How Consistent are The Current Conventional Celestial and Terrestrial Reference Frames and The Conventional Earth Orientation Parameters?

Abstract

Many applications in geodesy, geodynamics, astronomy and space navigation depend on the availability of accurate Earth orientation parameters (EOP). EOP are the orientational part of the transformation between terrestrial and celestial reference frames. The conventional EOP refer to conventional frames. The current conventional terrestrial reference frame, ITRF2008, and the attached EOP, IERS 08 C04, have been determined combining the Earth rotation parameters derived from the four observing techniques but keeping the celestial pole offsets obtained by VLBI unchanged. This set of EOP refers to ITRF2008, but it does not directly refer to the current conventional celestial reference frame, ICRF2. Therefore, the conventional reference frames and the IERS 08 C04 are not entirely consistent. In the paper we assess this inconsistency by VLBI data analysis. For test purposes, we have to fix coordinates on the frames. This approach causes small systematics of the EOP. These systematics are interpreted as the uncertainty of our assessment method that is about 30 μas and about 3 μas∕year. The VLBI-only terrestrial reference frame, VTRF2008, is consistent with ICRF2 at the 10 μas level. We thus interpret the differences between EOP based on this frame and EOP based on ITRF2008 as the inconsistency of IERS 08 C04 w.r.t. ICRF2. The largest difference was found for y p being −38.8 μas and −18.6 μas∕year. Applying our method, we also found differences in d U T1 of 11.3 μs when comparing EOP based on ITRF2008 and DTRF2008, an alternative TRF determined at DGFI, Munich. This is astonishing, because both frames are derived from identical input data. The orientation of a terrestrial reference frame depends to a significant part on the choice of stations for the no net rotation constraint. Our conclusion is that a single solution that involves the determination of both fundamental frames, ITRF and ICRF, is the only way to obtain conventional EOP that provide accuracy.