Report of International Association of Geodesy Section II: Advanced Space Technology for the period 1995-1999
Objectives of Section II
Section II, Advanced Space Technology, is engaged in new space techniques for geodesy and geodynamics. Its objectives are to anticipate and promote their implementation into geodetic/geodynamic work and, in general, support and coordinate the optimal use of modern space technology for the benefit of geodesy.
During the past four years the activities of the section include:
- Promotion of the realisation of space experiments for the improvement of our knowledge of the Earth's gravity field in the medium spatial wavelengths.
- Improvement of the coordination and combined use of the full range of geodetic space techniques, such us SLR, VLBI, GPS, DORIS, PRARE.
- Continuation of the successful work of WEGENER with a broadened, new scope.
- Stimulation of the geodetic use of interferometric SAR and of spaceborne sounding with global satellite navigation systems.
- Development of concepts on how to come to an optimal world wide distribution of geodetic/geophysical fundamental stations.
- Continuation and further improvement of the work of I.G.S.
The structure of the section was as follows:
Commission VIII: International Coordination of Space Techniques for Geodesy and Geodynamics (CSTG)
President: G.Beutler (Switzerland)
Secretary: H.Drewes (Germany)
SC 6: Wegener Project
President: S. Zerbini (Italy)
SC 7: Gravity Field Determination by Satellite Gravity Gradiometry
President: K.-H. Ilk (Germany)
Special Study Groups:
SSG 2.160: SAR Interferometry Technology
Chairman: R. Klees (The Netherlands)
SSG 2.161: Spaceborne Atmospheric GNS Soundings
Chairman: C. Rocken (USA)
SSG 2.162: Precise Orbits using Multiple Space Techniques
Chairman: A. Marshall (USA)/ R.Scharroo (The Netherlands)
International GPS Service (IGS)
Chairman of the Governing Board: G. Beutler (Switzerland)
Director of the Central Bureau: R.E. Neilan (USA)
Achievements and Prospects
Again we can look back to four very active years in space geodesy in general and section II work in particular. Finally, after many years of pushing and pressing, dedicated gravity satellite missions will come. The first one will be the German CHAMP mission that will be launched in early 2000. It will combine SST-hl and accelerometry. It will be followed by the US-German GRACE mission, to be launched in 2001, which is a low-low satellite to satellite tracking mission. The ESA gravity gradiometry mission GOCE is currently studied in parallel with three other Earth research missions. Two of them will be selected in fall 1999. It is of great advantage that the three experiments are complementary to each other in terms of determining the static and time variable gravity field . They will have an enormous impact on space geodesy and geodesy in general and they will bring geodesy even closer to all other disciplines of Earth sciences. It is equally important that with the approved missions ENVISAT and JASON the continuation of ocean altimetry is certain for the years to come. In addition, geodesy will benefit from the ice altimetry missions ICESAT and CRYOSAT. All of this will have an important impact on ocean, ice, geodynamic and sea level research. Decisions on GPS follow-on and add-on systems and on the future of GLONASS will be taken in the near future and will also affect their geodetic use. Geodetic observation techniques, such as laser ranging, VLBI, GPS, DORIS etc., and data analysis techniques are still improving with the focus being on precision, reliability, real-time capability and automation.
Geodetic space techniques serve (1) the realization of a global terrestrial reference system, (2) geodetic positioning and deformation measurement, (3) Earth rotation determination and (4) gravity field determination. The attained precision suggests to combine these four fields of application to one integrated observing and monitoring system. A precondition for this is, however, a better insight into the individual role of the various techniques as well as into their strengths and weaknesses. Progress in this direction is slow. The above idea of an integrated geodetic/geodynamic observing system has been chosen as theme for the section II symposium. It was held in Munich from 5 to 9 October 1998.
About the activities of the bodies of Section II , i.e. the special study groups, special commissions, CSTG and IGS it is referred to the respective chapters of this report. IGS has taken several new initiatives such as orbit analysis with the GLONASS satellites, real time orbit computation, GPS tracking of low orbiters and atmospheric sounding. All its work is very successful. The two questions of the future will be, whether IGS in its present form will be able to cope with its ever increasing range of services and, if in the near future atmospheric sounding will be used by weather services, i.e. commercially, whether routine real time orbit provision and data analysis would fit to IGS by-laws in their present form. In view of the success of IGS, CSTG decided to establish two new services: the International Laser Ranging Service (ILRS) and the International VLBI Service (IVS). It will be interesting to watch the development of these two services in view of the fact that their user communities are very different from that of the IGS. WEGENER continued its transition from a geodynamic laser tracking network, it once used to be, to an integrated regional geodynamic observing system. A recent special issue in Tectonophysics (294, 3-6, 173-347) provides an impressive picture of its current work.
One of the topics of the Munich symposium was the current structure of IAG and the need to modify it. It is felt that IAG should thoroughly review its current structure and take provisions for changes. Several facts have triggered this discussion: (1) Nowadays the major international research programs in Earth sciences are organized independent and outside of IAG and even IUGG. Should IAG define its own scientific programme? (2) Geodesy provides extremely valuable data for Earth sciences. However, this is more or less taken for granted by the other disciplines; it is not associated with IAG. (3) Space techniques have penetrated all geodetic fields, therefore it seems not warranted to "concentrate" them in one section. (4) The services, one of the most successful of IAG’s activities, are somewhere, almost invisibly, hidden in the structure. (5) Finally, it is important to think of the young generation, how one can attract young brilliant scientists to IAG and what IAG can offer to them. Section II proposed therefore to discuss this topic in Birmingham and at a special retreat of the IAG Executive Committee.