Very Long Baseline Interferometry (VLBI)
Very Long Baseline Interferometry (VLBI) 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 billions of light years away but beacons from satellites are also 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 to its scale determination. VLBI observations and analysis are thus critical for the realization of global references frames whose importance was highlighted and emphasized by a United Nations General Assembly Resolution on 26 February 2015.
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.
At TU Wien, we are involved in scheduling, correlation and analysis of VLBI observations. Specifically, we are using modules of the Vienna VLBI and Satellite Software (VieVS) for scheduling and analysis and the Vienna Scientific Cluster for correlation.