Reference Frames
Very Long Baseline Interferometry (VLBI) observations for geodesy and astrometry have been conducted since about mid--1979. These observations can be used to establish and define an astrometric quasi-inertial Celestial Reference Frame (CRF), positions and velocities of radio antennas that define a VLBI-based Terrestrial Reference Frame (TRF) and the Earth Orientation Parameters (EOP) that link the CRF and the TRF.
