# IAG Resolutions

## Adopted by the IAG Council at the XXV IUGG General Assembly,
Melbourne, Australia, June 28 – July 7, 2011

### Resolution 1

#### Gravity field satellite missions

The International Association of Geodesy,

*considering*,

the interest of the scientific community in knowing with
the highest accuracy and resolution the Earth gravity field
and its time evolution as one of the fundamental
components of the Earth system, also to understanding the
climate evolution of the Earth;

*acknowledging*,

the large experience acquired within the IAG in the last 10
years in analyzing data from dedicated satellite missions
like CHAMP, GRACE and GOCE for the purpose of esti-
mating the gravity field and its time variation;

*noting*,

the need for a long-term monitoring of the gravity field for
Earth System science beyond the mission lifetime of
GRACE and GOCE;

*urges*,

international and national institutions, agencies and
governmental bodies in charge of supporting Earth science
research to make all efforts in implementing new gravity
field satellite missions that would respond to the afore-
mentioned need for continued observation.

### Resolution 2

#### Second Realization of the International Celestial Reference Frame

The International Association of Geodesy,

*considering*,

1. that the International Union of Geodesy and Geophysics adopted at the 23rd General Assembly in Sapporo 2003 Resolution 4 on the first realization of the International Celestial Reference Frame;

2. that the International Astronomical Union (IAU) adopted Resolution B3 at its XXVII General Assembly (2009) (www.iau.org/static/resolutions/IAU2009_English.pdf) that resolves to consider the “Second Realization of the International Celestial Reference Frame (ICRF2)” as the fundamental realization of the International Celestial Reference System (ICRS) (see note 1);

3. that the celestial reference system and the nutation-precession model have a large influence on geodetic and geodynamic observations, analyses and interpretations;

4. that the ICRF2 was constructed by the International Earth Rotation and Reference Systems Service (IERS) and the International VLBI Service for Geodesy and Astrometry (IVS);

*recommends*

1. that the ICRF2 should be used as a standard for all future applications in geodesy and astrometry,

2. that the organizations responsible for geodetic VLBI observing programs take appropriate measures to continue existing and develop improved VLBI observing and analysis programs to both maintain and improve ICRF2,

3. that highest consistency between the ICRF, the International Terrestrial Reference Frame (ITRF), and the Earth Orientation Parameters (EOP) as observed and realized by the IAG and its components such as the IERS should be a primary goal in all future realizations of the ICRS.

*Note 1:* The Second Realization of the International Celestial Reference Frame by Very Long Baseline Interferometry, Presented on behalf of the IERS / IVS Working Group, Alan Fey and David Gordon (eds.). (IERS Technical Note 35) Frankfurt am Main: Verlag des Bundesamts für Kartographie und Geodäsie, 2009. See <www.iers.org/MainDisp.csl?pid=46-25772> or <hpiers.obspm.fr/icrs-pc/>.
# Structures for the Period 2011 – 2015

## International Union of Geodesy and Geophysics (IUGG)

### Executive Committee

**Bureau**

<table><tr><td>President:</td><td>Harsh Gupta (India)</td></tr><tr><td>Vice-President:</td><td>Michael Sideris (Canada)</td></tr><tr><td>Secretary General</td><td>Alik Ismail-Zadeh (Germany)</td></tr><tr><td>Treasurer:</td><td>Aksel W. Hansen (Denmark)</td></tr><tr><td>Members:</td><td>Isabella Ansorge (South Africa)<br/>Pierre Hubert (France)<br/>Kenji Satake (Japan)</td></tr></table>

**Retiring President:** Tom Beer (Australia)

**Presidents of the International Associations**

<table><tr><td>IACS:</td><td>Ian Allison (Australia)</td></tr><tr><td>IAG:</td><td>Chris Rizos (Australia)</td></tr><tr><td>IAGA:</td><td>Kathryn Whaler (UK)</td></tr><tr><td>IAHS:</td><td>Gordon Young (Canada)</td></tr><tr><td>IAMAS:</td><td>Athena Coustenis (France)</td></tr><tr><td>IAPSO:</td><td>Evgeny G. Morozov (Russia)</td></tr><tr><td>IASPEI:<br/>(Switzerland)</td><td>Domenico Giardini</td></tr><tr><td>IAVCEI:</td><td>Ray Cas (Australia)</td></tr></table>

### Finance Committee

<table><tr><td>Chair:</td><td>David Collins (UK)</td></tr><tr><td>Members:</td><td>Zoltan Hajnal (Canada)<br/>Jan Krynski (Poland)<br/>David Rhoades (New Zealand)</td></tr></table>

### International Associations

**International Association of Cryospheric Sciences**

President: Ian Allison (Australia)
President Elected: Charles Fierz (Switzerland)
Secretary General: Andrew Mackintosh (New Zealand)

**International Association of Geodesy**

President: Chris Rizos (Canada)
Secretary General: Hermann Drewes (Germany)

**International Association of Geomagnetism and Aero-nomy**

President: Kathryn Whaler (UK)
Secretary General: Mioara Mandea (France)

**International Association of Hydrological Sciences**

President: Gordon Young (Canada)
President Elect: Hubert Savenije (The Netherlands)
Secretary General: Christophe Cudennec (France)

**International Association of Meteorology and Atmospheric Sciences**

President: Athena Coustenis (France)
Secretary General: Hans Volkert (Germany)

**International Association for the Physical Sciences of the Oceans**

President: Evgeny G. Morozov (Russia)
Secretary General: Johan Rodhe (Sweden)

**International Association of Seismology and Physics of the Earth's Interior**

President: Domenico Giardini (Switzerland)
Secretary General: Peter Suhadolc (Italy)

**International Association of Volcanology and Chemistry of the Earth's Interior**

President: Ray Cas (Australia)
Secretary General: Joan Marti (Spain)

### Union Commissions

**Data and Information (UCDI)**

Chair: Peter Fox (USA)
Secretary: Adelina Geyer Traver (Spain)

**Geophysical Risk and Sustainability (GeoRisk)**

Chair: Kuniyoshi Takeuchi (Japan)
Secretary: Diana Greenslade (Australia)

**Mathematical Geophysics (CMG)**

Chair: Yehuda Ben-Zion (USA)
Secretary: Claudia Pasquero (Italy)

**Studies of Earth's Deep Interior (SEDI)**

Chair: Satoru Tanaka (Japan)
Secretary: Mike Bergman (USA)

### Inter-Unions Commission

**Commission on the Lithosphere: International Lithosphere Program (ILP)**

President: Sierd Cloetingh (The Netherlands)
Secretary General: Roland Oberhänsli (Germany)
International Association of Geodesy (IAG)

# 1. Executive Committee

## 1.1 IAG Bureau

IAG President: Chris Rizos (Australia)

Vice President: Harald Schuh (Austria)

Secretary Gen.: Hermann Drewes (Germany)

## 1.2 IAG Immediate Past President

Pres. 2007-2011: Michael G. Sideris (Canada)

## 1.3 IAG Commission Presidents

Commission 1 “Reference Frames”
President: Tonie van Dam (Luxembourg)

Commission 2 “Gravity Field”
President: Urs Marti (Switzerland)

Commission 3 “Earth Rotation and Geodynamics”
President: Richard Gross (USA)

Commission 4 “Positioning and Applications”
President: Dorota Brzezinska (USA)

## 1.4 Global Geodetic Observing System (GGOS)

GGOS Chair: Hansjoerg Kutterer (Germany)

## 1.5 Communication & Outreach Branch (COB)

COB President: József Ádám (Hungary)

## 1.6 Representatives of the Services

Representatives: Riccardo Barzaghi (Italy)
Tom Herring (USA)
Ruth Neilan (USA)

## 1.7 Members at Large

Members: Claudio Brunini (Argentina)
Richard Wonnacott (S. Africa)

## 1.8 Non-voting Members

Inter-Commission Committee on Theory (ICCT)
President: Nico Sneeuw (Germany)

IAG Ass. Secr.: Helmut Hornik (Germany)

IAG Past Presidents (before 2007)
1979-1983: Helmut Moritz (Austria)
1987-1991: Ivan I. Mueller (USA)
1991-1995: Wolfgang Torge (Germany)
1995-1999: Klaus-Peter Schwarz (Canada)
1999-2003: Fernando Sansó (Italy)
2003-2007: Gerhard Beutler (Switzerland)

IAG Past Secretaries General
1975-1991: Michel Louis (France)
1991-1995: Claude Boucher (France)
1995-2007: Christian Tscherning (Denmark)

# 2. IAG Office

Deutsches Geodätisches Forschungsinstitut
Secretary General: Hermann Drewes (Germany)
Assistant Secretary: Helmut Hornik (Germany)

# 3. IAG Communication & Outreach Branch

Hungarian Academy of Sciences / Budapest University of Technology and Economics
President: József Ádám (Hungary)
Secretary: Szabolcs Rózsa (Hungary)

# 4. Journal of Geodesy

Editor in Chief: Roland Klees (The Netherlands)

# 5. IAG Symposia Series

Editor in Chief: Chris Rizos (Australia)

Assistant Editor: Pascal Willis (France)
## 6. IAG Commissions

### Commission 1: Reference Frames

President: Tonie van Dam (Luxembourg)

Vice-Pres.: Gary Johnston (Australia)

### Commission 2: Gravity Field

President: Urs Marti (Switzerland)

Vice-Pres.: Srinivas Bettadpur (USA)

### Commission 3: Earth Rotation and Geodynamics

President: Richard Gross (USA)

Vice-Pres.: Aleksander Brzezinski (Poland)

### Commission 4: Positioning and Applications

President: Dorota Grejner-Brzezinska (USA)

Vice-Pres.: Allison Kealy (Australia)

## 7. IAG Global Geodetic Observing System (GGOS)

Chair: Hansjörg Kutterer (Germany)

Vice-Chair: Ruth Neilan (USA)

## 8. IAG Scientific Services

### IAG Bibliographic Service (IBS)

Chair: Annekathrin Michlenz (Germany)

### International Altimeter Service (IAS)

Chair: Wolfgang Bosch (Germany)

### International Bureau of Weights and Measures, Bureau International des Poids et Mesures (BIPM), Time Department

Director: Elisa Felicitas Arias (France)

### International Centre for Earth Tides (ICET)

Director: Jean-Pierre Barriot (France)

### International Centre for Global Earth Models (ICGEM)

Director: Franz Barthelmes (Germany)

### International Digital Elevation Models Service (IDEMS)

Director: Philippa Berry (UK)

### International DORIS Service (IDS)

Chair Governing Board: Pascal Willis (France)

Director Central Bureau: Laurent Soudarin (France)

Analysis Coordinator: Frank Lemoine (USA)

### International Earth Rotation and Reference Systems Service (IERS)

Chair of Directing Board: Chopo Ma (USA)

Director Central Bureau: Bernd Richter (Germany)

Analysis Coordinator: Tom Herring (USA)

### International Geoid Service (IGeS)

President and Director: Riccardo Barzaghi (Italy)

### International GNSS Service (IGS)

Chair of the Gov. Board: Urs Hugentobler (Germany)

Director Central Bureau: Ruth Neilan (USA)

Analysis Coordinator: Jake Griffiths (USA)

### International Gravimetric Bureau, Bureau Gravimetrique International (BGI)

Director: Sylvain Bonvalot (France)

### International Gravity Field Service (IGFS)

Chair: Rene Forsberg (Denmark)

Director Central Bureau: Iginio Marson (Italy)

Executive CB Secretary: Franco Coren (Italy)

### International Laser Ranging Service (ILRS)

Chair Governing Board: Graham Appleby (UK)

Director Central Bureau: Michael Pearlman (USA)

Secretary: Carey Noll (USA)

Analysis Coordinator: Erricos Pavlis (USA)

### International VLBI Service for Geodesy and Astrometry (IVS)

Acting Chair Dir. Board: Harald Schuh (Austria)

Director Coord. Center: Dirk Behrend (USA)

Analysis Coordinator: Axel Nothnagel (Germany)

### Permanent Service for Mean Sea Level (PSMSL)

Director: Lesley Rickards (UK)

## 9. IAG Inter-Commission Committee on Theory (ICCT)

President: Nico Sneeuw (Germany)

Vice-President: Pavel Novak (Czech Republic)
# Commission 1 – Reference Frames

http://iag.uni.lu

President: **T. van Dam** (Luxembourg)

Vice President: **G. Johnston** (Australia)

## Terms of Reference

Reference systems and frames are of primary importance for much Earth science based research and applications, satellite navigation as well as for practical applications in geo-information. A precisely defined reference frame is needed for an improved understanding of the Earth's rotation and its 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 aspects of how best to define reference systems and how reference systems can be used for practical and scientific applications. Commission 1 will closely interact with the other IAG Commissions, ICCT, Services and GGOS components where reference system aspects are of concern. Commission 1 is identical with Sub-commission B2 of COSPAR.

## Objectives

The main objectives of Commission 1 include:

* Definition, establishment, maintenance and improvement of the geodetic reference frames;

* Advanced terrestrial and space observation technique development for the above purposes;

* International collaboration for the definition and deployment of networks of terrestrially-based space geodetic observatories;

* Theory and coordination of astrometric observation for reference frame purposes.

* Collaboration with space geodesy/reference frame related international services, agencies and organizations;

* Promote the definition and establishment of vertical reference systems at global level, considering the advances in the regional sub-commissions;

* Work to maintain a reference frame that is valuable for global change studies.

## Structure

### Sub-Commissions

**SC 1.1:** Coordination of Space Techniques
Chair: T. Herring (USA)

**SC 1.2:** Global Reference Frames
Chair: C. Boucher (France)

**SC 1.3:** Regional Reference Frames
Chair: J. Torres (Portugal)

**SC 1.3a:** Europe
Chair: J. Ihde (Germany)

**SC 1.3b:** South and Central America
Chair: C. Brunini (Argentina)

**SC 1.3c:** North America
Chairs: J. Griffiths (USA), M. Craymer (Canada)

**SC 1.3d:** Africa
Chair: R. Wonnacott (South Africa)

**SC 1.3e:** Asia-Pacific
Chair: J. Dawson (Australia)

**SC 1.3f:** Antarctica
Chair: R. Dietrich (Germany)

**SC 1.4:** Interaction of Celestial and Terrestrial Reference Frames
Chair: J. Böhm (Austria)

### Joint Study Groups

**JSG 0.1:** Application of time series analysis in geodesy
(joint with ICCT and all Commissions, description see ICCT)
Chair: W. Kosek (Poland)

**JSG 0.2:** Gravity field modelling in support of height system realization
(joint with ICCT and Commission 2, description see ICCT)
Chair: P. Novák (Czech Republic)

**JSG 0.4:** Coordinate systems in numerical weather models
(joint with ICCT and all Commissions, description see ICCT)
Chair: Th. Hobiger (Japan)

**JSG 0.8:** Earth system interaction from space geodesy
(joint with ICCT and all Commissions, description see ICCT)
Chair: S. Jin (China)
**JSG 0.9:** Future developments of ITRF models and their geophysical interpretation (joint with ICCT and IERS, description see ICCT)
Chair: A. Dermanis (Greece)

**JSG 3.1:** Gravity and height change intercomparison (joint with Commissions 2, 3 and IGFS, description see Commission 3)
Chair: S. Rosat (France)

## Joint Working Groups

**JWG 1.1:** Tie vectors and local ties to support integration of techniques (joint with IERS)
Chair: P. Sarti (Italy)

**JWG 1.2:** Modelling environmental loading effects for reference frame realizations (joint with IERS)
Chair: X. Collilieux (France)

**JWG 1.3:** Understanding the relationship of terrestrial reference frames for GIA and sea-level studies (joint with Commission 3)
Chair: T. Schöne (Germany)

**JWG 1.4:** Strategies for epoch reference frames (joint with IERS)
Chair: M. Seitz (Germany)

**JWG 0.1.1:** Vertical datum standardization (joint with GGOS, IGFS, and Commission 2; description see GGOS)
Chair: L. Sánchez (Germany)

## Program of Activities

The program of activities for Commission 1 includes:

* Encourage, initiate, and support theoretical and applied research activities related to reference frames;

* Enforce Research and Development activities that impact the reference frame determination and its accuracy, as well as, the best and optimal usage of reference frames in Earth Science applications;

* Closely interact with all established IAG Services: IVS, IGS, ILRS, IDS and the IERS, including their Combination Centres and Working Groups;

* If necessary, improve the theory and application of the transformation between Celestial and Terrestrial Reference Systems and application of the theory to improve the consistency between ICRF, ITRF and EOPs, in cooperation with IVS and IERS;

* Explore advanced methodologies for the combination of products and raw observations of space geodetic techniques;

* Investigate all systematic error sources and factors limiting the precision of space geodetic techniques and their combination;

* Within each regional sub commission, encourage and

assist regional sub-commission countries to re-define and modernize their national geodetic systems so that they are compatible with the ITRF;

* Establish a dedicated Web site relating all Commission 1 activities.

## Steering Committee

* President: Tonie van Dam (Luxembourg)

* Vice President: Gary Johnston (Australia)

* Chair SC1.1: T. Herring (USA)

* Chair SC1.2: C. Boucher (France)

* Chair SC1.3: J. Torres (Portugal)

* Chair SC1.4: J. Böhm (Austria)

* Representatives of Services:

IERS: C. Ma

IDS: P. Willis

IGS: J. Griffiths

ILRS: G. Appleby

IVS: O. Titov

* Member at Large: L. Combrinck (South Africa)
# Sub-Commissions

## SC 1.1: Coordination of Space Techniques

Chair: Tom Herring (USA)

### Terms of Reference

The space geodetic observation techniques, including Very Long Baseline Interferometry (VLBI), Satellite and Lunar Laser Ranging (SLR/LLR), Global Navigation Satellite Systems (GNSS) such as GPS, GLONASS, GALILEO, and COMPASS, and the DORIS system, as well as altimetry, InSAR, LIDAR, and the gravity missions, contribute significantly to the knowledge about and the understanding of the three major pillars of geodesy: the Earth's geometry (point coordinates and deformation), Earth orientation and rotation, and the gravity field as well as its time variations. These three fields interact in various ways and they all contribute to the description of processes in the Earth System. Each of the space geodetic techniques contributes in a different and unique way to these three pillars and, therefore, their contributions are critical to the Global Geodetic Observing System (GGOS).

Sub-Commission 1.1 coordinates efforts that are common to more than one space geodetic technique, such as models, standards and formats. It shall study combination methods and approaches concerning links between techniques co-located at fundamental sites, links between techniques co-located onboard satellites, common modelling and parameterization standards, and perform analyses from the combination of a single parameter type up to a rigorous combination on the normal equation (or variance-covariance matrices) as well as at the observation level. The list of interesting parameters includes site coordinates (e.g. time series of combined solutions), Earth orientation parameters, satellite orbits (combined orbits from SLR, GPS, DORIS, altimetry), atmospheric refraction (troposphere and ionosphere), gravity field coefficients, geocentre coordinates, and others. One important goal of SC1.1 will be the development of a much better understanding of the interactions between the parameters describing geometry, Earth rotation, and the gravity field as well as developing methods to validate combination results, e.g., by comparing them with independent geophysical information.

To the extent possible SC1.1 should also encourage research groups to develop new observation techniques connecting or complementing the existing set of measurements. Sub-Commission 1.1 has the task to coordinate the activities in the field of the space geodetic techniques in close cooperation with GGOS, all of the IAG Services, and with COSPAR.

### Objectives

The principal objectives of the scientific work of Sub-Commission 1.1 in collaboration with GGOS are the following:

* Study systematic effects of and between space geodetic techniques.

* Develop common modelling standards and processing strategies.

* Comparison and combination of orbits derived from different space geodetic techniques.

* Explore and develop innovative combination aspects such as, e.g., GPS and VLBI measurements based on the same high-accuracy clock, VLBI observations to GNSS satellites, and the combination of atmospheric information (troposphere and ionosphere) of more than one technique.

* Establish methods to validate the combination results (e.g., with global geophysical fluids data).

* Explore, theoretically and practically, the interactions between the gravity field parameters, EOPs, and reference frames (site coordinates and velocities plus extended models), improve the consistency between these parameter groups, and assess, how a correct combination could be performed.

