation of new sensors for measuring absolutegravity (cold-atom absolute gravity meters).
x The support to the realization of national absolute gravity networks.
Finally, BGI also contributes with his collaborators to other research and development activities (software developments, research in geophysics and geodesy, etc.), to educational activities
in gravimetry (summer schools, tutorials, etc.).

relative gravity surveys (terrestrial, marine, airborne) in a
global reference frame. Even if a significant number of reference stations should have disappeared with time, this original IGSN71 database remains accessible and is still used insome countries for calibration of relative surveys. This
global gravity reference network will be advantageously replaced by the International Gravity Reference System &Frame (IGRS/IGRF) based on the increasing network of actual absolute gravity measurements and made available
from the above mentioned AGrav database.

Product and services

BGI also contributes to the realization of derived gravity
products aimed at supporting studies of the Earth gravity
field at global or regional scales. The products mostly usedby scientific users are the digital global grids from the World
Gravity Map (WGM) which represent the first gravity
anomalies (Bouguer, isostatic and surface free-air anomalies) computed in spherical geometry taking into account arealistic Earth model (see Figure 1). They include 1 minuteresolution terrain corrections computed from the contribution of most surface masses (atmosphere, land, oceans, inland seas, lakes, ice caps and ice shelves). The World Gravity Map is also available as a set of 3 global maps realized for
the Commission for the Geological Map of the World (CGMW),
UNESCO, International Union of Geodesy and Geophysics(IUGG) and International Union of Geological Sciences(IUGS). Maps available at: http://ccgm.org/en/16-catalogue.
Other global or regional gravity models and products computedfrom other contributors may also be made available from the
BGI website (contact BGI).

Global databases of land and marine gravity data
The databases of relative measurements contain over 12
million of observations compiled and computerized mostly
from land and marine gravity surveys. They have been extensively used for the definition of Earth gravity field models
and for many applications in geodesy, satellite orbit computation, oceanography, geophysics, etc. They provide today themost precise information available on the Earth gravity field
at short wavelengths complementary to airborne and satellite gravity measurements.
Global database of absolute gravity data
The database for absolute gravity measurements was set up
in 2008 in cooperation between BGI and BKG (Bundesamt
für Kartographie und Geodäsie, Germany) for collecting all
available information on absolute gravity measurements acquired on Earth and for ensuring storage and long term
availability of gravity data and processing details. It provides
today the most complete information on existing absolutegravity stations and measurements (raw or processed data,
description of stations, instruments, involved institutions,contacts, etc.). The database (AGrav) can be accessed by a web
based interface which provides publicly available meta-data
as well as complete datasets for community of users contributing to the archive. A simple exchange format was selectedwhich includes all relevant information and is known by the
majority of users avoiding additional effort. In this way the
upload of absolute gravity data to the database can be doneby the owner institutions, using a web based upload form.
Global database of gravity reference stations
Reference gravity stations established and connected to theformer IGSN71 and Potsdam reference systems have beenpreviously collected and archived at BGI. For several decades, these stations have provided the only available information on absolute gravity value for tying local or regional

Global or regional gravity grids and models

Other services
x Online tools for prediction gravity at a given site.
x Tools and software for data acquisition or validationx Attribution of DOI (Digital Object Identifier) for relative
and absolute gravity data set, products or software provided by contributors.

Key activities
Database & services
The current activities at BGI are mostly dedicated to consolidate and validate the IAG global gravity databases (relative
and absolute measurements) and to develop pertinent andupdated products and services for supporting long term sustainability and usability of gravity data for scientific purposes.

324

A new BGI website (to be achieved in 2020) will provide newservices and information to both users and contributors. Amongthe new functionalities, it will include:x a new version of the user interface for the Absolute gravity database (AGrav) providing improved functionalities
and links between BGI and IGETS observations,x a new version of the user interface for the Reference stations (former IGSN71 network),x a DOI searching tool for identifying gravity sources in agiven area.
Automatic procedures have been designed recently toassign an DOI reference number to any dataset archived in
the BGI databases (either from recent or old gravity surveys). National agencies contributing in the acquisition orcompilation of gravity measurements (from field, marine orairborne surveys) are thus encouraged to archive their data
in a such way in order to update the data coverage and accuracy for each country or region and to better improve therecognition of their contribution in a global frame throughthe assignment of a DOI. New products are also currently
under development at BGI for updating global or regional
gravity products (maps and grids) for educational and research purposes.
Support for global gravity products, standards &networks
BGI contributes within IAG, and its components IGFS,
GGOS and Commission 2 “Gravity Field”, to several activities and Joint Working Groups aimed at improving the
global knowledge and accuracy of the Earth gravity. It currently mostly brings its expertise and databases to the following projects:
IAG Joint Working Group 2.2.1 “Establishment of a
global absolute gravity reference system”
This IAG Joint Working Group, launched during decade2010 and chaired by H. Wziontek (BKG) and S. Bonvalot(BGI), aims at providing an accurate, homogeneous andlong-term gravity reference at global scale based on absolute gravity observations. This project which leads to thedefinition and set-up of a new International Gravity Reference System & Frame (IGRS/IGRF) has within his objectives : (i) The establishment of a global network of core andreference stations where the gravity can be monitored continuously at the microGal level (10-8 m.s-2) using the stateof-the-art of absolute gravity meters (corner cube or coldatoms) and possibly in collocation with other geodetic tech-

The Geodesist’s Handbook 2020

niques at GGOS Core stations ; (ii) The long-term traceability of the gravity measurements through international intercomparisons of absolute gravity meters ; (iii) The replacement of the former IGNS71 network by a modern network
based on laboratory and field measurements of the absolutegravity. See Wilmes et al. (2016) and Wziontek et al. (2020)
for more details.
IAG Joint Working Group 2.1.2 “Unified formats andprocessing software for high-precision gravimetry"
IAG Joint Working Group 2.2: “Validation of combined
gravity model EGM2020”
Evaluation of new gravity sensors
BGI is involved in the evaluation of new gravity sensors
such as those based on cold-atom technologies (Pereira et
Bonvalot, 2016). It has accompanied the evaluation of thefirst commercial Absolute Quantum Gravimeter (AQG) developed by MuQuans company (France). It has also participated to the evaluation of a first hybrid absolute gravity meter (composed of accelerometers and cold atom sensor) designed by ONERA (France) for moving platform (shipborneor airborne). An airborne absolute gravity survey, including
flights over sea and mountainous areas, has been carried out
successfully in France for assessing and comparing the performances and accuracy of this novel instrument with otherconventional airborne relative gravity meters and withground surface marine and land gravity data (study in process). This activity also directly contributes to the new IAG
Working Group “Novel Sensors and Quantum Technology
for Geodesy (QuGe)” and more specifically to its sub-working group “Quantum gravimetry in space and ground”.
Contribution to gravity surveys & networks
BGI associated research teams also contribute to the realization of gravity surveys and networks in the frame of national or international research projects with national agencies on the French territory or on other continents.
Other contributions
x Contribution to Newton’s Bulletin: BGI contributes
jointly with the International Service for Geoid (ISG) tothe edition of this Bulletin which publish technicalpapers on gravity data acquisition and processing.
x Contribution to International summer schools on gravity
or geoid in collaboration with ISG and IGFS.

