With the
reorganization of the IAG to take effect at the meeting in Sapporo, this report
is a final one for the Geodynamics Section V of the IAG. In the future, Geodynamics will retain its
identity as the new Commission 3, but sub-entities will change. Geodynamics
Section activities within the Commissions, Special Commissions, the Joint
Working Group, and the International Services are described in individual
reports below. In addition to the work
described below, Section V President Wilson headed the Scientific Organizing
Committee of the Seventh International Congress of Earth Sciences, in Santiago
Chile, October 2002, sponsored by IAG.
Additional information is contained in the report of Commission XIV
below. Section V Vice President
Veronique Dehant chaired the joint IAU-IUGG working group on Precession and
Nutation, overseeing development of new precession-nutation models, and
accounting for the non-rigid nature of the Earth and influences of geophysical
fluids. These studies have been
important in implementing fundamental changes in astrometry and modern space
geodesy. As discussed in the
International Earth Rotation Service (IERS) report below, the IERS began
implementing new IAU resolutions that fundamentally redefine the Celestial
Reference System (CRS) to take full advantage of precision available with
modern VLBI. The new
precession-nutation models are an important element of high precision geodesy
that enables the study of geodynamics.
As the IAG representative to the IERS Directing Board, Section V
President Wilson participated in a number of IERS activities, including two
workshops related to the implementation of the new CRS. Wilson has also participated in the IERS
Global Geophysical Fluids Center work of the IERS, which, as noted below, will
become a major element of IAG and Geodynamics Commission work in the future.
The executive officers of Section V (Wilson and Dehant) participated in the effort to map the old IAG onto the new structure adopted in Budapest IAG assembly, in 2001. This new structure places the IERS and other services on the same level as Commissions. This is important because in many ways the services like IERS have become leaders in setting geodetic practice. For example, the IERS conventions document forms, in effect, the geodetic standard in use today. Under the new IAG structure, it should be easier to coordinate activities of the services with those of the IAG, by establishing joint review of such standards and conventions. For example, the IAG plans an inter-commission committee on geodetic standards for this purpose, to carry on the work of Special Commission 3 (reported below). An example of inconsistency between IAG resolutions and the IERS conventions is the treatment of the zero-frequency terms in the Earth tides. This sort of conflict can be reconciled over the next few years in this new inter-commission committee on geodetic standards.
Under the
new IAG structure, the initial proposal is for Geodynamics (new Commission 3)
to include three main subcommissions.
One is concerned with crustal deformation, the second with the impact of
geophysical fluids on geodetic observations, and the third with earth tides. A subcommission on crustal deformation would
be expected to transfer many of the activities under the current Commission
XIV, as reported below, though some changes are possible. The subcommission on Earth tides would also
be expected to continue the work of the current Earth Tide Commission, as
reported below. The new activity,
geophysical fluids, is an outgrowth of Special Commission 8 (Sea Level and Ice
Sheets, reported below), the IAPSO/IAG special study group on non-tidal ocean
effects (reported below), and several special study groups on atmospheric and
related influences on earth rotation that were active over the past period of
over a decade. Redistribution of air
and water dominate the changes in Earth rotation and gravity field at many time
scales (days to decades). This
subcommission will link the new Geodynamics Commission 3 to other commissions,
and services. Notably, the
International Earth Rotation Service (IERS) has a geophysical fluids center,
and that activity should form the core of the new geophysical fluids
sub-commission. The bigger role of services in IAG, especially of IGS as the
biggest player in crustal deformation, should strengthen the activities related
to crustal deformation. There are many
other opportunities for the future under the new IAG. These are likely to grow out of IAG projects, in combination with
a multitude of new measurements available, including satellite-based gravity,
ice sheet heights from laser altimetery, as well as the expanding geodetic
networks of permanent GPS stations.