President: Michael G. Sideris
University of Calgary
Department of Geomatics Engineering
2500 University Drive N.W.

Calgary Alberta T2N 1N4


1. Introduction and Objectives

This report describes very briefly the activities of Section III for the period 1999-2001. Given the numerous activities and large number of significant accomplishment during the last two 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 study groups, commissions and services for the same period. These reports also provide web site addresses, where recent results, data sets, publications and other relevant information can be found.

The developments in the gravity field determination expressed in the formal IAG by-laws, for which Section III is 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; and
  5. reduction and estimation of gravity field quantities.


2. Structure

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

President: Michael G. Sideris (Canada)

Secretary: Gerd Boedecker (Germany)


Commission XIII: International Gravity and Geoid Commission

President: Martin Vermeer (Finland)


Special Study Groups:

SSG 3.167: Regional Land and Marine Geoid Modelling

Chair: I.N. Tziavos (Greece)

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

Chair: Will Featherstone (Australia)

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 (Germany)

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

Chair: C. Hwang (Taiwan)


International Services:

BGI: International Gravimetric Bureau

Director: J-P. Barriot (France)

IGeS: International Geoid Service

Director: F. SansÚ (Italy)


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

The Working Group on Inter-comparison of Absolute Gravimeters
The Working Group on World Gravity Standards
The Working Group on the Global Gravity Monitoring Networks
The Arctic Gravity Project
The Antarctic Gravity Project
The Sub-commission for Europe
The Sub-commission for North America
The Sub-commission for South America
The Sub-commission of South East Asia



3. 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 SectionIII held many business meetings and/or workshops, usually during the major 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, S„o Paulo, Brazil.
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.
Annual Meetings of the European Geophysical Society, and American and Canadian Geophysical Unions, 1999, 2000, 2001.


4. Summary and Outlook

All bodies of Section III have been operating very successfully and are meeting or exceeding the objectives they have 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 contributing to the work of the Section.

With IAG being in the process of reorganising its operations and internal structure, it is of course possible that many changes will take place in the near future. For example, with leadership from IGeS and the consent of BGI, NIMA, ICET and GFZ, the Section is proposing the creation of a new IAG service named International Gravity Field Service (IGFS). IGFS is being proposed as 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 is envisaged, as well.

After the IAG assembly in Budapest this fall, we will all be awaiting with great anticipation the new structure of IAG, and are looking forward to seeing the new place the Determination of the Gravity Field will have in it.


Michael G. Sideris

IAG Section III President              Calgary, June 2001


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