1. Introduction

 A new structure was given to the Commission VIII CSTG during the 35th IUGG General Assembly in Birmingham, UK, July 1999. The new president elected at this assembly is Hermann Drewes, and there were installed five subcommissions and one project:

-    Subcommission on the International Space Geodetic Network (ISGN),

Chair: John Bosworth

-    Subcommission on the Coordination and Combination of the Analysis in Space Geodesy,

Chair: Tom Herring

-    Subcommission on Precise Satellite Microwave Systems,

Chair: Pascal Willis

-    Subcommission on Multi-Mission Satellite Altimetry (SCOMMSA),

Chair: Wolfgang Bosch

-    Subcommission on Precise Orbit Determination for Low Earth Orbiting Satellites (POD/LEO),

Chair: Markus Rothacher

-    Project on Doris,

Chair: Gilles Tavernier


Besides of the subcommission and project chairmen, there are also four IAG Services and the ICSU Commission on Space Research represented in the CSTG Executive Committee:

-    International Earth Rotation Service (IERS), Representative: Claude Boucher

-    International GPS Service (IGS), Representative: Ruth Neilan

-    International Laser Ranging Service (ILRS), Representative: John Degnan

-    International VLBI Service for Geodesy and Astrometry (IVS), Representative: Wolfgang Schlüter

-    ICSU Commission on Space Research (COSPAR), Liaison: John Dow

Furthermore, the past president, Gerhard Beutler, is a member of the CSTG Executive Committee.


2. Activities of the Commission

 The CSTG Executive Committee met three times after its constituting meeting in Birmingham, namely in San Francisco, December 1999, in Warsaw, July 2000 and in Nice, March 2001. We’ll give just the most important highlight of each meeting:

The main topics at the San Francisco meeting were the setup and detailed discussions of the terms of reference of the subcommissions. Emphasis was laid on the cooperation of the CSTG subcommissions and other IAG entities, in particular the Special Study Groups (SSG) and Working Groups of the Services.

During the Warsaw meeting, there was a fundamental discussion on the relationship to COSPAR, in particular to its Panel on Satellite Dynamics (PSD). A variety of mutual interests of CSTG and PSD were seen which should be focussed on in the future work.

In Nice, there was an important topic on the role of CSTG in view of the new structure of IERS, in particular with respect to the CSTG Subcommission on Coordination and Combination of the Analysis in Space Geodesy. This subcommission coincides very much with the new IERS Combination Research Centers and the IERS Analysis Coordinator. A close cooperation and clear separation of the objectives was discussed.

The commission CSTG organized one joint symposium on "New Trends in Space Geodesy" together with POD during the 33rd Scientific Assembly of COSPAR in Warsaw, July 2000. More than 70 contributions (oral and poster) were presented in six thematic sessions during three complete days. The proceedings of this symposium will be published in the reviewed journal "Advances in Space Research".

Two CSTG Bulletins, No. 15 (80 pages) and No. 16 (86 pages), were edited in 1999 and 2000, another one is in preparation (2001). The Bulletins include reports of the subcommissions and services as well as individual contributions. More than 400 copies are printed and distributed of each edition of the CSTG Bulletins.


3. Activities of the Subcommissions

 3.1 Subcommission on the International Space Geodetic Network (ISGN)

The ISGN seeks to carry on the role of the GGSS in setting standards, documenting and disseminating best practice site criteria for all space geodetic sites. Of great importance in this work are the local survey ties between various techniques. In addition, the ISGN, working with the international space geodesy services, seeks to recognize and certify a "super-set" of multi-technique space geodesy sites that meet a set of rigorous criteria for the purpose of enhancing their long-term sustainability. These sites are and would continue to provide a wealth of high quality data for comparison of techniques, combined solutions and the underpinning for the International Terrestrial Reference Frame and the International Celestial Reference Frame.

The ISGN Chair has developed the following near term activities for the subcommission:

-    The ISGN Criteria document has been approved and will be distributed to all potential ISGN sites. A draft charter for the ISGN is being prepared.

-    The first set of candidate sites, meeting the ISGN criteria, has been selected. Letters of invitation to become part of the ISGN will be signed by the ISGN and CSTG chairs and sent to the organizations responsible for the certified candidate sites.

