Report of the International Association of Geodesy 2007-2011 ─ Travaux de l’Association Internationale de Géodésie 2007-2011

Global Geodetic Observing System (GGOS)
http://www.ggos.org
Chair: Markus Rothacher (Switzerland)
Vice Chair: Ruth Neilan (USA)Vice Chair: H.P. Plag (USA; until March 2010)

Structure
Bureau on Networks and Communications
Bureau on Conventions and Standards
Working Group on Data and Information Systems
Working Group on Satellite and Space Missions
Working Group on OutreachWorking Group on ITRS Standardization
Working Group on Contribution to Earth System Modelling
GGOS Coordinating Office
GGOS Portal
GGOS Science Panel
GGOS Themes
GGOS in the Group on Earth Observation (GEO)

Overview
The idea of a Global Geodetic Observing System (GGOS; originally called IGGOS, Integrated Global Geodetic Observing System) goes back to the IAG Section II Symposium in
Munich in 1998. In 2003 at the XXIII IUGG General Assembly in Sapporo the new IAG
structure was implemented and with it the GGOS Planning Group was set up. Four years later,
at the XXIV IUGG General Assembly in 2007, GGOS was accepted by the IAG Council as afull component of the IAG structure. More details may be found in (Beutler et al., 2009).
Table 1 summarizes the major events that happened since, i.e., in the report period 2007-2011.
In the following the most important developments are described in some more detail.
Table 1: Major GGOS Events 2007-2011
Date

Event

July 2007

XXIV IUGG General Assembly in Perugia, Italy: GGOS accepted as a full component of the
IAG by the IAG Council

January 2009

Establishment of the Bureau on Networks and Communication, Bureau on Standards andConventions, and the GGOS Portal

July 2009

The book “Global Geodetic Observing System: Meeting the Requirements of a Global
Society on a Changing Planet in 2020” published as the basis for the present and future
development of GGOS

January 2010

GGOS Coordinating Office starts its work

February 2010

GGOS Retreat in Miami: the three GGOS Themes for integrated products are initiatedReport of the International Association of Geodesy 2007-2011 ─ Travaux de l’Association Internationale de Géodésie 2007-2011

December 2010 GIAC (GGOS Inter-Agency Committee) is established
December 2010 GGOS Working Group on Contributions to Earth System Modelling established
January 2011

GGOS Web pages online

February 2011

GGOS Retreat: new vision, mission and goals for GGOS, new GGOS Terms of Reference
are set up

June 2011

XXV IUGG General Assembly in Melbourne, Australia: New GGOS chair is appointed by
the IAG Executive Committee. Action plans exist for the major components of GGOS.

GGOS 2020 Book
In early 2006 an effort was started to write a book describing the background of GGOS and its
perspectives for the year 2020. The final version of this book called “GGOS 2020 book” waspublished in 2009. This book was realized under the leadership of Hans-Peter Plag and Mike
Pearlman with contributions of the GGOS Science Panel as well as a large group of experts invarious neighbouring fields of geoscience (Plag et al., 2009). It marks a milestone in thedevelopment of GGOS. The full reference is given below.
Building up the GGOS Organizational Structure
The first two years after the establishment of GGOS as a full component of the IAG (theGlobal Geodetic Observing System of the IAG) were mainly used to build up the structurenecessary for GGOS to work. The components to be established were already lined out in the
GGOS 2020 book (see Figure 1).

Figure 1: GGOS Structure proposed in the GGOS 2020 Book (Plag & Pearlman, 2009), Chapter 10

Report of the International Association of Geodesy 2007-2011 ─ Travaux de l’Association Internationale de Géodésie 2007-2011

In January 2009 the following components could successfully be established:– Bureau for Networks and Communication: Cambridge Center for Astrophysics / NASA
(Director: M. Pearlman)– Bureau for Standards and Conventions: Research Group on Satellite Geodesy in Munich(FGS: FESG, DGFI, IAPG; director: U. Hugentobler, now D. Angermann)– GGOS Portal: BKG (Federal Agency of Cartography and Geodesy, Frankfurt; director:
Bernd Richter)
For the planned GGOS Bureau for Satellite and Space Missions no leading institution was
found and, therefore, the GGOS WG on Satellite and Space Missions was kept. The chair was
decided to be C.K. Shum, Ohio State University (OSU). Since 2010, this GGOS WG is led byIsabelle Panet (IGN, Paris) and Roland Pail (TU Munich).
An institution responsible to operate the GGOS Coordinating Office (CO) could be found in
the beginning of 2010, when the Italian Space Agency (ASI) volunteered to act as the GGOS
CO with Giuseppe Bianco as the director. The GGOS CO is now successfully organizing a lotof the day-to-day activities of GGOS and is also responsible for the GGOS web pages(www.ggos.org) and works closely together with the GGOS Portal at BKG.
With the GGOS CO the organizational structure of GGOS could be completed. In addition, a
new GGOS Working Group, the WG on Contributions to Earth System Modeling, wascreated in 2010 chaired by Maik Thomas at the Deutsches GeoForschungsZentrum (GFZ) in
Potsdam. With this new GGOS WG there are now five working groups in GGOS (seeTable 2).
An overview of the present structure is also given in Figure 2.
Table 2: Present GGOS Working Groups
GGOS WG

Chair(s)WG on Data and Information Systems

Bernd Richter, Carey Noll

WG on Satellite and Space Missions

Isabelle Panet, Roland Pail

WG on Contributions to Earth System Modeling

Maik Thomas

WG on ITRS Standardization

Claude Boucher

WG on Outreach

Giuseppe Bianco

Report of the International Association of Geodesy 2007-2011 ─ Travaux de l’Association Internationale de Géodésie 2007-2011

Figure 2: Present GGOS Structure

New GGOS Core Sites
In the period from 1970-1990 a rather rapid development of the global space geodetic infrastructure took place, initiated among others by the NASA Crustal Dynamics Project (CDP).
During the years to follow further developments were taking place but only at individual
stations, by individual institutions and for individual techniques. Some stations were evendecommissioned during this time period. With the arguments of GGOS at hand and due totechnique-specific initiatives (e.g. IVS2010, SLR), a new era of building up improved infrastructure has started. Figure 3 summarizes the present status of the GGOS core sites. It can beseen that a substantial progress was taking place during the last few years. In VLBI alone, it isexpected that more than 20 new telescopes will become operational in the next several years.
This gives an indication that the goal of establishing around 40 global GGOS core sites, as
recommended in the GGOS 2020 book, is indeed feasible with the joint effort of GGOS andthe IAG Services and the support of the national institutions responsible for the geodetic
infrastructure.

Report of the International Association of Geodesy 2007-2011 ─ Travaux de l’Association Internationale de Géodésie 2007-2011

Figure 3: Increasing number of GGOS core sites in the global networks (NASA, 2011)

GGOS Outreach
Besides the GGOS 2020 book several other articles, books and white papers were publishedduring the period 2007-2011.
– Chapter by Blewitt et al., 2010, in the book “Understanding Sea-Level rise and Variability” (Church et al, 2010)– White papers for the Ocean’09 meeting (Shum et al., 2009; Plag et al., 2009; Scott et al.,2009; http://www.oceanobs09.net/)– Springer book containing the final report of the German Geotechnologies Project(Flechtner et al., 2011)– Papers about GGOS (Plag et al., 2010; Plag et al., 2009; …)
In addition, leaflets, posters, one-page stories, and a GGOS booth were produced and presented at various meetings, especially at GEO Plenaries and Ministerial Summits.
Finally, with the help of BKG (Federal Agency of Geodesy and Cartography) the GGOS
portal (see below) could be established and new web pages were generated by the GGOS Coordinating Office (ASI).
Retreats, Workshops and Sessions
During the past four years quite a number of GGOS retreats, GGOS workshops and meetings
were organized. They are listed in Tables 3 and 4 with their internet link. Whereas the GGOS
retreats were held to make progress in the organization and further development of GGOS, theworkshops were focussing on specific scientific themes of relevance to GGOS. In addition,
GGOS sessions were proposed and held at almost every AGU and EGU Meeting.