* Study combination aspects of new geodetic methods such as Synthetic Aperture Radar (InSAR), LIDAR and optical image analysis methods.

* Additional objectives of Sub-Commission 1.1 are:

* Promotion of international scientific cooperation.

* Coordination of common efforts of the space geodetic techniques concerning standards and formats (together with the IERS and GGOS).

* Organization of workshops and sessions at meetings to promote research. - Establish bridges and common activities between SC1.1 and the IAG Services.

### Links to Services

Sub-Commission 1.1 will establish close links to the relevant services for reference frames, namely Global Geodetic Observing System (GGOS), International Earth Rotation and Reference Systems Service (IERS), International GPS Service (IGS), International Laser Ranging Service (ILRS), International VLBI Service for Geodesy and Astronomy (IVS), and International DORIS Service (IDS) and the International gravity services.
# Working Groups of Sub-Commission 1.1

## WG 1.1.1: Creation of common geodetic coordinate time series

Chair: Laurant Soudarin (France)

This working group, formed in collaboration with the IERS, will explore methods for creating position time series for the different geodetic techniques so that they can be displayed in a common format and consistent reference frame. The working group will explore, in the format and interfaces for time series. A common tool that can be used to display and compare these results will also be developed. The working group will have a representative from each technique combination centre, a representative from the ITRS combination centre, and that the GGOS portal manager. There should also be representatives from the geophysics/geodynamics and oceanography communities who are seen as the primary uses of this product. The final product of this working group will be recommendations on how the geodetic community should proceed in developing common positional time series and making such results readily available to the broad scientific community.

## WG 1.1.2: Investigate methods for merging geodetic imaging systems (InSAR, LIDAR and optical methods) into a geodetic reference system

Chair: Sebastian Leprince (USA)

With the development of new methods for studying surface deformations, such as InSAR, LIDAR and optical methods, this working group will explore the methods that should be used to ensure that these deformation measurements are made in a well-defined geodetic reference frame. Issues to be addressed include how to establish the reference frame for these classes of measurements, how to ensure the long-term stability of the reference frame, and to make recommendations for changes in future systems that would allow more robust reference frame realization.

# SC 1.2: Global Reference Frames

Chair: Claude Boucher (France)

## Terms of Reference

Sub-Commission 1.2 is engaged in scientific research and practical aspects of the global reference frames. It investigates the requirements for the definition and realization of the terrestrial reference systems (TRS) and frames (TRF), addresses fundamental issues closely related to TRS, such as global geodetic observatories or methods for the combined processing of heterogeneous observation- data.

Terrestrial Reference Systems refer to an important domain of Geodesy, involving both the theoretical and the applied aspects, as well as deep connections with Astronomy, Earth Sciences and Geo-information. This necessitates several visions:

* An astronomical vision, using the TRS to study translational and rotational motions of the Earth in inertial space;

* An Earth Science vision, using TRS to build physical models of the Earth system, and its various components (solid earth, oceans, atmosphere, hydrosphere);

* A metrological vision, using TRS together with suitable coordinate systems (geographical coordinates, map projections...) to define geographical position of objects in the Earth's vicinity (geo-referencing).

The work in this SC will be carried out in close cooperation with the International Earth Rotation and Reference Systems Service (IERS), other relevant IAG services (IGS, ILRS, IVS, IDS), and the IAG Global Geodetic Observing System (GGOS). Theoretical aspects will be investigated in cooperation with the Inter-Commission Committee on Theory.

Beyond IAG, cooperation with other relevant international organizations such as IAU, FIG or ISO will also be developed.

## Objectives

The following research topics will form the fundamental objectives during the next period:

* Relativistic modelling, including extension of the IAU model to geodesy, investigations on the use of emission coordinate systems;

* External evaluation of TRF;

* TRF by multi-technique data analysis versus hierarchical combinations;

* Global Geodetic Observatories, concepts and practical implementation;

* TRF versus dynamical topographic models;
* Relation with standardization or certification activities (ISO, GEO...).

## Links to Services

Sub-Commission 1.2 will be closely linked to the relevant services, in particular the International Earth Rotation and Reference Systems Service, (IERS), the International GNSS Service (IGS), the International Laser Ranging Service (ILRS), the International VLBI Service for Geodesy and Astronomy (IVS), and the international DORIS Service (IDS).

## Working Groups of Sub-Commission 1.2

### WG 1.2.1: External Evaluation of Terrestrial Reference Frames

Chair: Xavier Collilieux (France)

The scientific community has recognized the need for a highly accurate terrestrial reference frame (TRF) for Earth Science applications. Although geodetic measurements are very precise, uncertainty in the modelling of the measurements and correlations between estimated parameters make it complicated to assess geocentric station coordinates. While a precision at a few-millimetre level is thought to be achievable, it is difficult to supply a precise figure of the current coordinate accuracy. The reliability of the station velocities is notably essential to the study of climate change. Any error in the rate of the origin and scale definition of the TRF will especially map directly into the station velocities and into other products such as sea level rise estimates.

The aim of this task force is to review all the methods that could be used to assess the accuracy of the origin, scale and orientation (and/or their time variations) of a TRF. All the activities in which the adopted TRF has a quantitative influence will be studied in order to derive possible constraints on the TRF. Methods that involve datasets that have not been used to derive the TRF will be especially emphasized (tide gauges, gravity, geophysical models etc...). As an example, the quality of ITRF2008 will be investigated using various methods in order to derive the most complete error budget.

## Objectives

* Investigate methods to evaluate TRF accuracy, especially TRF datum parameters;

* Supply an assessment of ITRF2008 quality using all available relevant methods.

## Specific program activities

* Study all the activities in which the adopted TRF has a quantitative influence;

* Maintain a bibliography about TRF evaluation with any type of data and model;

* Evaluate the interest to derive external constraints on TRF datum fixation, i.e. on its origin, scale, orientation and their time evolutions.

### WG 1.2.2: Global Geodetic Observatories

Chair: Perguido Sarti (Italy)

An effective integration of space geodetic instruments at the observing sites is a crucial issue for the computation of the terrestrial reference frame. In fact, the computation of the global terrestrial frame depends, on the one hand, on the number, distribution and quality of the co-located sites and, on the other hand, on the accuracy of the tie vectors that express the relative position of the co-located instruments.

The ITRF is a geodetic product that serves Earth and space sciences. Although, its significance and exploitation goes beyond scientific research: societal application, natural hazards mitigation and Earth observations go beyond purely scientific uses and has an impact on the whole society.

Geophysical research requires a wider concept of integration where co-locations are realized not only with space and terrestrial geodetic instruments but also with other geophysical sensors like seismometers, weather stations, lidars, radio-sondes, gravimeters, tide gauges, radiometers, etc...

In this perspective, the integration of geodetic and geophysical sensors must be realized at the highest level of precision providing the relative positions in a consistent frame at local and global scales.

The task force will examine and revise the state of the art in local tie surveying and tie vector estimation, spotlighting the current deficiencies and promoting cooperation on the relevant research topics. The definition of reference points for each instrument as well as the related calibration issues will also be considered, in close cooperation with individual technique services (IGS, IVS, ILRS, IDS, PSMSL, IGFS...). The most recent and highest standards achieved in the integration of geodetic instruments will be transposed to the problem of co-locating, operating and managing a wider class of geophysical instruments with the purpose of defining the guidelines for their effective co-location and integration towards the creation of multipurpose geophysical observatories.
Other types of considerations will be also investigated,
such as operational issues, international governance,
labelization, standardization and certification.

Objectives

* Revise the needs related to the co-location of geophysical sensors;

* Revise existing tie vector estimation processes methods and accuracies;

* Transpose the state of the art of tie vector estimation to non-geodetic instruments;

* Liaise with IERS, IAG and GGOS;

* Set guidelines on geophysical co-location surveying and management.

SC 1.3: Regional Reference Frames

Chair: João Torres (Portugal)

Terms of Reference

Sub-Commission 1.3 deals with the definitions and realiza-
tions of regional reference frames and their connection to
the global International Terrestrial Reference Frame
(ITRF). It offers a home for service-like activities address-
ing theoretical and technical key common issues of interest
to regional organisations.

Objectives

In addition to the specific objectives of each regional sub-
commission, the main objectives of SC1.3 as a whole are:

* Develop specifications for the definition and realization of regional reference frames, including the vertical component with a special consideration of gravity and other data;

* Coordinate the activities of the regional sub-commissions focusing on exchange and share of competences and results;

* Develop and promote operation of GNSS permanent stations, in connection with IGS whenever appropriate, to be the basis for the long-term maintenance of regional reference frames;

* Promote actions for the densification of regional velocity fields;

* Encourage and stimulate the development of the AFREF project in close cooperation with IGS and other interested organizations;

* Encourage and assist countries, within each regional sub-commission, to re-define and modernize their national geodetic systems, compatible with the ITRF.

Program of Activities

* Organize inter-regional workshops addressing activities, results and key issues of common interest to the regional sub-commissions;

* Develop analysis strategies and compare methods for the implementation of the regional reference frames and their expression in the ITRF, with the full interaction with the IGS;

* Consider studying and promoting consistent specifica-
tions for the generation of GNSS-based velocity field
solutions;

* Consider developing tectonic deformation models that will enable transformation of locations within a defined reference frame between different epochs;

* At regional levels, contribute to the realization and improvement of local surveys in the collocation sites, with full cooperation with the Sub-commission 1.2 Global Reference Frames.
## SC 1.3a: Europe

Chair: Johannes Ihde (Germany)

Secretary: Alessandro Caporali (Italy)

### 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 close cooperation with the pertinent IAG components (Services, Commissions, and Inter-commission projects) and EuroGeographics, the consortium of the National Mapping and Cadastral Agencies (NMCA) in Europe.

### Structure

* EUREF is composed of representatives from European IAG member countries;

* The TWG (Technical Working Group) is composed of members elected by the plenary, members in charge of special projects and ex-officio members.

### Program of Activities

* Continue to develop the EUREF Permanent Network (EPN) in close cooperation with IGS, for the maintenance of the European Terrestrial Reference Frame, as a contribution to the ITRF and as an infrastructure to support practical applications for precise positioning and referencing geo-information;

* Extend the Unified European Levelling Network (UELN) and prepare it to be computed under a geokinematic approach using the European Combined Geodetic Network (ECGN) for a long-term maintenance of the European Vertical Reference Frame;

* Support new developments in reference frame realization and application by introducing new technologies like real-time data transfer and products, as well as Galileo for precise positioning;

* Establish a dense velocity field model in Europe for the long-term maintenance of the European reference frame;

* Consider the contribution to the IAG Program GGOS (Global Geodetic Observing System) using the installed infrastructures managed by the EUREF members;

* Promote the adoption of the reference systems defined by 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;

* Organize annual symposia addressing activities carried out at national and Europe-wide levels related to the global work and objectives of EUREF.

## SC 1.3b: South and Central America

Chair: Claudio Brunini (Argentina)

Vice-Chair: Laura Sánchez (Germany)

### 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 is concerned with the definition, realization and maintenance of a modern geodetic reference infrastructure for South and Central 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

The main purposes of the Sub-commission 1.3b are:

* To determine, maintain and make available a geocentric reference frame (a set of stations with high-precise geocentric positions and their variation with time, as a regional densification of the global ITRF;

* To support the SIRGAS countries in the establishment and maintenance of national geodetic reference networks as local densifications of SIRGAS in order to guarantee accessibility to the global ITRF at national and local levels;

* To establish a unified vertical reference system supporting the determination and precise combination of physical and geometric heights as well as their variations with time;

* Contribute to the GGOS program by developing and implementing state-of-the-art products based on the SIRGAS observational infrastructure;

* To promote, support, and coordinate the efforts of the Latin American and Caribbean countries to achieve these objectives.

### Structure

The structure of the Sub-commission 1.3b is based on the functioning bodies of SIRGAS. There are currently three Working Groups:

* WG 1.3b.1: Reference System
  Chair: Virginia Mackern (Argentina)

* WG 1.3b.2: SIRGAS at National Level
  Chair: William Martínez (Colombia)

* WG 1.3b.3: Vertical Datum
  Chair: Roberto Luz (Brazil)

The SIRGAS Executive Committee (as it is named in the SIRGAS statutes) is composed of:

* SC 1.3b Chair: C. Brunini (Argentina)

* SC 1.3b Vice-Chair: Laura Sánchez (Germany)
* WG 1.3b.1 Chair: Virginia Mackern (Argentina)

* WG 1.3b.2 Chair: William Martínez (Colombia)

* WG 1.3b.3 Chair: Roberto Luz (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:

* Promotion of the IGS and IERS standards within the SIRGAS countries to ensure the adequate installation, maintenance, and analysis of continuously operating GNSS stations;

* Establishment of a SIRGAS National Processing Centre in all the member countries;

* Refinement of the SIRGAS station hierarchy. At present, two classes are considered: core and densification stations (the establishment of other categories is under consideration);

* 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.;

* Experimental processing of the GLONASS observational data to identify a suitable analysis strategy and to evaluate if these results can be combined with the corresponding GPS products;

* Promotion and implementation of real-time services based on the SIRGAS infrastructure to make available the reference frame to more users;

* The kinematics of the SIRGAS frame, up to now, have been 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.

According to this, it is necessary:

* To model non-linear station movements within the reference frame computation;

* 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;

* To evaluate the feasibility of computing and using near-real 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:

* Continental adjustment of the national vertical networks in terms of geo-potential numbers;

* Combined analysis of tide gauge registrations, GNSS positioning and satellite altimetry observations to determine the dynamic ocean topography at the classical vertical datums;

* Determination of potential differences between the reference tide gauges and the global reference surface;

* Stronger cooperation with the Sub-Commission 2.4b (Gravity and Geoid in South and Central America - GGSCA) to promote national initiatives regarding the modernization of the gravity reference networks and the computation of geoid models of high resolution.

Hourly SIRGAS ionospheric models (vTEC) based on the GNSS SIRGAS stations have been generated since 2006 on a regular basis. The SIRGAS ionospheric model is being upgraded to include 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 computing water vapour estimations.

## SC 1.3c: North America

Chairs: J. Griffiths (USA) and M. Craymer (Canada)

### 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. Some of these issues include:

* Densification of the ITRF reference frame in North America and the promotion of its use;

* Maintenance and future evolution of plate-fixed geometric reference frames for North America, including the North American Datum of 1983 (NAD83) and any possible successors;

* Maintenance and future evolution of vertical datums (ellipsoidal and orthometric), including the North American Vertical Datum of 1988 (NAVD88) and the International Great Lakes Datum (IGLD);
* Effects of crustal motion, including post-glacial rebound and tectonic motions along, e.g., the western coast of North America and in the Caribbean;

* Standards for the accuracy of geodetic positions;

* Outreach to the general public through focused symposia, articles, workshops and lectures, and technology transfer to other groups.

## Working Groups

### WG 1.3c.1: North American Reference Frame (NAREF)

Chairs: Michael Craymer (Canada) & Jake Griffiths (USA)

#### Program of Activities

To densify the ITRF reference frame in the North American region by organizing the computation of weekly coordinate solutions and their associated precision information for continuously operating GPS stations that are not part of the current IGS global network.

* A cumulative solution of coordinates 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 and disseminate the weekly and cumulative solutions.

### WG1.3c.2: Plate-Fixed North American Reference Frame

Chair: J. Griffiths (USA)

#### Program 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 scientific and geomatics communities by providing a consistent, mm-accuracy, stable reference with which scientific and geomatics results (e.g., positioning in tectonically active areas) can be produced and compared.

### WG1.3c.3: Reference Frame Transformations in North America

Chair: M. Craymer (Canada)

#### Program of Activities

To determine consistent relationships between international, regional and national reference frames/datums in North America, to maintain (update) these relationships as needed and to provide tools for implementing these relationships.

## SC 1.3d: Africa

Chair: R. Wonnacott (South Africa)

### 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 organisations and the National and Regional Mapping Organisations of Africa, the aims and objectives of Sub-commission 1.3d (Africa) are:

* To define the continental reference system of Africa. The goal is to establish and maintain a unified geodetic reference network as the fundamental basis for the national 3-d reference networks fully consistent and homogeneous with the global reference frame of the ITRF;

* To realize a unified vertical datum and support efforts to establish a precise African geoid, in concert with the African Geoid project activities;

* To establish continuous, permanent GPS stations such that each nation or each user has free access to, and is at most 500km from, such stations;

* To provide a sustainable development environment for technology transfer, so that these activities will enhance the national networks, and numerous applications, with readily available technology;

* To understand the necessary geodetic requirements of participating national and international agencies and;

* To assist in establishing in-country expertise for implementation, operations, processing and analyses of modern geodetic techniques, primarily GPS.

#### Program of Activities

It is envisaged that the regionalization of AFREF will follow an approach that consists of three major phases:

* The establishment of a framework of permanent or semi-permanent GPS base stations throughout the region that will become part of the worldwide IGS stations network;

* The densification of the network of permanent or semi-permanent base stations, largely on a country-by-country basis, to determine the relationship between the national geodetic system and the ITRS, and to refine the transformation parameters necessary to relate the national systems to a common ITRF;

* The third and equally important phase of the project will be to address the development of a more refined geoid
model for Africa and the definition of a common vertical datum for the continent. This will be done in collaboration with the IAG Africa Geoid Project (Project 2.3 Commission 2).

It is further planned to hold workshops and seminars to
strengthen the science and knowledge of geodesy and
GNSS within Africa and their application to the develop-
ment of reference frames.

SC 1.3e: Asia-Pacific

Chair: John Dawson (Australia)

Terms of Reference

To improve regional cooperation that supports the realisa-
tion and densification of the International Terrestrial Refer-
ence frame (ITRF). This activity will be carried out in
close collaboration with the Geodetic Technologies and
Applications Working Group of the Permanent Committee
for GIS Infrastructure in Asia and the Pacific (PCGIAP),
which operates under the purview of the United Nations
Regional Cartographic Conference for Asia and the Pacific
(UNRCC-AP).

Objectives

The objectives of the Sub-commission1.3e are:

* The densification of the ITRF and promotion of its use in the Asia Pacific region;

* To encourage the sharing of GNSS data from Continuously Operating Reference Stations (CORS) in the region;

* To develop a better understanding of crustal motion in the region;

* To promote the collocation of different measurement techniques, such as GPS, VLBI, SLR, DORIS and tide gauges, and the maintenance of precise local geodetic ties at these sites; and

* To outreach to developing countries through symposia, workshops, training courses, and technology transfer activities.

Program of Activities

The activities of this sub-commission will principally be
those of the Asia-Pacific Reference Frame (APREF), see
http://www.ga.gov.au/earth-monitoring/geodesy/asia-pacific-
reference-frame.html, together with the Geodetic Techno-
logies and Applications Working Group of the Permanent
Committee for GIS Infrastructure in Asia and the Pacific
(PCGIAP).

SC 1.3f: Antarctica

Chair: R. Dietrich (Germany)

Terms of Reference

Sub-commission 1.3f (Antarctica) is focusing on the defi-
nition and realization of a unified reference frame for Ant-
arctica, which will be consistent with the global Inter-
national Terrestrial Reference Frame (ITRF). It will estab-
lish close links to corresponding activities within the
Scientific Committee on Antarctic Research (SCAR).

Objectives

* Maintenance and densification of the precise geodetic reference network in Antarctica by permanent observations and GPS campaigns;

* Realization of an unified vertical datum including GPS ties of tide gauges;

* Providing unified reference for other GPS applications like airborne gravimetry, ground truthing for satellite missions, geodynamics and glaciology;

* Develop technologies for remote geodetic observatories.

Structure

The structure of SC1.3f is yet to be finalized in close
collaboration with the SCAR program GIANT (Geodetic
Infrastructure for Antarctica).

Program of Activities

* Organization of GPS campaigns in Antarctica, maintenance of the data archive;

* Extend activities for the operation of remote permanent GPS stations;

* Data analysis and determination of the Antarctic GPS network as a regional densification of ITRF;

* Support airborne surveys and satellite missions with precise terrestrial reference;

* Provide homogeneous site velocities for e.g. glacial isostatic adjustment determination;

* Collaborate with IAG Sub-Commission 3.4 Cryospheric Deformation.