International Gravimetric Bureau (BGI)

325

Fig. 1: Example of downloadable gravity product: 2 minutes global grid from the World Gravity Map (source BGI)

Users & contributors information
General terms of use
Data, products or software available at BGI are mostly dedicated to support scientific and academic activities. Digital
gravity data or products are distributed free of charge to research or academic institutions or to data contributors according to the conditions given below. Other users, individual or private companies, are invited to specify in their request the expected use of the data and products. See BGI
website for diffusion and charging policies.
x Access to non-confidential or non-proprietary relative
gravity measurements is provided free of charge to
public institutions or data contributors over geographic
areas limited to 20°x20° or on the base of a maximum
number of 10000 data points (land data) and/or 100000
data points (marine data). Retrieval of full data coverage
for a whole country is not included in that case. All otherrequests (for larger datasets, for extended geographic
area or for a whole country) as well as massive data retrieval will be subject to an evaluation by BGI who
might require a specific protocol of use of the data or ask
authorization of the proprietary Institutions. Charges
might be applied.

x Access to the Absolute gravity database is provided freeof charge. Database consultation and retrieval is done
through the Web interfaces at BGI and BKG mirror sites.
Confidential data or proprietary data may appear withrestricted information (metadata only).
x Access to the Reference gravity stations database(IGSN71 network) is provided free of charge. Note thatreference gravity stations (especially those determinedand described decades ago) may have been destroyed or
modified.
x Access to other additional services is also provided freeof charge: global or regional gravity anomaly grids,
Prediction of gravity value on Earth, Software,
Documentation, etc.
Users of BGI data are invited to make reference to the specific DOI (Digital Object Identifier) provided by BGI alongwith the distributed data for each query.
Archiving and referencing data to BGIThe contribution of countries, agencies and scientists involved in surface gravity data acquisition (relative or absolute measurements from field, marine or airborne surveys)
is essential for improving the global coverage and accuracy

326

of the Earth gravity field and for contributing to the determination of the new International Gravity Reference Frame(IGRF). The archiving of such incoming gravity sets alsoenables BGI to better validate the gravity observations in a
global reference frame and restore them in standard and unified formats useful for the end users.
Contributors interested in archiving their gravity observations or derived products as non-confidential or as proprietary data (to be defined by the contributors themselves) areinvited to contact BGI. A Digital Object Identifier (DOI)
will be delivered to any institution or author for archiving
their own dataset resulting from gravity survey or gravity
data compilation. This new service aims at ensuring a proper
reference and recognition to the authors and institutions who
have acquired or compiled gravity data and a better traceability of improvements in the global gravity data coverage
from local or regional surveys. DOI attribution may be also
extended to relevant software for gravimetric applications(data processing or modeling) or other related information(maps, grids, reports).
x Contributors with data from land, marine or airborne
surveys are invited to contact BGI (bgi@cnes.fr). ASCII
data files containing all necessary information andquantities are preferred (station coordinates, gravity
measurements and accuracies; gravity corrections;reference geographic, height and gravity systems, etc.).
x Contributors with data from corner cube or cold-atom
absolute gravity measurements are invited to contact
either BGI (bgi@cnes.fr) or BKG (agrav@bkg.bund.de)
Both laboratories and field measurements are welcome
to contribute as parts of the reference and core stationand of the national infrastructures building the new
International Gravity Reference System & Frame.
For any contribution (relative or absolute gravity data), it isreminded that BGI will keep the status of diffusion (with orwithout restrictions of redistribution) as specified by the
proprietary institution.

Structure and membership
Since 2003, BGI is one of the services of the International
Gravity Field Service (IGFS) which coordinates within the
IAG, the servicing of the geodetic and geophysical community with gravity field-related data, software and information.
The BGI central office (management, secretariat andtechnical staff) is located in Toulouse, France, in the premises of the Observatoire Midi-Pyrénées. Since 1998, BGI is
supported by French agencies and works in close collaborations with universities and research teams involved in gravimetry and geodesy (see list below):

The Geodesist’s Handbook 2020

x
x
x
x
x
x
x
x
x
x
x
x
x
x

Centre National d'Etudes Spatiales (CNES)
Bureau de Recherches Géologiques et Minières (BRGM)
Centre National de la Recherche Scientifique (CNRS)
Institut National des Sciences de l'Univers (INSU)
Institut National de l’Information Géographique etForestière (IGN)
Institut de Recherche pour le Développement (IRD)
Service Hydrographique et Océanographique de laMarine (SHOM)
Institut Français de Recherche pour l’Exploitation de laMer (IFREMER)
Institut de Physique du Globe de Paris (IPGP)
Ecole et Observatoire des Sciences de la Terre (EOST)
Ecole Supérieure des Géomètres et Topographes (ESGT)
Université de Toulouse (GET/OMP)
Université de Montpellier (Géosciences Montpellier)
Université de Brest (Géosciences Océan)

It also contribute in France to research groups and networks
such as Groupe de Recherches en Géodésie Spatiale(GRGS), Réseau Sismologique et Géodésique Français(RESIF), Pôle de données Système Terre (DataTerra/
Form@Ter).
Each supporting organization has a representative member in the BGI Advisory Board. The Advisory Board (whoalso includes a representative member of IAG) contributes
once a year to the orientation and evaluation of the BGI activities. The program of BGI activities is also evaluated anddiscussed by the IGFS Advisory Board at each IGFS meetings and IUGG General Assemblies. A partnership has been
also established between BGI and the Federal Agency for
Cartography and Geodesy (BKG), Germany, for the realization and the maintenance of the global database of absolutegravity measurements (AGrav) and with the Research Institute of Geodesy, Topography and Cartography (VUGTK),
Czech Republic for metrology applications.

