SECTION III:

“DETERMINATION OF THE GRAVITY FIELD”

REPORT OF THE PRESIDENT FOR THE PERIOD 1999-2003

M.G. Sideris

Introduction and Objectives

This report describes very briefly the activities of Section III for the period 1999-2003. Given the numerous activities and large number of significant accomplishment during the last four years, this report should be used only as a “road map” of Section III’s activities and, for completeness and detailed information, the interested reader should consult the reports of the special study groups, commissions and services for the same period. In the provided web site addresses, recent results, data sets, publications and other relevant information can be found.

The developments in the gravity field determination expressed in the past IAG by-laws, for which Section III was responsible, are:

1. absolute and relative terrestrial gravity measurements;
2. gravity networks and control stations;
3. non-tidal gravity variations;
4. determination of the external gravity field and geoid from different gravity field data types;
5. reduction and estimation of gravity field quantities.

Structure

In order to achieve its objectives, the Section established the following Structure:

President: Michael G. Sideris (Canada)

Secretary: Gerd Boedecker (Germany)

http://www.ucalgary.ca/~sideris/IAG/sectionIII.html

Commission XIII: International Gravity and Geoid Commission

President: Martin Vermeer (Finland)

Vice-presidents: Rene Forsberg (Denmark) and Michael G. Sideris (Canada)

Secretary: Jacques Liard (Canada)

http://www.iag-iggc.org/

Special Study Groups:

• SSG 3.167: Regional Land and Marine Geoid Modelling

Chair: I.N. Tziavos (Greece)

http://olimpia.topo.auth.gr/ssg3167

• SSG 3.177: Synthetic Modelling of the Earth’s Gravity Field

Chair: Will Featherstone (Australia)

http://www.cage.curtin.edu.au/~will/iagssg3177.html

• SSG 3.184: Use of Remote Sensing Techniques for Validating Heights and Depths

Chair: Philippa Berry (UK)

• SSG 3.185: Merging Data from Dedicated Satellite Missions with Other Gravimetric Data

Chair: Nico Sneeuw (Canada)

• SSG 3.186: Altimetry Data Processing for Gravity, Geoid and Sea Surface Topography Determination

Chair: C. Hwang (Taiwan)

http://space.cv.nctu.edu.tw/IAG/main.html

International Services:

BGI: International Gravimetric Bureau

Director: J-P. Barriot (France)

http://sirius-ci.cst.cnes.fr:8110/bgi_debut_a.html

IGeS: International Geoid Service

Director: F. Sanso (Italy)

http://www.iges.polimi.it

A substructure was also put in place, whereby the above bodies established sub-commissions and working groups as needed, to tackle specific problems or research areas. These include:

• Working Croup on Intercomparison of Absolute Gravimeters (Chair: Leonid Vitushkin).
• Working Croup on the Arctic Gravity Project (Chair: René Forsberg).
• Working Croup on Antarctica (Chair: Alessandro Capra).
• Sub-commission for Europe (Chair: Ambrus Kenyeres).
• Sub-commission for South-America (Chair: Denizar Blitzkow).
• Sub-commission for South-East Asia (Chair: Bill Kearsley).
• Sub-commission for North America (Chair: Marc Veronneau).

All bodies of Section III operated very successfully and met or exceeded the objectives they had set for themselves. This is evident from the list of publications, scientific exchanges, and meetings and workshops organized. Congratulations are due not only to the chairs and secretaries of the various bodies but also to the individual members who contributed to the work of the Section.

Major Meetings and Schools

Section III was involved directly or indirectly in the organization of many scientific meetings, workshops and international schools. Also, the various bodies within Section III held many business meetings and/or workshops, usually during major international conferences. Of particular important for their service to our colleagues in developing countries are the international schools for the determination and use of the geoid, organized by the International Geoid Service. A non-exhaustive list is given below.

• 4th International School on the Determination and Use of the Geoid, February 21-25, 2000, Johor, Malaysia.
• South America Geoid Workshop, May 17-19, 2000, Sao Paulo, Brazil.
• Arctic Gravity Project meeting June 7 - 8, 2000, St. Petersburg, Russia 
• IAG Symposium on Gravity, Geoid, and Geodynamics 2000 (GGG2000), July 31 - August 4, 2000, Banff, Alberta, Canada.
• IAG Symposium on Vertical Reference Systems, February 20 - 23, 2001, Cartagena, Colombia.
• International Comparison of Absolute Gravimeters, June 18 - August 4, 2001, BIPM, Sèvres, France.
• IAG 2001 Scientific Assembly, September 2 - 8, 2001, Budapest, Hungary.
• BGI/ICET Summer Course on Gravity Measuring Techniques, September 4-11 2002, Louvain-La-Neuve, Belgium.
• Instrumentation and Metrology in Gravimetry workshop, October 28 - 30, 2002, European Center for Geodynamics and Seismology (ECGS), Walferdange, Luxembourg
• Third Meeting of the IGGC August 26 - 30, 2002, Thessaloniki, Greece.
• International School on the Determination and Use of the Geoid, Aug. 30 – Sept. 5, 2002, Thessaloniki, Greece.
• Annual Meetings of the European Geophysical Society, and American and Canadian Geophysical Unions, 1999, 2000, 2001, 2002, 2003.
• IAG/IUGG General Assembly, June 30 – July 11, 2003, Sapporo, Japan.

From the old IAG structure to the new one

With IAG being in the process of reorganizing its operations and internal structure, the work of Section III will continue mostly under Commission 2 (Gravity Field) in the new structure. The new Commission 2 will be derived mainly from the existing Section III, with elements of Sections II, IV and V. The five proposed major thematic areas of the new Commission 2 are:

1. Gravimetry and Gravity Networks
2. Precise Geoid Determination
3. Gravity Field Determination from Satellite Altimetry
4. Dedicated Gravity Satellite Missions
5. Temporal variations of the Gravity Field

with sub-commissions on

• Gravimetry and Gravity Networks
• Spatial and Temporal Modelling of the Gravity Field
• Dedicated Gravity Satellite Missions

Several study groups similar to the ones that exist currently would again be established to (i) investigate more specific topics and (ii) coordinate regional efforts of gravity mapping, geoid determination, vertical datums, etc. In addition, the establishment of a new Inter-commission Committee on Planetary Geodesy is currently under study.

Commission 2 will have very strong links to the newly established International Gravity Field Service (IGFS). IGFS consists of:

• Bureau Gravimetrique International (BGI)
• International Centre of Earth Tides (ICET)
• International Geoid Service (IGeS) I, in Milano
• International Geoid Service (IGeS) II, at NIMA
• International Centre of Global Earth Models (ICGEM), at GFZ

IGFS will be a unified structure aiming at collecting, validating and distributing data and software for the purpose of determining the gravity potential and the surface of the Earth a accurately as possibly. The publication of a joint Information Bulletin between the IGeS and BGI is envisaged, as well.

It is evident that under the new structure of IAG, Gravity Field will have again the very prominent place it deserves.

Acknowledgements.

Section III was probably the most active section within IAG in the past four years. This would not have been possible without the tremendous leadership of the section officers, the support of the IAG Executive, and the hard work of all participating colleagues. Many thanks are therefore due to all contributors from the international scientific community for advancing our field of research. I am certain that this tradition will continue in the future with the work of the new Commission 2 under the leadership of its newly elected President, Chris Jekeli.