Models for the implementation by N. Capitaine (Syrte, Observatoire de Paris, France)
The implementation of the IAU 2000 resolutions requires the adoption of (i) the IAU 2000 model (Resolution B1.6) to replace the IAU 1976/1980 precession-nutation for the motion of the Celestial Intermediate Pole (CIP) in the Geocentric Celestial Reference System (GCRS), (ii) a conventional model (Resolution B1.7) for high frequency motions of the CIP in the International Terrestrial Reference System (ITRS) and (iii) the conventional relationship for defining UT1 (Resolution B1.8) as proportional to the Earth Rotation Angle (ERA) between the Celestial and Terrestrial Ephemeris Origins (CEO and TEO). Two equivalent ways of implementing these resolutions in the transformation from ITRS to GCRS can be used, namely (a) the new paradigm, based on a direct use of the CEO and the ERA and (b) the classical paradigm, based on the direct use of the equinox and GST, but using the CEO and the ERA indirectly. Implementation of the resolutions has required computation of expressions compliant with the new precession-nutation model, to be used in the ITRS/GCRS transformation once the relationship ERA (UT1) is adopted. Equivalent expressions have been provided in scientific papers published in 2002 and 2003 for all the models necessary to implement the IAU 2000 system, using either the CEO-based or the equinox-based transformations.
Status of the IERS implementation by D.D. McCarthy (U. S. Naval Observatory)
The International Earth rotation and Reference system Service (IERS) has implemented the IAU resolutions of the 24th General Assembly in its products. The IERS Conventions now provides an outline of the procedures to be used along with software consistent with those procedures. IERS Bulletins A and B have made the data required to implement the resolutions available since January, 2003. To assist users in the transition period between the previous system and that recommended by the 24th General Assembly, the IERS also continues to provide data consistent with the previous system. It also plans to make available a file of frequently asked questions to assist users in the transition between systems.