Contacts
Bureau Gravimétrique International
Observatoire Midi-Pyrénées
14, Avenue Edouard Belin
31401 Toulouse Cedex 9, France
Phone: 33-5 61 33 29 80 / 33-5 61 33 47 04
E-mail: bgi@cnes.fr

International Gravimetric Bureau (BGI)

327

Staff members & experts

Cited references

Central bureau (France)
S. Bonvalot (GET/OMP, Toulouse)
L. Seoane (GET/OMP, Toulouse)
G. Balmino (GET/OMP, Toulouse)
A. Briais (GET/OMP, Toulouse)
S. Bruinsma (GET/OMP, Toulouse)
G. Gabalda (GET/OMP, Toulouse)
F. Reinquin (GET/OMP, Toulouse)

Pereira Dos Santos, F. et S. Bonvalot (2016). Cold Atom
Absolute Gravimetry. In: Grafarend Ed., Encyclopediaof Geodesy. Springer. http://link.springer.com/referenceworkentry/10.1007/978-3-319-02370-0_30-1.

Correspondants (France)
S. Merlet (LNE/SYRTE, Paris)
M. Diament (IPG, Paris)
T. Gattacceca (IGN, St Mandé)M-F. Lalancette (SHOM, Brest)
D. Rouxel (SHOM, Brest)
C. Salaun (SHOM, Brest)
G. Martelet (BRGM, Orléans)A. Peyrefitte (BRGM, Orléans)J.-P. Boy (EOST, Strasbourg)
J.-D. Bernard (EOST, Strasbourg)
J. Hinderer (EOST, Strasbourg)
N. Le Moigne (GM, Montpellier)Germany
H. Wziontek (BKG, Leipzig)
R. Falk (BKG, Leipzig)
A. Rulke (BKG, Leipzig)
Czech Republic
V. Palinkas (VUGTK, Pecny)

Wilmes H., Vitushkin L., Pálinkáš V., Falk R., Wziontek H.,
Bonvalot S. (2016). Towards the Definition and Realization of a Global Absolute Gravity Reference System.
In: Freymueller J.T., Sánchez L. (eds) International
Symposium on Earth and Environmental Sciences for
Future Generations. International Association of Geodesy Symposia,
vol 147.
Springer,Cham.
https://doi.org/10.1007/1345_2016_245
Wziontek H., Bonvalot S., Falk R., Gabalda G., Makinen J.,
Palinkas V., Rulke A., Vitushkin L. (2020). Status of
the International Gravity Reference System and Frame.
Journal of Geodesy (in press).

328

The Geodesist’s Handbook 2020

International Service for the Geoid (ISG)
President: Mirko Reguzzoni (Italy)
Director: Daniela Carrion (Italy)
http://www.isgeoid.polimi.it

Mission / Objectives

Products

The main tasks of ISG are:x to collect geoid estimates worldwide, when possible validate them, and disseminate them upon request among
the scientific community. Other auxiliary data useful forthe geoid determination may also be collected by ISG,
without redistributing data that are already provided byother IAG services;x to collect, test and when allowed distribute software forthe geoid determination;
x to conduct researches on methods for the geoid determination, also defining optimal procedures for merging all
available data and models;x to organize international schools on geoid determination
addressing both theoretical and practical topics, possibly
every two years. During the schools, students are trainedin the use of the relevant software for geoid computation;
x to support agencies or scientists in computing local andregional geoid models, especially in developing countries, also organizing special training courses;
x to disseminate training material and software on geoid
computation, e.g. lecture notes of the schools;
x to issue the Newton’s Bulletin, which has a technical andapplied nature, collecting papers and reports on gravity
and geoid;x to establish and update a website to present the service
activities, show and distribute the geoid models, software and publications, announce news and the organization of international schools on geoid determination.
Data and software given to ISG remain property of theauthors, who decide upon the conditions of use and can allow, restrict or deny their distribution. ISG itself can indeed
perform geoid computations within different projects, whileremaining a non-profit institution.

x Database of local and regional geoid models, in the formof grids or sparse points, stored and distributed in a homogeneous file format;
x Software archive for local geoid estimation, for terrain
gravity effect calculation and for handling global models;x Documentation on data and software;x International schools and on request training courses on
geoid computation;x Lecture notes and other geoid related publications;x Newton’s Bulletin and the former IGeS Bulletin;x Research results on gravity and geoid matters.

Future Programs/Development
Beyond institutional activities, the following research topics
are worth of specific mention:
x computation of improved geoids for Italy and the Mediterranean area;
x integration of ground, air-borne, ship-borne and satellite
gravity data for geoid modelling;x integration of local, regional, continental and global geoid models;x participation within GGOS to the study of the height datum unification problem;x participation within IGFS to the validation of new global
gravity models;x study of improved methodologies for the determinationof the geoid at local and global level.

International Service for the Geoid (ISG)

Structure
ISG is an official IAG service that is coordinated by IGFS
and is also related to the activities of the IAG Commission
2 on Gravity Field. Its structure, tools and activities are illustrated in the ISG reports to the Advisory Board of IGFS.
The Service is hosted by the Department of Civil andEnvironmental Engineering at Politecnico di Milano. ISG
staff is currently composed by researchers and a secretaryfrom Politecnico di Milano. They nominate, upon recommendation of IGFS, a President for its international representation and a Director for the operative management. In
addition, the ISG advisors are scientists who have or have
had an outstanding activity in the field of geoid determination and can also represent ISG in both research and teaching activities.

329

At present, the following distinguished scientists are ISG
advisors:
N. Pavlis(USA)
M. Sideris(Canada)J. Huang(Canada)R. Forsberg(Denmark)
J. Ågren(Sweden)U. Marti(Switzerland)
H. Denker(Germany)
L. Sánchez(Germany)
I. Tziavos(Greece)
D. Blitzkow(Brazil)
W. Featherstone (Australia)
H. Abd-Elmotaal (Egypt)
C. Hwang(Chinese Taipei)
Finally, within the structure of ISG, Working Groups can beestablished for specific purposes, limited in time.

330

The Geodesist’s Handbook 2020

Permanent Service for Mean Sea Level (PSMSL)
Head: E. A. Bradshaw (UK)
http://www.psmsl.org

Development

Products

Since 1933, the Permanent Service for Mean Sea Level(PSMSL) has been responsible for the collection, publication, analysis and interpretation of sea level data from theglobal network of tide gauges. It is based at the National
Oceanography Centre (NOC), which on the 1st November
2019 began operating as an independent self-governing organization – a charitable company limited by guarantee.
Funding is provided by the UK Natural Environment Research Council (NERC). The PSMSL continues to be one of
the main data centres for both the International Association
for Physical Sciences of the Oceans (IAPSO) and the IAG.
The PSMSL operates under the auspices of the International
Science Council (ISC) and reports formally to IAPSO’s
Commission on Mean Sea Level and Tides. The PSMSL isa regular member of the World Data System of ISC.

