Reports from Services and Working Groups: summary

THE IERS REPORT FOR 2000-2003

Vondrák, Jan
Astronomical Institute
Academy of Sciences of the Czech Republic, Prague

The IERS was established in 1987 by the IAU and the IUGG. Its main tasks are to establish and maintain the celestial and terrestrial reference frames (ICRS, ITRS) and to publish the time series of Earth orientation parameters (EOP). To be more product-oriented, the Service has been reorganized in 2000. It is now represented by decentralized components: the autonomous Technique Centers (IGS, IVS, ILRS - International services by themselves, and in near future IDS), Product Centers (re-sponsible for producing ICRS, ITRS, EOP, Rapid service/prediction of EOP, Conventions, Global geo-physical fluids). In addition to these, Combination Research Centers are responsible for the research and the development of new procedures, software, etc. for regular products. The Analysis Coordinator has the principal responsibility to ensure the quality and internal consistency of the products. The IERS Workshops (April and November 2002) were concentrated on the proper implementation of the IAU 2000 Resolutions, on the combination of the results obtained by different techniques, and on the interaction between the motions of global geophysical fluids and the rotating Earth. The IERS Retreat (April 2003) led to the change of the name of the IERS (International Earth rotation and Reference frames Service) and to starting a new Combination Pilot Project.
Co-Authors: Richter, Bernd (BKG, Frankfurt am Main, Germany), Rothacher, Markus (Technical Uni-versity Munich, Munich, Germany)

 

IVS REPORT 2000-2003

Ma, Chopo
GSFC, USA

The International VLBI Service for Geodesy and Astrometry organizes the VLBI observing program and analysis to determine the celestial reference frame and the orientation of the Earth with respect to the celestial reference frame. The observing program now includes two weekly 24-hr sessions and one monthly 24-hr session for Earth orientation as well as sessions that maintain the ICRF. Future plans include further temporal densification and improvement of the catalog of stable southern hemisphere sources.

 

REPORT OF THE COMMISSION 19 WORKING GROUP PRECESSION-NUTATION

Dehant, Veronique
Royal Observatory of Belgium

The last adopted nutation model is the model of Mathews et al. (2002). This model has been studied and compared with other models before adoption.The remaining residuals between the observations and the theory are discussed. The sub-diurnal nutation have been examined by some scientists of the WG chaired by A. Brzezinski. The results of the discussion will be given. Geophysical fluids effects on nutations are also examined.

 

WG DISCUSSION ON THE EQUINOX OFFSET OF THE IAU 2000 MODEL

Capitaine, Nicole
Syrte, Observatoire de Paris, France

The IAU 2000 precession-nutation model has to be associated with the frame bias between the model at the reference epoch and the Geocentric Celestial reference System (GCRS). The two first components of this bias are the pole offsets of the model at J2000 with respect to the GCRS pole. They have been used for the implementation of the IAU 2000 model in the computation of the GCRS CIP X, Y coordinates, either directly for providing expressions for these coordinates to be used in the new paradigm, or indirectly through a specific bias rotation to be used in the classical paradigm. The third component of the frame bias, which is the GCRS right ascension of the mean equinox at J2000, cannot be derived directly from VLBI observations, which are insensitive at the first order to the position of the ecliptic. Consequently, the current VLBI procedure in fact ignores the equinox offset, introducing in this way a small spurious distortion (i.e. second order terms in the realization of the CIP). This paper gives a summary of the IAU Working Groups discussion on this issue and explains how this offset has been taken into account in the implementation of the IAU 2000 precession-nutation.