THE
INTERNATIONAL GRAVITY AND GEOID COMMISSION OF IAG
Report
on Activities Martin VermeerChairman 1.
Establisment and Terms of Reference The decision to establish this IAG Commission was taken
in July 1999 in Birmingham, UK, at the IUGG/IAG General Assembly,
merging the activities of the International Gravity Commission and the
International Geoid commission. The objective was to establish a
stronger focus for the scientific study of the gravity field of the
Earth. Terms of Reference were drawn up to guide the work of
the Commission. They can be found at the Web address http://www.iag-iggc.org/Trms0001.htm. 2. The working groups of the Commission 2.1 The WG on Intercomparison of Absolute Gravimeters The Working Group on Intercomparison of Absolute
Gravimeters, headed by Leonid Vitushkin, has been particularly active.
Dr. Vitushkin has worked to establish not only the IGGC's Working
group, but a similar working group involving the same scientific
community, but belonging to the sphere of international metrology
under the auspices of the Bureau International des Poids et Mesures (BIPM,
http://www.bipm.org) in Paris, France. For this purpose the creation of a new Consultative
Committee has been proposed for absolute gravimetry. The impetus for
this was a letter (July 15, 1999) by three leading Russian
geophysicists representing the National Geophysical Committee and its
Geodesy Section, addressed to the President of IAG explaining the need
to bring absolute gravimetric work within a metrological framework.
The precise organizational arrangement is yet to be decided in October
2001 (Letter November 23, 2000, Jean Kovalevsky, Comité International
des Poids et mesures). The objective is to establish a close collaboration
between the metrological community on the one hand, and the
geodetic-geophysical community on the other. In preparing these initiatives, Dr. Vitushkin visited
Helsinki, Finland in October 4 - 6, 2000 on the invitation of the
Director-General of the Finnish Centre for Metrology and
Accreditation, Ulla Lähteenmäki. The undersigned participated in the
discussions that took place. 2.2 The Arctic Gravity project Also the Arctic Gravity Project (ArcGP), another
working group within IGGC, was very active under the leadership of René
Forsberg and the contructive attitudes of several circumarctic
countries, among which Russia, the United States, Canada, Denmark and
Norway. In spite of the obvious political sensitivity of the
stated objective of producing a gravity survey map of the Arctic Ocean
at 5' resolution, good progress was made. Gravimetric data appears to
exist from a large number of sources and techniques (shipborne,
airborne, submarine, ice surface, satellite altimetry…) to cover all
of the target area with the possible exception of a small banana
shaped region. The first meeting of the Working Group took place in St
Petersburg, Russia, in a small mansion outside the city. The meeting,
in which the undersigned participated, was both productive and
pleasant. A second meeting in Canada is to be convened these
days. The ArcGP has its own web site, address http://www.nima.mil/GandG/agp/. 2.3 The Antarctic Gravity Project The Working Group on Antarctica of the IGGC has been
headed by Alessandro Capra of the University of Bologna. Dr. Capra
also heads the Physical Geodesy project within the Geodesy program
(GIANT) of the Geodesy and Geographic Information group of SCAR, the
Scientific Committee on Arctic Research. The purpose of this WG is, similarly to ArcGP. the
compilation of a gravimetric data base with a view of determining a
high resolution geoid model of the Antarctic area. See the Web site http://www.scar-ggi.org.au/geodesy/physgeod/index.htm. 2.4 Other Working Groups The creation of the following WG's was decided at the
first IGGC Assembly meeting in Banff, Canada, cf. section 5.1
3 The Subcommissions The following Subcommissions have been established at
the outset of the IGGC: 3.1 North America The Subcommission for North America, chaired by Marc Véronneau,
was off for a good start, with gravity and DEM measurement and
compilation and geoid determination going on in several member
countries. Meetings held include:
This Subcommission has also the Caribbean and Central
America within its field of operations and letters of invitation were
sent to all the countries of Central America, Cuba, The Bahamas and
the Dominican Republic, which have not yet responded. The Subcommission's Web site is at: http://www2.geod.nrcan.gc.ca/~marc/GGSCNA/GGSCNA.html (requires a
password). 3.2 Europe The Subcommission for Europe, chaired by Ambrus
Kenyeres. A report on its activities was presented at the GGG2000
meeting. It can be found at http://www.iag-iggc.org/SC_Europe2000.htm. The Computing Centre for the European Geoid at the
University of Hannover (Heiner Denker) has expressed an interest in
continued involvement in this computational effort. It is intended, in
close co-operation with EUREF, to use a highly reliable GPS/levelling
data set as fiducial control for future geoid model determinations. 3.3 South America The Subcommission for South America, headed by Denizar
Blitzkow. A meeting has been held in Cartagena, Colombia, see section
5.2. Geoid determination activities for the area are ongoing, as are
gravity surveys and establishment of digital terrain models. 3.4 South-East Asia The Subcommission for South-East Asia, headed by Bill
Kearsley. Activities in this area are hampered by the lack of an
existing IAG framework for co-ordinating activities in the region.
Nevertheless, as a success can be reported the IAG Geoid School in
Johor, Malaysia, in February 2000. 4 ServicesThe Services currenty under the auspices of the IGGC
are:
Both services have been active in their mandated fields
of activity. It should be stressed that the operations of both are
made possible mostly by national sources of financing within France
and Italy, respectively. The IGGC can only play a co-ordinating role
for both in order to enable them to better execute their mandates. A first Directing Board meeting of both services was
held during the Banff meeting, cf. section 5.1. Web sites of both services are:
5 Meetings 5.1 Banff At the GGG2000 (Gravity, Geoid, and Geodynamics)
meeting, July 31 - August 4, 2000, in Banff, Canada, the Assembly of
the IGGC met for the first time, on the first of August. A number of
decisions was taken, mainly confirming the proposed study groups and
subcommissions and their chairpersons, as well as the terms of
Reference. The Minutes are found here: http://www.iag-iggc.org/minutes2000.htm. 5.2 Cartagena A symposium called the IAG Symposium on Vertical
Reference Systems was convened February 20 - 23, 2001 in Cartagena,
Colombia, where besides the Subcommission for South America, also the
Subcommission for South America met in a splinter meeting. Unfortunately the undersigned was unable to attend, but
a letter was sent to the organizers expressing the support of the IGGC
to the symposiom, and expressing good wishes for its success. 5.3 Nice In preparation for the 2001 meeting of the IAG
Executive Commmittee, a proposal was circulated drafted by several
people within the Executive, aimed at the creation of a GFFS,
”Gravity Field and Figure of the Earth Service”, which would serve as a formal umbrella for
and a
couple of services to be newly established. One such service, for
which official support was promised by the GeoForschungsZentrum in
Potsdam, Germany (Letter Ch. Reigber , March 23, 2001), was a Service
for the Intercomparison of Global Spherical Harmonic Expansions. The publication of a joint Information Bulletin is
envisaged. The undersigned asked the proposal to be placed on the
agenda for discussion; unfortunately again such discussion took place
in his absence forced by other commitments. 6 Web siteA web site, http://www.iag-iggc.org for the Commission
was set up and s being maintained by the Secretary, Jacques Liard at
his affiliation, Natural Resources Canada. Their provision of hosting
facility and bandwidth is gratefully acknowledged.
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