The database of the PSMSL contains over 72000 stationyears of monthly and annual values of mean sea level (MSL)
from over 2360 tide gauge stations around the world received from approximately 200 national authorities. On average, approximately 800 stations per year are entered into
the database. This database is used extensively throughout
the sciences of climate change, oceanography, geodesy andgeology, and is the main source of information for international study groups such as the Intergovernmental Panel on
Climate Change (IPCC).
Data for all stations are included in the PSMSL METRIC (or total) data set. The METRIC monthly and annual
means for any one station-year are necessarily required tobe measured to a common datum, although, at this stage,
datum continuity between years is not essential. The year toyear datum checks become essential, however, if the data
are subsequently to be included in the PSMSL 'Revised Local
Reference (RLR)' component of the data set.
The 'Revised Local Reference (RLR)' dataset of the
PSMSL contains records for which time series analysis ofsea level changes can be performed. Long records from thisdataset have been the basis of all analyses of secular changes
in global sea level during the last century. The geographicaldistribution of longer RLR records contains significant geographical bias towards the northern hemisphere, a situation
which is being rectified by the establishment of the GLOSS
global sea level network.
The PSMSL is also responsible for the Higher Frequency Delayed Mode (HF DM) data set of sea level information from the GLOSS Core Network. This consists of theoriginal sea level measurements from each site (typicallyhourly values) which provide a strategic backup to the MSL
information of the main PSMSL data set.

Mission/Objectives
Changing sea levels will have a major impact on human life
over the next 100 years. We need mean sea level data to
study climate change, the impact of human activities ondensely populated areas, the economic impacts of sea level
rise and to plan coastal engineering. The mission of the
PSMSL is to provide the community with a full Service forthe acquisition, analysis and interpretation of sea level data.
Aside from its central role of operation of the global sea
level data bank, the PSMSL provides advice to tide gauge
operators and analysts. It occupies a central managementrole in the development of the Global Sea Level Observing
System (GLOSS) and hosts important international study
groups and meetings on relevant themes. The Sea Level Futures Conference that took place in July 2018 to mark the85th Anniversary of the PSMSL is one such meeting.

Permanent Service for Mean Sea Level (PSMSL)The PSMSL received funding from the European Union
Horizon 2020 EuroSea project to create an international archive to preserve and deliver Global Navigation Satellite
Systems Interferometric Reflectometry (GNSS-IR) data andto integrate these data with existing sea level observing networks. GNSS-IR sensors provide an alternative method toobserve sea level. As well as recording the sea level,
these sensors will also provide vertical land movement information from one location.
In addition, the PSMSL provides a range of sea levelproducts (e.g. interactive anomaly and trend maps, tables ofsea level trends) for its users. These findings are input tonational and international scientific study groups regularly.
A range of training materials and software products are also
made available via its web site which can be consulted formore information.

Structure/Governing Board Members
The PSMSL reports formally to the IAPSO Commission on
Mean Sea Level and Tides (President Dr. G.T. Mitchum,USA). It is also served by an Advisory Group, which at present consists of Prof. G. T. Mitchum (University of South
Florida, USA), Prof. P. L. Woodworth. (National Oceanography Centre, UK), Dr. P. Knudsen (Danish National Space
Center), Dr. R. Bingley (Nottingham University, UK) and
Dr. G. Woppelmann (Universite de La Rochelle, France).
The Advisory Group is currently under review and membership will be updated in 2020. Suggestions for improvements

331

in PSMSL activities may be sent directly to the PSMSL or
via the IAPSO Commission or via any member of the Advisory Group.

Points of Contact
Permanent Service for Mean Sea Level
National Oceanography Centre
Joseph Proudman Building
6 Brownlow Street
Liverpool L3 5DA, UK.
Email: psmsl@noc.ac.uk
Web site: www.psmsl.org
Telephone: +44 (0)151-795-4800
Fax: +44 (0)151-795-4801

Staff members
E. A. Bradshaw (Head)
K. M. Gordon
S. Jevrejeva
A. P. Matthews
A. Hibbert
J. Williams
S. Williams
C. Wilson
L. J. Rickards (former Director)

332

The Geodesist’s Handbook 2020

IAG on the Internet
Szabolcs Rózsa, IAG Communication and Outreach Branch
http://www.iag-aig.org

The IAG maintains an Internet site, which is a valuable
source of information not only about the Association itself,
but also about its scientific disciplines. The primary goal of
the website is to communicate with the IAG members, andmake information available to the wider Geoscience community in the world as a whole.
Since the maintenance of the IAG website belongs to theactivities of the Communication and Outreach Branch(COB) it is still hosted at the Department of Geodesy and
Surveying of the Budapest University of Technology andEconomics (BME), Budapest, Hungary. The geographicaldistribution of the visitors of the IAG website can be seen
on Figure 1 for the period of January, 2019 to June 2019.
The layout of the website was redesigned in 2019 to fully
support handheld devices, such as tablets, smartphones, etc.

Topic of the Month
The Topic of the Month section of the opening page aims topromote important scientific achievements and activities tothe wider public. The latest scientific results, the establishment of international and interdisciplinary research projects
and all other information, which may have a great impact on
the geodetic community, can be posted to this section of thewebsite.
Since the COB intends to publish a new topic in eachmonth, Geodesists are kindly encouraged to submit new topics to the COB e-mail address: iagcob@iag-aig.org
The Topics of the Month must include an image and ashort introduction, too. Both are published on the opening
page of the website, and more details are given on separate
pages.

Publishing on the IAG Website
The IAG COB encourages all the IAG Members and Geodesists in general to publish information on the IAG website.
News, conference calls, job announcement, etc. can be submitted to the IAG COB for publication. Contributions canbe sent to the following e-mail address: iagcob@iag-aig.org.

IAG on Social MediaIn order to address the younger generations, the COB has
opened the IAG page on Facebook and Twitter. As of June
10, 2020, the Facebook page http://www.facebook.com/ InternationalAssociationOfGeodesy has 1767 'likes'. The age
distribution of the likers can be seen on Figure 2. The Twitter site of IAG is available at http://www.twitter.com/
iag_cob. As of June 10, 2020 IAG has 804 followers on
Twitter. We would like to encourage everyone who is interested in Geodesy to follow these pages, since the latest information published on the IAG website are available on Facebook and Twitter, too. The followers of these pages areautomatically notified about the latest IAG news.
However, our appropriate presence on the social media
needs more frequent news on Geodesy and IAG. We would
like to encourage IAG members and geodesists in general toprovide us input to be published on these sites! Please feel
free to contact the COB for publishing such geodesy related
information, because it really helps to improve the outreachactivities of IAG.
We do appreciate your help and cooperation!