Report of the International Association of Geodesy 2007-2011 ─ Travaux de l’Association Internationale de Géodésie 2007-2011

Table 3: Retreats organized by GGOS
GGOS Retreat

Place

Date

GGOS Retreat 2007

Oxnard, California

February 19-21, 2007

GGOS Retreat 2008

Bertinoro, Italy

March 25-28, 2008

GGOS Retreat 2010

Miami, USA

February 1-4, 2010

GGOS Retreat 2011

Zurich, Switzerland

February 2-4, 2011

Table 4: Workshops organized or co-organized by GGOS
GGOS Workshop

Place

Date

Web page

The GGOS Contribution to GEOSS and an
Observing System for Geohazards andDisaster Prevention

Frascati, Italy

November 56, 2007

http://earth.esa.int/workshops/2007Geohazards/

Unified Analysis Workshop 2007

Monterey, USA

December 57, 2007

http://www.iers.org/

IGCP 565 Workshop 1: Science of geodetic
monitoring of the hydrological cycle

San Francisco,USA

December 11, http://www.igcp565.org/ work2008
shops/SanFrancisco/

Understanding Glacial Isostatic Adjustment

Espoo, Finland

June 23-26,
2009

Towards a Roadmap for Future Satellite
Gravity Missions

Graz, Austria

September
http://www.igcp565.org/ work30-October 2, shops/Graz/2009

Unified Analysis Workshop 2009

San Francisco,USA

December 11- http://www.iers.org/
12, 2009

IGCP 565 Workshop 2b: From Satellite
Gravity Observations to Products

San Francisco,USA

December 12- http://www.igcp565.org/ work13, 2009
shops/SF_2009/

IGCP 565 Workshop 3: Separating
Hydrological and Tectonic Signals inGeodetic Observations

Reno, USA

October 1113, 2010

http://www.igcp565.org/ workshops/Reno_2010/

Observing and Understanding Earth
Rotation

Shanghai, China

October 25–
28, 2010

http://202.127.24.12/dct/

http://dynaqlim.fgi.fi/files/
GGOS_DynaQlim.htm

GGOS Themes
In view of the complexity of the Earth system as a whole, GGOS decided to start with a small
set of integrated and interdisciplinary themes/products of high importance to science andsociety. The three themes selected are:
– Theme 1: Global Unified Height System (Chairs: M. Sideris, J. Ihde)– Theme 2: Geohazards (global Earth surface deformations and strain rates for geohazards
assessment and disaster prevention) (Chairs: T. Dixon, R. Gross)Report of the International Association of Geodesy 2007-2011 ─ Travaux de l’Association Internationale de Géodésie 2007-2011– Theme 3: Understanding and Forecasting Sea-Level Rise and Variability (Chairs: C.K.
Shum., P. Woodworth)
These themes are described in more details in a later section of this report.
GEO activities
GGOS, representing the IAG in the Group on Earth Observation (GEO), has been contributing to the GEO activities by participating in the GEO Committees and Working Groups and in
the GEO Plenaries and Ministerial Summits and by proposing own tasks or subtasks within
GEO. The two major subtasks within GEO for which GGOS is responsible are the subtask on“Global Geodetic Observing System” and on “Global Geodetic Reference Frames”. These
will also be part of the GEO Work Plan 2011-2015, that will be the last GEO work plan before the end of the GEO 10-Year Implementation Plan for GEOSS, the Global Earth Observing System of Systems. Details are given below.
GIAC
In November 2009 a group of national geodetic institutions met for the first time to discuss
the establishment of an Intergovernmental Committee for GGOS. This initiative was started
by Reiner Rummel (TU Munich) and Dietmar Grünreich (BKG), because the global groundinfrastructure for space geodesy is far from ideal and not sustainably financed. Since the
GGOS concept builds on long-term observation series, the sustainability of the existing IAG
Services and the infrastructure they use is a key issue that needs to be approached.
The Frankfurt Declaration written during this meeting states “The overall goal of this initiative is to improve the sustainability of IAG Services in general and in particular, the long term
coverage of the in-situ space geodetic networks in time and distribution and to increase thevisibility and effectiveness of Geodesy to global geo-observation programs”.
In the time to follow it was decided that before going through the very difficult work offorming a GGOS Intergovernmental Committee (GIC), a GGOS Inter-Agency Committee(GIAC) should be formed. This happened at a meeting of the GIAC Planing Group in San
Francisco on December 9, 2010. By now, around 15 major institutions signed the Frankfurt
Declaration and became member of GIAC.
GIAC will support GGOS in attaining its goals by working towards an appropriate intergovernmental agreement that facilitates planning, securing, and maintaining geodetic infrastructure and operation of the Services based on the needs of science and society, and by promoting GGOS to international entities that require intergovernmental representation.

References
Beutler, G., R. Rummel (2011): Scientific Rationale and Development of the Global Geodetic Observing
System, In: Geodesy for Planet Earth, Proceedings of the 2009 IAG Symposium, Buenos Aires, Argentina,
August 31 - 4 September 2009, Eds. Kenyon S., Pacino M.C.; Marti U. (Eds.), ISBN 978-3-642-20337-4.
Blewitt, G., Z. Altamimi, J. Davis, R. Gross, Ch.-J. Kuo, F.G. Lemoine, A.W. Moore, R.E. Neilan, H.-P. Plag,
M. Rothacher, C.K. Shum, M.G. Sideris, T. Schöne, P. Tregoning, S. Zerbini (2010): Geodetic Observations andGlobal Reference Frame Contributions to Understanding Sea-Level Rise and Variability, in "Understanding SeaLevel Rise and Variability", Eds: J.A. Church, Ph.L. Woodworth, Th. Aarup, W.S. Wilson, Wiley-Blackwell,ISBN 978-1-4443-3452-4, 256-284.

Report of the International Association of Geodesy 2007-2011 ─ Travaux de l’Association Internationale de Géodésie 2007-2011

Flechtner, F., Th. Gruber, A. Güntner, M. Mandea, M. Rothacher, T. Schöne, J. Wickert (Eds.) (2010): System
Earth via Geodetic-Geophysical Space Techniques, ISBN 978-3-642-10227-1, Springer-Verlag BerlinHeidelberg.
Plag, H.P., M. Pearlman (Eds.) (2009): Global Geodetic Observing System: Meeting the Requirements of a
Global Society on a Changing Planet in 2020, Springer Verlag, DOI 10.1007/978-3-642-02687-4_3.
Plag et al. (2009): Observations as decision support for coastal management in response to local sea levelchanges, white paper for OceanObs’09 conference, https://abstracts.congrex.com/scripts/jmevent/abstracts/.
Plag, H.P., R. Gross, M. Rothacher (2009): Global Geodetic Observing System for geohazards and globalchange. Géosciences, 9, April/May 2009, 96-103.
Plag, H.P., M. Rothacher, M. Pearlman (2009): The Global Geodetic Observing System – Part 1, theOrganization. Geomatics World, Jan/Febr 2009, 26-28.
Plag, H.P., M. Rothacher, M. Pearlman (2009): The Global Geodetic Observing System – Part 2, the System.
Geomatics World, March/April 2009, 22-25.
Plag, H.-P., R. Gross, M. Rothacher (2009): Global Geodetic Observing System for Geohazards and Global
Change, in Geosciences, BRGM's journal for a sustainable Earth, 9, 96-103.
Plag, H.-P., M. Rothacher, M. Pearlman, R. Neilan, C. Ma (2009): The Global Geodetic Observing System, in
Solid Earth (SE), edited by K. Satake, Advances in Geosciences, Vol. 13, 105-127.
Plag H.-P., C. Rizos, M. Rothacher, R. Neilan (2010): The Global Geodetic Observing System (GGOS):
Detecting the Fingerprints of Global Change in Geodetic Quantities, in Advances in Earth Observation of Global
Change, 125-143, DOI: 10.1007/978-90-481-9085-0_10.
Rothacher M., H. Drewes, A. Nothnagel, B. Richter (2010): Integration of Space Geodetic Techniques as theBasis for a Global geodetic-Geophysical Observation System (GGOS-D): An Overview, in System Earth via
Geodetic-Geophysical Space Techniques, Flechtner, F., Gruber Th., Güntner A., Mandea M., Rothacher M.,
Schöne T., Wickert J. (Eds.), ISBN 978-3-642-10227-1, 529-538.
Rothacher M., D. Angermann, T. Artz, W. Bosch, H. Drewes, S. Böckmann, M. Gerstl, R. Kelm, D. König, R.
König, B. Meisel, H. Müller, A. Nothnagel, N. Panafidina, B. Richter, S. Rudenko, W. Schwegmann, M. Seitz,
P. Steigenberger, V. Tesmer, D. Thaller (2010): GGOS–D: Homogeneous Reprocessing and Rigorous Combination of Space Geodetic Observations, Journal of Geodesy, online first, DOI: 10.1007/s00190-011-0475-x.
Scott et al. (2009): Integrating satellite altimetry and key observations: what we’ve learned, and what’s possible
with new technologies, white paper for OceanObs’09, https://abstracts.congrex.com/scripts/jmevent/abstracts/.
Shum et al. (2009): Geodetic observations of ocean surface topography, ocean currents, ocean mass, and ocean
volume changes, White paper for OceanObs’09 conference, https://abstracts.congrex.com/scripts/jmevent/abstracts/.