Organize meetings and workshops on Antarctic geodesy
jointly with related SCAR activities in order to
strengthen the international cooperation and to make
optimum use of field logistics and infrastructure.
## Working Groups of Sub-Commission 1.3

### WG 1.3.1: Integration of Dense Velocity Fields into the ITRF

Chair: Carine Bruyninx (Belgium)

The main task of this WG is to study and promote consistent specifications for the generation of GNSS-based velocity field solutions and their combination in order to derive a unified dense velocity field in a common global reference frame.

#### Members

* Carine Bruyninx (Belgium)

* John Dawson (Australia)

* Ambrus Kenyeres (Netherlands)

* Jake Griffiths (USA)

* Mike Craymer (Canada)

* Laura Sanchez (Germany)

* Alvaro Santamaria Gomez (Spain)

* Juliette Legrand (Belgium)

* Zuheir Altamimi (France)

### WG1.3.2: Deformation Models for Reference Frames

Chair: Richard Stanaway (Australia)

The primary aim of the WG is to develop tectonic deformation models that will enable transformation of locations within a defined reference frame between different epochs. Such deformation models are essential to support precise point positioning applications and CORS/NRTK operations within deforming zones.

#### Members

* R. Stanaway (Australia)

* Christopher Pearson (New Zealand)

* Paul Denys (New Zealand)

* Kevin Kelly (USA)

* Rui Fernandes (Portugal)

* Craig Roberts (Craig Roberts)

* Graeme Blick (New Zealand)

* Chris Crook (New Zealand)

* John Dawson (Australia)

* Mikael Lilje (Sweden)

* Laura Sanchez (Germany)

* Rob McCaffrey (USA)

* Norman Teferle (Luxembourg)

## SC 1.4: Interaction of Celestial and Terrestrial Reference Frames

Chair: Johannes Böhm (Austria)

#### Terms of Reference

In recent years, significant progress has been made in astronomical and geophysical modelling for the analysis of space geodetic observations. Thus, there is the need to investigate the impact of those models on the terrestrial and celestial reference frames (TRF and CRF), and on the consistency between the TRF, CRF, and the Earth orientation (EOP) parameters. Special attention needs to be paid to Very Long Baseline Interferometry (VLBI) observations, since it is the only technique to provide consistent sets of TRF/EOP/CRF. However, the present realization of the ITRF (ITRF2008) is based on a combination of VLBI, GNSS, SLR, and DORIS observations, whereas the present realization of the ICRF (ICRF2) is determined from a single VLBI solution. Consequently, research has to be carried out to integrate the ITRF and ICRF solutions, and also new options like VLBI observations to satellites should be considered for future improvement of the consistency. The GAIA mission scheduled for launch in 2013 is expected to achieve an optical realization of the CRF with precision similar to or better than the ICRF2 and with at least an order of magnitude more objects. As the set of extragalactic objects suitable for both optical and radio observation is limited, such objects will have to be identified, and investigations have to be carried out to permit the best possible connection between the radio and optical CRF realizations.

### Working Groups of Sub-Commission 1.4

#### WG 1.4.1: Geophysical and Astronomical Effects and the Consistent Determination of Celestial and Terrestrial Reference Frames

Chair: Zinovy Malkin (Russia)

WG 1.4.1 is created to promote and coordinate investigations of 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 Very Long Baseline Interferometry (VLBI) as the only technique nowadays that can provide highly consistent global solutions for TRF, CRF, and EOP.
## Objectives

* Encourage and develop cooperation and collaboration in theoretical studies, simulations, and processing of real data aimed at a better understanding of the impact of geophysical and astronomical modelling on TRF, CRF, and EOP derived from VLBI observations.

* Advance means of comparing models as well as TRF, CRF, and EOP realizations.

* Compare different theoretical models and their realizations used by VLBI analysis centres. Study the propagation of differences in those models to differences in geometric and astrometric products.

* Develop practical recommendations for VLBI analysis centres and the IERS Conventions Centre on the optimal models to be used during processing of VLBI observations.

## Members

* Z. Malkin (Russia)

* J. Böhm (Austria)

* S. Lambert (France)

* C. Ma (USA)

* R. Haas (Sweden)

* H. Spicakova (Austria)

* R. Heinkelmann (Germany)

* D. MacMillan (USA)

## WG 1.4.2: Co-location on Earth and in Space for the Determination of the Celestial Reference Frame

Chair: Sebastien Lambert (France)

VLBI is the only technique sensitive to the “quasi inertial” celestial reference frame, and the most recent realization of the International Celestial Reference System, the ICRF2, was determined in a VLBI-only solution. The other space geodetic techniques (GNSS, DORIS, SLR) define a dynamical celestial reference frame, but all techniques are combined to determine the International Terrestrial Reference Frame (ITRF) without adding the estimation of sources to that combination, thus causing inconsistencies between the ICRF and the ITRF.

The goal of WG 1.4.2 is to investigate the impact on the ICRF when combining VLBI observations with those from satellite techniques. Historically, this combination is based on local tie information at the co-location sites, but in the future troposphere ties and even space ties could also be used, i.e., observing the GNSS constellation or a dedicated micro-satellite like GRASP with VLBI, so that a fully consistent system is created.

## Objectives

* Support the realization of a full combination of the VLBI/ GNSS/DORIS/SLR at the normal equation level including estimates of radio source coordinates. This should be done in close cooperation with the IERS Working Group on the Combination at the Observation Level;

* Investigate various analysis options (local and troposphere ties, twin telescopes) on the results (TRF, EOP, CRF);

* Analyze VLBI observations to GNSS satellites.

* Simulate the effect of VLBI observations to GNSS and SLR satellites and assess the impact on the CRF;

* Simulate future micro satellite missions like GRASP in VLBI analysis software packages;

* Simulate the benefits of the upcoming VLBI2010 equipment to propose recommendations for the near future.

## Members:

* S. Lambert (France)

* Z. Malkin (Russia)

* C. Ma (USA)

* J. Böhm (Austria)

* R. Haas (Sweden)

* R. Heinkelmann (Geodesy)

* Y. Kwak (Korea)

* Le Poncin-Lafitte

* L. Plank (Austria)

* M. Seitz (Germany)

* V. Tornatore (Italy)

## WG 1.4.3: Realization of Celestial Reference Frames

Chair: Chopo Ma (U.S.A.)

To achieve further progress regarding the realization of celestial reference frames it is essential to review the current status, to identify deficiencies and to make proposals for improvements. This task is closely related to various components of the IERS and the techniques analysis coordinators (in particular of the IVS), and requires a close cooperation between the different groups. The activities include the survey of the current status of CRF realization, a review regarding the implementation of IERS Conventions and IAG Fundamental Parameters and different space techniques for CRF realization.

The International Celestial Reference Frame (ICRF2) realized by VLBI is currently defined by the radio positions of 295 extragalactic objects (IERS TN 35, Fey,
Gordon and Jacobs, eds., 2009). The ICRF2 was endorsed by the IAU in 2009 and by the IUGG in 2011. The noise floor is ~40 µas and the uncertainty of the axes is ~10 µas. Precise positions of 3414 extragalactic radio sources are included in the ICRF2 catalogue.

The GAIA (Global Astrometry Interferometer for Astrophysics) mission scheduled for launch in 2013 is expected to achieve an optical realization of the CRF with precision similar to or better than the ICRF2 and with at least an order of magnitude more objects. However, as the set of extragalactic objects suitable for both optical and radio observation is limited, one goal of the Working Group is to identify such objects, oversee the relevant observations, and analyze the data to permit the best possible connection between the radio and optical CRF realizations.

For geodetic use the CRF realization must be accessible from the ground. For the foreseeable future this connection will be through VLBI observations. In cooperation with the IVS and IERS, this Working Group will oversee the maintenance and improvement of the ICRF2, in particular the set of sources used for geodetic observations and the ICRF2 defining sources.

# Joint Working Groups of Commission 1

## JWG 1.1: Tie vectors and local ties to support integration of techniques
(Joint with IERS)

Chair: Peirguido Sarti (Italy)

### Terms of Reference

Tie vectors are crucial elements of the combination of space geodetic solutions. Their accuracy straightforwardly refers to their capability of expressing the relative position of the co-located space geodetic instruments to conventional reference points. They enter the combination of space geodetic solutions as additional observations and can be eventually regarded as the fifth technique involved in the combination. Their role is not strictly limited to the provision of the necessary information for the combination since accurate tie vectors can also highlight the presence of technique- and site-specific biases. In particular, tie vectors can support the investigation of technique-dependent systematic errors and the ability of each technique to connect electronic and conventional reference points.

The whole process related to the planning of on-field operations and the surveying carried out with either terrestrial or GPS methods (i.e. the local tie procedure) needs to be constantly revised and when necessary improved. The definition of new local tie approaches remains central to the activity promoted by the working group. As a group of experts, the working group aims at promoting discussions and serving as a forum for the evaluation of existing as well as new procedures. Equally important, the working group aims at improving the existing analysis strategies applied to the local tie observations and to the data post-processing. The ultimate scope is to achieve the utmost level of accuracy of the tie vector. The consistency between tie vectors and space geodetic solutions is recognized as a crucial aspect on which the improvement of the International Terrestrial Reference Frame depends.

An important by-product of the combination of space geodetic solutions is represented by the post-fit residuals. They are empirically determined during the combination process and express the discrepancies between space geodetic solutions and tie vectors. Particularly, the values of the post-fit residuals of the combination can serve as preliminary indicators of the quality of the space geodetic solution and/or tie information at one specific site. As such, they can highlight the necessity to investigate further the co-location and the techniques involved in the tie. This specific use of post-fit residuals is extremely interesting and promising although their handling requires much attention. Many factors may combine to the final post-fit residual value. The accuracy of the tie vectors has to be certain to effectively use the co-location post-fit residuals for inferring something about site dependent or technique
dependent systematic errors. This clearly highlights the
need to attempt a revision of the quality of the existing tie
vectors and possibly verify their formal accuracy not only
empirically, on the base of the post-fit residuals
themselves, but on the base of other factors such as their
age and their length.

The working group should serve as a reference for the
know-how and the good practice on co-location issues for
the geodetic community. It should be ready to support new
survey activities, assisting and advising remotely, and it
should promote re-surveying if necessary. The link with
the relevant branches of GGOS has to be ensured during
the terms of the working group activity. Finally, the link
between the working group and the single IAG technique
services is considered essential and a permanent flow of
relevant information must be constantly pursued.

Objectives

• Research objectives:

- Revise existing local tie procedures

- Investigate existing tie vector estimation processes

- Develop and define new methods

- Direct research towards the investigation of technique
  specific systematic effects

• Coordination objectives:

- Liaise with IERS combination centres

- Liaise with IAG technique service

• Outreach:

- Support local tie operations and tie vector estimation

- Spread the know-how

- Set guidelines

Members

• Claudio Abbondanza (USA)

• Zuheir Altamimi (France)

• Giuseppe Bianco (Italy)

• Xavier Collilieux (France)

• John Dawson (Australia)

• Bruno Garayt (France)

• Maria Hennes (Germany)

• Ulla Kallio (Finland)

• Jim Long (USA)

• Chuck Meertens (USA)

• Valerie Michel (France)

• Axel Nothnagel (Germany)

• Mike Pearlman (USA)

• Jean-Claude Poyard (France)

• Pierguido Sarti (Italy)

• Jerome Saunier (France)

• Ralf Schmid (Germany)

• Manuela Seitz (Germany)

• Luca Vittuari (Italy)

• Pascal Willis (USA)

JWG 1.2: Modelling environmental loading
effects for reference frame realiza-
tions

(Joint with IERS)

Chair: Xavier Collilieux

Terms of Reference

The accuracy and precision of current space geodetic tech-
niques are such that displacements due to non-tidal surface
mass loading are measurable. Many scientific studies have
already considered atmospheric loading corrections at the
observation level. The modelling of other non-tidal loading
effects has also been investigated by various authors. In
parallel, a posteriori corrections have been shown to
slightly decrease the variance factor of a Terrestrial Refer-
ence Frame (TRF) multi-technique combination but the
improvement at some sites was also counterbalanced by
degradation at others.

There still exist open questions regarding the application of
loading corrections for the generation of operational geo-
detic products, either a priori or a posteriori: accuracy of
the models in all frequency bands - sub-daily band is the
most important for a priori corrections -, too few studies
regarding available loading model agreement have been
carried out, proper mass conservation of all contributions
and degree 0 of each contribution, methods that should be
use for interpolating the loading displacements, required
model resolution, reference loads that are or should be
used for geodetic products, contribution of ice melting at
high latitude which is not modelled in current continental
water loading models. The optimal usage of loading
models is still to be defined in all possible applications.

The goal of this working group is to ensure that the optimal
usage of a loading model is made for TRF computation.

Objectives

The principle objectives of the scientific work are to
investigate if loading corrections are necessary for TRF
adjustment and if necessary, investigate the optimal
methods to deal with loading effects in the ITRF construc-
tion.

• Determine how best to apply loading corrections: observation level or daily averages?

* If corrections are applied at the observation level, how can the displacement signal be reapplied to the station displacement time series?

* Address whether all geodetic techniques see the same level of loading contributions. In particular, some studies have shown that GPS seems to have larger annual and semi-annual signals than other geodetic methods and calculations from geophysical fluid loading.
## Specific program activities

* Compare and assess differences between existing load models for a given effect.

* Maintain a bibliography on the available models and their evaluation.

* Assessment of the propagation of loading model errors into the site coordinates and the ITRF.

* Define whether models should be applied at the observation level or in the post-processing. In this case, define the best method (if any) to handle loading effects at the observation level (filtering?, interpolation etc...).

* Tie results/findings to IERS conventions.

* Collect user opinions about what signals they need in station position time series (loading corrected or not).

## Members

* Zuheir Altamimi(France)

* Johannes Böhm (Austria)

* Jean-Paul Boy (France)

* Tom Herring (USA)

* Laurent Metivier (France)

* Gerard Petit (France)

* Jim Ray (USA)

* Paul Tregoning (Australia)

* Tonie van Dam (Luxembourg)

* Christopher Watson (Australia)

* Xiaoping Wu (USA)

## JWG 1.3: Understanding the relationship of terrestrial reference frames for GIA and sea-level studies

(Joint with Commission 3)

Chair: Tilo Schöne (Germany)

## Terms of Reference

The combination and assimilation of GNSS information into Glacial Isostatic Adjustment (GIA) models, the correction of GIA effects on altimetry or tide gauges, or combined studies using information from the different sources requires a common understanding of the individual reference frame realizations.

Today the ITRF realization and their respective updates form the basis for the individual space geodetic techniques. But, in every researcher's daily life, individual realizations are used. For example, the IGS time series are in a respective IGS frame close to ITRF, or satellite orbits for radar altimetry are using DORIS-augmented frames. GIA models employ their own ITRF-independent reference.

Many studies now use information or combinations of the above techniques with the different reference frame realizations. This leads to inconsistencies and misinterpretations. This project is proposed to evaluate the different reference frame realizations. The focus will be on the reference frame realizations in GNSS, DORIS, radar altimetry, and GIA modelling.

## Objectives

* To provide a reference document for GNSS, DORIS, and radar altimetry satellite missions that identifies discrepancies in the reference frames.

* To suggest implementation/combination schemes, where possible.

## Program of Activities

* Review the individual radar altimetry and satellite missions with the following goals:

- Evaluate the type of reference frames;

- Evaluate the handling of loading tides and conventions used;

- Evaluate time-variable gravity field effects in orbit determination;

- Possibly extend results to the use of geocentre motion for sea level studies.

* Review the GNSS reference frame realizations

- Review ITRF2008/IGS08 realization (IGS repro, TIGA)

- Evaluate handling of loading tides, and other conventions

* Review the DORIS reference frame realization

- Review in view of the realizations used in RA processing for satellites carrying DORIS;

- Evaluate the handling of loading tides and conventions used.

* Review the reference frame realization in GIA models.

## Members

* Matt King (United Kingdom)

* Pascal Willis (France)

* Sergei Rudenko (Germany)

* Daniela Thaller (Germany)

* Christopher Watson (Australia)

* Xiaoping Wu (USA)

* Xavier Collilieux (France)

* Tonie van Dam (Luxembourg)

* Mirko Scheinert (Germany)

* Mark Tamisea (United Kingdom)

* Erik Ivins (USA)

* Maik Thomas (Germany)

* Cecep Subarya (Indonesia)
## JWG 1.4: Strategies for epoch reference frames

(Joint with IERS)

Chair: Manuela Seitz (Germany)

### Terms of Reference

The International Terrestrial Reference Frame (ITRF) is based on a mathematical model, which describes the station movement as a piece-wise linear function of time. This motion is mainly driven by lithosphere plate motion and crustal deformations, which are assumed to be linear and constant over long time periods. Thus, the ITRF provides a very high long-term stability. Even if the linear component dominates the station motion, most of the station positions show additional non-linear effects. The most important causing reasons are atmospheric and hydrospheric mass load changes, which lead to seasonal and long-period position variations, and seismic events causing co-seismic abrupt and post-seismic exponentially decreasing movements of the stations. The approximation of non-linear seismic station motions within the ITRF is performed by estimating offsets and piece-wise constant velocities. Loading effects are not considered as they are very difficult to model or parameterize. One possible solution to overcome this problem would be to compute time series of epoch reference frames, which would provide the station positions at consecutive epochs. The mentioned types of non-linear station motion would be captured very well by such time series of epoch reference frames. A second advantage of epoch reference frame would be that a new solution could be available with a short time delay after a seismic event, when updated coordinates are requested.

Today, GPS-based weekly reference frames are a standard product of the IGS and serve as a near real-time reference frame. The datum of these frames is realized by an alignment to ITRF, which depends on the set of stations used for the alignment - due to station non-linear motions – and which does not account for a motion of the centre of figure w. r. t. the centre of mass. Epoch reference frames based on the combination of the four different techniques contributing to the ITRF would provide geocentric frames consistent to the ITRF.

The national reference frames consist of station positions at a certain epoch or are fixed to a moving plate and do often not consider regional station motions. Station positions resulting from today's measurements are derived in the actual ITRF or epoch reference frames and need to be transformed to the officially defined national reference frames. Especially, in the case of seismic active areas, the network geometry changes significantly over time and cannot be well represented by the current ITRF with linear station motions. Strategies must be developed, which allow for a transformation with a minimal reduction of accuracy.

### Objectives

The primary objective of the Working Group is to develop strategies for the computation of epoch reference frames, by combining the space geodetic techniques VLBI, SLR, GNSS and DORIS on the normal equation level and to assess their potentials in accuracy, stability and global availability to provide recommendations to the IERS.

The development of computation strategies for epoch reference frames will comprise the following main topics: (i) evaluation of the individual contribution of techniques to an epoch reference frame, (ii) analysis of the technique and combined solutions w. r. t. a suitable temporal resolution of the reference frame, (iii) development of strategies for the weighting of the techniques and the implementation of the terrestrial difference vectors (local ties) for epoch reference frame computations, (iv) study of the datum realization for combined epoch solutions, and (v) finally, the accuracy and stability of the reference frame series will be assessed and recommendations to the IERS will be prepared.

The application of epoch reference frames, in particular on regional level, are a further important aspect, which will be kept in mind. But the full consideration of this topic would be beyond the scope of the actual WG and might be the topic of a subsequent WG.

### Planned Activities

* Analysis of the need for an epoch reference frame for practical and scientific applications;

* Development of strategies for the computation of epoch reference frames;

* Analysis of possible frequencies of epoch TRF (weekly, monthly, quarterly, ...);

* Set-up of a webpage for dissemination of information and presentation and communication of research results;

* Organization of conference sessions / workshops;

* Contribution to international meetings and conferences;

* Common publications of WG members.