IAG on the Internet

333

Figure 1. The geographical distribution of the page visits of the IAG website (http://www.iag-aig.org) between January,
2019 and June, 2019.

Figure 2. The age distribution of Facebook likers (above: 25% of likers are women, below: 75% of likers are men)

334

The Geodesist’s Handbook 2020

Publications of the International Association of Geodesy (IAG)

I. Journal of Geodesy
Twelve issues per year:
Annual subscription or sale by unit (Springer-Verlag)
Springer Verlag
Tiergartenstrasse 17
D – 69121 Heidelberg
Germany
www.springer.com

II. Geodesist’s Handbook
Quadrennial special issues of the Journal of Geodesy, published since 1980, contain the present IAG laws and rules,
summaries of the latest IAG General Assemblies, and thestructures and the program descriptions for all the IAG components of the respective upcoming period.

III. IAG Symposia SeriesPeer reviewed proceedings of selected IAG Symposia.
Available at Springer-Verlag (see under I.). Latest issues:
Vol. 146: van Dam, T. (Ed., 2017) REFAG 2014 Proceedings of the IAG Commission 1 Symposium
Kirchberg, Luxembourg, 13–17 October, 2014
Vol 147. Freymueller, Jeffrey T., Sánchez, Laura (Eds.,
2018) International Symposium on Earth and Environmental Sciences for Future Generations,
Proceedings of the IAG General Assembly, Prague, Czech Republic, June 22- July 2, 2015
Vol 148. Vergos, Georgios S., Pail, Roland, Barzaghi, Riccardo (Eds., 2019) International Symposium on

Gravity, Geoid and Height Systems 2016, Proceedings Organized by IAG Commission 2 andthe International Gravity Field Service, Thessaloniki, Greece, September 19-23, 2016
Vol 149. Freymueller, Jeffrey T., Sánchez, Laura (Eds.,
2019) International Symposium on Advancing
Geodesy in a Changing World, Proceedings ofthe IAG Scientific Assembly, Kobe, Japan, July
30 – August 4, 2017
Vol 150. Mertikas, Stelios P., Pail, Roland (Eds., 2020)
Fiducial Reference Measurements for Altimetry,
Proceedings of the International Review
Workshop on Satellite Altimetry Cal/Val Activities and Applications
Vol 151. Novák, P., Crespi, M., Sneeuw, N., Sansò, F.
(Eds., 2021) IX Hotine-Marussi Symposium on
Mathematical Geodesy, Proceedings of the Symposium in Rome, June 18 – 22, 2018

IV.
Travaux de l’Association Internationale de Géodésie (IAG Reports)
The IAG Reports (Travaux de l'Association Internationalede Géodésie) are published on the occasion of the IAG General and Scientific Assemblies every two years and containthe reports of all IAG components and sub-components.
They were published as printed volumes until 2003 (since1991 also available in digital form) and since 2005 online
only at http://www.iag-aig.org/travaux and at http://office.iag-aig.org/iag-publications-reports-position-papers.
Printed versions may be ordered at the IAG Office (iag.office@maanmittauslaitos.fi).

Publications of the International Association of Geodesy (IAG)

335

Geodetic Data Centres

Geodetic Publication Series

The IAG Communication and Outreach Branch (COB)
compiles and maintains a list of Geodetic Data Centres.
All data compiled in this list are regularly revised by the
IAG National Correspondents.
Considering the fact that addresses are subjected to frequent changes, the directory is stored as a file in the web tosustain the possibility of updates whenever useful. All information is also available at the IAG Website(https://www.iag-aig.org/geodetic-data-centers).
All available data are stored in the IAG Website as soon
as the responsible National Correspondent sends them to the
IAG COB (address see below). All National Correspondents
are kindly asked to inform the COB1 on any change.

The IAG Communication and Outreach Branch (COB)
compiles and maintains a list of Geodetic Publication Series. All data compiled in this list are regularly revised by
the IAG National Correspondents.
Considering the fact that addresses are subjected to frequent changes, the directory is stored as a file in the web tosustain the possibility of updates whenever useful. All information is also available at the IAG Website(https://www.iag-aig.org/publication-series).
All available data are stored in the IAG Website as soon
as the responsible National Correspondent sends them to the
IAG COB (address see below). All National Correspondents
are kindly asked to inform the COB1 on any change.

Educational Establishments for Geodesy

IAG Directory

The IAG Communication and Outreach Branch (COB)
compiles and maintains a list of addresses of Educational
Establishments for Geodesy. All data compiled in this list
are regularly revised by the IAG National Correspondents.
Considering the fact that addresses are subjected to frequentchanges, the directory is stored as a file in the web to sustain
the possibility of updates whenever useful. All informationis also available at the IAG Website (https://www.iagaig.org/educational-institutions).
All available data are stored in the IAG Website as soon
as the responsible National Correspondent sends them to the
IAG COB (address see below). All National Correspondents
are kindly asked to inform the COB1 on any change.

Due to the General Data Protection Regulation, IAG ceases
to publish the IAG Directory. For contact details, pleasecontact the IAG Office at iag.office@maanmittauslaitos.fi.

1

IAG Communication and Outreach Branch (COB)
Department of Geodesy and Surveying
Budapest University of Technology and Economics
P.O.Box 91
H-1521 Budapest, Hungary
tel +36-1-463 3222/3213, Fax +36-1-463 3192
e-mail iagcob@iag-aig.org / szrozsa@iag-aig.org

336

The Geodesist’s Handbook 2020

Delegates to the IAG Council
Markku Poutanen (Secretary General)

ALBANIAEng. Msc. Bilbil Nurçe
Polytechnic University of Tirana
Civil Engineering Faculty
Street "Muhamet Gjollesha" Nr. 54
Tiranabillnurce@gmail.com

AUSTRIA
Prof. Dr. Johannes Böhm
Vienna University of Technology
Department of Geodesy and Geoinformation
Gußhausstraße 27-29
1040 Wien
johannes.boehm@geo.tuwien.ac.at

ALGERIADr. Hassen Abdellaoui
National Institute of Mapping and Remote Sensing (INCT)
Algeria
contact@inct.dz