Report of the International Association of Geodesy 2007-2011 ─ Travaux de l’Association Internationale de Géodésie 2007-2011

Bureau on Networks and Communications
Chair: M. Pearlman (USA)Role of the Bureau
The role of the Bureau is to promote the further development of sustained infrastructureneeded to satisfy the long-term (10-20 years) requirements for the reference frames and themonitoring of global change signals. GGOS provides observations of variations in Earthshape, gravity field and rotation, which are fundamental for monitoring of climate and globalchange. The global geodetic reference frame, the International Terrestrial Reference Frame(ITRF) provides the foundation for most Earth metric observations and for observations in the
lunar and planetary systems. GGOS provides observations of variations in Earth shape,
gravity field and rotation, which are fundamental for monitoring of climate and global change.
These observations depend on sustained geodetic ground networks with stations of sufficientmeasurement quality and global distribution.
The reference frame requirement is to establish an ITRF with an accuracy of 1 mm and astability of 0.1 mm/year, which represents an improvement of 10-20 beyond the current
quality. The main driver for this requirement is the monitoring of sea level, but other applications are not far behind (Plag, H-P and Pearlman, M.R., 2009). These requirements will be
met with a ground network of globally distributed stations with co-located VLBI, SLR,
GNSS, DORIS, and may include other systems such as gravimeters, seismometers, tidegauges, etc. These have been termed GGOS Fundamental Stations (see Figure 4).
In this role the Bureau will plan and advocate for the implementation of:– Ground-based network of Fundamental Stations with co-located VLBI, SLR, GNSS,DORIS required to establish an ITRF that has an accuracy of 1 mm and a stability of 0.1
mm/year, which represents an improvement of 10-20 beyond the current quality;– Implementation of a ground-based GNSS network to make the ITRF of this quality available everywhere on the surface of the Earth for 24 hours a day;– Implementation of the ground-based tracking network to support planned missions;– Integration of techniques including gravity field, tide gauges, etc to support GGOS
themes.
Progress– Bi-annual meetings at AGU and EGU the services to exchange information and plans;– Files have been implanted to provide on-line access to network station and data
product information including local ties, mis-closure files, etc. See: http://observingsystem-portal.bkg.bund.de/lang_en/nn_261332/sid_10CCEAF2FA145E6
BF8AE876363 B45F00/GGOS-Portal/EN/GGOS-Products/GGOS-Products.html– Simulation underway to scope the size and properties of the co-location network– Thirty globally distributed, well positioned, co-location stations with modern technology and proper conditions will be required to define the reference frame that willmeet to requirements;

Report of the International Association of Geodesy 2007-2011 ─ Travaux de l’Association Internationale de Géodésie 2007-2011– Half of these co-location stations must track GNSS satellites with SLR to calibrate
the GNSS orbits;– Dense network of GNSS ground stations to distribute the reference frame globally sothat users anywhere on the Earth may refer their measurements in the reference frame
24 hours a day.
– IAG services continue to upgrade their technologies and expand their networks– SLR: KHz ranging; increased automation, improved electronics;– VLBI: new VLBI 2010 design includes much wiser band width, faster slewing;– GNSS: multiple constellations, more frequencies, SLR retro-reflectors;– DORIS: new ground beacons, additional satellites.
– Co-location network is expanding with the addition of the Yarragadee site, work underway at Metsahovi, and serious discussions underway at several other sites (see Figure 5);– The first version of a GGOS Site Requirements Document for co-located (Fundamental )sites is now available, see: http://cddis.gsfc.nasa.gov/docs/GGOSSiteRequirements_ v1.
pdf– Work continues on intersystem vector measurements at co-located sites with the IERS
WG on Site Survey and Co-location; these vectors are critical for inter-relating themeasurements from the separate techniques;– Call for Participation for participation in the GGOS network has been prepared and isawaiting a decision by the GGOS Steering Committee and the GIAC;– Outreach activities have been underway with talks given at AGU, EGU and AOGS, andvisits with group interested in implementing a Fundamental Stations including groups in
Colombia and Brazil;– Proposal pending at NASA/HQ to support the completion of prototype VLBI 2010 and
SLR systems with a follow-on phase to build and implement a number of units;
Plan– Continue advocating for the establishment of that GGOS Network of Fundamental
Stations; continue the items in process above;– Continue the simulation activities to quantify the anticipated evolution of the reference
frame as a function of phased deployment; systematic errors, additional space objects,
tracking scenarios, GRASP satellite for co-location in space, etc.
– Complete the prototype SLR and VLBI and a prototype new technology Fundamental
Station at GSFC;– Issue the Call for Participation periodically to enhance participation and the establishmentof partnerships to implement Fundamental Stations.
Deliverables
Although this is a task of promoting and advocating, the goal of this task with the help of the
GIAC is:– Implementation of new technologies at the space geodesy ground stations– Additional co-located ground stations to expand global coverageReport of the International Association of Geodesy 2007-2011 ─ Travaux de l’Association Internationale de Géodésie 2007-2011– Improved data quantity and quality for more accurate and stable reference frame andmore accurate orbit determination to support active missions– Improved integrated data products such as the ITRF, sea level, unified global heightmodel, etc.

References
Plag, H-P and Pearlman, M.R., “Global Geodetic Observing System Meeting the equirements of a Global
Society on a Changing Planet in 2020, Springer, XLIV, ISBN: 978-3-642-2686-7, 332 p., 2009

Figure 4: Fundamental Station

Figure 5: Co-located VLBI and SLR Network. Nearly all stations have GNSS and some have DORIS

Report of the International Association of Geodesy 2007-2011 ─ Travaux de l’Association Internationale de Géodésie 2007-2011

Bureau on Conventions and Standards
Chair: U. Hugentobler (Germany)
GGOS WG on Conventions, Models, Analysis
The GGOS WG on Conventions, Models, Analysis (CMA) – the predecessor of the GGOS
Bureau on Conventions and Standards – was led by H. Drewes. Objectives of the WG were toensure the consistency between all (geometric and gravimetric) products by using common
standards, conventions and models in data analysis, parameterisation and representation; toimprove the geodetic algorithms, parameterisation and physical models to the point, where an
overall accuracy and consistency of products better than 1 ppb can be achieved; to stimulate
and coordinate efforts aiming at a combined analysis of all space geodetic observation techniques, integrating all parameters common to more than one space geodetic technique.
An extended form was prepared by the WG in order to review the used constants, conventions, models and parameters used by the IAG Services and Commissions and distributed in2007. The form polled questions on used numerical constants, geodetic conventions, geophysical models, and estimated parameters. Activities included the participation at and contribution to the GGOS Unified Analysis Workshop on December 5-7, 2007, in Monterey, CA.
Activities in 2007 and 2008 focused on the analysis of effects produced by the use of different
conventions and models on the different estimated parameters in the context of GGOS-D, acooperative project supported by the German Federal Ministry of Education and Research
performed by four institutions (Helmholtz-Zentrum Potsdam Deutsches GeoForschungsZentrum, Deutsches Geodätisches Forschungsinstitut, Federal Agency for Cartography andGeodesy, University of Bonn). Further activities were performed in conjunction with research
projects related to mass transports and Earth rotation.
GGOS Bureau on Conventions and Standards
The GGOS Bureau on Conventions and Standards was installed in 2009 – as the successor of
the CMA – after the acceptance of the corresponding proposal submitted by the Forschungsgruppe Satellitengeodäsie (FGS) by the GGOS Steering Committee Meeting in December
2008. The Bureau is jointly operated by Forschungseinrichtung Satellitengeodäsie (FESG)
and Institut für Astronomische und Physikalische Geodäsie (IAPG) of Technische Universität
München, Munich, Germany, and the Deutsches Geodätisches Forschungsinstitut (DGFI),
Munich, Germany. Members of the Bureau were initially U. Hugentobler (Chair), D. Angermann (Secretary), J. Bouman, M. Gerstl, T. Gruber, B. Richter, P. Steigenberger.
Objectives of the Bureau are to keep track of the strict observance of adopted geodetic
standards, standardized units, fundamental physical constants, resolutions and conventions in
the generation of products issued by the IAG Services; to review examine and evaluate
standards, constants, resolutions and conventions adopted by IAG or its components andpropose necessary updates; to identify gaps, inconsistencies, and deficiencies in standards andconventions and to initiate steps to close them; to propose the adoption of new standards andconventions as far as necessary; and to propagate standards and conventions to the wider
scientific community and promote their use.
Actions of the Bureau included the compilation of the relevant resolutions, review of the
IERS Conventions, comments to numerical constants of IERS Conventions 2010, presentations on standards and conventions and activities of the Bureau at the IAG Scientific Assem-

Report of the International Association of Geodesy 2007-2011 ─ Travaux de l’Association Internationale de Géodésie 2007-2011

bly, September 2009, Buenos Aires, Argentina, at the Unified Analysis Workshop 2009,
December 2009 in San Francisco, CA, at the Plenary Meeting of ISO TC211, May 2010, inSouthampton, UK, and at the IAG Commission 1 Symposium Reference Frames for Applications in Geosciences, October 2010 in Paris.
In order to improve balance between Bureau members affiliated to geometric and gravimetricresearch fields and to improve the performance of the Bureau the membership was restructured beginning of 2011. New Chair of the Bureau is D. Angermann, Secretary is T. Gruber.
Additional members are J. Bouman, R. Heinkelmann, U. Hugentobler, L. Sanchez, P. Steigenberger, affiliated are J. Ihde, J. Kusche. First task was the preparation of the section related todata analysis and combination of the GGOS Action Plan. A main goal is the development of a
new geodetic reference system as consistent set of best estimates of geodetic parameters.

