Vienna VLBI Center
Geodetic 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 and spacecrafts 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. A highly stable ITRF with station velocities accurate at the 0.1 mm/year level is a prerequisite to reliably observe mean sea level rise at the order of 3 mm/year and global change phenomena.
The importance of Global Geodetic Reference Frames (GGRF) for any kind of positioning and navigation was recognized at highest levels when in February 2015 the United Nations General Assembly adopted the resolution "A Global Geodetic Reference Frame for Sustainable Development" - the first resolution recognizing the importance of a globally-coordinated approach to geodesy. And VLBI certainly plays an important and unique role here.
VLBI 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. An error of one millisecond in UT1-UTC, which is the difference between the Earth rotation angle and atomic time, corresponds to an error of half a meter at the equator and kilometers at distances like those to Mars.
At TU Wien, we are contributing to activities of the International VLBI Service for Geodesy and Astrometry by scheduling, correlation, and analysis of VLBI observations. Together with the Federal Agency of Metrology and Surveying (Bundesamt für Eich- und Vermessungswesen BEV), we are running the IVS Analysis Center VIE. Basis for our operational and research activities is the Vienna VLBI and Satellite Software (VieVS).