-    Letters to other potential space geodetic sites that are deficient in some areas of the ISGN Criteria will be prepared and sent to the organizations responsible for the sites. The letters will review the concerns and encourage the sites to take the necessary remedial actions.

-    Work with the IERS, the space geodetic services and other CSTG elements to resolve a list of survey tie discrepancies. At a splinter meeting at the EGS meeting in March 2001, the ISGN began the organization of an international team of geodetic surveyors to assist in resolving outstanding site survey omissions and inaccuracies. The team members agreed to work on local survey tie issues within their areas of responsibility and report back to ISGN.

-    The ISGN will prepare and distribute a recommended set of survey field procedures and analysis procedures to be reviewed by the membership.

- The ISGN will continue to maintain the Global Space Geodetic Site Information Summary within the NASA GSFC CDDIS and will continue to disseminate information on the best practices for site selection, layout, monumentation, surveying and documentation.


3.2 Subcommission on Coordination and Combination of the Analysis in Space Geodesy

The objective of the subcommission is to study the algorithms and procedures for optimally combining measurements of space geodetic techniques. Main topics for the actual period are

-    the updating of the SINEX format to include information appropriate for all space geodetic systems,

-    investigations of strategies for combining geodetic results and data,

-    analysis of results from combinations with emphasis on results that are unexpected.


The subcommission participated in two international meetings which had sessions associated with combination issues:

-    GPS 99, Tsukuba, Japan (see CSTG Bulletin No. 16)

-    GEMSTONE, Tokyo, Japan (see Proceedings CRL, Koganei)


3.3 Subcommission on Precise Satellite Microwave Systems

 The role of the subcommission is seen in supporting new and emerging techniques. Emphasis will be laid on the advocacy of geodetic interests in the discussion on the GALILEO mission. Contacts have been made to individuals who are represented in the bodies of the mission development. The important meetings on the European level are intensively followed.


3.4 Subcommission on Multi-Mission Satellite Altimetry (SCOMMSA)

 The main objectives of the subcommission are

-    to promote free access to all altimeter data for scientific investigations,

-    to study synergies among different altimeter missions and other remote sensing techniques,

-    to set up the requirements for altimeter data structures, standards etc.

-    investigate the establishment of an international altimeter service.

An international discussion on the organization, functionality, content and structure of a multi-mission altimeter data base system was started. This data base will be the first step towards a better access and use of altimetry for scientific research.


3.5 Subcommission on Precise Orbit Determination for Low Earth Orbiting Satellites

 The primary scientific goals of the subcommission are the studies of

-    different LEO orbit modeling approaches,

-    the impact of global parameters on LEO orbits,

-    mission-dependent data structures and standards

-    LEO orbits derived from different observation techniques.


Different data sets of LEO GPS data are made available for groups that are interested to test their software packages, e.g., those from TOPEX/Poseidon, GPS/MET, CHAMP, SAC-C. The data format issue has been discussed in various meetings.


The subcommission participated in the following international meetings:

-    IGS network Workshop, Oslo, June 2000;

-    IGS Analysis Workshop, Washington, September 2000;

-    LEO Workshop, Potsdam, February 2001.


3.6 Project on Doris

 The project shall coordinate the activities towards the installation of an International Doris Service (IDS). For this purpose, a joint CSTG/IERS Doris Pilot Experiment was carried out. The project prepared and released the Terms of Reference of the experiment, which were discussed during the AGU Fall Meeting, San Francisco, December 1999. The chairman of the CSTG Subcommission is simultaneously the chairman of the Pilot Experiment and strongly involved in its realization.

The project was very well represented and involved in the organization of the Doris Days, Toulouse, May 2000. A considerable step forward to an international operational product generation was achieved. The individual components of a future service and its interaction, however, have still to be improved. The project is on the way, but still not completely mature for the installation of a service.


4 Conclusion

 The Commission CSTG and its Subcommissions have been active in the international coordination of space techniques by organizing of and participating in several research projects and international meetings. They are publishing their results in international journals and CSTG Bulletins. The Commission and most of the Subcommissions have their own web home pages in the internet (www.dgfi.badw.de/cstg). There is a frequent interaction and cooperation of the individual components of the Commission focused in the annual Executive Committee meetings.


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