Report of the International Association of Geodesy 2007-2011 ─ Travaux de l’Association Internationale de Géodésie 2007-2011

Working Group on Data and Information Systems
Chairs: B. Richter (Germany) and C. Noll (USA)WG Members– Bernd Richter chair / IERS /GGOS portal manager– Carey Noll chair / ILRS
– Guiseppe Bianco /GGOS CO– Ruth Neilan IGS– Laurent Soudarin IDS– Pascal Willis IDS– Dirk Behrend IVS

Geometry– Franz Barthelmes ICGEM– Jean-Pierre Barriot ICET
– Sylvain Bonvalot BGIGravity– Lesley Rickards PSMSL

Sea Level– Felicitas Arias BIPM

Time Service

GGOS Portal
The GGOS portal is thought to provide a unique access point for all data, products and information relevant in the framework of GGOS to serve Earth sciences and applications. Basically, it will provide a platform for services to deliver data, to get and use these data for processing products and to get the products.
GGOS data are classified in three different levels:– L0 level are all raw data,– L1 level are all RINEX files (meta data, receiver, station), and– L2 level and higher are the data and products that are provided by the IAG services)available on the GGOS portal through meta data files on the portal’s data base (timeseries).
Process from L0 to L2 level data: the loose service solution (e.g. IGS, ILRS, IDS, IVS, ...)
undergo a transformation into the current ITRF(combination centre) from the raw data into a
constrained combined solution (time series), which will be the official solution of these data.
The data and metadata of each space technique should be identified through the GGOS portal.
The GGOS Portal basically serves two different kinds of user: data providing user (IAG
services and authorised non-IAG institutions) and data consuming user. Generally any registered user can upload data into the portal. Non-IAG institution’s data and products will be
included into the GGOS Portal only after having successfully passed a review process by theworking group DIS and accepted finally by the GGOS EC. Further, each IAG and non IAG
service has to specify their data by corresponding metadata.

Report of the International Association of Geodesy 2007-2011 ─ Travaux de l’Association Internationale de Géodésie 2007-2011

Web site
The GGOS web site and the GGOS Portal web site will be two independent web sites:– The GGOS web site will provide information about GGOS, the products and backgroundknowledge to interested user.
– The GGOS Portal will be used as a platform to exchange data and products presented
topically ordered (natural hazards, science applications, geodetic applications, satellite
missions, techniques and services).

Figure 6: Service oriented architecture of the GGOS Portal

The GGOS Portal is based on service oriented architecture (see Figure 6). A prototype isready and has been reviewed by the WG DIS and the GGOS EC. The preliminary test versionof the GGOS Portals web presentation can be found under http://observing-systemportal.bkg.bund.de. The GGOS web site and the GGOS portal web site cross linked for reference information and data respectively.
In general, the category “Topics” provides general information to the topics specified. To
provide the information the WG DIS and the GGOS EC has asked several individuals to
detailed information to fill the various fields of interest.

Report of the International Association of Geodesy 2007-2011 ─ Travaux de l’Association Internationale de Géodésie 2007-2011

The category “Discovery” will provide the possibility search for data and products based on
available meta data.
GGOS Portal Meta Data
Three possibilities for the meta data description were discussed in the EG DIS:
– xml file template provided by the portal manager,– a meta data block within the SINEX file, which includes not to distribute the SINEX files
to the user,– meta data editor.
For the GGOS Portal the GeoNetwork is embedded into the GGOS Portal web page as metadata editor. The GeoNetwork (see http://geonetwork-opensource.org/ ) is based on the principles of Free and Open Source Software (FOSS) and International and Open Standards forservices and protocols (a.o. from ISO/TC211 and OGC). The use in numerous Spatial Data
Infrastructure initiatives across the world guaranteed the long-term support. The GeoNetwork
tripod consists of a meta data editor, a search tool and map service interfaces.
The available ISO meta data catalogue has been discussed within the WG DIS and tailored to
the necessary geodetic applications. The used fields to describe the individual data are specified in the document presented at the GGOS / IERS UAW workshop in Monterey, Ca.
http://www.iers.org/nn_10902/IERS/EN/Organization/Workshops/Workshop2007Monterey
Programme.html?__nnn=true#doc74712bodyText4 see Sess. 6“UAW_PosPap_Session_6_GGOS_Portal_and Metadata_Flow_Annexes_1.pdf”. Communication by email discussions and working group meeting on May 2, 2010.

Report of the International Association of Geodesy 2007-2011 ─ Travaux de l’Association Internationale de Géodésie 2007-2011

Working Group on Satellite and Space Missions
Chairs: I. Panet (USA) and R. Pail (Germany)
December 2008 – November 2010
The GGOS Satellite Mission Working Group (SMWG) is established in December 2008,
under the lead of C.K. Shum, and 20 members agreed to serve on this Working Group. An
initial Terms of Reference has been drafted.
In August 2009, international collaborations were discussed with James Jong-Uk Park and hiscolleagues at the Korea Astronomy and Space Science Institute. In August 17–25, C.K. Shummet and discussed with Chinese scientists from Institute of Geodesy and Geophysics, State
Seismology Bureau, Shanghai Astronomical Observatory, Institute of Mechanics/Mathematics, in Urumqi and Beijing, China, on GRACE research and China’s laser interferometry
instrument research and development collaborations. Also their participation in GEO/IAG
Future Gravity Field Mission Workshop, to be held in Graz, September 2009, was discussed.
In September 2009, the Working Group jointly submitted an invited abstract to the IAG Symposia, Geodesy for Planet Earth, IAG, Buenos Aires, August 31– September 4, 2009,http://www.iag2009.com.ar/, Sub-Session 7.1: Past Progress and Future Plans, Session 7, The
Global Geodetic Observing System: Science and Applications (Convenors: Richard Gross,
Hans-Peter Plag, Luiz Paulo Fortes,). The title of the invited paper was: Status and Prospectsof the GGOS Satellite Mission Working Group, by Shum et al.
Several Working Group members participated in a joint GGOS/IGCP565 – IAG – GEO
Workshop “Towards a Roadmap for Future Satellite Gravity Missions”, which was held from
September 30 to October 2, 2009, in Graz, Austria. The workshop aimed at bringing together
stakeholders in satellite gravity missions in order to establish a roadmap for future satellite
gravity missions that outlines the sensor developments, mission concept developments, andmission implementation, and that is consistent with anticipations of the major space agencies,
CEOS, and GEO, and with the needs of key user groups (such as IGWCO, the GEO Water
Tasks, GOOS and GCOS, Earth scientists, and GGOS itself). The outcome of this workshop
is summarized in documents available at http://www.iag-ggos.org/workshops/Graz. It identifies the need for a continuous observation of the time variable gravity field in order to implement an operational observing system for mass redistribution, global change, and natural
hazards.
In the course of the workshop, several informal discussions take place with scientists on international collaborations to advocate GRACE Stop-Gap (defined as “mission to extending thecurrent GRACE observational data span using the current GRACE technology and with thepossibility to host an experimental laser interferometry sensor, to be launched no later than2015”), and GRACE follow-on (the laser interferometry satellite-to-satellite tracking)missions. There were extensive discussions of different country/space agencies launching acoordinated GRACE constellation with multiple pairs of GRACE Stop-Gap and/or follow-on
satellites to mitigate background signal aliasing errors.
In April 2010, a support letter was sent to Johnny Johannessen, NERSC, Isabelle Panet,
Institut Géographique National, Thomas Gruber, and Roland Pail, for their “Earth System
Mass Transport Mission (e.motion)” proposal to ESA’s Earth Explorer Opportunity Mission
under the EE-8-Call. Unfortunately the proposal was not selected to proceed into the next

Report of the International Association of Geodesy 2007-2011 ─ Travaux de l’Association Internationale de Géodésie 2007-2011

phase. The e.motion team composed by a multi-disciplinary science team and an industrial
team working in the area of satellite gravimetry, including members of the Satellite Mission
Working Group, will continue to work together with the goal to define a next generation
gravity field mission.
December 2010 – ongoing
In December 2010, Isabelle Panet and Roland Pail agree to be nominated as the new CoLeads for the GGOS Satellite Missions Working Group.
In a Working Group meeting on April 2, 2011, the objectives and tasks of the SMWG for theupcoming period was extensively discussed, an Action Plan was drafted, and the charter has
been reviewed. The list of members of the Working group is revised, and it is decided toinvite also representatives of space agencies to become members in order to strengthen theseinterfaces.

Report of the International Association of Geodesy 2007-2011 ─ Travaux de l’Association Internationale de Géodésie 2007-2011

Working Group on Outreach
Chair: G. Bianco (Italy)
The GGOS Working Group on Outreach and Education (WGOE) has been approved during
the 11th meeting of the GGOS Steering Committee held on December 2010 in San Francisco,and modified during the GGOS Strategy Retreat held in February 2011 in Zurich. It is chairedby the GGOS Coordinating Office.
The WGOE activity in this initial period has been concentrated on a new edition of a brochurewhich shall describe GGOS’ scope and duties according to the GGOS 2020 book as well as to
the Terms of Reference and other strategic indications.