AZERBAIJAN
Acad. Prof. Dr. Fakhraddin Kadirov
Head of Dept. “Geodynamics & Seismology”
Geology & Geophysics Institute, ANAS
Av. H. Javid 119
1143 Baku
kadirovf@gmail.com

ARGENTINA
Ing. Jaime Ricardo Soto
Universidad Nacional de La Plata, Facultad de Ingeniería
Unidad de Investigación y Desarrollo en GPS y Metrologia
Calle 116 esq. 47
1900 La Plata – Prov. de Buenos Aires
cg.snuggi@gmail.com; jrsoto1@gmail.com
ARMENIA
Dr. Grigor Avetyan
Yerevan State University
1 Alex Manoogian Street
Yerevan, 0049
rector@ysu.am
AUSTRALIA
Dr. Shin-Chan Han
School of Engineering
University of Newcastle
University Drive, Callaghan, NSW 2308
shin-chan.han@newcastle.edu.au

BELGIUM
Dr. Carine Bruyninx
Koninklijke Sterrenwacht van België
Ringlaan 31180 Brussels
carine.bruyninx@oma.be
BOSNIA & HERZEGOVINA
Ass. Prof. Dr.sc. Dipl.Eng. Medzida Mulic
University of Sarajevo, Faculty of Civil Engineering
Department of Geodesy
S. Tomica br. I/III
71000 Sarajevo
medzida_mulic@gf.unsa.ba, medzida_mulic@yahoo.com

Delegates to the IAG Council

BRAZIL
Prof. Denizar Blitzkow
Universidade de São Paulo, EPUSP-PTR
Caixa Postal 61548
Sao Paulo, SP, 05413-001
dblitzko@usp.br
BULGARIA
Prof. D. Sc. Ivan Georgiev
Bulgarian Academy of Sciences
National Institute of Geophysics, Geodesy and Geography
Acad. G. Bonchev Str. Bl. 31113 Sofia
ivan@bas.bg
CANADA
Prof. Georgia Fotopoulos
Queen's University
Dept. of Geological Sciences and Geological Engineering
36 Union Street, Miller Hall/Bruce Wing
Kingston, ON, K7L 3N6
gf26@queensu.ca
Dr. Jeong Woo Kim
University of Calgary
Department of Geomatics Engineering
2500 University Drive NW
Calgary, AB, T2N 1N4
jw.kim@ucalgary.ca
CHILE
Lt.Col. Crístian Iturriaga Sáez
Departamento de Ingeniería Military Geographic Institute of Chile – IGM
Avenida Santa Isabel 1651
Santiago
ding@igm.cl
CHINA
Dr. Prof. Yamin Dang
Chinese Academy of Surveying & Mapping (CASM)
28 Lianhuachi Xi RD
Beijing, 100830
dangym@casm.ac.cn, dangym2015@163.com
CHINA - TAIPEIProf. Ming Yang
National Cheng Kung University
Department of Geomatics
No 1, University Road
Tainan, Taiwan, 701
myang@mail.ncku.edu.tw

337

COLOMBIA
Eng. William Martínez-Diaz
Instituto Geográfico Agustín Codazzi - IGAC
División de Geodesia
Carrera 30 No. 48-51
Bogotá, D.C.
wialmadi@gmail.com
COSTA RICA
Dr. Jorge Moya
Head of Centro Nacional de Procesamiento de Datos GNSS(CNPDG)
Universidad Nacional
Apartado 86-3000
Herediajorge.moya.zamora@una.cr
CROATIA
Assoc. Prof. Dr. Tea Duplancic Leder
Faculty of Civil Engineering, Architecture and Geodesy
University of Split
Matice hvratske 15
21000 Split
T: 385 21 303 408
tleder@gradst.hr
Prof. Dr. Bosko Pribicevic
Faculty of Geodesy
University of Zagreb
Kaciceva 26
10000 Zagreb
bpribic@geof.hr
CZECH REPUBLIC
Prof. Dr. Pavel Novák
University of West Bohemia, Faculty of Applied Sciences
Univerzitni 22306 14 Pilsen
panovak@kma.zcu.cz
DENMARK
Niels Andersen
Deputy Director, National Space Center, DTU
Elektrovej, Building 328, room 106
2800 Kongens Lyngby
na@space.dtu.dk
EGYPT
Prof. Dr. Mostafa Mousa Mohamed Rabah
Civil Engineering Department, Faculty of Engineering
Benha University, Shobra, Cairo
mostafa-rabah@yahoo.com

338

ESTONIA
Prof. Dr. Artu Ellmann
Tallinn University of Technology
Ehitajate tee 519086 Tallinn
artu.ellmann@ttu.ee
FINLAND
Dr. Jyri Näränen
FGI - Finnish Geospatial Research InstituteDepartment of Geodesy and Geodynamics
Geodeetinrinne 202430 Masalajyri.naranen@nls.fi
FRANCE
Dr. Marie-Françoise Lequentrec-Lalancette
Directrice Technique de la Recherche et de l'innovation
Service hydrographique et océanographique de la marine(SHOM)
13 rue du Chatellier
29228 Brest Cedex 2
marie-francoise.lalancette@shom.fr
GEORGIA
Associate Professor Dr. Tengiz Gordeziani
Javakhishvili Tbilisi State University
0160 Tbilisi
tengizgordeziani@gmail.com
GERMANY
Prof. Dr.-Ing. Jürgen Müller
Leibniz Universität Hannover, Institute of Geodesy
Schneiderberg 50
30167 Hannover
mueller@ife.uni-hannover.de
GHANA
Prof. Geophrey Anornu
Kwame Nkrumah University of Science and Technology
Department of Civil Engineering
Kumasianoprof@hotmail.co.uk, anoprof1@yahoo.com
GREECE
Prof. Ilias N. Tziavos
Aristotle University of Thessaloniki
School of Rural and Survey Engineering
Department of Geodesy and Surveying
541 24 Thessaloniki
tziavos@topo.auth.gr

