by Gerhard Beutler, IAG President

 

IAG Scientific Assemblies take place at four-year intervals, midway between the IAG/IUGG General Assemblies. The IAG held its Scientific Assembly in 2005 in Cairns, Australia, midway between the General Assemblies in Sapporo in 2003 and in Perugia 2007. It had the general title Dynamic Planet 2005. The conference attracted more than 750 scientists from all over the world. 60 countries were represented.

The Cairns Scientific Assembly was a joint assembly of IAG, IAPSO (International Association for the Physical Sciences of the Ocean), and IABO (International Association for Biological Oceanography). We all know that IAG is the scientific organisation in the field of geodesy, promoting scientific cooperation and research in geodesy on a global scale and contributing to it through its various research activities. IAPSO has the prime goal of promoting the study of scientific problems relating to the oceans and the interactions taking places at the sea floor, coastal, and atmospheric boundaries. IABO has the objective to promote the advancement of knowledge of the biology of the sea.

From this description of IAG, IAPSO, and IABO (taken from the conference’s homepage) it is clear that strong links between IAG and IAPSO must exist. This is reinforced by the fact that there were three joint IAG/IAPSO sessions in Cairns, namely on ocean circulation and the contributions from the new gravity field missions, on global sea-level change (altimetry, GNSS, and tide gauge measure­ments), and on oceanography and geodesy in polar regions. Needless to point out that the three topics are of primary interest to geodesy.

These joint symposia were accompanied by eight “pure” IAG symposia on frontiers in the analysis of space geodetic measurements, on gravity field determination, on Earth processes, on advances in the realization of global and regional reference frame, on GGOS (Global Geodetic Observing System), on the geodesy of the planets, on systems and methods for airborne mapping, on geophysics and hazards and disaster monitoring, and, last but not least, on atmospheric studies using space geodetic techniques.

Each session contained oral and poster presentations. It must have been difficult for the scientific program committee to make a proper selection. Viewed from my perspective, there was no difference in quality between posters and oral presentations – the poster sessions had the advantage that drinks were served and a direct contact with the authors was easily established. We are indepted to the scientific organizing committee chaired by Paul Tregoning of the Local Organizing Committee, and by Michael Sideris for the IAG liaison.

As many events took place in parallel, and as there also was administrative work to be handled on top of the scientific program, it was impossible for an individual to get a comprehensive overview of the conference. From what I could see the quality of the vast majority of the papers was outstanding, and they gave an excellent picture of the developments in the fields covered.

Knowing that this is somewhat unfair, I cannot resist the temptation to make a few very personal comments based on that part of the program I could follow or was involved in.

From the IAG side the assembly truly was a joint assembly. I had the impression that there are not only strong links between geodesy and oceanography, but that an interdisciplinary field is being established. This is undoubtedly thanks to the gravity missions with their strong oceanographic component. This is of course the IAG interpretation. The IAPSO president might as well say that this is undoubtedly thanks to the oceanography missions, which have a strong geodetic component. We know of course that the former interpretation is the correct one …

The interest in the session on advances in the realization of global and regional reference frame was as a matter of fact so great that there was not enough room in the auditorium – the only case where one might speak of a logistics problem. The interest also indicates that the geodetic contribution to Earth sciences is viewed as an extremely important component of the IAG work. The progress made was only possible thanks to the excellent work of the IAG services (in particular the IERS, IGS, IVS, ILR, and IDS), and commissions 1 and 4.

Originating from celestial mechanics, I was of course very much impressed by the results coming out of the gravity missions CHAMP and GRACE. Many, if not most, results are interdisciplinary in nature: Who would, for example, have believed twenty years ago that we would be able to make statements about the global water circulation by analysing gravity signals?

I also became aware of problems related to the GRACE mission (e.g., in the IAG session on frontiers in the analysis of space geodetic measurements). Right now, it is not fully understood why the accuracy of results considerably lags behind theoretical expectations. According to my understanding the reasons are currently sought in the field of separating the observed signal into its physical sources.

When attending the session on gravity field determination I was (again due to my background in celestial mechanics) amazed by the multitude of methods developed to determine the Earth’s gravity field from space missions. From the celestial mechanics point of view there is “of course” one and only one correct method, and this is the “head through the wall method”, which models the observations (GPS phases, K-band measurements between satellites, accelerometer measurements) directly by the parameters describing the force field acting on the satellite. From the fact that more “artistic” methods (based on the energy integral or the Jacobi integral, on the reconstruction of the potential, on first and second derivatives of kinematically determined trajectories) are very successful, currently, one might be allowed to conclude that the celestial mechanics modelling part is not yet fully under control. These thoughts may also raise the question as to whether the conclusions in the previous sentence are completely correct!