### Members

* Thomas Artz (Germany)

* Juan Baez (Chile)

* Mathis Bloßfeld (Germany)

* Xavier Collilieux (France)

* Hermann Drewes (Germany)

* Guido Gonzales (Mexico)

* Erricos Pavlis (USA)

* Takeshi Sagiya (Japan)

* Laura Sanchez (Germany)

* Manuela Seitz (Germany)

* Hana Spicakova (Austria)

* Peter Steigenberger (Germany)

* Daniela Thaller (Switzerland)
# Commission 2 – Gravity Field

http://www.iag-commission2.ch

President: **U. Marti** (Switzerland)
Vice President: **S. Bettadpur** (USA)

## Terms of Reference

The accurate determination of the gravity field and its temporal variations is one of the Three Fundamental Pillars of modern geodesy (besides of Geometry and Earth rotation). This is essential for applications in positioning and navigation, metrology, geophysics, geodynamics, oceangoing, 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 of knowledge, technology, and international cooperation in the geodetic domain associated with Earth's gravity field. In the last two periods from 2003 until 2011, Commission 2 has achieved its primary goals and is ready for the next 4-year period. Since most of the scientific themes are of long-term interest, the structure of Commission 2 essentially continues on the same basis as the last period.

Commission 2, at the start of the new period, consists of six sub-commissions (SCs), one Project (P) plus several study groups (SGs) and working groups (WGs), all of them jointly with another Commission or a service (JP, JSG, JWG). The sub-commissions cover the following scientific topics:

* terrestrial, airborne, ship borne gravimetry and relative/absolute gravity networks;

* spatial and temporal gravity field and geoid modelling;

* dedicated satellite gravity missions;

* regional geoid determination;

* satellite altimetry (established in 2007)

* gravity and mass displacements (established in 2011)

The former Commission 2 projects for the continental geoid determination (CP2.1 to CP2.6) have been transferred into new regional Sub-Commissions (in analogy to Commission 1) in order to give them a more permanent status inside the IAG. Their principal goal is to improve the collaboration and the data exchange (gravity, GPS/levelling, digital terrain data) inside a certain region and to aim to a geoid model with a higher resolution than satellite only models.

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 a cross-disciplinary stimulus for work in several topics of interest to the commission.

The main tasks of Commission 2 in the next four years are among others:

* Analysis of GOCE data and the release of improved global Gravity field models (satellite only models and in combination with terrestrial data and altimetry)

* Promoting GRACE follow-on missions for assuring the continued monitoring of global gravity and mass flux changes

* Defining and Realizing a new Gravimetric Reference System (IGRS) to replace the outdated IGSN71 and assuring the future of the comparison campaigns of absolute gravimeters

* Establishing of a service for easy accessing Satellite Altimetry data (IAS)

* Transferring the former 'Global Geodynamics Project' (GGP) into a service 'Global Geodynamics' inside the IGFS.

* Assisting the IGFS and its components in improving their visibility and their services

* Assisting GGOS in the realization of a World Height System (WHS)

* Improve the knowledge of the interaction between gravity change and mass transport (Gravity and Mass Displacement)

* Assisting the regional sub-commissions in establishing contacts and in acquiring data.

The necessary WGs and SGs can be established at any time and they can be dissolved when they reached their goals or if they are not active.

## Objectives

The main objectives of Commission 2 are as listed in the IAG by-laws:

* Terrestrial, marine and airborne gravimetry

* Satellite gravity field observations

* Gravity field modelling

* Time-variable gravity field

* Geoid determination

* Satellite orbit modelling and determination

* Satellite altimetry for gravity field modelling
# Structure

## Sub-Commissions

**SC 2.1:** Gravimetry and Gravity Networks
Chair: Leonid F. Vitushkin (Russia)

**SC 2.2:** Spatial and Temporal Gravity Field and Geoid Modelling
Chair: Yan Ming Wang (USA)

**SC 2.3:** Dedicated Satellite Gravity Missions
Chair: Roland Pail (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: David Avalos (Mexico)
**SC 2.4d:** Gravity and Geoid in Africa
Chair: Hussein Abd-Elmotaal (Egypt)
**SC 2.4e:** Gravity and Geoid in the Asia-Pacific
Chair: Will Featherstone (Australia)
**SC 2.4f:** Gravity and Geoid in Antarctica
Chair: Mirko Scheinert (Germany)

**SC 2.5:** Satellite Altimetry
Chair: Xiaoli Deng (Australia)

**SC 2.6:** Gravity and Mass Displacements
Chair: Shuanggen Jin (China)

**JSG 0.3:** Comparison of current methodologies in regional gravity field modelling (joint with ICCT and Commission 3, see ICCT)
Chairs: M. Schmidt and Ch. Gerlach (Germany)

**JSG 0.4:** Coordinate systems in numerical weather models (joint with ICCT and all Commissions, see ICCT)
Chair: Th. Hobiger (Japan)

**JSG 0.5:** Multi-sensor combination for the separation of integral geodetic signals (joint with ICCT and Commission 3, see ICCT)
Chair: F. Seitz (Germany)

**JSG 0.6:** Applicability of current GRACE solution strategies to the next generation of inter-satellite range observations (joint with ICCT, see ICCT)
Chairs: M. Weigelt (Germany), A. Jäggi (Switzerland)

**JSG 0.7:** Computational methods for high-resolution gravity field modelling and nonlinear diffusion filtering (joint with ICCT and Commission 3, see ICCT)
Chairs: R. Čunderlik, K. Mikula (Slovakia)

**JSG 0.8:** Earth system interaction from space geodesy (joint with ICCT and all Commissions, see ICCT)
Chair: S.G. Jin (China)

**JSG 3.1:** Gravity and height change intercomparison (joint with Commissions 1, 3, and IGFS, description see Commission 3)
Chair: S. Rosat (France)

# Joint Projects

**JP 2.1:** Joint Project 2.1 on Geodetic Planetology (JP-GP) (joint with Commissions 1, 2 and 3, and ICCT)
Chairs: O. Baur (Austria) and S. Han (USA)

## Joint Study Groups

**JSG 0.1:** Applications of time series analysis in geodesy (joint with ICCT and all Commissions, see ICCT)
Chair: W. Kosek (Poland)

**JSG 0.2:** Gravity field modelling in support of height system realization (joint with ICCT, and Commissions 1, see ICCT)
Chair: P. Novak (Czech Republic)

# Joint Working Groups

**JWG 2.1:** Techniques and metrology in absolute gravimetry (joint with IGFS)
Chair: V. Palinkas (Czech Republic)

**JWG 2.2:** Absolute gravimetry and absolute gravity reference system (joint with IGFS)
Chair: H. Wilmes (Germany)

**JWG 2.3:** Assessment of GOCE geopotential models (joint with IGFS)
Chair: J. Huang (Canada)
**JWG 2.4:** Multiple geodetic observations and interpretation over Tibet, Xinjiang and Siberia (TibXS) (joint with Commission 3)
Chair: Ch. Hwang (Taiwan)

**JWG 2.5:** Physics and dynamics of the Earth's interior from gravimetry (joint with Commission 3)
Chair: I. Panet (France)

**JWG 2.6:** Ice melting and ocean circulation from gravimetry (joint with Commission 3)
Chair: J. Schröter (Germany)

**JWG 2.7:** Land hydrology from gravimetry (joint with Commission 3)
Chair: A. Eicker (Germany)

**JWG 2.8:** Modelling and inversion of gravity - solid Earth coupling (joint with Commission 3)
Chair: C. Braitenberg (Italy)

**JWG 0.1.1:** Vertical datum standardization (joint with GGOS, IGFS and Commission 1, description see GGOS)
Chair: L. Sánchez (Germany)

## Steering Committee

* President: Urs Marti (Switzerland)

* Vice President: Srinivas Bettadpur (USA)

* Chair SC 2.1: Leonid F. Vitushkin (Russia)

* Chair SC 2.2: Yan Ming Wang (USA)

* Chair SC 2.3: Roland Pail (Germany)

* Chair SC 2.4: Hussein Abd-Elmotaal (Egypt)

* Chair SC 2.5: Xiaoli Deng (Australia)

* Chair SC 2.6: Shuanggen Jin (China)

* Chair JP 2.1: Oliver Baur (Austria)

* Representative of the IGFS: Rene Forsberg (Denmark)

* Member at large: Maria Cristina Pacino (Argentina)

* Member at large: Yoichi Fukuda (Japan, past president)

The steering committee will meet at least once per year. These meetings are open for all interested IAG members.

## 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 the Commission and summarized in annual reports to the IAG Bureau.

The principal symposium that will be organized by Commission 2 and the IGFS in the next period will be held in Venice in October 2012. A second symposium will be organized by the IGFS in 2014. The other two symposia where a Commission 2 meeting will be held are the IAG scientific assembly 2013 in Potsdam and the IUGG General Assembly 2015 in Prague.

The status of Commission 2, including its structure and membership, as well as links to the internet sites of its sub-entities and parent and sister organizations and services, will be updated regularly and can be viewed on the web site: http://www.iag-commission2.ch.
# Sub-Commissions

## SC 2.1: Gravimetry and Gravity Networks

Chair: Leonid F. Vitushkin (Russia)

### Terms of Reference and Objectives

IAG Sub-commission 2.1 "Gravimetry and gravity networks" promotes scientific studies of the methods and instruments for terrestrial, airborne, shipboard and planetary gravity measurements, establishment of gravity networks and improvement of strategy in the measurement of gravity networks provided by growing number of absolute gravity determinations and the sites for such determinations. The Sub-commission provides the geodesy-geophysics community with the means to access the confidence in gravity measurements at the well-defined level of accuracy through organizing, in cooperation with metrology community, Consultative Committee on Mass and Related Quantities and its Working Group on Gravimetry (CCM WGG), Regional Metrology Organizations (RMO) the international comparisons of absolute gravimeters on continental scale. The Sub-commission proceeds from such point-wise gravimetry to precise gravimetry/gradiometry which should cover, in particular, the land-sea border areas to resolve still existing problem of significant biases and errors in determination. The Sub-commission promotes such research and development by stimulating airborne and shipboard gravimetry and gradiometry. It encourages and promotes special absolute/relative gravity campaigns, techniques and procedures for the adjustment of the results of gravity surveys on a regional scale.

The Sub-commission supports the development of the International Gravity Reference System (IGRS) for GGOS technically and through organization of comparisons of absolute gravimeters at the sites of IGRS in cooperation with relevant metrological bodies.

The Sub-commission in collaboration with metrology community promotes the implementation of the system of metrological support (calibration, verification, comparisons) of absolute gravimeters belonging to geodesy-geophysics community.

In collaboration with JWG 2.2 "Absolute Gravimetry and Absolute Gravity Reference System" the Sub-commission works on the standardization of absolute gravity data, software for absolute gravity measurement and appropriate information. The Sub-commission will encourage regional meetings or workshops dedicated to specific problems, where appropriate.

To meet these goals, the SC 2.1 sets up the Joint Working Group JWG 2.1: "Techniques and Metrology in Absolute Gravimetry" and appointed the Steering Committee consisted of the members which are the specialists in the fields of gravimetry related to the activities of SC2.1 and the contact persons for European, East Asia and Western Pacific, South America and North America Gravity Networks)

### Program of Activities

* selection in collaboration with Commission 2 – IGFS JWG 2.2 and CCM WGG of the sites for regional comparisons of absolute gravimeters, as the basis for IGRS

* supporting the CCM and RMO Key Comparisons of absolute gravimeters on four-yearly and two year scale, correspondingly

* providing the results of comparisons of absolute gravimeters to data base AGrav at BKG-BGI

* supporting the scientific investigations of absolute and relative (including the superconducting) gravimeters on static and moving platforms

* organization of the Third IAG Commission 2 Symposium "Terrestrial Gravimetry. Static and mobile measurements – TGSMM-2013"

### Steering Committee

* Chair: Leonid Vitushkin (Russia)

* Vice Chair: Hideo Hanada (Japan)

* Matthias Becker (Germany, Relative Gravimetry and European Gravity Networks)

* Herbert Wilmes (Germany, Absolute Gravimetry Data and Absolute Gravity Reference System)

* Vojtech Palinkas (Czech Republic, Techniques, Metrology and Comparisons of Absolute Gravimeters)

* David Crossley (USA, Superconductive Gravimetry)

* Uwe Meyer (Germany, Aerogravimetry and Gradiometry)

* Dag Solheim (Norway, Shipboard Gravimetry)

* Yoichi Fukuda (Japan, East Asia and Western Pacific Gravity Networks)

* Maria Cristina Pacino (Argentina, South America Gravity Networks)

* Mark Eckl (USA, North America Gravity Networks)
# SC 2.2: Spatial and Temporal Gravity Field and Geoid Modelling

Chair: Yan Ming Wang (USA)

## Terms of Reference

Sub-Commission 2.2 (SC2.2) promotes and supports scientific research on modelling the Earth's gravity field, including determination of the geoid which is partially inside the Earth's topography.

In today's satellite age, satellite gravity missions deliver very accurate long to medium wavelength of the gravity field, and the Global Positing System provides positions with cm or better accuracy anywhere on planet Earth. On the other hand, gravity and other related data have been collected and monitored by using airplanes, moving vehicles, relative/absolute gravity projects and networks, and other means. The SC2.2 aims at bringing together scientists concerned with all aspects of the diverse areas of geodetically relevant theory and its applications. Its goal is to advance theories and computational methods to ensure that the static and time varying gravity fields are modelled with the required accuracy.

## Objectives

Research related to gravity field determination, e.g., studies of the geodetic boundary value problem (free and fixed boundary value problems); development and refinement of gravity/topographic reduction theories; exploration and implementation of numerical methods of partial differential equations for Earth's gravity field determination (e.g., domain decomposition, spectral combination and others).

In more details, this includes:

* Studies of the effect of topographic density variations on the Earth's gravity field, including the geoid.

* Rigorous yet efficient calculation of the topographic effects, refinement of the topographic and gravity reductions.

* Studies on harmonic downward continuations.

* Non-linear effects of the geodetic boundary value problems on geoid determination.

* Optimal combination of global gravity models with local gravity data.

* Exploration of numerical methods in solving the geodetic boundary value problem (domain decomposition, finite elements, and others).

* Studies on data requirements, data quality, distribution and sampling rate, for a cm- accurate geoid.

* Studies on the interdisciplinary approach for marine geoid determination, e.g., research on realization of a global geoid consistent with the global mean sea surface observed by satellite altimetry.

* Studies on airborne, shipborne gravimetry and the application of satellite altimetry in geodesy.

* Studies on $W_0$ determination, and on global and regional vertical datum realization.

* Studies on ocean, solid-Earth and polar tides.

* Studies on time variation of the gravity field due to post-glacial rebound and land subsidence.

* Studies on geocentre movement and time variation of $J_n$ and its impact on the geoid.

## Program of Activities

* Organizing meetings and conferences.

* Inviting the establishment of Special Study Groups on relevant topics.

* Reporting activities of SC2.2 to the Commission 2.
## SC 2.3: Dedicated Satellite Gravity Missions

Chair: Roland Pail (Germany)

### Terms of Reference

Sub-commission 2.3 promotes scientific investigations concerning the dedicated satellite gravity field missions CHAMP, GRACE and GOCE, the development of alternative methods and new approaches for global gravity field processing also including complementary gravity field data types, as well as interfacing to user communities and relevant organizations.

### Objectives

The successful launches of the German CHAMP (2000), the US/German GRACE (2002) and the ESA GOCE (2009) missions have led to a revolution in global gravity field mapping by space-borne observation techniques. Due to the fact that they are the only measurement system which can directly observe mass and mass transport in the Earth system, they provide valuable contributions to many geoscientific fields of application, such as geodesy, hydrology, oceanography, glaciology, and solid Earth physics. These missions have proven new concepts and technologies, such as high-low satellite-to-satellite tracking (SST) using the GPS constellation, low-low SST based on microwave ranging, and satellite gravity gradiometry (SGG), as well as space-borne accelerometry. GRACE has produced consistent long- to medium-wavelength global gravity field models and its temporal changes. GOCE provides high-accuracy and high-resolution static gravity field models. In combination with complementary gravity field information from terrestrial data, satellite altimetry, an even higher spatial resolution can be achieved. Additionally, based on challenging user requirements, concepts of future gravity field missions are developed and investigated.

### Program of Activities

The focus of this sub-commission will be to promote and stimulate the following activities:

* generation of static and temporal global gravity field models based on observations by the satellite gravity missions CHAMP, GRACE, and GOCE, as well as optimum combination with complementary data types (SLR, terrestrial and air-borne data, satellite altimetry, etc.).

* investigation of alternative methods and new approaches for global gravity field modelling, with special emphasis on functional and stochastic models and optimum data combination.

* identification, investigation and definition of enabling technologies for future gravity field missions: observation types, technology, formation flights, etc.

* communication/interfacing with gravity field model user communities (climatology, oceanography/altimetry, glaciology, solid Earth physics, geodesy, ...).

* communication/interfacing with other IAG organizations, especially the GGOS Working Group for Satellite Missions and the GGOS Bureau for Standards and Conventions

### Steering committee

* Chair: Roland Pail (Germany)

* Srinivas Bettadpur (USA)

* Sean Bruinsma (France)

* Frank Flechtner (Germany)

* Thomas Gruber (Germany)

* Gerhard Heinzel (Germany)

* Cheinway Hwang (Taiwan)

* Torsten Mayer-Gürr (Austria)

* Federica Migliaccio (Italy)

* Ulrich Meyer (Switzerland)

* Pieter Visser (the Netherlands)
# SC 2.4: Regional Geoid Determination

Chair: Hussein Abd-Elmotaal (Egypt)

## Terms of Reference and Objectives

Sub-Commission 2.4 is concerned with the following areas of investigation:

* Regional gravity and geoid sub-commissions: data sets, involved institutions, comparison of methods and results, data exchange, comparison with global models, connection of regional models

* Gravimetric geoid modelling techniques and methods, available software, new alternative geoid determination techniques

* GPS/levelling geoid determination: methods, comparisons, treating and interpretation of residuals, common treatment of gravity and GPS/levelling for geoid determination

* Geoid applications: GPS heights, sea surface topography, integration of geoid models in GPS receivers, vertical datums.

* Other topics: topographic effects, downward and upward 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 will assist local, regional and national authorities in their projects of gravity field determination. It will help in organizing courses and symposia for gravity field determination.

## Steering Committee

* Chair: Hussein Abd-Elmotaal (Egypt)

* Chair SC2.4a: Heiner Denker (Germany)

* Chair SC2.4b: Maria Cristina Pacino (Argentina)

* Chair SC2.4c: David Avalos (Mexico)

* Chair SC2.4d: Hussein Abd-Elmotaal (Egypt)

* Chair SC2.4e: Will Featherstone (Australia)

* Chair SC2.4f: Mirko Scheinert (Germany)

# SC 2.4a: European Gravity and Geoid

Chair: Heiner Denker (Germany)

## Terms of Reference

The primary objective of the sub-commission is the development of improved regional gravity field models (especially geoid/quasigeoid) 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.

The modelling will be based mainly on terrestrial gravity and terrain data in combination with the latest available global geopotential models. In this context, the upgrade of the terrestrial data sets as well as the inclusion of the CHAMP and GRACE based global geopotential models lead to significant improvements. The evaluation of the present European Gravimetric Geoid 2008 (EGG2008) by GNSS and levelling data indicates an accuracy potential of 1 – 3 cm on a national basis, and 2 – 5 cm at continental scales, provided that high quality and resolution input data are available within the area of interest. Further improvements are expected from the utilization of the GOCE based geopotential models as well as from further upgrades of the terrestrial data base.

## Structure

The regional sub-commission for Europe SC2.4a has national delegates from most of the countries in Europe and reports to sub-commission 2.4. The existing contacts and successful cooperation with the respective delegates and national and international agencies shall be continued and extended.

## Program of Activities

* Utilization of new geopotential models based on the GOCE mission.

* Identification and acquisition of new terrestrial data sets including gravity, terrain, and GPS/levelling data.

* Merging and validation of all data sets.

* Refinement of the mathematical modelling and numerical tests.

* Investigation of different data combination approaches.

* Computation of new geoid and quasigeoid models.

* Evaluation of the results by GNSS/levelling data.