The Geodesist’s Handbook 2020

HUNGARY
Prof. Dr. József ÁdámBudapest University of Technology and Economics
Department of Geodesy and Surveying
P.O. Box 91
1521 Budapest
adam.jozsef@epito.bme.hu
ICELAND
Mr. Magnus Gudmundsson
National Land Survey of Iceland
Stillholt 16-18
300 Akranes
magnus@lmi.is
INDIA
Dr. Virendra M. Tiwari
Director
CSIR-National Geophysical Research Institute (NGRI)
Uppal Road
Hyderabad, 500 007 Telangana
director@ngri.res.in, virendra.m.tiwari@gmail.com
INDONESIA
Hasanuddin Z. Abidin
Institute of Technology of Bandung
Faculty of Earth Science and Technology
Department of Geodesy and Geomatics Engineering
Jl. Ganesa 10
Bandung 40132
hzabidin@gd.itb.ac.id, hzabidin@gmail.com
IRAN
Prof. Dr. Vahid Ebrahimzadeh Ardestani
Institute of Geophysics
P.O. Box 14155-6466, Tehran
ebrahimz@ut.ac.ir
IRELAND
Ms. Katy Fitzpatrick
Ordnance Survey Office
Phoenix Park, Dublin, 8
katy.fitzpatrick@osi.ie
ISRAEL
Dr. Gilad Even-Tzur
Technion – Israel Institute of Technology
Faculty of Civil and Environmental Engineering
Division of Mapping and Geo-Information Engineering
Haifa, 32000
eventzur@tx.technion.ac.il

Delegates to the IAG Council

ITALY
Prof. Mattia Crespi
Universitá di Roma “La Sapienza”
Facoltá di Ingegneria Civile e Industriale
Dipartimento di Ingegneria Civile, Edile e Ambientale
Via Eudossiana, 1800184 Romemattia.crespi@uniroma1.it, mattia.crespi@gmail.com
Dr. Paolo Messina
CNR - Institute of Environmental Geology andGeoengineering
Area della Ricerca Roma1, Via Salaria Km 29,300
00015 Montelibretti
paolo.messina@cnr.it, paolo.messina@igag.cnr.it
JAPANProf. Manabu Hashimoto
Kyoto University, Disaster Prevention Research InstituteGokasho,Uji
Kyoto, 611-0011
hashimoto.manabu.7e@kyoto-u.ac.jp
KOREA
Dr. Jungho Cho
Korea Astronomy & Space Science InstituteSpace Science Division
776 Daedeok-daero, Yuseong-gu
Daejeon, 34055
jojh@kasi.re.kr

339

MEXICO
Dr. Enrique CabralInstituto de Geofisica - UNAM
Ciudad Universitaria
04510, Mexico, D.F.
ecabral@geofisica.unam.mx
MOZAMBIQUE
Mr. José Luis Quembo
Centro Nacional de Cartografia e Teledetecção
(CENACARTA)
Caixa Postal 83, Maputo
jlquembo@gmail.com
NETHERLANDS
Prof. Dr. ir. Peter J.G. Teunissen
Delft University of Technology
Faculty of Civil Engineering and Geosciences
Department of Geoscience and Remote Sensing
PO Box 5048
2628 CN Delftp.j.g.teunissen@tudelft.nl, P.Teunissen@curtin.edu.au
NEW ZEALAND
Dr. Matt Amos
Land Information New Zealand
PO Box 5501
Wellington 6145
mamos@linz.govt.nz

LATVIADr. sc. ing. Jānis Kaminskis
Department of Geomatics
Riga Technical University
Meza street I, K1-l 14
LV-1048 Riga
janis.kaminskis@rtu.lv, iugg.lv@lza.lv

NICARAGUA
Mr. Marvin Corriols
IGG/CIGEO UNAN
De la Rotonda Universitaria 1 km al Sur
Villa Fontana, Apdo.
6631 Managua
marvincorriols@hotmail.com

Dr. sc. ing. Gunārs Silabriedis
University of Latvia
Jelgavas Street 3
LV-1004 Riga
gunars.silabriedis@lu.lv

NIGERIA
Prof. Francis I. Okeke
University of Nigeria
Faculty of Environmental Sciences, Enugu Campus
Enugu
francisokeke@yahoo.com, francis.okeke@unn.edu.ng

LUXEMBOURG
Ing. Germain Breger
Administration des Services du Géomètre
Ville de Luxembourg
3, rue du Laboratoire,
1911 Luxembourg
gbreger@vdl.lu

NORTH MACEDONIA
Prof. Dr. Zlatko Srbinoski
Ss Cyril and Methodius University
Faculty of Civil Engineering, Department of Geodesy
Blvd. Partizanski odredi 24, PO Box 560
1000 Skopje
srbinoski@gf.ukim.edu.mk

340

The Geodesist’s Handbook 2020

NORWAY
Dr. Halfdan Pascal Kierulf
Geodetic Institute
Norwegian Mapping Authority
3507 Honefoss
halfdan.kierulf@kartverket.no

RUSSIA
Dr. Viktor P. Savinykh
Moscow State University of Geodesy and Cartography
4 Gorokhovsky lane
105064 Moscow
president@miigaik.ru, vp@miigaik.ru

PAKISTAN
Mr. Rauf Ahmed
Deputy Director
Survey of Pakistan
Murree Road
Rawalpindi
dtr@surveyof Pakistan.gov.pk

SAUDI ARABIA
Dr. Abdullah Arrajehi
King Abdulaziz City for Science & Technology (KACST)
P.O. Box 6086
Riyadh 11442
arrajehi@kacst.edu.sa

PERU
M.Sc. Edmundo Norabuena
Instituto Geofísico del PerúCalle Calatrava 216, Urb. Camino RealLa Molina
Lima 12enorab@geo.igp.gob.pe

SERBIA
Prof. Dr. Oleg Odalović
Department of Geodesy and Geoinformatics
Faculty of Civil Engineering
University of Belgrade
Bulevar kralja Aleksandra 73
11000 Belgrade
odalovic@grf.bg.ac.rs

POLAND
Prof. Dr. Jan Krynski
Institute of Geodesy and Cartography
Modzelewskiego St. 27
02-679 Warsaw
krynski@igik.edu.pl

SLOVAK REPUBLIC
Assoc. Prof. Juraj Janák
Slovak University of Technology
Radlinskeho 11
813 68 Bratislava
juraj.janak@stuba.sk

Prof. Dr. Pawel Wielgosz
University of Warmia and Mazury
Institute of Geodesy
Oczapowskiego St. 1
10-719 Olsztyn
pawel.wielgosz@uwm.edu.pl

SLOVENIA
Prof. Dr. Bojan Stopar
University of Ljubljana
Faculty of Civil and Geodetic Engineering
Geodetic Department
Jamova 21115 Ljubljana
bojan.stopar@fgg.uni-lj.si

PORTUGAL
Eng. João Manuel Agria Torres
Estrada de Oeiras, 64
2780-278 Oeiras
jagriatorres@gmail.com
ROMANIA
Prof. Dr. Johann Neuner
Technical University of Civil Engineering
Bdul Lacul Tei, nr. 124
020396 Bucharest
neuner@utcb.ro