Report of the International Association of Geodesy 2007-2011 ─ Travaux de l’Association Internationale de Géodésie 2007-2011

Working Group on ITRS Standardization
Chair: C. Boucher (France)
The Working group was established by the GGOS SC14 (San Francisco, December 2008) toinvestigate the interest in and feasibility of an ISO standardization document related to ITRS.
The WG Work Plan identified three major issues:– to identify and get all useful information about existing standardization activities underthe ISO umbrella which are somewhat linked to ITRS. One can also investigate, to someextent, standardization beyond ISO, either international bodies or even national agencies– to define various options to get an ISO document referring to ITRS
– to report to GGOS
Survey of existing standards
Three types of standardization documents has been identified:– documents of the ISO TC 211 “Geographical information-Geomatics” ISO TC 211– Geographical information. Spatial referencing by coordinates (ISO 19111)– documents of the ISO TC 20 “Aircraft and Space Vehicles” ISO TC 20/SC 14– Space systems. Reference coordinate systems– Space systems. Orbit determination and estimation. Process for describing techniques– documents related to the European INSPIRE directive
Options for a standard on ITRS
Various strategies were considered to bring the issue to ISO. The French standardization
agency (AFNOR) performed a feasibility study. France was finally ready to start the process.
Content of the standard
The content of the standardization document related to ITRS was also considered. The proposed content includes general information on terminology, a definition of ITRS and an overview of the multiple realizations, including the primary one (ITRF), the regional densifications such as EUREF and the links with GNSS providers.
The WG submitted its final report to the 18th GGOS SC meeting in Vienna (2010)

Report of the International Association of Geodesy 2007-2011 ─ Travaux de l’Association Internationale de Géodésie 2007-2011

Working Group on Contribution to Earth System Modelling
Chair: M. Thomas (Germany)
PurposeIn December 2010 the new Working Group on “Contributions to Earth System Modelling”
has been established. The main purpose of the WG is to promote the development of a physically consistent numerical Earth system model that is simultaneously be applicable to all geodetic parameters, i.e., Earth rotation, gravity field and deformation, in order to allow homogeneous processing, interpretation, and prediction of these observables. Thus the WG is expected to finally contribute to a deeper understanding of dynamical and complex interacting
processes in the Earth system integrally reflected in geodetic monitoring data.
Motivation
Traditionally, various independent models tailored to specific spatial and temporal scales andto specific dynamical processes in individual sub-systems of the Earth are applied in order toestimate particular contributions to observed variations of geodetic parameters. Although it iswell known that the individual sub-systems are coupled via fluxes of mass, energy andmomentum, these interactions are generally not adequate considered or even neglected, andthe total amount of geophysical excitation is mostly described by a simple linear addition of
the individual contributions. Another deficiency results from the fact that the various estimates are based on different standards and parameters and use diverse analysis strategies andformats.
Thus, in order to ensure physical consistency, in particular mass conservation, and to consider
feedbacks a modular model approach with individual modules representing sub-systems orcomponents interacting through boundary conditions is mandatory.
Goals
The long-term goal is the development of a modular numerical Earth system model for the
homogeneous and physically consistent processing, interpretation and prediction of geodetic
parameters. This implicates the following objectives:– development of a physically consistent modular Earth system model considering the interaction and relationship between surface deformation, Earth rotation and gravity field
variations as well as interactions and physical fluxes between relevant sub-systems;– promotion of homogeneous processing of geodetic monitoring data (de-aliasing, reduction) by process modelling to improve analyses of geodetic parameter sets;– contributions to the interpretation of geodetic parameters derived from different observation techniques by developing model based strategies to separate underlying physicalprocesses;– application of forward modelling and inversion methods in order to predict geodetic
quantities and to invert geodetic observations for the underlying causative processes;– development and implementation of coupling algorithms to ensure consistent interactions
and physical fluxes among sub-systems;

Report of the International Association of Geodesy 2007-2011 ─ Travaux de l’Association Internationale de Géodésie 2007-2011– contributions to the integration of geodetic observations based on different techniques inorder to provide a tool for validation and consistency tests of various geodetic products.
First steps
In the initial phase of the WG the activities are focussing on near-surface fluid dynamics
which dominate short-term variations of geodetic parameters (Figure 7). For the near-surface
modular system model approach a list of appropriate models for the representation of individual sub-systems is being generated and consistent standards, parameters, analysis strategies
and formats for all components of the model approach are being defined. After a constitutive
meeting of the WG, that is planned in 2011 and will be open to non-members also, relevantinteractions among subsystems and appropriate parameterizations, in particular to represent
the dynamic links between near-surface fluids and the “solid” Earth, shall be identified. The
next step will be the development of strategies for the separation of temporal variations ofEarth rotation, gravity and deformation into individual causative physical processes.

Figure 7: The modular 4d Earth system model approach for near-surface dynamics.

Report of the International Association of Geodesy 2007-2011 ─ Travaux de l’Association Internationale de Géodésie 2007-2011

GGOS Coordinating Office
Chair: Giuseppe Bianco (Italy)
The GGOS Coordinating Office (CO) has been established in February, 2010, and is managed
by the Italian Space Agency’s Space Geodesy Centre located in Matera, Italy.
The main activities carried out by the GGOS CO have been:– Enforcing the GGOS secretariat– Managing the GGOS Executive Committee periodic teleconferences;– Managing the GGOS correspondence
Another important activity done by the GGOS CO has been the new edition of the GGOS web
page (www.ggos.org) which has been put on line on March, 2011 (see Figure 8). The web site
will be mostly devoted to organization and documentation aspects.

Figure 8: GGOS web site home pageReport of the International Association of Geodesy 2007-2011 ─ Travaux de l’Association Internationale de Géodésie 2007-2011

GGOS Portal
Chair: Bernd Richter (Germany)
The GGOS portal will provide a unique access point for all data, products and information
relevant in the framework of GGOS to serve Earth science and applications. Basically, it will
provide a platform for services to deliver data, to get and use these data for processing
products and to get these products.
GGOS data are classified in three different levels:– L0 level are all raw data,– L1 level are all RINEX files (meta data, receiver, station), and– L2 level and higher are the data and products that are provided by the IAG services)available on the GGOS portal through metadata files on the portal’s data base (timeseries).
The GGOS Portal basically serves two different kinds of user: the data-providing user (IAG
services and authorised non-IAG institutions) and the data-consuming user. Generally any
registered user can upload data into the portal. Non-IAG institution’s data and products will
be included into the GGOS Portal only after having successfully passed a review process by
the working group DIS and accepted finally by the GGOS EC. Further, each IAG and nonIAG service is required to specify their data by corresponding metadata.
The GGOS Portal will be used as a platform to exchange data and products presented topically ordered (natural hazards, science applications, geodetic applications, satellite missions,
techniques and services).
The GGOS Portal is based on a service-oriented architecture. A prototype is ready and has
been reviewed by the DIS WG and the GGOS EC (see Figure 9). The preliminary test versionof the GGOS Portal web presentation can be found under http://observing-systemportal.bkg.bund.de. The GGOS web site and the GGOS portal web site cross linked for reference information and data respectively.
In general, the category “Topics” provides general information on a selected scientific topic .
To provide the information the WG DIS and the GGOS EC has asked several individuals toprovide detailed information to fill the various fields of interest.
The category “Discovery” will provide a search capability for data and products based on
available metadata.
GGOS Portal Metadata
Three possibilities for the metadata description were discussed in the DIS WG:– xml file template provided by the portal manager,– a metadata block within the SINEX file, which includes not to distribute the SINEX files
to the user,– metadata editor.

Report of the International Association of Geodesy 2007-2011 ─ Travaux de l’Association Internationale de Géodésie 2007-2011

The GeoNetwork is embedded into the GGOS Portal web page as metadata editor (see Figure10). The GeoNetwork (see http://geonetwork-opensource.org/ ) is based on the principles ofFree and Open Source Software (FOSS) and International and Open Standards for services
and protocols (a.o. from ISO/TC211 and OGC). The use in numerous Spatial Data Infrastructure initiatives across the world guaranteed the long-term support. A range of standards is
implemented like metadata standards (ISO19115/ISO19119/ISO19110 following ISO19139,
FGDC and Dublin Core), Catalog interfaces (OGC-CSW2.0.2 ISO profile client and server,
OAI-PMH client and server, GeoRSS server, GEO OpenSearch server, WebDAV harvesting,GeoNetwork to GeoNetwork harvesting support) and Map Services interfaces (OGC-WMS,
WFS, WCS, KML and others) through the embedded GeoServer map server.

Figure 9: GGOS Portal (screen shot main page Topics)

Report of the International Association of Geodesy 2007-2011 ─ Travaux de l’Association Internationale de Géodésie 2007-2011

Figure 10: GeoNetwork page “Advanced search” presently under test not yet implemented

The available ISO metadata catalogue has been discussed within the DIS WG and tailored to
the necessary geodetic applications. The used fields to describe the individual data are specified in the document presented at the GGOS / IERS UAW workshop in Monterey, Ca.
http://www.iers.org/nn_10902/IERS/EN/Organization/Workshops/Workshop2007MontereyProgramme.html?__nnn=true#doc74712bodyText4 see Sess. 6“UAW_PosPap_Session_6_GGOS_Portal_and Metadata_Flow_Annexes_1.pdf”.