* Study of applications, such as vertical datum definition and unification, dynamic ocean topography estimation, etc.
## SC 2.4b: Gravity and Geoid in South America

Chair: Maria Cristina Pacino (Argentina)

Co-Chair: Denizar Blitzkow (Brazil)

### Terms of Reference and Objectives

The Sub Commission 2.4b entitled Gravity and Geoid in South America, as part of the Commission 2 of IAG, was established as an attempt to coordinate efforts to establish a new Absolute Gravity Network in South America, to carry out gravity densification surveys, to derive a geoid model for the continent as a height reference and to support local organizations 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:

* To re-measure existent absolute gravity stations and to encourage the establishment of new stations.

* To validate fundamental gravity network from different countries in order to establish a single and common gravity network for South America.

* To adjust national gravity networks and to link them together.

* To obtain and to maintain files with data necessary for the geoid computation like gravity anomalies, digital terrain models, geopotential models and satellite observations (GPS) on the levelling network of different countries.

* To provide a link between the different countries and the IGFS in order to assure access to proper software and geopotential models for local geoid computation.

* To compute a global geoid model for South and Central America using the available data. To encourage countries to cooperate by releasing data for this purpose.

* To encourage and eventually support local organizations in different countries endeavouring 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.

* To organize and/or encourage the organization of workshops, symposia or seminars on gravity and geoid determination in South America.

* To test and to use future geopotential models derived from the modern missions (GRACE and GOCE) as well as any new combined model (e.g. EGM2008).

* To support the IAG Sub-Commission 1.3b (Reference Frame for South and Central America, SIRGAS) in the

activities related to the unification of the existing vertical datums.

* Establish close connections with SC2.4c (Gravity and Geoid in North and Central America) to have a good overlap of data coverage in Central America and the Caribbean.

## SC 2.4c: Gravity and Geoid in North and Central America

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 in order to achieve a common vertical datum. The region involved will encompass Iceland, Greenland, Canada, the U.S.A. (including Alaska and Hawaii), Mexico, countries forming Central America, the Caribbean Sea and the northern parts of South America.

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 be served by having access to a common model for translating oceanographic effects to terrestrial datums for various scientific, commercial, engineering and disaster preparedness applications. Likewise, it shall serve as the basis for a forthcoming International Great Lakes Datum model in 2015 (IGLD 15).

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), digital density 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 bench marks, 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 will collect 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 neighbouring countries in the development of a geoid model for their respective country with an overlap (as large as possible) over adjacent countries. Each solution will be
compared, the discrepancies 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 more advanced members to contribute their own expertise and software. The Sub-commission will encourage training and education initiative of its delegates (e.g., IGeS geoid school, graduate studies and IPGH technical cooperation projects). Starting on 2011 the Sub-commission will organize regular meetings with representatives of Central American and Caribbean countries to promote an increase of expertise as well as to create a wide network of specialists.

The chair of the Sub-commission will meet with the equivalent European and South American projects to discuss overlap regions and to work towards agreements to exchange data. Finally, the members of the Sub-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 2.4c are open to everyone with interests in geodesy, geophysics, oceanography and other related topics.

The delegates will communicate primarily using e-mail. However, the sub-commission plans to arrange annual meetings. Preferably, these meetings will be held during international conferences where most delegates will be present; however, some meetings will be held within the region to minimize travel costs. Minutes of meetings will be prepared and sent to all delegates of the Sub-commission.

## Delegates

* Chair: David Avalos (Mexico)

* Rene Forsberg (Denmark)

* Marc Véronneau (Canada)

* Dan Roman (USA)

* Laramie Potts (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)

# SC2.4d: Gravity and Geoid in Africa

Chair: Hussein Abd-Elmotaal (Egypt)

## Terms of Reference

The African Gravity and Geoid regional sub-commission (AGG) belongs to the Commission 2 of the International Association of Geodesy (IAG). The main goal of the African Gravity and Geoid regional sub-commission is to determine the most complete and precise geoid model for Africa that can be obtained from the available data sets. Secondary goals are to foster cooperation between African geodesists and to provide high-level training in geoid computation to African geodesists.

## Objectives and Activities

The objectives and activities of the regional sub-commission are summarized as follows:

* Identifying and acquiring data sets - gravity anomalies, DTMs, GPS/levelling.

* Training of African geodesists in geoid computation.

* Merging and validating gravity data sets, producing homogenous gravity anomalies data set ready for geoid computation.

* Computing African geoid.

* Evaluating the computed geoid using GPS/levelling data.

## Steering Committee

* Chair: Hussein Abd-Elmotaal (Egypt)

* Charles Merry (South Africa)

* Ahmed Abdalla (Sudan)

* Benahmed Daho (Algeria)

* J.B.K. Kiema (Kenya)

* Joseph Awange (Kenya)

* Ludwig Combrinck (South Africa)

* Prosper Ulotu (Tanzania)

## Delegates

* Addisu Hunegnaw (Ethiopia)

* Adekugbe Joseph (Nigeria)

* Albert Mhlanga (Swaziland)

* Francis Aduol (Kenya)

* Francis Podmore (Zimbabwe)

* Godfrey Habana (Botswana)

* Hassan Fashir (Sudan)

* Ismail Ateya Lukandu (Kenya)

* Jose Almeirim (Mozambique)

* Karim Owolabi (Namibia)
* Peter Nsombo (Zambia)

* Saburi John (Tanzania)

* Solofo Rakotondraompiana (Madagascar)

* Tsegaye Denboba (Ethiopia)

# SC 2.4e: Gravity and Geoid in the Asia-Pacific

Chair: Will Featherstone (Australia)

## Context

Depending on one's definition of the Asia-Pacific (AP) region, this SC could cover as many as 48 counties. Moreover, these countries are very diverse in terms of language, political persuasions, governments and wealth. This poses a significant challenge for the exchange of gravity and geoid data and expertise.

Not only unique to the AP region, the management and administration of gravity and the geoid can be vastly different in each country, making the coordination of such a group challenging. Taking Australia as an easy example, the gravity database is administered by a different government division to the administration of the national quasigeoid model.

## Terms of Reference and Objectives

Promote the cooperation in and knowledge of gravity, geoid and closely related studies in the Asia-Pacific region. The executive committee should be small to ensure efficiency, but the larger committee should comprise one member from each participating country. Because of the need to carry national authority, the national member is logically the officer in the country's geodetic authority responsible for its quasi/geoid and/or vertical datum matters.

Because of the synergy that exists between the objectives of this SC and those of the Geodesy Working Group of the UN Permanent Committee for GIS Infrastructure for Asia and the Pacific (PCGIAP), it is logical to liaise with this working group.

## Program of Activities

Liaise with the Geodesy Working Group of the PCGIAP and other nations in the Asia-Pacific region, initially through the production of a flier that outlines the benefits of cooperation and data sharing.

Audit, document and catalogue the gravity and geoid-related that exists – including airborne campaigns. It is also important to establish a protocol for sharing the data. National authorities may be reluctant to give all the data available and at the precision available. It should be possible for geoid evaluation purposes, however, to decrease the resolution and accuracy of data shared along common borders without either comprising the precision of the geoid significantly, or the security of the national data shared.

## Topics of interest

### a) Gravity and Related Data

Explore ways in which we may

* share available gravity data (e.g. via International Gravity Bureau)

* share available DEMs along common borders (National Geodetic Authorities)

* combine resources for terrestrial gravity surveys along common borders

* combine resources for airborne gravity surveys in the region.

### b) Quasi/geoid Control

Explore ways in which countries of the region may cooperate by

* sharing geometric (GNSS/levelling and vertical deflections) geoid control data

* combining efforts in global GNSS campaigns

* undertaking joint campaign for the connection of regional vertical datums.

### c) Education & Research

Encourage and sponsor, for the region,

* meetings and workshops, in cooperation with the International Geoid Service, to foster understanding in the evaluation and use of gravimetric quasi/geoids, and in their application to efficient height determination with GNSS.

* technical sessions in scientific and professional conferences

* research into matters of common concern/interest.
## SC 2.4f: Gravity and Geoid in Antarctica
(AntGG)

Chair: Mirko Scheinert (Germany)

### Terms of Reference and Objectives

Antarctica is the region which still possesses the largest data gaps in terrestrial gravity. Especially with regard to the latest satellite gravity field mission GOCE the polar data gap in terrestrial gravity deteriorates the model solutions. Generally, also the existing Antarctic gravity data coverage is heterogeneous and exhibits inconsistencies. However, globally distributed gravity data are needed for the global high-resolution determination of the Earth's gravity field. Regionally densified Antarctic gravity data shall be used for a validation of global gravity field models and, finally, for a regional improvement of the Antarctic geoid. Nevertheless, due to the vast extension of 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. AntGG shall pursue this objective and shall facilitate the necessary coordination to release gridded gravity datasets for Antarctica. It plays an important role to improve the cooperation between all interested scientists of geodesy and of neighbouring disciplines, mainly geophysics.

### Program of Activities

* Promoting the collection of surface and airborne gravity data in Antarctica

* Promoting new gravity surveys in Antarctica, especially airborne gravimetry

* Promoting the establishment and (re-)measurement of reference gravity stations utilizing absolute gravity meters

* Promoting the scientific exchange of latest developments in technology (esp. airborne gravimetry) and data analysis

* Evaluation of existing and new surface and airborne gravity data, validation of global gravity field models in Antarctica

* Investigation of optimum strategy for the combination of gravity data of different sources, release of gridded gravity anomaly dataset(s) for Antarctica

* 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)

* Detlef Damaske (Germany)

* Fausto Ferraccioli (UK)

* Christoph Förste (Germany)

* René Forsberg (Denmark)

* Larry Hothem (USA)

* Wilfried Jokat (Germany)

* Gary Johnston (Australia)

* Steve Kenyon (USA)

* German L. Leitchenkov (Russia)

* Jaakko Mäkinen (Finland)

* Yves Rogister (France)

* Kazuo Shibuya (Japan)

* Michael Studinger (USA)

* Yuande Yang (China)

### Associates

* Matt Amos (New Zealand)
# SC 2.5 Satellite Altimetry

Chair: Xiaoli Deng (Australia)

## Terms of Reference

For long-term geodetic and climate change studies, a series of repeat-track radar altimeter satellite missions (e.g., Geosat/GFO, TOPEX/Jason-1/-2/-3, ERS-1/-2/Envisat, CryoSat-2, Altika, and Sentinel-3) have made and will continue to monitor ocean surface height globally. Missions of the CryoSat-2 InSAR/SAR altimetry and ICEsat-1/-2 laser altimetry are significantly improving observations of the cryosphere, sea-ice and ice-covered oceans. CryoSat-2 altimetry in its conventional LRM and SAR modes, will be the best chance to improve the marine gravity field by a factor of two in the near future. The future planned Surface Water and Ocean Topography (SWOT) wide-swath synthetic aperture radar interferometry (InSAR) altimetry mission is about to map high spatial resolution oceanic submesoscale variability and surface water hydrology. Another potential technology under development is the so-called GNSS-R altimetry or reflectometry. With these existing and new technological advances in altimetry, the purpose of this IAG sub-commission is to promote innovative research involving the use of historic and future altimeter observations on the studies of local, regional, and global geophysical processes, with emphasis on emerging cross-disciplinary applications using satellite altimetry, and in combination with other data sets, including *in situ* hydrography data (XBT/MBT/Argo) and GRACE/GOCE. The research results and potential data products will benefit IAG's Global Geodetic Observing System (GGOS) and the International Altimetry Service (IAS).

## Objectives

General objectives of the Sub-Commission 2.5 will include:

* To establish a close link between this sub-commission and international altimeter services to bridge the gaps on new research and application data products or services not currently available, in terms of establishing scientific forums to discuss new result results, and as expert users, suggesting to altimeter services to develop more efficient procedures and new data products involving cross-disciplinary applications using satellite altimetry;

* To promote innovative applications of satellite altimetry, including evaluations and cross-disciplinary applications of future satellite altimetry;

* To continue developing techniques to improve altimeter data quality towards new data products in coastal zones including coastal ocean, estuaries, and coastal land;

* To promote cross-disciplinary research to improve the determinations of the shapes and temporal variations of

land/ice/ocean surfaces, such as studies of coastal ocean variability, regional sea level change, mountain glaciers/ice-sheet ablations/accumulations, permafrost degradation, coastal and ice-shelf ocean tides, vertical displacements at major tectonic-active zone and due to other geophysical processes;

* To improve the marine geoid, mean dynamic ocean topography, temporal variations induced by solid Earth processes and global terrestrial water cycle; and

* To establish a specific connection with relevant altimetry observing systems in IAG's GGOS and IAS.

## Program of Activities

This sub-commission will organize independent workshops or special sessions in major meetings to promote altimetric applications in interdisciplinary earth sciences, and to increase the visibility of IAG in altimetric science. Special study groups will be established to investigate important issues.

## Steering Committee

* Chair: Xiaoli Deng (Australia)

* Vice Chair: C.K. Shum (USA)

* Ole Andersen (Demark)

* Cheinway Hwang (Taiwan)

* Walter Smith (USA)

* David Sandwell (USA)

* Per Knudsen (Demark)

* Wolfgang Bosch (Germany)
## SC 2.6: Gravity and Mass Displacements

Chair: Shuanggen Jin (China)

### Terms of Reference

The variation of gravity field is related to the physical processes and dynamics of the Earth's interior, Earth system coupling and in particular interactions between atmosphere, hydrosphere, cryosphere, land surface and the solid Earth. Nowadays the gravity field, derived from terrestrial and space gravimetry (e.g. CHAMP, GRACE, and GOCE...) with unprecedented accuracy and resolution, provides a unique opportunity to investigate gravity-solid earth coupling, the structure of the globe from the inner core to the Earth's crust, physics and dynamics of the Earth's interior, and mass flux such as within the ocean-land water cycle. It also contributes to a better understanding of the interactions in the Earth's interior and its response to climate change.

### Objectives:

* To model and inverse gravity-solid Earth coupling, e.g. crust thickness, isostatic Moho undulation, mass loadings, basin formation, thermal effects on density, gravity tensor and gravity field related deformation as well as interactions with the Earth' interior.

* To understand the physics and dynamics of the Earth's interior using gravity and other geophysical measurement techniques.

* To quantify Earth's mass flux and their interactions and, in particular, to study gravity role in the understanding of the ocean-land-cryosphere cycle.

* To promote/communicate with gravity-related communities (Oceanography, Hydrology, Cryosphere, Solid-Earth, Geodesy...)

### Program of Activities

The Sub-commission will establish Work Groups (WGs) on relevant topics, and model and inverse gravity-Earth System coupling, structure and dynamics of the Earth's interior and their interactions. A Steering Committee will work closely with members and other IAG Commissions/Sub-Commissions to obtain mutual goals. Also it will promote and jointly sponsor special sessions at IAG Symposia and other workshop/conferences.

### Steering Committee

* Chair: Shuanggen Jin (China)

* Co-Chair: Jürgen Kusche (Germany)

* Carla Braitenberg (Italy)

* Annette Eicker (Germany)

* Isabelle Panet (France)

* Jens Schröter (Germany)

* Séverine Rosat (France)

## Joint Projects

### JP 2.1: Geodetic Planetology (JP-GP)

Chairs: Oliver Baur (Austria) and Shin-Chan Han (USA)

### Terms of Reference

Precise knowledge about the thermal evolution, composition, shape and dynamics of extra-terrestrial bodies is increasingly accessible from science data collected by space-geodetic methods. With growing opportunities from the past, current and future satellite missions to the planets of the solar system and other bodies in outer space, it is timely to explore various space-geodetic theory and methodologies to enhance the scientific return of the planetary missions for improved understanding of the planets or satellites.

In the last decades, geodetic planetology has experienced considerable advance. Data collected by spacecraft orbiting the Earth's moon (e.g., Lunar Prospector, SELENE/Kaguya, Lunar Reconnaissance Orbiter), Mars (Mars Global Surveyor, Mars Odyssey, Mars Reconnaissance Orbiter), Venus (Magellan), and Mercury (Messenger) revealed increasingly detailed structures of the gravity field, shape, surface and atmosphere of these celestial bodies. Forthcoming missions to the Earth's moon (GRAIL), Mercury (BepiColombo), Jupiter (JUNO), and the Jovian system (EJSM-Laplace) will ensure ongoing progress. The space-geodetic methods used in planetary geodesy include range and range-rate orbit tracking, VLBI, altimetry, and photogrammetric remote sensing; these observation techniques are well-known from terrestrial applications.

The main motivation to constitute a Joint Project on Geodetic Planetology (JP-GP) within the IAG is the scientific proximity of planetary geodesy to the activities of the IAG Commissions, the ICCT and the IAG services. This proximity particularly holds to Commission 1 (Reference Frames), Commission 2 (Gravity Field), Commission 3 (Earth Rotation and Geodynamics), and the ICCT. High-
accuracy determination of reference frames is the basis for
the quantification of dynamic processes on and beneath a
body's surface, the detection of variations in its rotational
behaviour and precise orbit determination of satellites. The
gravity field is a key quantity to assess information on a
body's composition and interior structure; furthermore,
knowledge about the gravity field allows for the tailored
orbit design of artificial satellites, for instance with regard
to robotic and human landing. Rotation characteristics of
celestial bodies include length-of-day variations, polar
motion, precession, nutation or libration. These areas of
research require sophisticated physical and mathematical
modelling in the framework of a concise theoretical back-
ground. In summary, promoting geodetic planetology is an
inter-disciplinary effort, and hence demands for collabora-
tion with all IAG components.

Within the 4-year horizon 2011-2015, the JP-GP will start
to initiate and promote geodetic research of extra-terrestrial
bodies. Furthermore, in terms of sustainable follow-on
activities, the project envisages the establishment of an
Inter-Commission Committee on Geodetic Planetology for
the next period 2015-2019. Towards that goal, the JP-GP
aims to:

* support scientific activities related to the gravity field and orbit determination, topography, physical shape (geoid), interior structure and rotation characteristics of planetary bodies, together with the establishment and maintenance of reference frames;

* encourage the cooperation between the terrestrial geodesy and planetary geodesy communities by promoting the exploitation of synergies;

* provide an international platform for the transfer of
  knowledge and experience on geodetic theory and data
  analysis including radio science, altimetry, and stereo
  images;

* coordinate interdisciplinary research activities.

Organization

The JP-GP is joint with the ICCT and the Commissions 1, 2, and 3, with Commission 2 being the lead commission. The activities of the JP-GP are coordinated by a Steering Committee consisting of the President, the Vice President, representatives from the Commissions 1, 2, and 3 (one representative from each commission), and a representative from the ICCT.

Objectives

The main objective of the JP-GP is to initiate and promote
geodetic research of extra-terrestrial bodies. In particular,
the JP-GP will

* act as a framework for geoscientific discussion and co-operation concerning the study of the planets of the solar system and other bodies in outer space;

* promote the integration of advanced space-geodetic methods for planetary purposes, including the development of tailored methodologies for data exploitation and interpretation;

* support interdisciplinary activities of the ICCT in geodetic theory and data analysis;

* help to develop future geodetic technologies and mission designs for planetary geodesy;

* explore the possibility of sustainable collaboration with the IAU/IAG Working Group on Cartographic Coordinates and Rotational Elements (WGCCRE)

* establish an Inter-Commission Committee on Geodetic Planetology for the period 2015-2019.

Output

The outputs after the 4-year time frame 2011-2015 are:

* Establishment of geodetic planetology within the IAG;

* Organization of a Workshop with interdisciplinary emphasis;

* Establishment of an Inter-Commission Committee on Geodetic Planetology for the period 2015-2019.

