Reference frame-induced errors in VLBI earth orientation determinations

Abstract

This paper presents how Very Long Baseline Interferometry (VLBI) realizes the Earth Orientation Parameters (EOP) and which accuracy can be theoretically reached depending on the involved reference frames. The definition of EOP is based on the transformation between the Geocentric Celestial Reference System (GCRS) and the International Terrestrial Reference System (ITRS). The ITRS part is in common for all the space geodetic techniques. The method applied here utilizes the uncertainty of the orientation of the actual set of radio sources of a VLBI observing session related to GCRS and the uncertainty of the orientation of the set of terrestrial network stations related to ITRS for the assessment of the uncertainty of the EOP. The uncertainty of the initial orientation of the GCRS is about 35 μ as and the uncertainty of the orientation stability is about 0.7 μ as=year. In addition small systematics are present due to the aberration caused by the rotation of our galaxy at the level of 5 μ as=year. The uncertainty of the initial orientation of the ITRS of about 800 μ as is about 20 times larger, while the uncertainty of the orientation rate of about 80 μ as=year is about 100 times larger compared to the corresponding celestial values. The initial orientation and the orientation stability of ITRS could bemuchmore precisely defined by constraining it to the GCRS via the EOP.