Report of the International Association of Geodesy 2007-2011 ─ Travaux de l’Association Internationale de Géodésie 2007-2011

GGOS Science Panel
Chair: Richard Gross (USA)Members
Jonathan Bamber (UK)Anny Cazenave (France)
Athanasios Dermanis (Greece)
Andrea Donnellan (USA)
Roger Haagmans (The Netherlands)
Paul Poli (UK)Matt Rodell (USA)
Reiner Rummel (Germany)
Seth Stein (USA)John Wahr (USA)Victor Zlotnicki (USA)The GGOS Science Panel is a multi-disciplinary group of experts representing the geodetic
and relevant geophysical communities that provides scientific advice to GGOS in order tohelp focus and prioritize its scientific goals. The Chair of the Science Panel is a member of
the GGOS Steering Committee and all members of the Science Panel are invited to participate
in meetings of the GGOS Steering Committee. The Chair of the Science Panel is also a guestof the GGOS Executive Committee and is invited to participate in its meetings and teleconferences. This close working relationship between the Science Panel and the governanceentities of GGOS ensures that the scientific expertise and advice required by GGOS is readily
available.
Activities
Besides participating in GGOS Steering and Executive Committee Meetings, the Science
Panel has been actively promoting the goals of GGOS by helping to organize relevant
sessions at major scientific conferences. GGOS-related sessions have been organized eachyear during 2006–2011 at the General Assemblies of the European Geosciences Union andeach year during 2007–2010 at the Fall Meetings of the American Geophysical Union (AGU).
In addition, a GGOS session was organized at the 2009 Scientific Assembly of the IAG. And
plans have been made to organize sessions relevant to GGOS at the XXV General Assemblyof the IUGG that will be held during 28 June – 7 July 2011 in Melbourne Australia and at the2011 Fall Meeting of the AGU that will be held during 5–9 December 2011 in San Francisco,Calif.
In addition to helping organize sessions at scientific conferences, the GGOS Science Panelalso convenes topical workshops in order to foster discussion about the geodetic observations
and infrastructure required by different scientific disciplines. Two such workshops were convened during 2007–2011:
Understanding Glacial Isostatic Adjustment: A Joint DynaQlim/GGOS Workshop
The Global Geodetic Observing System of the International Association of Geodesy and theInternational Lithosphere Program Regional Co-ordination Committee DynaQlim jointly
organized a workshop on “Understanding Glacial Isostatic Adjustment” that attracted 36
international participants to Espoo, Finland during June 23-26, 2009. The objectives of thisworkshop were to: (1) review the current state of the science in modelling glacial isostatic
adjustment, (2) review the use of geodetic measurements to both constrain and to test GIA
models, (3) identify obstacles to improving GIA models, and (4) identify the improvements toReport of the International Association of Geodesy 2007-2011 ─ Travaux de l’Association Internationale de Géodésie 2007-2011

the global geodetic observing system that are required to advance our understanding of glacialisostatic adjustment. Workshop participants made a number of recommendations regarding
geodetic observations and infrastructure, including those summarized below.
Isolating the GIA signal in geodetic observations is an important prerequisite to advancing ourunderstanding of the GIA process. Workshop participants identified gravity observations fromGRACE as being key in this regard because of its ability to use the differing fingerprints of
GIA and present-day ice mass change to aid in their separation. The continued acquisition oftime variable gravity observations from space was strongly recommended by the workshop
participants.
The BIFROST network in Fennoscandia has demonstrated the importance of regional networks of GNSS receivers, surface gravity instruments, and seismometers (not necessarily
collocated) for understanding the GIA process. Such networks should be established in otherareas of uplift. Measurements from such high-latitude networks can also be used to improve
the terrestrial reference frame (TRF), which is currently stable to only about 1 mm/yr. Since
the GIA-induced motion of the geocentre (the offset of the centre-of-mass of the Earth fromthe centre of the network of observing stations) is estimated to be between 0.1 mm/yr and 1
mm/yr, the stability of the TRF needs to be improved by at least an order of magnitude so that
estimates of this small signal are not corrupted by errors in the reference frame within which
the measurements are being taken.
A summary of the workshop was published in Eos, Transactions of the American GeophysicalUnion [Gross, R., and M. Poutanen, Geodetic observations of glacial isostatic adjustment, Eos
Trans. AGU, 90(41), 365, 2009] and the proceedings of the workshop will be published as a
special issue of the Journal of Physics and Chemistry of the Earth.
Observing and Understanding Earth Rotation: A Joint GGOS/IAU Science Workshop
The Global Geodetic Observing System of the International Association of Geodesy andCommission 19 (Rotation of the Earth) of the International Astronomical Union jointly
organized a workshop on “Observing and Understanding Earth Rotation” that attracted 90
participants from 12 countries to Shanghai, China during October 25-28, 2010. The objectivesof this workshop were to: (1) assess our current ability to observe the Earth’s time varying
rotation, (2) assess our current understanding of the causes of the observed variations, (3)assess the consistency of Earth rotation observations with global gravity and shape observations, (4) explore methods of combining Earth rotation, gravity, and shape observations togain greater understanding of the mass load acting on the surface of the solid Earth, and (5)identify improvements in the global geodetic observing system needed to further our understanding of the Earth’s variable rotation.
Measurements of the Earth’s time varying rotation have been traditionally provided by opticalastrometry and the space-geodetic techniques of satellite and lunar laser ranging (SLR and
LLR), very long baseline interferometry (VLBI), global navigation satellite systems (GNSS)
like the global positioning system (GPS), and Doppler orbitography and radio positioning
integrated by satellite (DORIS). However, the launch of the GRACE twin gravity satellites inMarch 2002 and the densification of the global GNSS ground receiver network afford newopportunities for studying the Earth’s rotation. GRACE is directly observing the effect ofmass redistribution on the Earth’s rotation, and the global network of GNSS ground receivers
can be used to infer changes in the load acting on the Earth’s surface and its effect on the
Earth’s rotation from observations of changes in the Earth’s shape.

Report of the International Association of Geodesy 2007-2011 ─ Travaux de l’Association Internationale de Géodésie 2007-2011

In the future, greater understanding of the processes causing not only the Earth’s rotation but
also its gravity and shape to change will be obtained by integrating Earth rotation, gravity, andshape measurements into a global geodetic observing system. This integration is one of theessential goals of GGOS and this workshop took us one step closer to that goal.
A summary of the workshop was published in Eos, Transactions of the American GeophysicalUnion [Gross, R., H. Schuh, and C.-L. Huang, Spin, wobble, and nutation, Eos Trans. AGU,
92(4), 31, 2011] and the proceedings of the workshop will be published as a special issue of
the Journal of Geodynamics. This special issue will consist not only of papers presented at theworkshop but will also include other contributions on this topic that are submitted in responseto an open call for papers.

Report of the International Association of Geodesy 2007-2011 ─ Travaux de l’Association Internationale de Géodésie 2007-2011

GGOS Themes
Chairs: Michael Sideris (Canada), Tim Dixon (USA) and C.K. Shum (USA)
Overview
The idea to establish GGOS themes goes back to the Workshop on Future Satellite Gravity
Missions in Graz in September 2009, where Reiner Rummel presented his thoughts about
Thematic (Geodetic) Observing Systems. Because of the complexity of the Earth system it
makes sense, instead of working on the entire complex Earth system at once, to first consider
Thematic (Geodetic) Observing Systems (and Models) in order to be able:– to cope with the complexity of the Earth system– to work on an integrated but limited / manageable part of the Earth system– to get an independent control– to generate suitable integrated GGOS products
Examples of such thematic geodetic observing systems are the themes „Ice Mass Balance“,„Continental Water Balance“ or „Sea Level Change“ (see Figure 11).

Figure 11: Example of a Thematic Geodetic Observing System on “Ice Mass Balance” (Thomas, EOS, 2001)

In a second and later step the Thematic (Geodetic) Observing Systems would then beconnected and linked to the Global (Geodetic) Observing System:– as partial systems of global Earth system studies– for Earth rotation studies on global mass balance, where mass and motion have to be
combined– for consistency and quality checks between the Thematic (Geodetic) Observing Systems

Report of the International Association of Geodesy 2007-2011 ─ Travaux de l’Association Internationale de Géodésie 2007-2011

In preparation for the GGOS Retreat in February 2010 in Miami, three thematic (geodetic)
observing systems or integrated products were selected (as a start):– Theme 1: Global Unified Height System (Chairs: M. Sideris, J. Ihde)– Theme 2: Geohazards (global Earth surface deformations and strain rates for geohazards
assessment and disaster prevention) (Chairs: T. Dixon, R. Gross)– Theme 3: Understanding and Forecasting Sea-Level Rise and Variability (Chairs: C.K.
Shum., Phil Woodworth)The progress made since the GGOS Retreat 2010 in Miami is described in the following
sections of this report.