This brings me to the activities and session on GGOS, IAG’s project on the establishment of the Global Geodetic Observing System. A milestone was reached at the Cairns symposium:

• From 2003 to 2005 the GGOS Project was in its definition phase. It was chaired by Prof. Christopher Reigber from the GeoForschungsZentrum in Potsdam, and Prof. Hermann Drewes from DGFI (German Geodetic Research Institute) in Munich was the secretary of the Project.
• The work of the group is contained in a 26 page document called “GGOS: Implementation Plan”. It covers the GGOS objectives, science rationale, the status of GGOS in 2005, including its links to GEO and GGOS, and makes proposals for the future developments of GGOS. The report was accepted by the IAG Executive as a working document, on which the further development of GGOS should be based.
• In the time period 2003-2005 the GGOS Project, which was based on IUGG resolution No. 3 of the IUGG General Assembly 2003 in Sapporo (see Geodesist’s Handbook 2004, p. 700), could be established within the Group on Earth Observation (GEO). IAG, represented by GGOS, became a participating organization in GEO and was rather active developing the GEOSS (Global Earth Observation System of Systems) and the implementation plan associated with it.
• Furthermore, strong links were established with IGOS (Integrated Global Observing Strategy) working under the auspices of UNESCO. It is planned to firmly relate GGOS to IGOS-P through a three-step procedure in the near future:
• 1. GGOS shall become a member of IGOS-P as a new Global Observing System;
  2. GGOS shall establish links to the existing IGOS-P Themes, allowing GGOS to influence the development of the different theme-specific strategies, and to determine the way in which GGOS can best serve the observing systems implemented under these strategies;
  3. GGOS shall, together with relevant members of IGOS-P, develop the Earth System Dynamics Theme further and prepare a proposal for consideration by the IGOS-P members.

·         Due to the retirement of Prof. Christoph Reigber as Director of GFZ, Department 1, a new leadership had to be found for GGOS. At the IAG Executive committee, Prof. Markus Rothacher was appointed Chair of the GGOS Project, and Ruth Neilan (Director, IGS Central Bureau) and Prof. Hans-Peter Plag (University of Reno) as Vice-Chairs of the Project. The Executive Committee thanked Proffs. Reigber and Drewes for their work over the period 2003-2005, and wished the new team all the best for the upcoming implementation phase.

Let me mention two other important issues. Based on an initiative by Dr. Wolfgang Bosch, chair of the inter-commission project on Satellite Altimetry, the IAG Executive Committee adopted the following resolution:

On the occasion of the Dynamic Planet 2005 conference in Cairns, Australia, the International Association of Geodesy, IAG, and the International Association of the Physical Science of the Ocean, IAPSO, both recognize satellite altimetry as an important space technique with interdisciplinary application in oceanography, geodesy, hydrology, and glaciology, demonstrating that satellite altimetry has to be an essential component of any global observing system such as GOOS, GGOS.

•IAG and IAPSO also recognize the necessity to set up and maintain the longest possible time series of altimeter observations with up-to-date geophysical corrections and consolidated geocentric reference, which implies a close attention to the long-term stability of altimeter and ancillary sensors.

•IAG and IAPSO therefore recommend to establish a mission-independent International Altimeter Service with the primary objective to serve operational and scientific users with altimeter data and value-added products, to coordinate and cooperate with space agencies, processing centres, and scientific laboratories, and other existing services.

We hope that IAPSO will come up soon with a similar resolution.

The existing good relationships between FIG (Fédération Internationale des Géomètres) were underlined by the further development of the document Liaison between the International Federation of Surveyors (FIG) and the International Association of Geodesy (IAG). We owe thanks to Matt Higgins of the FIG for the draft of the document. It was discussed at a splinter meeting in Cairns. The document is based on an MoU between IAG and FIG signed in 2000, and attempts to formulate concrete common fields of interest and common activities. The IAG entities are invited to contribute to the document. Once screened, it will be made publicly available.

The IAG Assembly, 22-26 August 2005, in Cairns, Australia was a full success. This was, to a large extent, due to the hard work of the Local Organizing Committee, which was chaired by Prof. Chris Rizos, president of the IAG Commission 4, and his team. Not only the scientific program, but also the social program, the barrier reef, and the cordial hospitality of our hosts will be remembered for a long time. Thanks to everybody for making the IAG Scientific Assembly 2005 a success!

 

Gerhard Beutler

IAG President