Very Long Baseline Interferometry VLBI
Very Long Baseline Interferometry is a microwave-based space geodetic technique that measures the difference in arrival times of signals from a radio source by cross correlation. Most commonly the observed radio sources are extragalactic objects but beacons from satellites have also been used.
VLBI plays a unique role in the practical realization and maintenance of the International Celestial Reference Frame (ICRF) and contributes significantly to the International Terrestrial Reference Frame (ITRF), in particular for its scale. It is the only technique that provides the full set of Earth orientation parameters, which are indispensable for positioning and navigation on Earth and in space and give valuable information about interactions within the Earth system. In particular, direct measurements of nutation parameters and of the Earth rotation angle (UT1 - UTC) are uniquely provided by VLBI. Furthermore, several other geodynamic, atmospheric, and astronomical parameters can be derived from the long history of VLBI measurements starting in the late 1970ies. In 1999, the International Association of Geodesy (IAG) accepted the International VLBI Service for Geodesy and Astrometry (IVS) as an official IAG Service, and since then, the coordination of world-wide VLBI observation and analysis has improved significantly, leading to valuable results for the whole scientific community.
Vienna VLBI Software
The research group of Advanced Geodesy at Vienna University of Technology is a Special Analysis Center of the International VLBI Service for Geodesy and Astrometry. A major focus is on the development of Vienna VLBI Software (VieVS). The group's activities within IVS are well described in the IVS Annual Reports.