M. Vermeer
Chair: J. Liard
The International Association of Geodesy's International Gravity and
Geoid Commission was established in 1999 at the IAG meeting in Birmingham, UK,
merging the activities of the earlier International Gravity Commission and
International Geoid Commission. belongs
to Section III: Determination of the Gravity Field.
The Commission has a Web page at http://www.iag-iggc.org/
. The Terms of Reference are at http://www.iag-iggc.org/Trms0001.htm.
Services under the auspices of the
are the Bureau Gravimétrique International, Toulouse, France, Director:
Jean-Pierre Barriot, and the International Geoid Service, Milano, Italy,
Director: Fernando Sansó. Web sites of both services are:
During its first period of operation, a number of fruitful activities
took place. Starting at the formal level, the Assembly met, or tried to meet,
three times:
and at http://www.iag-iggc.org/iggc2000.pdf
The Chair's address at: http://olimpia.topo.auth.gr/GG2002/KEYNOTE/Vermeer.pdf
At these same meetings, we strived to also organize meetings of the
Directing Boards of the Bureau Gravimétrique International and of the
International Geoid Service; not successfully on every occasion.The Services
have done much valuable work during the reporting period.
http://www.ecgs.lu/html/workshop/workshop_img/img_2002.html
Many of the working groups and subcommissions have been active. Some of
our success stories, not exhaustive, are listed here.
The Arctic Gravity Project under the inspiring leadership of René
Forsberg and the contructive attitudes of several circumarctic countries, among
which Russia, the United States, Canada, Denmark and Norway, held two meetings
(St. Petersburg, Russia, 2000, and Ottawa, Canada, 2001) and came to a successful
conclusion with the release of an Arctic gravity data set in 2002. Weblink: http://www.nima.mil/GandG/agp/
Thanks to the constructive attitudes of several circumarctic countries,
among which Russia, the United States, Canada, Denmark and Norway, a gravity
survey map of the Arctic Ocean at 5' resolution was successfully produced and
published.
This Working Group 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, collection and analysis
of physical geodesy data, for the development of a new high resolution Geoid
for the Antarctic. Weblinks: http://www.scar-ggi.org.au/geodesy/physgeod/index.htm http://www.geoscience.scar.org/
In the Working Group on Intercomparison of Absolute Gravimeters, under
the leadership of Dr. Leonid Vitushkin of the Bureau International des Poids et
Mesures (BIPM, http://www.bipm.org/ ) in
Paris, France, a successful co-operation framework was developed between the
absolute gravimetry and metrology scientific ommunities, aimed at making absolute
gravity measurements with ballistic gravimeters metrologically traceable. This
must be continued in the future.
To this end, Dr. Vitushkin has established in addition to the Working group a similar working group
involving the same scientific community, but belonging to the sphere of
international metrology under the auspices of the BIPM. In this matter Dr.
Vitushkin visited Helsinki, Finland in 2000 on invitation by the Finnish Centre
for Metrology and Accreditation, and also found time to discuss with MV.
A letter (appendix) was sent by Fernando Sansó in his capacity as IAG
President, and MV as Chair, to the Dr.
T.J. Quinn of the Bureau International des Poids et Mesures, stressing the
importance of measuring geophysical quantities such as gravity in a
metrologically traceable way, mentioning the CIPM Working Group on Gravimetry
as an example.
The Subcommission for North America, chaired by Marc Véronneau, has been
active, both in terms of meetings and in terms of geoid determination
activities.
A number of Canadian Geoid Workshops have been organized (serial numbers
5-7, in May 2001, 2002, 2003 respectively) typically in conjunction with
Canadian Geophysical Union meetings to which some members of
the Sub-Commission for North America attended. Furthermore, the
Sub-Commission met at the IAG international symposium of February 2001 in
Cartagena (Canada/Mexico), at the US National Geodetic Survey office in
November 2001 (Canada/USA) and during the ArcGP meeting in Ottawa
(Canada/Greenland/Denmark).
Letters of invitation to join the Sub-Commission for North America were
sent to geodetic representatives of all Central America countries and some
Caribbean Islands countries. The terms of Reference of the Sub-Commission were
published in English and Spanish in the "revista Cartografica"
journal.
The primary objective for the Sub-Commission for North America is
achieving independently a common geoid model for the overlapping areas between
each country. The geoid solutions for Greenland, USA and Canada have
significantly converged towards a single solution; however still some areas
require some attention (e.g., the Pacific North-West region of USA). Mexico is
resuming gravity data collection and followed a series of theoretical and
practical geoid courses from Prof. P. Vanicek (UNB) and Dr. J. Janak at INEGI
office in Aguascalientes, Mexico.
The activities of the Subcommission have been rather informal.
This Subcommission was chaired by Denizar Blitzkow.
Considerable efforts were made in the period 2001-2003 in improving the
quality, the fundamental station networks and the gravity densification in
South America, with special emphasis to Argentina, Brazil, Chile, Ecuador and
Paraguay.
The Subcommission for South-East Asia, headed by Bill Kearsley, was
involved in organizing the IAG Geoid School in Johor, Malaysia, in February
2000.
The Subcommission for Europe, chaired by Ambrus Kenyeres, has been
active. A number of initiatives were started:
The Computing Centre for the European Geoid at the University of
Hannover (Heiner Denker) has expressed an interest in continued involvement in
the computational effort and determining the next generation European geoid
model under the new IAG structure after Sapporo. This could take the form of a
Project.
This important work must continue.
"As representatives of part of the geophysical community, i.e., the
community of physical geodesists involved in the study of the Earth's gravity
field, we are well aware of the importance of measuring geophysical quantities
such as gravity in a metrologically traceable way.
"At a time when the mapping of the Earth's gravity field, with terrestrial
methods, airborne techniques and new satellite missions, is making great
strides and will potentially benefit mankind immensely, it is important to
remain aware of the metrological basis of all the measurements collected in
these efforts, so that theory can be validly applied.
"Of course, gravity is only one example of geophysical quantities
of great relevance to society; there are a great many others. For all these
quantities, measuring them in a metrologically traceable fashion is just as
important.
"In this respect we greatly appreciate the long-standing interest
of the BIPM in gravimetry and the efforts that the BIPM is making to formalize
the link of the measurement of geophysical quantities to the metrology
community. The organization by the CIPM of the Working Group on Gravimetry,
which was done in close co-ordination with the IGGC, stands as a good example
of this."