Steering Committee

* Chair: Oliver Baur (Austria)

* Vice Chair: Shin-Chan Han (USA)

* Commission 1 Representative: Tonie van Dam (Luxembourg)

* Commission 2 Representative: Urs Marti (Switzerland)

* Commission 3 Representative: Richard Gross (USA)

* ICCT Representative: Nico Sneeuw (Germany)

Members

* Markus Antoni (Germany)

* Brent Archinal (USA)

* Ali Ardalan (Iran)

* Georges Balmino (France)

* Veronique Dehant (Belgium)

* Shuanggen Jin (China)

* Anno Löcher (Germany)

* Jürgen Müller (Germany)

* Nico Sneeuw (Germany)

* Dimitrios Tsoulis (Greece)

* Pieter Visser (Netherlands)
# Joint Working Groups of Commission 2

## JWG 2.1: Techniques and Metrology in Absolute Gravimetry

(Joint with the IGFS)

Chair: Vojtech Palinkas (Czech Republic)

### Terms of Reference

Absolute ballistic gravimeters have become the primary measurement standards for the determination of free-fall acceleration. Currently the only way for the realization of the gravity reference is realized by the comparisons of the absolute gravimeters, which has to be organized and accomplished in such a way that the high requirements in gravity measurements in geosciences and metrology are fulfilled. Principal tasks of the Working Group are thus closely connected with the four-yearly International Comparisons of Absolute Gravimeters (ICAGs) and relevant Regional International Comparisons of Absolute Gravimeters (RICAGs) in the frame of regional structures of metrology community. Regional Metrology Organizations (RMO) at the sites selected on a continental scale.

The Working Group will participate on the organization of comparisons under close cooperation with the BIPM Working Group on Gravimetry of Consultative Committee on Mass (CCM) and Related Quantities (CCM WGG) and the IAG Joint Working Group on Absolute Gravimetry and Absolute Gravity Reference System (JWG2.2). The connection between ICAGs and RICAGs has to be established by means of reliable absolute gravimeters participating in both kinds of comparisons. An important benefit of a distributed network of Regional Comparison Sites would be that it makes an invaluable contribution to establishing a Global Gravity Reference System. The sites should be related to RMO, for example, EURAMET – European Metrology Organization, SIM – Inter-American Metrology System, APMP - Asia-Pacific Metrology Program, etc.).

The Joint Working Group aims to deal with technical and metrological aspects in absolute gravimetry and theirs realization within a system of comparisons. The increasing demand for reliability and confidence in absolute gravity measurements requires further progress in the comparisons under certain aspects: organization, measurement optimization, combination of different methods of measurements, data analysis, estimation of uncertainties or investigations of systematic effects. In keeping with the above mentioned, the technical protocol of the comparisons has to be developed according to the rules of the international Mutual Recognition Arrangement for national measurement standards and for calibration and measurement certificates issued by National Metrology Institutes.

The WG will work in a close cooperation with metrology community on the implementation of the system of calibration and verification of absolute gravimeters at relevant National Metrology Institutes and designated institutes as other possibility, besides the comparisons, to determine the metrological characteristics of absolute gravimeters.

The relevance to the Working Group is that its members are the specialists as well from geodetic and geophysical communities, as from the metrological community, and this working group focuses more to participation of individual scientists than the more official CCM WGG where the membership is related to the institutes responsible for the traceability in gravimetry. Such inter-communications within the Working Group as well as a linkage between this group and CCM WGG will make it possible to develop the ICAGs and RICAGs to be supported by both communities.

### Objectives

* The participation in the organization (in collaboration with CCM WGG and JWGAG2.2) of the four-year period ICAGs and additional RICAGs at the sites selected on a continental scale.

* The elaboration of criteria and recommendations for a distributed network of Comparison Sites.

* The progress of the comparisons of absolute gravimeters in terms of optimization, measurement methods, data analysis, investigations of systematic effects and uncertainties.

* The development of the technical protocol of the comparisons.

* The collaboration with metrology community for the implementation of the system of calibration and verification of absolute gravimeters.

### Members

* Chair: Vojtech Palinkas (Czech Republic)

* Henri Baumann, (Switzerland)

* Matthias Becker (Germany)

* Reinhard Falk (Germany)

* James Faller (USA)

* Olivier Francis (Luxemburg)

* Alessandro Germak (Italy)

* Jacques Hinderer (France)

* Zhiheng Jiang (BIPM)

* Jacques Liard (Canada)

* Jaakko Makinen (Finland)

* Sebastien Merlet (France)

* Christian Rothleitner (Luxembourg)

* Diethard Ruess (Austria)

* Sergiy Svitlov (Ukraine)
* Ludger Timmen (Germany)

* Michel Van Camp (Belgium)

* Leonid Vitushkin (Russian Federation)

* Herbert Wilmes (Germany)

* Shuqing Wu (China)

## Corresponding Members

* Martin Amalvict (France)

* Ernst Boyarsky (Russian Federation)

* Nicholas Dando (Australia)

* Gleb Demianov (Russian Federation)

* Andreas Engfeld (Sweden)

* Filippo Greco (Italy)

* Vladimir Kaftan (Russian Federation)

* Jan Krynski (Poland)

* Chiungwu Lee (Taiwan)

* Nicolas Le Moigne (France)

* Shigeki Mizushima (Japan)

* Jan Mrlina (Czech Republic)

* Andrzej Pachuta (Poland)

* Alfredo Esparza Ramires (Mexico)

* René Reudink (The Netherlands)

* José Manuel Serna Puente (Spain)

* Dru Smith (USA)

* Yury Stus (Russian Federation)

* Simon Williams (United Kingdom)

* Daniel Winester (USA)

* Alexander Yankovsky (Russian Federation)

## JWG 2.2: Absolute Gravimetry and Absolute Gravity Reference System

(Joint with the IGFS)

Chair: Herbert Wilmes (Germany)

## Terms of Reference and Objectives

IAG Sub-Commission 2.1 “Gravimetry and Gravity Networks” promotes scientific investigations of gravimetry and gravity networks and terrestrial, airborne, shipboard and planetary gravity measurements. One of the outputs of the SC 2.1 activities is the result of gravity measurements, i.e. the gravity data.

The International Gravity Field Service IGFS coordinates the servicing of the geodetic and geophysical community with gravity field related data, software and information. The IAG’s scientific community demands more detailed information on the Earth’s gravity field and its changes, and precise terrestrial absolute gravity (AG) observations are an important contribution to monitoring and understanding mass transports e.g. by hydrological and atmospheric variations or by changes in the solid Earth’s geometry.

The role of absolute gravimetry increases with the growing number of absolute ballistic gravimeters and the rising number of AG measurements worldwide. The philosophy of gravity measurements has changed from rare AG determinations at a few principal network stations to repeated absolute gravity observations at global networks in combination with geometric geodetic observations. At selected sites, the AG observations are complemented by the high sensitivity of continuously observing superconducting (relative) gravimeters.

GGOS, the IAG Global Geodetic Observing System integrates different geodetic techniques, models and approaches to ensure a long-term, precise monitoring of the Earth's shape, the Earth's gravity field and the Earth's rotational motion. Consistent and precise absolute gravity measurements from a global network would be a valuable contribution to the GGOS infrastructure.

Up until now the Working Group of Absolute Gravimetry has been contributing to the development of the absolute gravity database AGrav which reached operational status and became a fixed part of the BGI (International Gravimetric Bureau) services. The database provides an overview of existing AG stations, observations, instruments and institutions, and facilitates the cooperation. Multidisciplinary cooperation and the combination of gravity data with other geodetic observation types is going to be essential for our future work.
The realisation of a global gravimetric reference relies upon well calibrated instruments and standards which in the case of absolute gravity determination is realized by the repeated comparison of the measuring instruments. Comparisons are carried out as four-yearly International Comparisons of Absolute Gravimeters (ICAGs) and as additional Regional International Comparisons of Absolute Gravimeters (RICAGs). Whereas these comparisons are prepared and carried out by JWG 2.1 this project at hand makes use of the comparison results and the data of the calibrated instruments. Triggered by BIPM's decision to close the comparison site at its premises, future ICAG and RICAG sites will develop to a distributed network with global distribution. Together with additional absolute gravity reference and comparison sites such a network gains the potential to build up a new International Gravity Reference System where the precise gravity reference is available and gravity field variations are monitored. This working group will contribute to this realisation and to the establishment of the necessary standards. The new International Gravity Reference System will be developed to replace the former IGSN71 (International Gravity Standardization Network 1971).

The proposed Working Group on Absolute Gravimetry will focus upon the following objectives:

* Continue the operation and improvement of the AGrav database for global absolute gravity measurements

* Provide AG metadata and data for GGOS to be used for the combination of AG measurements with geometric measurements (GNSS, SLR, VLBI) and for specific investigations

* Extend the AG database to store the comparison results from ICAG and RICAG sites

* Establish a new International Gravity Reference System based upon a distributed network of AG comparison and reference sites which can replace IGSN71

* Contribute to the agreement about the necessary standards and corrections

* Contribute to the Global Geodynamics Project GGP by the storage of repeated AG observations necessary for the determination of superconducting gravimeter drift and calibration parameters

## Members

* Chair: Herbert Wilmes (Germany)

* Jonas Ågren (Sweden)

* Martine Amalvict (France)

* Henri Baumann (Switzerland)

* Nicholas Dando (Australia)

* Mark Eckl (USA)

* Reinhard Falk (Germany)

* Domenico Iacovone (Italy)

* Jan Krynski (Poland)

* Jacques Liard (Canada)

* Jaakko Mäkinen (Finland)

* Urs Marti (Switzerland)

* Vojtech Palinkas (Czech Republic)

* Diethardt Ruess (Austria)

* Victoria Smith (UK)

* Gabriel Strykowski (Denmark)

* Ludger Timmen (Germany)

* Michel van Camp (Belgium)

* Leonid Vitushkin (Russia)

* Hartmut Wziontek (Germany)

## Corresponding Members

* Mauro Andrade de Sousa (Brazil)

* Roger Bayer (France)

* In-Mook Choi (Korea)

* Andreas Engfeldt (Sweden)

* Yoichi Fukuda (Japan)

* Jose Manuel Serna Puente (Spain)

* Olga Gitlein (Germany)

* Mirjam Bilker Koivula (Finland)

* Alessandro Germak (Italy)

* Jacques Hinderer (France)

* Janis Kaminskis (Latvia)

* Steve Kenyon (USA)

* Jakub Kostelecky (Czech Republic)

* Dennis McLaughlin (USA)

* Tomasz Olszak (Poland)

* Bjorn Ragnvald Pettersen (Norway)

* Rene Reudink (the Netherlands)

* Heping Sun (China)

* V.M. Tiwari (India)
## JWG 2.3: Assessment of GOCE Geopotential Models

(Joint with the IGFS)

Chair: Jianliang Huang (Canada)

Co-Chair: Christopher Kotsakis (Greece)

## Terms of Reference and Objectives

The GOCE mission by European Space Agency is mapping the Earth's gravity field with the same level of accuracy as GRACE and a higher spatial resolution. GRACE and GOCE are complementary in terms of spectral sensitivity. A series of GOCE and GRACE& GOCE-based global gravity models have been released since 2010. Assessment of these models is commonly based on comparisons with other independent data that are direct and indirect observations of the Earth's gravity field. Such data include geoid heights from GPS and spirit levelled heights, airborne and surface gravity measurements, marine geoid heights from mean oceanographic sea surface topography models and altimetry observations, orbits from other geodetic and altimetry satellites etc. In response to the call of having an independent, coordinated and inclusive team for the assessment of the new GOCE models, a Joint Working Group (JWG) has been approved by IGFS and the IAG Commission 2 during IUGG 2011 in Melbourne, Australia. Its objectives are to develop new standard validation/calibration procedures, and to perform the quality assessment of GOCE-, GRACE&GOCE-based satellite-only and combined solutions for the static Earth's gravity field.

The Joint Working Group reports to IGFS and the Commission 2.

## Program of Activities

* The JWG creates opportunities through communication and conferences for international cooperation to develop and propose new standard methods for evaluating global EGMs using external data. A specific research area of interest will be the issue of how to handle the different spectral content of satellite-based global gravity field models and terrestrial gravity data.

* The JWG assesses new GOCE and GRACE&GOCE models.

* The JWG organizes a special session in the next IAG Commission 2 conference in Venice, Italy, in 2012.

* The JWG publishes assessment papers in a dedicated issue of the Newton's Bulletin in 2013.

## Members

* Hussein Abd-Elmotaal (Egypt)

* Jonas Ågren (Sweden)

* Ben Ahmed Daho Sid Ahmed (Algeria)

* Riccardo Barzaghi, on behalf of IGeS (Italy)

* Denizar Blitzkow (Brazil)

* Minkang Cheng (USA)

* Sten Claessens (Australia)

* Artu Ellmann (Estonia)

* Christoph Förste (Germany)

* Thomas Gruber (Germany)

* Ali Kilicoglu (Turkey)

* Jiancheng Li (China)

* Pavel Novak (Czech Republic)

* Maria Cristina Pacino (Argentina)

* Dan Roman (USA)

* Gabriel Strykowski (Denmark)

* Viliam Vatrt (Czech Republic)

* Matthias Weigelt (Germany)

## Corresponding members

* P. G. Vipula Abeyratne (Sri Lanka)

* Heiner Denker (Germany)

* Cheinway Hwang (Taiwan)

* Chris Jekeli (USA)

* Jaroslav Klokočnik (Czech Republic)

* Charles Merry (South Africa)

* Peter Morgan (Australia)

* Nikolaos K. Pavlis (USA)

* Marcelo Santos (Canada)

* Claudia Tocho (Argentina)
## JWG 2.4: Multiple geodetic observations and interpretations over Tibet, Xinjiang and Siberia (TibXS)
(Joint with Commission 3)

Chair: Cheinway Hwang (Taiwan)

Vice Chair: Wenbin Shen (China)

### Terms of Reference and Objectives

Tibet, Xinjiang and Siberia (TibXS) are regions with active plate tectonics. Evidences from satellite gravimetry and altimetry show the hydrological evolutions over these regions are sensitive to global climate change. For example, inter-annual lake level changes over Tibet and Xinjiang from satellite altimetry are found to be connected to El Nino Southern Oscillation (ENSO). Lakes in central Asia originating in Xinjiang and lakes in eastern Siberia show sharp changes in lake levels that can be explained by climate change. Recent terrestrial gravity, GRACE and GPS observations suggest that the crust over the Tibetan plateau is thickening, and the Himalayan glaciers appear to be thawing. Satellite altimetry is a potential tool to study vertical displacement and permafrost thawing and changes in the active layers in Siberia and Tibet. With more satellite gravimetry and altimetry data to come, decadal changes over TibXS in many aspects can be investigated in connection to global climate change and dynamics of the crust and the upper mantle.

Under the support of IAG commission 2, two international workshops on multiple geodetic observations and interpretations have been held in Urumqi (2009; http://space.cv.nctu.edu.tw/altimetryworkshop/TibXS2009/TibXS2009.htm) and Xining (2011; http://space.cv.nctu.edu.tw/altimetryworkshop/TibXS2011/TibXS2011.htm). The results presented in these workshops have been or will be published in two special issues of the journal Terrestrial, Atmospheric and Oceanic Sciences (TAO). In response to the call to continue the geodetic studies over TibXS, this working group is established and reports to IAG Commission 2 over 2011-2015. The objective is to investigate the long-term records from different geodetic sensors to understand the geodynamic process and climate change over TibXS. This WG will report to IAG Commission 2.

### Program of Activities:

* This WG will organize international workshops to investigate the results from multiple geodetic observations over TibXS.

* This WG will establish a link between the geodetic community and the geophysical community to interpret the geodetic results.

* This WG will assess satellite results from GRACE, COSMIC and its follow-on, altimetry and SAR and other remote sensing platforms over TibXS using in situ observations such as superconducting gravimeter and absolute gravimeter data, GPS data, lake gauge and glacier stake and snow pit measurements.

* This WG will publish papers dedicated to the subjects of the WG in journal special issues.

### Members of the Standing Committee

* B F Chao (Taiwan)

* Kosuke Heki, (Japan)

* Jeff Freymuller, (USA)

* CK Shum (USA)

* He-Ping Sun (China)

* Qi Wang (China)

### Members

* Xiaoli Deng (Australia)

* Xiao-Li Ding (Hong Kong)

* Xiaodong Song (USA)

* Wenke Sun (China)

* Nikolay Shestakov (Russia)

* VM Tiwari (India)

* Carla Braitenberg (Italy)
## JWG 2.5: Physics and dynamics of the Earth's interior from gravimetry
(Joint with Commission 3)

Chair: Isabelle Panet (France)

### Terms of Reference

To develop approaches for the determination of the physical properties of the Earth interior and its dynamics, from the joint use of gravity and other geophysical measurement techniques. Insights from earthquakes signals and normal modes will be considered. The objective is to better constrain the structure in the mantle and the core as well as their interactions.

### Goals

The following, non-restrictive list of goals is proposed (to be discussed in the WG):

**Methodological goals:**

* to develop methods for extracting a geodynamic signal of interest, related to Earth mantle and/or core, from noisy data (satellite gravity data and other measurements). Some important points: separation from the geofluid variations, in the case of temporal gravity variations, separation from surface contributions, in the case of static gravity.

* to review and develop approaches for the combination of heterogeneous geophysical and gravity data at different spatial and/or temporal scales.

**Application goals:**

* to review the existing methods and propose approaches for the joint use of seismic and surface/satellite gravity data to infer Earth structure at various scales. The use of magnetic data will also be considered.

* to review and estimate expected amplitudes of core signals in gravity and other geophysical observations,

* to review and address the observation of Earth normal modes in gravity and other geophysical measurements,

* to address the extraction of solid Earth deformations from satellite gravity data combined with surface displacement measurements,

* to address the determination of mantle viscosity from satellite gravity combined with other measurements, from the analysis of post-seismic deformations of large earthquakes / GIA, ....

### Members

* Chair: Isabelle Panet (France)

* Shuanggen Jin (China)

* Valentin Mikhailov (Russia)

* Séverine Rosat (France)

* Bert Vermeersen (The Netherlands)

* Tonie Van Dam (Luxembourg)

* Virendra Tiwari (India)

* Lei Wang (USA)

* Kosuke Heki (Japan)

* Fred Pollitz (USA)
## JWG 2.6: Ice melting and ocean circulation from gravimetry

(Joint with Commission 3)

Chair: Jens Schröter (Germany)

### Terms of Reference

The working group will primarily address the contribution of ice melting to the global and regional sea level. Specifically observation of the Earth's ocean- water and ice sheet variations at all spatial and temporal scales will be considered from GRACE data and other sensors, e.g., Altimetry, ICESat, InSAR and GPS. Furthermore the fate of the melt-water in the ocean, its distribution and impact on ocean circulation will be studied.

### Goals

* to estimate individual mass and volume change of major ice sheets and ice caps using a synthesis of different techniques

* separate geometric change on long time scales (e.g. GIA) as well as elastic response/loading/self attraction of sea water from the estimates of volume change in land ice and ocean

* use estimates of land storage of water from JWG 2.7 to close the global water cycle and to improve removal of leakage of land signals into ocean estimates

* close the ocean's regional volume budget by observing sea level from altimetry, steric expansion of sea water from ocean measurements and ocean modelling and mass change from a combination of GRACE and other observations (e.g. GPS, tide gauges, ocean bottom pressure recorders...)

* consider the impact of increased inflow of melt-water into the ocean on ocean circulation, sea level and mass/heat transports

* and finally describe and understand trends and contributions to global and regional sea level rise

### Members

* Chair: J. Schröter
(Germany)

* J. Bamber (UK)

* D. Chambers (USA)

* JL. Chen (USA)

* M. Horwath (Germany)

* J. Kusche (Germany)

* SB. Luthcke (USA)

* E. Rignot (USA)

* Sasgen (Germany)

* C.K. Shum (USA)

* D. Stammer (USA)

* CR. Wilson (USA)

* DG Vaughan (UK)

* Velicogna (USA)

* B. Wouters (The Netherlands)

* HJ. Zwally (USA)

## JWG 2.7: Land hydrology from gravimetry

(Joint with Commission 3)

Chair: Annette Eicker (Germany)

### Terms of Reference

The working group will be dedicated to the development of new strategies and algorithms for using time-variable gravity data from GRACE and data from complementary sensors in the understanding of the terrestrial water cycle. This includes the development of tools and products to encourage adoption of geodetic data by the hydrological community, application and validation of GRACE to investigate water storage changes and the improvement of model reliability and predictability (calibration, assimilation). This Working group was proposed by SC2.6 (Gravity and Earth System).

### Goals

The following, non-restrictive list of goals is proposed (to be discussed in the WG):

* to tailor GRACE products towards the specific requirements of hydrological applications (regional solutions, spatial/temporal constraints,...)