GGOS Theme 1: Unified Global Height System
Chairs: Michael Sideris, Johannes Ihde
The Inter-Commission Project 1.2: Vertical Reference Frames (ICP1.2) is a common projectof IAG Commission 1 and 2 (http://whs.dgfi.badw.de). From beginning of 2010 the activities
of ICP1.2 were integrated in GGOS as Theme 1.
The definition and realization of a World Height System (WHS) is a fundamental requirementof GGOS (Global Geodetic Observing System). In the same way as the ITRS/ITRF provides ahigh precision geometrical reference frame, the WHS shall provide the corresponding highprecision physical reference frame for studying the system Earth.
The results of the work of the ICP1.2 in the first term 2003 – 2007 are documented in Conventions for the Definition and Realization of a Conventional Vertical Reference System(CVRS), Ihde et al. 2007. The main objective for the second term 2007 – 2011 is the initiationof a pilot project for a WHS realization (WHS-PP).
In July 2010 the description of the WHS Pilot Project with a call for information aboutplanned contributions was send out. The deadline for final contributions Survey of WHS-PP
results is May 2011 and the final report will be given at IAG General Assembly 2011.
The four WHS-PP Work Items are:
1. Analysis centres for determining and monitoring the relationship between a conventional W0 and the potential of the Earth gravity field level surface closely coinciding withthe mean sea surface
2. Regional processing centres and global combination centres for GNSS/levelling stations
with coordinate time series in the current ITRF linked to TIGA stations and geo-potential
numbers referred to the RHS at defined epochs
3. Investigations on the accuracy of computing point values Wp of the gravity potential bymeans of high resolution gravity field models and regional densifications of gravity data
4. Operative determination of physical WHS heights in regions with a weak geodetic infrastructure including and development of an information system (registry) providing
relevant data

Report of the International Association of Geodesy 2007-2011 ─ Travaux de l’Association Internationale de Géodésie 2007-2011

At the end of the second term of ICP1.2 and after the work of the various WIs is completed,the ICP1.2 will prepare a final report and recommendations on how to best realize the WHS(including all relevant issues such as the computation and adoption of a "best" W0 value, an
optimal global geoid surface, etc.) This report will be presented at the IAG General Assemblyin Melbourne.
In the future, the work of ICP should continue in the form of a GGOS Integrated Product (i.e.,
Theme 1) for the establishment and maintenance of a WHS. The International Gravity Field
Service (IGFS) should take the leading role there and report directly to GGOS. GGOS has toclarify inconsistencies in the numerical parameters for integrated geodetic applications. Conventions for the definition and realization of the parameters of the MSSL have also to beagreed.

GGOS Theme 2: Geohazards
Chairs: Tim Dixon, Richard Gross
Geodetic measurements have a fundamental role to play in the understanding and mitigationof many natural hazards. Most hazard assessment requires comparing measurements before
and after some event in order to detect a change. Examples include volcano monitoring,coastal subsidence associated with flood hazards, subsidence associated with tunnel construction or excess groundwater/oil extraction, and earthquake co-seismic offsets and post-seismic
activity. While GNSS measurements have been very successfully used to study these andother geohazards, Synthetic Aperture Radar (SAR) is being increasingly used because of its
superior spatial resolution. But whether using GNSS or SAR measurements, the successful
detection of a change on the ground from space requires accurate reference frames, satellite
orbits, atmospheric models, etc. The objective of GGOS Theme 2 on Geohazards is to improve the effectiveness of the geodetic community in geohazard identification, assessment,
prioritization, prediction, warning, and research.
Much progress has been made in the past decade on improving change detection on the
ground from space but more progress is needed. In particular, continued refinement of theaccuracy and stability of the ITRF, improved ultra-rapid GNSS orbits including lower refresh
rates, better clock estimates for precise point positioning, better atmospheric models, lower
latency ultra-precise SAR orbits, and better regional coverage of InSAR images are allneeded. GGOS can play a very effective role in advocating for the improvement in geodetic
infrastructure and data analysis needed for geohazards applications, not only by itself but also
by working with other groups such as the GEO Supersites Initiative.
The Geohazard Supersites is a GEO initiative to better understand the geophysical processes
causing geohazards <http://supersites.earthobservations.org>. It consists of a global partnership of scientists and satellite and in situ data providers (multi-sensor InSAR, seismic, andGNSS) having the goal of supporting national authorities and policy makers in risk assessment and mitigation strategies. A closer working relationship between GGOS and the GEO
Supersites Initiative would aid Theme 2 in meeting its objective.

Report of the International Association of Geodesy 2007-2011 ─ Travaux de l’Association Internationale de Géodésie 2007-2011

GGOS Theme 3: Understanding and Forecasting Sea-Level Rise and Variability
Chairs: C.K. Shum, Phil WoodworthThis activity was initiated primarily as a demonstration Theme to show the value of geodesy,and GGOS in particular, to a high-profile area of science and applications. Sea level is anyway an important geodetic quantity (traditionally being the basis of the geodetic datums ofmany countries), but it is also of great scientific and public interest, especially with regard topotential sea-level rise, local land motion, and flooding of coastal environments and infrastructures.
The Theme is managed by a group of scientists comprising Philip Woodworth, C.K. Shum,
Tilo Schöne, Mark Tamisiea and Per Knudsen. At its outset, it set itself three broad topics ofactivity:
1. Identification of the requirements for a proper understanding of global and regional/local
sea-level rise and variability, and the associated land motion, especially in so far as they
relate to geodetic monitoring provided by the GGOS infrastructure, and their current links
to external organizations (e.g. GEO).
2. Identification of the organizations or individuals who can take forward each requirement,or act as points of contact for each requirement where they are primarily the responsibilityof bodies not related to GGOS.
3. Identification of a preliminary set of practical (as opposed to scientific) pilot projects,
which will demonstrate the viability, and the importance of geodetic measurements tomitigation of sea-level rise at a local or regional level. This identification will be followedby construction of proposals for pilot projects and their undertaking.
These topics are described in detail in the Theme Action Plan (latest version dated 6 April2011). Although some thoughts are expressed in the Action Plan on how to take forward thefirst two topics, in practice progress has been made only in organizing the third topic.
This topic is based on a proposal by H-P Plag two years ago. It is concerned with the forecasting of sea-level change over various timescales, focussing on the sea-level rise to be expected in the medium term (e.g. less than 30 years) at major cities and population centres for
input to coastal defence planning. Such projects would be of considerably greater utility toplanners than the 2100 projections provided by IPCC Assessments, for example, a timescaleof 30 years being long enough for many civil engineering schemes to be undertaken.
Our feeling is that such demonstration activities could benefit from previous experience withprojects such as the Thames Estuary 2100 study for London and similar studies in the Netherlands, Denmark, US Pacific and Atlantic coasts etc. Potential areas for further study might
include Manila, Bangkok, Shanghai, Djakarta, Lagos and other large Asian and African cities
for which submergence (natural or anthropogenic) and/or storm surge risk of flooding are
major considerations, or countries such as Bangladesh or Egypt which include large deltas
where high rates of sea level rise are a natural phenomenon to be lived with. (A relevant
reference here is to the ‘Cities at Risk’ international activities, start.org/programs/cities-atrisk.)
Our plan is to issue a Call for Proposed Projects under this action by the middle of 2011,
which will require (geodetically) integrated approaches to studies of sea level change on 30
year (forecast) timescales. The projects will be publicised through GGOS using a standard

Report of the International Association of Geodesy 2007-2011 ─ Travaux de l’Association Internationale de Géodésie 2007-2011

format and will be open to both, existing or past projects as well as to new ones, the latter
benefitting potentially from support from GGOS in their search for funding. The value of
including existing or past projects is that they can be used immediately to demonstrate thevalue of the action.

Report of the International Association of Geodesy 2007-2011 ─ Travaux de l’Association Internationale de Géodésie 2007-2011

GGOS in the Group on Earth Observation (GEO)
Representative to the Plenary: Markus Rothacher (delegation head), Ruth Neilan, Susanna
Zerbini (Science and Technology Committee), Bernd Richter (Architecture and Data Committee)
Overview
GGOS, representing the IAG within GEO, has been actively involved in GEO since the IAG
became a participating organization of GEO in 2005. The main contributions made by the
GGOS representatives are– GGOS tasks within the GEO Work Plan 2007-2011– Participation in GEO Committees and Working Groups– Participation in the GEO Plenary Meetings and Ministerial Summits
This work is especially important, because it makes GGOS much more visible to the outside
world and leads to contacts to all major international organizations in the field of Global Erath
Observation.
Main tasks within GEO Work Plan 2007-2011
Based on an initiative of H.P. Plag GGOS is presently contributing with two major tasks to
the GEO Work Plan 2007-2011 and is involved in a third:
DA-09-02: Data Integration and Analysis. Subtask DA-09-02c: Global Geodetic Reference
Frames. Task leader from IAG/GGOS is Zuheir Altamimi. Before March 2010 it
was H.P. Plag.
AR-09-03: Advocating for Sustained Observing Systems. Subtask AR-09-03e: Global Geodetic Observing System (GGOS). Task leader Mike. Pearlman.
ST-09-02: Promoting Awareness and Benefits of GEO in the Science and Technology
Community. Susanna Zerbini is the representative of GGOS here.
These tasks will also be continued in the GEO Work Plan 2011-2015. More details may befound below.
GEO Committees and Working Groups
The participation of GGOS in a number of GEO Committees and Working Groups from2007-2011 is summarized in Table 5. Major efforts were done in the GEO Science and Technology Committee , the GEO Architecture and Data Committee and the GEO User Interface
Committee. More details are given below. GGOS was also represented in the GEO Working
Group on Tsunami during its rather short existence.

