Very Long Baseline Interferometry

Very Long Baseline Interferometry (VLBI) consists of two antennas separated by any distance on Earth, pointing at the same radio source and collecting the signal in the same frequency bands. These sources emit radio waves which are propagating through the universe like an expanding sphere. When these wave-fronts reach the Earth's surface, they arrive as a plane wave perpendicular to the antenna's pointing direction. The emitted signal consists of a continuous sequence of waves. First the reference antenna is reached and after a certain time delay the wave front strikes the second (remote) antenna. This time-of-arrival difference is called time delay and is the main measurement type for geodetic and astrometric applications. Figure 3 [2] depicts the VLBI concept schematically (IVS, 2012) (http://ivscc.gsfc.nasa.gov/ [3]).

Prof. Dr. Dr. h.c. Harald Schuh [5]

Chair of Satellite Geodesy

Dept. for Geodesy and Geoinformation Sciences           Technical University of Berlin
Faculty VI
Secr. H 12
Main building
Room H 5121
Straße des 17. Juni 135
10623 Berlin
+49 30 314 23205
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