SPAIN
Prof. Miguel J. Sevilla
Universidad Complutense
Facultad de Ciencias Matemáticas
28040 Madrid
sevilla@mat.ucm.es
SWEDENDr. Jonas Ågren
Swedish Mapping, Cadastre and Registry Authority
Geodetic Research Division
801 82 Gävle
Jonas.Agren@lm.seDelegates to the IAG Council

SWITZERLAND
Dr. Elmar Brockmann
Federal Office of Topography swisstopo
Senftigenstr. 264
3084 Wabern
elmar.brockmann@swisstopo.ch
THAILAND
Lt. Gen. Krit Rammon, Director
Royal Thai Survey Department
Royal Thai Armed Forces Headquarters
Ministry of Defense
Kalayanamaitri Street, Phranakhon
Bangkok, 10200
krit_ra@hotmail.com
TURKEY
Dr. Col. Eng. Osman Atila Akabali
Head of Geodesy Department
General Directorate of Mapping
06590 Cebeci/Cankaya,
Ankaraatila.akabali@harita.gov.tr
UNITED KINGDOM
Prof. Peter J. Clarke
Newcastle University
School of Civil Engineering and Geosciences
G.12 Cassie Building
Newcastle upon Tyne NE1 7RU, UK
Peter.Clarke@newcastle.ac.uk

341

URUGUAY
Cnel. Operador Geógrafo Norbertino Suárez
Director
Instituto Geográfico Militar
Av. 8 de octubre 3255
Montevideo
nsuarez@sgm.gub.uy, norbertinosuarez@gmail.com
USA
Prof. Matthew Pritchard
Department of Earth & Atmospheric Sciences
Cornell University
3124 Snee Hall
Ithaca, NY, 14583
Pritchard@cornell.edu
VIETNAM
Dr. Le Anh Dung
Vietnam Institute of Geodesy and Cartography
479 Hoang Quoc Viet, Cau Giay
Hanoi
ladungvigac@gmail.com

342

The Geodesist’s Handbook 2020

IAG Representatives to Scientific Bodies
Markku Poutanen (Secretary General)

IAG Representatives to the Services
BGI:
ICGEM:IDEMS:IDS:
IERS:
IGETS:IGFS:
IGS:

Urs Marti (Switzerland)
Riccardo Barzaghi (Italy)
Riccardo Barzaghi (Italy)
Ernst Schrama (Netherlands)
Tom Herring (USA)Severine Rosat (France)
Urs Marti (Switzerland)
Basara Miyahara (Japan)
Zuheir Altamimi (France)ILRS:
Urs Hugentobler (Germany)
ISG:
Cheinway Hwang (China-Taipei)
IVS:
Johannes Böhm (Austria)
PSMSL: Per Knudsen (Denmark)

IAG Representatives to External Bodies
IUGG Commissions
CCEC (Comm. on Climate & Environmental Changes):
Annette Eicker (Germany)
CMG (Commission on Mathematical Geophysics):
Shin-Chan Han (Australia)
GRC (Geophysical Risk and Sustainability):
Kosuke Heki (Japan)
SEDI (Study of Earth's Deep Interior):
Carla Braitenberg (Italy)
UCDI (Union Commission for Data and Information):
Sonia M. A. Costa (Brazil)
UCPS (Union Commission on Planetary Sciences):
Shuanggen Jin (China),
Pieter Visser (Netherlands)

IUGG Committees; contact IUGG SGIUGG Capacity Building and Education Committee:
Hansjoerg Kutterer (Germany)IUGG Statutes and By-Laws Committee:
Jeff Freymueller (USA)IUGG Visioning Committee
Harald Schuh (Germany)
Other bodies
ABLOS (Advisory Board on the Law of the Sea):
Niels Andersen (Sweden),
Juan Carlos Baez (Chile),
Sunil Bisnath (Canada),Marie-Françoise Lequentrec (France)
GEO (Group on Earth Observation), Plenary:Richard Gross (USA),
Allison Craddock (USA)
Representatives to Committees nominated by GGOS
Basara Miyahara (Japan)
IAU Commission A2 Rotation of the Earth:
Robert Heinkelmann (Germany)
ISO (International Standards Organization): TC211
Geographic Information/Geomatics:
Detlef Angermann, (Germany)
Markku Poutanen (Finland)
Control Body for Geodetic Registry Network:
Michael Craymer (Canada),
Larry Hothem (USA)SIRGAS (Geocentric Reference System for the Americas):
Hermann Drewes (Germany)
UNOOSA (UN Office for Outer Space Affairs): ICG
Allison Kealy (Australia)
UN-GGIM (UN Global Geospatial Inf. Management):
Zuheir Altamimi (France)

IAG Representatives to Scientific Bodies

WG GGRF Infrastructure:
Chris Rizos (Australia)
WG GGRF Data Sharing and Geodetic Standards:
Detlef Angermann (Germany)WG GGRF Education and Capacity Building:Maria Cristina Pacino (Argentina)
WG GGRF Outreach and Communication:
Szabolcs Rozsa (Hungary)WG GGRF Governance:
Harald Schuh (Germany)
UN-GGIM: Geospatial Societies (former JBGIS):
Zuheir Altamimi (France)343

IAG Representatives in IUGG Liaisons toInternational and Intergovernmental Organizations
ICS Committee on Data for Science and Technology(CODATA): Kirsten Elger (Germany)
ICS Commission on Space Research (COSPAR)
Christopher Kotsakis (Greece)
ICS World Data System (WDS)
Kirsten Elger (Germany)
Consultative Committee for Time and Frequency (CCTF):
Felix Perosanz (France)
Pan-American Institute for Geography and History(PAIGH): Laura Sánchez (Germany)

Funding Open access by the Agreement with the International Associationof Geodesy (IAG)
Open Access This article is licensed under a Creative Commons Attribution
4.0 International License, which permits use, sharing, adaptation,
distribution and reproduction in any medium or format, as long as you
give appropriate credit to the original author(s) and the source, provide alink to the Creative Commons licence, and indicate if changes were made.
The images or other third party material in this article are included in thearticle’s Creative Commons licence, unless indicated otherwise in a credit
line to the material. If material is not included in the article’s Creative
Commons licence and your intended use is not permitted by statutory
regulation or exceeds the permitted use, you will need to obtain permission
directly from the copyright holder. To view a copy of this licence, visit
http://creativecommons.org/licenses/by/4.0/.