* to review existing approaches and develop new strategies for GRACE post-processing (filtering issues, bias correction associated with the leakage problem)

* to discuss the separation of the GRACE mass signal into different storage compartments

* to compare the satellite data with model output and complementary data sets (super-conducting gravimeters, ground water observation,...)

* to review and develop strategies to compare and combine heterogeneous data sets given on different temporal and spatial scales

* to compare and develop approaches to use GRACE and alternative sensor data to calibrate hydrological modeling and to assimilate the observations into the models

* to develop strategies for innovative use of GRACE products for hydrometeorology

### Members

* Annette Eicker (Germany)

* Petra Döll (Germany)

* Jean-Paul Boy (France)

* Andreas Güntner (Germany)

* Laurent Longevergne (France)

* Himanshu Save (USA)

* Benjamin Zaitchik (USA)
## JWG 2.8: Modelling and Inversion of Gravity-Solid Earth Coupling

(Joint with commission 3)

Chair: Carla Braitenberg (Italy)

### Terms of Reference

To model and invert gravity-solid Earth coupling, e.g. explore situations in which gravitative forces have been an important agent in the evolution of the lithosphere. The topics of interest range from the evolution of crustal thickness, isostatic Moho response, lithospheric thickness, lithospheric slab pull, lithospheric cooling, gravity field related deformation. Explore where and to what extent density variations in crust and mantle affect mass loading and geodynamics. We consider the effect of density changes in time through thermal heating and cooling, including magnetic loading, underplating and basin evolution. Methodological aspects include the development of forward and inversion algorithms in a spherical Earth, the use of the gravity tensor and the new GOCE observations. This Working Group belongs to the initiatives coordinated by Sub-Commission 2.6.

### Goals

* Create a platform in which density models can be tested through geodynamic models. This needs the interaction of the geodynamic modeller with the geophysical modeller, and allows a consistency check of the density models from the point of view of observations of the potential field and of geodynamics. Vice versa the geodynamic models producing density variations are checked against consistency with density models constrained by further geophysical observations.

* Create a reference database covering the subject of gravity-solid earth coupling (mass loading, underplating, isostatic Moho, crustal thickness, lithospheric thickness, dynamic topography versus mass loading).

* Create a database on methodology of gravity forward and inversion calculations, spherical calculations

* Create a kit of software tools that have been tested and verified by the working group and that will be shared among the members of the working group. It shall cover the different aspects of the goals of the WG. If several software-programs are made available they can be benchmarked against each other.

* Set up a social networking page for the members of the working group.

* Organize a practical-theoretical school on Modelling and Inversion of Gravity-Solid Earth Coupling

### Members

* Carla Braitenberg (Italy)

* Jon Kirby (Australia)

* Shuanggen Jin (China)

* Erik Ivins (USA)

* Xiapoping Wu (USA)

* Valeria Barbosa (Brazil)

* Jörg Ebbing (Norway)

* Holger Steffen (Canada)

* Daniele Sampietro (Italy)

* Sabine Schmidt (Germany)

* Rezene Mahatsente (Germany)

### Corresponding members

* Séverine Rosat (France)

* Leonardo Uieda (Brazil)

* Rebekka Steffen, (Canada)

* Carlos Chaves (Brazil)

* Andres Tassara (Chile)

* Mario Gimenes (Argentina)
# Commission 3 - Earth Rotation and Geodynamics

http://euler.jpl.nasa.gov/IAG-C3

President: **R. Gross** (USA)

Vice President: **A. Brzezinski** (Poland)

## Terms of Reference

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 our planet. This includes the entire range of phenomena associated with Earth rotation and Earth orientation such as polar motion, length of day, precession and nutation, the observation and understanding of which are critical to the transformation between terrestrial and celestial reference frames. It includes tidal processes such as solid Earth and ocean loading tides, and crust and mantle deformation associated with tectonic motions and isostatic adjustment.

During the last few decades many geophysicists have come to use geodynamics in a more restricted sense to address processes such as plate tectonics and postglacial rebound 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 and the deformation of the solid Earth. The purpose of Commission 3 is to promote, disseminate, and, where appropriate, to help coordinate research in this broad arena.

Sub-Commission 3.1 (Earth Tides and Geodynamics) addresses the entire range of tidal phenomena including its effect on Earth rotation. Sub-Commission 3.2 (Crustal Deformation) addresses the entire range of global and regional crustal deformation including intraplate deformation, the earthquake deformation cycle, aseismic phenomena such as episodic tremor and slip, and volcanic deformation. Sub-Commission 3.3 (Earth Rotation and Geophysical Fluids) addresses the space-time variation of atmospheric pressure, seafloor pressure and the surface loads associated with the hydrological cycle, and Earth's (mainly elastic) responses to these mass redistributions. Sub-Commission 3.4 (Cryospheric Deformation) addresses the Earth's instantaneous and delayed responses to ice mass changes, including seasonal (cyclical) mass changes and progressive changes associated with climate change. This group also studies postglacial rebound at all spatial scales and the elastic deformation taking place in the near-field of existing ice sheets and glaciers. Sub-Commission 3.5 (Tectonics and Earthquake Geodesy) addresses the integration of space and terrestrial approaches for studying the kinematics and mechanics of tectonic plate boundary zones, and in particular of the Eurasian/African/Arabian boundary zone.

Commission 3 interacts with GGOS, other Commissions and Services of the IAG as well as with other organizations such as the International Astronomical Union (IAU). For example, the recent space mission GRACE has expanded our common interests with IAG Commission 2 (Gravity Field) since temporal changes in gravity are associated with both the drivers of Earth deformation (e.g. changing ice and loads) and with Earth's response to these and other forcing.

## Objectives

* To promote cooperation and collaboration on the theory, modelling and observation of Earth rotation and geodynamics.

* To ensure development of research in Earth rotation and geodynamics by organizing meetings, symposia, and sessions at conferences and general assemblies, by creating working groups on specific topics, and by encouraging the exchange of ideas and data and the comparison of methods and results with the goal of improving accuracy, content, methods, theories, and understanding of Earth rotation and geodynamics.

* To serve the geophysical community by facilitating interactions with organizations that provide the data needed to study Earth rotation and geodynamics.

## Structure

### Sub-Commissions

**SC 3.1:** Earth Tides and Geodynamics

Chair: S. Pagiatakis (Canada)

**SC 3.2:** Crustal Deformation

Chair: M. Poutanen (Finland)

**SC 3.2a:** Global Crustal Deformation

Chair: J. Freymueller (USA)

**SC 3.2b:** Regional Crustal Deformation

Chair: M. Hashimoto (Japan)

**SC 3.3:** Earth Rotation and Geophysical Fluids

Chair: M. Thomas (Germany)

**SC 3.4:** Cryospheric Deformation

Chair: M. King (UK)
**SC 3.5:** Tectonics and Earthquake Geodesy
Chair: H. Ozener (Turkey)

## Joint Study Groups

**JSG 0.1:** Application of time series analysis in geodesy (joint with ICCT and all Commissions, description see ICCT)
Chair: W. Kosek (Poland)

**JSG 0.3:** Comparison of current methodologies in regional gravity field modelling (joint with ICCT and Commission 2, see ICCT)
Chairs: M. Schmidt, Ch. Gerlach (Germany)

**JSG 0.4:** Coordinate systems in numerical weather models (joint with ICCT and all Commissions, description see ICCT)
Chair: Th. Hobiger (Japan)

**JSG 0.5:** Multi-sensor combination for the separation of integrated geodetic signals (joint with ICCT and Commission 2, see ICCT)
Chair: F. Seitz (Germany)

**JSG 0.7:** Computational methods for high-resolution gravity field modelling and nonlinear diffusion filtering (joint with ICCT and Commission 2, description see ICCT)

**JSG 0.8:** Earth system interaction from space geodesy (joint with ICCT and all Commissions), description see ICCT)
Chair: S. Jin (China)

**JSG 3.1:** Gravity and height change intercomparison (joint with IGFS, Commissions 1 and 2)
Chair: S. Rosat (France)

**JWG 2.8:** Modelling and inversion of gravity-solid Earth coupling (joint with Comm. 2, description see Comm. 2)
Chair: C. Braitenberg (Italy)

## Program of Activities

Commission 3 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 or geophysics. Some events will be focused narrowly on the interests of the sub-commissions and other entities listed above, and others will have a broader commission-wide focus.

## Steering Committee

* President: R. Gross (USA)

* Vice President: A. Brzezinski (Poland)

* Chair SC 3.1: S. Pagiatakis (Canada)

* Chair SC 3.2: M. Poutanen (Finland)

* Chair SC 3.2a: J. Freymueller (USA)

* Chair SC 3.2b: M. Hashimoto (Japan)

* Chair SC 3.3: M. Thomas (Germany)

* Chair SC 3.4: M. King (UK)

* Chair SC 3.5: H. Ozener (Turkey)

* Chair JSG1: S. Rosat (France)

* Representatives of Services:

* IERS: Brian Luzum (USA)

* IGFS: S. Bettadpur (USA)

* Members at large: B. Chao (China - Taipei)

## Joint Working Groups

**JWG 1.3:** Understanding the relationship of terrestrial reference frames for GIA and sea-level studies (joint with Comm. 1, description see Comm. 1)
Chair: Tilo Schöne (Germany)

**JWG 2.4:** Multiple geodetic observations and interpretation over Tibet, Xinjiang and Siberia (TibXS)
(joint with Comm. 2, description see Comm. 2)
Chair: Ch. Hwang (Taiwan)

**JWG 2.5:** Physics and dynamics of the Earth's interior from gravimetry
(joint with Comm. 2, description see Comm. 2)
Chair: I. Panet (France)

**JWG 2.6:** Ice melting & ocean circulation from gravimetry (joint with Comm. 2, description see Comm. 2)
Chair: J. Schroeter (Germany)

**JWG 2.7:** Land hydrology from gravimetry (joint with Comm. 2, description see Comm. 2)
Chair: A. Eicker (Germany)
# Sub-Commissions

## SC 3.1: Earth Tides and Geodynamics

Chair: S Pagiatakis (Canada)

Co-Chair: J Bogusz (Poland)

### Terms of Reference

SC 3.1 addresses the entire range of Earth tidal phenomena, both on the experimental as well as on the theoretical level.

Earth tide observations have a very long tradition. These observations led to the discovery of the Earth's elasticity which allows deformation and variations in Earth orientation and rotation parameters. The phenomena responsible for these variations include the full range of periodic and non-periodic phenomena such as Earth tides and ocean tidal loading, atmospheric dynamics as well as plate tectonics and intraplate deformation. The periods range from seismic normal modes over to the Earth tides and the Chandler Wobble and beyond. Thus, the time scales range from seconds to years and for the spatial scales from millimetres 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 tidal potential and ocean loading are a prerequisite to answer such questions.

Further, direct and indirect tidal phenomena affect the position of fiducial sites and have to be corrected to provide accurate spatial referencing. Such referencing is needed for the 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 as well as to climate change by providing important constraints to geophysical models both, to global and local scales.

Modern gravimetry has helped improve our knowledge on the Earth's global gravity field and its temporal variations, structure and dynamics. Notably, superconducting gravimeters allow continuous monitoring of the gravity signal at selected sites with a precision of better than $10^{-10}$ m. These geophysical observations together with other geodetic observations and geological information provide the means to better understand the structure, dynamics and evolution of the Earth system.

The Chair of SC 3.1 also chairs the Directing Board of the International Centre of Earth Tides - ICET. The Board comprises the Director of ICET, the Chair of GGP plus five additional members. The ICET Directing Board has

the responsibility, among others, to monitor the operations of, and provide guidance and supervision to ICET in order to ensure fulfilment of the scientific goals and objectives of the Global Geodynamics Project and of the resolutions of the International Symposia on Earth Tides.

### Objectives

Objectives of SC 3.1 include:

* To study and implement new observational techniques and improve existing ones, including clinometric and extensometric techniques;

* To advance tidal data analyses and prediction methods;

* To enhance the models on the interaction among solid Earth, ocean, and atmospheric tides;

* To research the effects of the atmosphere on gravity and other geodetic observations;

* To study the response of the Earth at tidal and non-tidal forcing frequencies;

* To study the interplay between tides and Earth rotation;

* To study tides on the planets;

* To study the effects of ocean loading and global water distribution;

* To create and coordinate working groups on specific topics of interest and relevancy to the understanding of our planet;

* To develop, coordinate and promote international conferences, programs and workshops on data acquisition, analysis and interpretation related to the research fields mentioned above;

* To contribute to the definition and realisation of the International Terrestrial Reference Frame via advanced geodynamic models at global, regional and local scales;

* To promote the systematic calibration and intercomparison of absolute and superconducting gravimeters;

* To promote interdisciplinary research in Earth and planetary tides.

The objectives of the IAG Global Geodetic Observing System (GGOS) are to a significant extent aligned with those of SC 3.1:

* The integral effect on Earth rotation of all angular momentum exchange inside the Earth, between land, ice, hydrosphere and atmosphere, and between the Earth, Sun, Moon, and planets,

* The geometric shape of the Earth's surface (solid Earth, ice and oceans), globally or regionally, and its temporal variations, whether they are horizontal or vertical, secular, periodical or sudden, and

* by adding the Earth's gravity field-stationary and time variable-mass balance, fluxes and circulation are in close relation to our objectives. Therefore, SC 3.1 also relates to 'Tidal effects in the framework of GGOS'.
## Structure and Activities

SC 3.1 has a Chair and a Co-Chair. National representatives are involved in the organization of conferences as well as in the considerations concerning the award of the *Paul Melchior Medal*, formerly known as the Earth Tides Commission Medal.

Besides the organization of special sessions at international meetings, SC 3.1 will continue to organize a symposium every four years. Between these symposia, a comprehensive SC meeting together with the GGP-project will continue to be organized. SC 3.1 will continue to publish the outcome of these meetings in proceedings, either as stand-alone publications or as special issues of scientific journals.

SC 3.1 is linked to the Sub-Commissions 3.2 and 3.3, and the next Earth Tide Symposium will be organized as a joint meeting covering a broad range of topics.

The GGP (Global Geodynamics Project) was promoted by the SC during the previous term, and future cooperation is a main focus of SC 3.1. Other Inter-Commission Projects and Joint Study Groups can be included if possible.

SC 3.1 will also cooperate with GGOS, as mentioned above.

## SC 3.2: Crustal Deformation

Chair: M Poutanen (Finland)

Co-Chair: J Freymueller (USA)

http://iagsc32.fgi.fi/

## Terms of Reference

There are many geodetic signals that can be observed and are representative of the deformation mechanisms of the Earth's crust at different spatial and temporal scales. This includes the entire range of tectonic phenomena including plate tectonics, intraplate deformation, the earthquake deformation cycle, aseismic phenomena such as episodic tremor and slip, and volcanic deformation. The time scales range from seconds to years and from millimetres to continental dimension for the spatial scales.

Space geodetic measurements now provide the means to observe deformation and movements of the Earth's crust at global, regional and local scales. This is a considerable contribution to global geodynamics by supplying primary constraints for modelling the planet as a whole, but also for understanding geophysical phenomena occurring at local scales. Some phenomena are potentially hazardous, like earthquake related phenomena. On the other hand, there are many slow deformations which are not hazardous, but in long time scales may have considerable effects. These include steady tectonic deformations and postglacial rebound.

One of the key issues nowadays is the definition and stability of global and regional reference frames. Crustal deformations in all time and spatial scales as well as mass transfer will affect reference frames. Gravimetry, absolute, relative, and nowadays also spaceborne, is a powerful tool providing information to the global terrestrial gravity field and its temporal variations. Combined with GNSS observations providing geometric deformation and data from other geophysical and geological sources provide the means to understand the structure, dynamics and evolution of the Earth system.

## Organizational Aspects

The Sub-Commission is divided into two Sub-Sub-Commissions, 3.2a Global Crustal Deformation and 3.2b Regional Crustal Deformation. There will be some inevitable overlap between "global" and "regional", so there are good opportunities for joint discussions and work on these topics between the two parts of the Sub-Commission. There is also a natural relationship with IAG Commission 1, as the reference frame definition must be consistent with the actual crustal deformation.
The work of the Sub-Commissions will be organized as working-group like. There will be invited a core group of people who will agree to meet regularly and try to evaluate different models or approaches for computing or evaluating these effects. Due to global distribution of participants, electronic meetings and e-mails will be an essential part of the organization. The Sub-Commission aims to organize 1-2 topical symposia during the 4-year period.

## Objectives

General objectives of the Sub-Commission 3.2 will include:

* To study crustal deformation in all scales, from plate tectonics to local deformation;

* To contribute reference frame related work in order to better understand deformations, and to improve global, regional and local reference frames and their dynamical modelling;

* To study sea-level fluctuations and changes in relation to vertical tectonics along many parts of the coastlines and in relation to environmental fluctuations/changes affecting the geodetic observations;

* To promote, develop and coordinate international programs related to observations, analysis and data interpretation for the fields of investigation mentioned above;

* To organize and co-organize meetings and symposia related to the topic.

Objectives of Sub-Commission 3.2a, Global Crustal Deformation will include:

* The long-range impacts of great earthquakes and post-seismic deformation on reference frame and relevant geodetic quantities.

* The limits of plate stability and what part of plates could be considered "plate interior" as opposed to "plate boundary" regions.

* Studies to distinguish between slow distributed deformation and errors in the reference frame geocenter, or other non-tectonic effects.

Objectives of Sub-Commission 3.2b, Regional Crustal Deformation will include:

* Studies of deformation during the seismic cycle including episodic slow events and postseismic transients. The strain build-up during interseismic period near the trench axes is one of the central topic in relation to the Tohoku-Oki earthquake.

* The strain partitioning in fault systems with reference to block or continuum mechanics.

* Volcanic and anthropologic deformations also belong among the topics of 3.2b, but activities will be mostly focused on two first items.

## SC 3.3: Earth Rotation and Geophysical Fluids

Chair: M Thomas (Germany)

Co-Chair: J Chen (USA)

## Terms of Reference

Mass transport in the atmosphere-hydrosphere-mantle-core system, or the 'global geophysical fluids', causes observable geodynamic effects on broad time scales. Although relatively small, these global geodynamic effects have been measured by space geodetic techniques to increasing, unprecedented accuracy, opening up important new avenues of research 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 geocentre shifts for all geophysical fluids are the relevant quantities. They are observed using global-scale measurements and are studied theoretically as well as by applying state-of-the-art models; some of these models are already constrained by such geodetic measurements.

## Objectives

The objective of the SC is to serve the scientific community by supporting research and data analysis in areas related to variations in Earth rotation, gravitational field and geocentre, caused by mass re-distribution 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.

The SC complements and promotes the objectives of GGOS with its central theme "Global deformation and mass exchange processes in the Earth system" and the following areas of activities:

* quantification of angular momentum exchange and mass transfer;

* deformation due to mass transfer between solid Earth, atmosphere, and hydrosphere including ice.

## Program of Activities

SC 3.3 follows the program of activities defined by Commission 3. In order to promote the exchange of ideas and results as well as of analysis and modelling strategies, sessions at international conferences and topical workshops will be organized. 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, hydro-
logy, ocean, combination) and its non-operational compo-
nent for core, mantle, and tides. SC 3.3 will have close
contacts to the GGOS activities, in particular to the
activities of the newly established GGOS Working Group
'Contributions to Earth System Modelling'. Our meetings
will be announced through the Commission 3 web site at
http://euler.jpl.nasa.gov/IAG-C3.