Report of the International Association of Geodesy 2007-2011 ─ Travaux de l’Association Internationale de Géodésie 2007-2011

Table 5: Representatives of GGOS in GEO Committees and Working Groups
PeriodGEO Committee / WG

Representatives

2007-2010

GEO Science and Technology Committee

S. Zerbini, M. Pearlman, M. Rothacher

2007-2010

GEO Architecture and Data Committee

B. Richter, C. Noll, R. Neilan, H.P. Plag

2007-2010

GEO User Interface Committee

H.-P. Plag, C.K. Shum, C. Boucher

2007-2010

GEO Capacity Building and Outreach Committee

C. Rizos, H. Drewes, L. Combrinck

2007-2010

GEO WG on Tsunami Activities

H.-P. Plag, T. Schöne

2010-…

GEO Science and Technology Committee

S. Zerbini, R. Gross

2010-…

GEO Architecture and Data Committee

B. Richter, C. Noll

2010-…

GEO User Interface Committee

J. Park, C. Rizos

2010-…

GEO Capacity Building and Outreach Committee

M. Pearlman, R. Neilan, L. Combrinck

GEO Plenaries and Ministerial Summits
During the period from 2007 to 2011 the GGOS representatives participated in all the GEO
Plenary and Ministerial Summits. Table 6 lists these GEO events and the activities of GGOS
during these events. The main emphasis was on getting contacts and connections to UN
organizations and other international bodies and to promote GGOS within GEO. A GGOS
booth was realized and a considerable amount of outreach material (leaflets, posters,brochures, 1-page stories, …) and used at many of the GEO Plenaries.
Table 6: GEO Plenary Meetings and Ministerial Summits from 2007-2011
GEO Event

GGOS Activities

GGOS Participants

GEO Plenary IV and Ministerial GGOS booth set up with the help of GFZ and R.
Summit, Cape Town, South
Wonnacott. Many contacts to international organiAfrica, Nov. 2007
zations to promote GGOS

M. Rothacher, R.
Neilan, H.P. Plag

GEO Plenary V, Bucharest,
Romania, Nov. 2008

GGOS booth set up with the help of GFZ and R.
Wonnacott. Many important contacts to UN
organizations

M. Rothacher, H.P.
Plag

GEO Plenary VI, Washington
DC, USA, Nov. 2009

GGOS booth, GGOS outreach material, flyers,
videos; contacts to international organizations

M. Rothacher, H.P.
Plag, R. Neilan, M.
Pearlman, S. Zerbini

GEO Plenary VII and Ministerial Summit, Beijing, China,
Nov. 2010

Official statement of GGOS in Min.Summit,
GGOS booth, contacts with many internationalorganizations

M. Rothacher, R.
Neilan, C. Rizos, S.
ZerbiniReport of the International Association of Geodesy 2007-2011 ─ Travaux de l’Association Internationale de Géodésie 2007-2011

GEO Science and Technology Committee
Main Representative: Susanna Zerbini
The GEO Science and Technology Committee (STC) was established in 2006 and since thenmet 16 times in different locations all around the world. Susanna Zerbini, representing
IAG/GGOS, participated to most of these meetings and provided an active contribution to thedevelopment of the STC activities. Detailed information on the meeting outcomes is available
at http://www.earthobservations.org/com_stc_me.shtml.
The STC engages the scientific and technological communities in the development, implementation and use of a sustained Global Earth Observation System of Systems (GEOSS) in
order to ensure that GEO has access to sound scientific and technological advice. Objectivesof the STC are:– Enable GEO to make decisions on best available and sound scientific and technologicaladvice, through the solicitation of input from a broad, trans-disciplinary scientific andtechnological community– Ensure scientific and technological integrity and soundness of GEO Annual Work Plans.
– Monitor and review output and deliverables of GEO Annual Work Plans.
– In collaboration with GEO Members and participating organizations, and through trans-parent processes, identify individual experts and groups to participate in GEO working
groups.
– Facilitate linkages and partnership with major relevant international research programs aswell as organizations willing to contribute to GEO activities.
During the reporting period, the STC was engaged in several different activities.
The Role of Science and Technology in GEOSS
A document was prepared which describes the “Role of Science and Technology in GEOSS”.
It was published in 2008 and it can be downloaded from http://ec.europa.eu/research/ environment/pdf/geoss.pdf. This document describes the role of science and technology in advancing
the GEOSS through the GEO 2007-2009 Work Plan. The STC is working to strengthen thisrole by encouraging the wider scientific and technology community to participate as contributors to and benefactors of a sustained GEOSS.
STC is responsible for and/or overlooking several GEO tasks. IAG/GGOS contributes to oneof them: ST-09-02.
TASK-ST-09-02 Title: Promoting Awareness and Benefits of GEO in the Science and Technology Community.
The task definition is: Promoting awareness and benefits of GEOSS in the scientific and technological communities in order to engage the research community in GEO and GEOSS withthe goal to achieve breakthroughs in the understanding of the Earth’s changing environmentand global integrated Earth system. The scientific community should collaborate within GEO
to address interactions between the components of the global integrated Earth system, andconnect natural and socioeconomic sciences.

Report of the International Association of Geodesy 2007-2011 ─ Travaux de l’Association Internationale de Géodésie 2007-2011

Activities include: (i) form links with major scientific research enterprises in each societal
benefit area; (ii) actively encourage relevant scientists and technical experts to contribute to
GEOSS in a truly participatory way; (iii) reach out to the world’s diverse scientific and technological communities and make GEOSS more visible and attractive to them; (iv) contact
universities and laboratories to involve them in GEOSS activities; and (v) organize a GEO
presence at major symposia and other meetings, for example through plenary presentations orside events.
IAG/GGOS is actively engaged in several of the above mentioned activities, in particular, as
regards activities from (ii) to (v).
Following the GEO-V Plenary (November 2008), the STC took action to develop a STC
roadmap. This roadmap was finalized in early 2009 and subsequently approved by the STC. It
can be downloaded from http://www.earthobservations.org/documents/committees/stc/stc_
roadmap_20091202.pdf.
The status of the roadmap is being checked during the STC meetings
Roadmap
This roadmap identifies and motivates the path that the STC of the GEO has decided topursue to achieve its objectives. It primarily addresses the Committees of GEO, its Task
Teams, working groups and Communities of Practise. It also addresses the Science and Technology (S&T) communities within the scope of the Societal Benefit Areas of the GEOSS andthe S&T communities needed to build, deploy, access and sustain the GEOSS.
Gap Analysis Strategy
The GEO Executive Committee (ExCom), during its 19th meeting, recognized that the GEO
community needed an overall strategy for analysis of observational and structural gaps. This
lead to an Action (19.11) which involves the STC, the Monitoring and Evaluation Working
Group and other interested members of the GEO Community to draft an initial outline of aprocess that can eventually lead to a coherent overall mechanism being put in place forrequired GEO/GEOSS gap analyses.

GEO Architecture and Data Committee
Main Representative: Bernd Richter
The Architecture and Data Committee (ADC) supports GEO in all architecture and data
management aspects of the design, coordination, and implementation of the Global Earth
Observation System of Systems (GEOSS) for comprehensive, coordinated, and sustained
Earth observations.
During the time span the GEOSS Common Infrastructure had been implemented. Startingwith three Web-Portals and three clearinghouses benchmark tests and reviews lead to one
Web-Portal hosted by ESA and one clearinghouse set up by USGS. Also necessary
recommendations for standards and interoperability in GEOSS have been developed as wellas the data sharing principles.

Report of the International Association of Geodesy 2007-2011 ─ Travaux de l’Association Internationale de Géodésie 2007-2011

GGOS contributed to the GEO work plan by two tasks supporting an integrated GEOSS under
the guidance of the Architecture and Data Committee.
AR-09-03: Advocating for Sustained Observing Systems / Subtask: e) Global Geodetic
Observing System (GGOS)
This sub-task is led by IAG (mpearlman@cfa.harvard.edu)
Promote the further development of sustained infrastructure needed to satisfy the long-term(10-20 years) requirements for the reference frames and the monitoring of global change
signals. GGOS provides observations of variations in Earth shape, gravity field and rotation,
which are fundamental for monitoring of climate and global change. GGOS observations
contribute to at least seven of the SBAs. Moreover, with the global geodetic reference frames(International Terrestrial Reference Frame (ITRF) and International Celestial Reference
Frame), GGOS provide the foundation for most Earth observations. Among other components, geodetic monitoring of global change crucially depends on globally sustained geodetic ground networks.
DA-09-02: Data Integration and Analysis / Subtask: c) Global Geodetic Reference FramesThis sub-task is led by IAG (zuheir.altamimi@ensg.ign.fr)
Ensure the availability of accurate, homogeneous, long-term, stable, global geodetic reference
frames as a mandatory framework and the metrological basis for Earth observation. Identify
steps towards such consistent high-accuracy global geodetic reference frames for Earth observation and the observing systems contributing to GEOSS. Promote the use of common orinteroperable reference frames within GEOSS.

GEO User Interface Committee
A very substantial amount of work in the GEO User Interface Committee (UIC) (as well as inother GEO committees) was done by Hans-Peter Plag. He was the main representative of
GGOS in this committee until March 2010.

GEO Capacity Building Committee
Since March 2010 GGOS is also involved in the GEO Capacity Building Committee. The
main representatives are Mike Pearlman and Ruth Neilan.