Elements of Geodetic and Astrometric Very Long Baseline Interferometry

This text is an open tutorial document for educational purposes, e.g., for newcomers to geodetic and astrometric Very Long Baseline Interferometry (VLBI) but also for the specialists wanting to expand their knowledge about topics which are not in their main focus. It is supposed to be a living document with changes and additions to be made at reasonable intervals. 

VLBI is an observing technique which has applications in geodesy, astrometry and astronomy. Observing instruments are radio telescopes which receive electromagnetic radiation emitted by compact objects in space either far distant such as quasars or nowadays also closer to Earth such as spacecraft and satellites. Geodetic VLBI aims at determining (a) telescope coordinates and their kinematic movements for establishing and
maintaining terrestrial reference frames, (b) the (angular) parameters of the Earth’s variable rotation, (c) the angular positions of galactic and extra-galactic radio sources establishing and maintaining celestial reference frames, and (d) the positions of artificial transmitters in space near the Earth.