Steering Committee

• D. Salstein (USA; atmosphere)

• R. Gross (USA; oceans)

• R. Ray (USA; tides)

• J. Chen (USA; hydrology), Co-Chair

• E. Ivins (USA; mantle)

• T. van Hoolst (Belgium; core)

• M. Thomas (Germany; Earth system), Chair

• M. Watkins (USA, gravity/geocentre)

• T. van Dam (Luxembourg; loading)

SC 3.4: Cryospheric Deformation

Chair: M. King (UK)

Co-Chair: Sh. Abbas Khan (Denmark)

**Terms of Reference**

Past and present changes in the mass balance of the Earth's glaciers and ice complexes induce present-day deformation of the solid Earth on a range of spatial scales, from the very local to global. Of principal interest is geodetic observations that validate, or may 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. Using geometric measurements alone, elastic and GIA deformations cannot be separated without additional models or observations. Reference frames of GIA models do not allow direct comparison to measurements in an International Terrestrial Reference Frame and ambiguity currently exists over the exact transformation between the two. Furthermore, there is no publicly available and easy-to-use tool for model computations of elastic effects based on observed elevation/mass changes over the spatial scales of interest (small valley glaciers to large ice streams) and including gravitational/rotational feedbacks. This SC will focus on resolving these technical issues and work on dissemination of these measurements within the glaciological community (notably IACS).

Program of Activities

* Organize a workshop to discuss separation of elastic and GIA signals in key regions of interest, including Greenland, Antarctica, Patagonia and Alaska.

* Organize a workshop with WG 2.6.3 “Glacial isostatic adjustment (GIA) Model and Effects” and SC 1.2 “Global Reference Frames” on global reference frames for validation of GIA models.

* Encourage the inter-comparison and public release of elastic computation code, and advertise its existence.

* Interact where possible with those working on alternative measurements of the same signals (gravimetric or Earth rotation).

* Organize a workshop (with IACS) on “Present-day changes in the mass balance of Earth's glaciers and ice sheets”.
**Steering Committee**

* D. Argus (USA)

* V. Barletta (Denmark)

* R. Bennett (USA)

* M. Bevis (USA)

* P. Clarke (UK)

* I. Howat (USA)

* E. Ivins (USA)

* Sh. Abbas Khan (Denmark), Co-Chair

* M. King (UK), Chair

* L. Metevier (France)

* R. Motyka (USA)

* G. Nield (UK)

* R. Riva (The Netherlands)

* M. Craymer (Canada)

* J. Davis (USA)

* R. Dietrich (Germany)

* J. Freymueller (USA)

* A. Groh (Germany)

* I. Sasgen (Germany)

* G. Sella (USA)

* G. Spada (Italy)

* P. Tregoning (Australia)

* T. van Dam (Luxembourg)

* P. Whitehouse (UK)

* P. Willis (France)

* F. Wu (USA)

**SC 3.5: Tectonics and Earthquake Geodesy**

Chair: H. Ozener (Turkey)

**Terms of Reference**

Space and terrestrial geodesy provide key observations to investigate a broad range of the Earth's natural systems. These data are collected, analyzed, and interpreted by geodesists and other scientists. Studies of crustal deformation rely on the continuous and/or repeated acquisition of geodetic measurements and their analysis in the frame of active tectonics, and on their combination with results obtained from other geological and geophysical investigations (seismology, neotectonics, gravity, rock physics, electromagnetic, ...).

The evolution of geodetic techniques in the past decade, with unprecedented achievements in the precise detection and monitoring of 3D movements at the millimetre level has opened new prospects for the study of Earth kinematics and geodynamics. However, these achievements also raise new issues that have to be properly taken into account in the processing and analysis of the data, demanding a careful inter-disciplinary approach.

Areas that involve the broad collision zone between Europe, Africa and Arabia, provide natural laboratories to study crucial and poorly understood geodynamic processes. The recent occurrence of giant earthquakes (with Mw > 9), unexpected and in subduction areas with weak geodetic monitoring provide further challenges to the scientific community. Although these active zones were systematically monitored in the last decade by different research groups using a variety of space geodesy and other methods, in general the data analysis and interpretation have been done from the perspective of one discipline and have rarely followed an integrated approach. Never completely explored, the existence of these data (geodata) justifies a new, integrated approach including different observational techniques and input from other disciplines in the Earth sciences (geology, seismology, tectonics, ...). This should lead to the development of interdisciplinary work in the integration of space and terrestrial approaches for the study of, for instance, the Eurasian/African/Arabian plate boundary deformation zone (and adjacent areas), and contribute to the establishment of a European Velocity Field. With this objective, it is important to promote stronger international cooperation between Earth scientists interested in plate boundary zones.

Towards this goal the SC aims to:

* Actively encourage the cooperation between all geoscientists studying the Eurasian/African/Arabian plate boundary deformation zone, by promoting the exploitation of synergies;
* Reinforce the study of subduction zones in Mediterranean regions and elsewhere by increasing and developing infrastructures and geodetic stations;

* Be a reference group for the integration of the most advanced geodetic and geophysical techniques by developing consistent methodologies for data reduction, analysis, integration, and interpretation;

* Act as a forum for discussion and scientific support for international geoscientists investigating the kinematics and mechanics of the Eurasian/African/Arabian plate boundary deformation zone;

* Promote the use of standard procedures for geodetic data acquisition, quality evaluation, and processing, particularly GNSS data;

* Promote earthquake geodesy and the study of seismically active regions with large earthquake potential;

* Promote the role of Geodesy in tectonic studies for understanding the seismic cycle, transient and instantaneous deformation, and creeping versus seismic slip on faults.

## Objectives

The primary goals of the SC are to:

* Continue as a framework for geodetic cooperation in the study of the Eurasian/African/Arabian plate boundary zone;

* Identify and develop a “Wegener Supersite”;

* Develop scientific programmes in earthquake geodesy for subduction zones (e.g., Hellenic Arc) and possible occurrence of giant earthquakes and associated tsunamis;

* Foster the use of space-borne, airborne and terrestrial hybrid techniques (high-resolution GNSS, InSAR, GOCE, GRACE, ENVISAT, SENTINELLE, LIDAR, ...) for Earth observation;

* Define effective integrated observational strategies for these techniques to reliably identify and monitor crustal movements and gravity variations over all time-scales;

* Facilitate and stimulate the integrated exploitation of data from different techniques in the analysis and interpretation of geo-processes;

* Organize periodic workshops and meetings with special emphasis on interdisciplinary research and interpretation and modelling issues;

* Reinforce cooperation with African and Arab countries and colleagues with scientific projects, that can contribute to understanding the kinematics and dynamics of the Eurasian/African/Arabian plate boundary zone and promote the growth of such research and geodetic expertise in these countries.

## Program of Activities

* Build a web-portal and an associated geo-database that enables access to metadata, processed results, and when

possible historical data from continuous GNSS stations and episodic geodetic campaigns, as well as other derived products such as strain rates, velocity fields, etc.;

* Promote the application of standards for GNSS network establishment, data acquisition, and guidelines for data processing and reliability checks;

* Define strategies for a full exploitation of different geodata (GNSS, gravimetry, InSAR, etc.);

* In coordination with the IGS and other relevant organizations, establish a GNSS analysis centre specially dedicated to process permanent and episodic campaign data, not analyzed by other GNSS centres, which will contribute to the development of a joint velocity field (EUROVEL) that can support kinematic and geodynamic modelling;

* Organize bi-annual conferences to serve as high-level international forums in which scientists from all over the world can look at a multi-disciplinary interpretation of geodynamics, and strengthen the collaboration between countries in the greater Mediterranean region.

## Links to Services

The SC will establish links to relevant services, such as:

* EUREF;

* 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);

* Regional Reference Frame Northern Africa (AFREF);

* Global Geodetic Observing System (GGOS);

* Supersites;

* UNAVCO.

## Steering Committee

* H. Ozener (Turkey), Chair

* S. Zerbini (Italy)

* R. Reilinger (USA)

* M. Meghraoui (France)

* B. Ambrosius (The Netherlands)

* L. Bastos (Portugal)

* M. Becker (Germany)

* C. Bruyninx (Belgium)

* A. Caporali (Italy)

* L. Combrink (South Africa)

* J. M. Davila (Spain)

* T. Mourabit (Morocco)

* J. M. Nocquet (France)

* W. Spakman (The Netherlands)

* S. Stein (USA)

* S. Tatevian (Russia)

* T. van Dam (Luxembourg)

* S. Kahlouche (Algeria)

* S. M. Mahmoud (Egypt)

* A. ArRajehi (Saudi Arabia)
# Joint Study Groups

## JSG 3.1 Gravity and Height Change Intercomparison

(joint with Commissions 1 and 2)

Chair: S. Rosat (France)

http://www.srosat.com/iag-jsg/

This Study Group is joint between the International Gravity Field Service (IGFS), Commission 1 on Reference Frames, Commission 2 on Gravity Field, and Commission 3 on Earth Rotation and Geodynamics. The activities of this new JSG will be concerned with the comparison of ground and space gravity measurements with geometric measurements of surface deformation.

The motivation of this JSG is to study surface deformation by comparing site displacement observations with both ground- and space-based gravity measurements. Issues that will arise when comparing site displacement with gravity measurements are differences in spatial and temporal scales and differences in sensitivity.

# Terms of Reference

Surface deformations are continuously recorded from space or from the ground with increasing accuracy. Vertical displacements and time-varying gravity are representative of various deformation mechanisms of the Earth occurring at different spatial and temporal scales. We can quote for instance post-glacial rebound, tidal deformation, hydrologic loading, co-seismic deformation and volcanic deformation. The time scales involved range from seconds to years and the space scales range from millimetres to continental dimension. Large-scale deformation are well monitored by space geodetic measurements from monthly spatially-averaged GRACE measurements while local deformation are precisely monitored by daily GNSS or VLBI solution and sub-daily gravimeter data at a site. The intercomparison of the space- and ground-gravity measurements with vertical surface displacements enable to infer more information on the structure, dynamics and evolution of the Earth system. In particular, we will focus on the transfer function of the Earth at various time scales related to the elastic and visco-elastic properties of the Earth.

The activities of this JSG will interact with the SC 1.2 on Global Reference Frames and with GGP (Global Geodynamics Project), reporting to the IGFS, Commission 1 (Reference Frames), Commission 2 (Gravity Field), and Commission 3 (Earth Rotation and Geodynamics).

# Objectives

The objectives of this JSG are:

* Love numbers determination (h, k, l) using co-located gravity and displacement measurements;

* Study of the gravity-to-height ratio dg/du at various time and length scales in order to discriminate vertical motion from mass transfer;

* Development of standardized procedures and tools to convert surface gravity points of measure into space-comparable gravity field (e.g. EOF);

* Tidal deformation analysis at long periods in displacements (from VLBI and GNSS) and in gravity (from superconducting gravimeters);

* Applications to co-seismic deformation, volcanic deformation, hydrological loading, ice-melting unloading.

# Program of Activities

This JSG will propose a session at the 17th Earth Tides Symposium in Cairo, Egypt, 24-28 September 2012.

A session will be also proposed at the next IAG Scientific Assembly in 2013 and at the next IUGG General Assembly in 2015.

# Members

* Chair: S. Rosat (France)

* J. A. Sampedro (Spain)

* O. Francis (Luxembourg)

* Y. Fukuda (Japan)

* R. Haas (Sweden)

* S. Lambert (France)

* L. Metivier (France)

* Y. Rogister (France)

* H. Steffen (Canada)

* P. Tregoning (Australia)

* P. Valty (France)

# Corresponding Members

* C. Kroner (Germany)

* S. Zerbini (Italy)
# Commission 4 – Positioning and Applications

http://www2.ceegs.ohio-state.edu/IAG-Comm4/

President: **D. Grejner-Brzezinska** (USA)

Vice President: **A. Kealy** (Australia)

## Terms of Reference

To promote research that leverages current and emerging positioning techniques and technologies to deliver practical and theoretical solutions for engineering and mapping applications. Commission 4 will carry out its work in close cooperation with the IAG Services and other IAG entities, as well as via linkages with relevant entities within scientific and professional sister organizations.

Recognizing the central role of Global Navigation Satellite Systems (GNSS) in providing high accuracy positioning information today and into the future, Commission 4 will focus on developing tools that enhance and assure the positioning performance of GNSS-based positioning solutions for a range of geodetic applications.

The Sub-Commissions will develop theory, strategies and tools for modelling and/or mitigating the effects of interference, signal loss and atmospheric effects as they apply to precise GNSS positioning technology. They will address the technical 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.

## Structure

### Sub-Commissions

**SC 4.1:** Alternatives and Backups to GNSS
Chair: G. Retscher (Austria)

**SC 4.2:** Geodesy in Geospatial Mapping and Engineering
Chair: J. Wang (Australia)

**SC 4.3:** Remote Sensing and Modelling of the Atmosphere
Chair: M. Santos (Canada)

**SC 4.4:** Applications of Satellite and Airborne Imaging Systems
Chair: Z. Li (UK)

**SC 4.5:** High-Precision GNSS Algorithms and Applications
Chair: Y. Gao (Canada)

**SC 4.6:** GNSS-Reflectometry and Applications
Chair: S. Jin (China)

### Joint Study Groups

**JSG 0.1:** Application of time series analysis in geodesy (joint with ICCT and all Commissions, see ICCT)
Chair: W. Kosek (Poland)

**JSG 0.4:** Coordinate systems in numerical weather models (joint with ICCT and all Commissions, see ICCT)
Chair: Th. Hobiger (Japan)

**JSG 0.8:** Earth system interaction from space geodesy (joint with ICCT and all Commissions, see ICCT)
Chair: S. Jin (China)

### Joint Working Group

**JWG 0.2.1:** New technologies for disaster monitoring and management (joint with GGOS, description see GGOS)
Chair: I.D. Doukas (Greece)

### Steering Committee

* President: D. Grejner-Brzezinska (USA)

* Vice President: A. Kealy (Australia)

* Chair SC 4.1: G. Retscher (Austria)

* Chair SC 4.2: J. Wang (Australia)

* Chair SC 4.3: M. Santos (Canada)

* Chair SC 4.4: Z. Li (UK)

* Chair SC 4.5: Y. Gao (Canada)

* Chair SC 4.6: S. Jin (China)

* Representatives of Services: IGS: A. Krankowski (Poland)

* Members at large: P. Wielgosz (Poland)

### Representatives of external bodies

**ISPRS:** Ch. Toth (USA)

**FIG:** G. Roberts (UK)

**ION:** L. Hothem (USA)
# Sub-Commissions

## SC 4.1: Alternatives and Backups to GNSS

Chair: G. Retscher (Austria)

Vice-Chair: V. Gikas (Greece)

Secretary: L. Bonenberg (UK)

### Terms of Reference

To coordinate research and other activities that address broader areas of alternatives and backups to GNSS positioning using multi-sensor system theory and applications, with a special emphasis on integrated guidance, navigation, positioning and orientation of airborne and land-based platforms. The primary sensors of interest will be inertial navigation systems; however the important role of other emerging techniques used for indoor and pedestrian navigation environmental monitoring is also recognized. The Sub-commission will carry out its work in close cooperation with other IAG Entities, as well as via linkages with relevant scientific and professional organizations, such as ISPRS, FIG, IEEE and ION.

### Objectives

* To follow the technical advances in navigation sensors and algorithms, including autonomous vehicle navigation, based on

* positioning sensors and techniques such as pseudolites, INS, including MEMS IMU, wheel sensors, ultrasonic and magnetic sensors, and

* positioning methods based on cellular networks and their hybrid use with GNSS.

* To investigate positioning sensors and techniques integrated in modern smart phones and other mobile devices.

* To follow the technical advances in vision-based sensors, such as CCD cameras in smart phones for indoor positioning and navigation.

* To standardize definitions and measurements of sensor related parameters.

* To study and report on the performance of stand alone and integrated navigation systems.

* To report on the development, possibilities and limitations of new emerging technologies.

* To stimulate new ideas and innovation in

* navigation algorithms, sensor calibration, synchronization and inter-calibration,

* real-time sensor information processing,

* sensor and data fusion, and

* automation techniques for information extraction from multi-sensor systems using expert systems.

* To study and monitor the progress in new applications (not limited to conventional navigation) of multi-sensor systems (transportation, engineering, car navigation, environmental monitoring personal navigation, indoor navigation, etc.).

* To promote research collaboration and to organize and to participate in professional workshops, seminars, and meetings.

* To promote research and collaboration with countries with no or limited access to modern multi-sensor technology.

* To establish a web page providing information on the SC 4.1 activities, technology updates, and professional meeting calendar.

### Working groups

#### WG 4.1.1: Ubiquitous Positioning Systems

(joint with FIG)

Chair: A. Kealy (Australia)

Co-chair: G. Retscher (Austria)

### Description

This WG group will focus on the development of shared resources that extend our understanding of the theory, tools and technologies applicable to the development of ubiquitous positioning systems. It has a major focus on:

* Performance characterization of positioning sensors and technologies that can play a role in the development of ubiquitous positioning systems.

* Theoretical and practical evaluation of current algorithms for measurement integration within ubiquitous positioning systems.

* The development of new measurement integration algorithms based around innovative modelling techniques in other research domains such as machine learning and genetic algorithms, spatial cognition etc.

* Generating formal parameters that describe the performance of current and emerging positioning technologies that can inform FIG and IAG members.

Specific projects to be undertaken include

* Reporting on the performance characteristics of a broad range of MEMS inertial sensors derived from extensive practical testing and benchmarking.

* Reporting on performance characterization of positioning technologies: the development, possibilities and limitations of new technologies.

* Establishing components of an open source platform for researchers to rapidly deploy sensors as well as evaluate and develop integration algorithms.
* Developing and report on taxonomy for users of ubiquitous positioning systems that shows the performance capabilities of sensors and typical applications.

* Establishing links between the outcomes of this WG and other IAG and FIG WGs.

## WG 4.1.2: Interference and Jamming

Chair: A. Soloviev (USA)

Co-chair: TBD

### Description

This WG group will focus on gaining a deeper understanding of the impact of unintentional interference and intentional jamming on GNSS navigation capabilities for civil users; and, methods for improving the robustness of GNSS receivers in interference and jamming environments. It has a major focus on:

* Characterization of the impact of interference and jamming on the GNSS performance via review of open literature publications.

* Evaluation of algorithms and methods that enable radio-frequency (RF) awareness.

* Evaluation of GNSS signal processing methods for interference and jamming suppression that are not subject to international traffic in arms (ITAR) regulations and can be thus adopted by the civil community without any restrictions.

* Evaluation of multi-sensor fusion methods for improved interference robustness.

Specific projects to be undertaken include:

* Reporting on the characterization of interference/jamming impact.

* Reporting on algorithms and methods that enable RF awareness.

* Reporting on non-ITAR GNSS-only interference suppression technologies.

* Reporting on the benefits of multi-sensor fusion for enhancing the navigation robustness in interference/jamming environments.

* Establishing links between the outcomes of this WG and other IAG and FIG WGs.

## WG 4.1.3: Emerging Technologies

Chair: K. Zhang (Australia)

Co-chair: L. Bonenberg (UK)

### Description

This working group will focus on the investigation and development of emerging technologies for innovative positioning and tracking applications. This is not limited to traditional navigation and this WG hopes to cooperate with other WGs on other forms of navigations such as indoor positioning and pedestrian navigation. With new technologies depending on wireless communication this WG plans to monitor relevant changes in legislature and support industry and academy interested in this area. Group actions aim to extend our knowledge and enhance our capability in positioning and tracking in order to complement the GNSS.

Current group focus includes:

* Utilisation of emerging technologies by the industry.

* Promotion and knowledge exchange about new technologies.

* Reporting the development trends, possibilities and limitations of emerging positioning technologies, such as Locata, RFID, UWB and smart phones.

* Promoting the utilisation of new technologies by the industry.

* Developing innovative positioning algorithms using current and emerging technologies and theoretical and practical evaluation of these developments.

* Promoting industry and academy interest into licensing and legislature regime relating to the emerging technologies.

* Reporting on such legislature efforts.

* Generating formal parameters that describe the performance of emerging positioning technologies that can inform both FIG and IAG members.

* Establishing working links between this WG and other IAG and FIG WGs.

Specific techniques include:

* New RFID systems with stable transmitted signal strength.

* Smart phones as multi-sensor integrated platforms.

* Low-cost vision-based positioning techniques (single/stereo cameras built in smart phones).

* UWB.

* Locata and other indoor/outdoor pseudolite systems.

* Multi-GNSS positioning techniques.

Specific algorithms include:

* Cooperative positioning.

* Ubiquitous positioning (cooperation with WG 4.1.1)

* Single camera-based positioning (cooperation with WG 4.1.4).