The Very Long Baseline Interferometry

The Very Long Baseline Interferometry (VLBI) is an interferometric technique used in radio astronomy in which a set of radio telescopes or antennas located in different part of the planet (or in space) observe simultaneously the object under study. The data taken at each antenna are stored and marked with a very accurate time information (atomic clock). In deferred time, but also possible online and in real time, all the data are read in a very powerful computer (called correlator) that recreates the exact conditions of the experiments and make interfere the signals recorded at each antenna, to obtain the images of the observations.

The main advantage of this technique is that there are no limitations on the distance between the antennas, allowing them to be completely independent and not physically connected. Since the resolution of an interferometer is directly proportional to the separation between its elements, the VLBI is the astronomical technique that provides the highest spatial resolution (sharpness), of the order of milliarcseconds or microarcseconds (equivalent to the size of a coin on the Moon seen from Earth).

The field of application of this technique is very broad, some of themost important, in which the I.G.N. is involved, are:

  • Astronomy: definition of the celestial frame, maser emissions, nuclei of active galaxies, quasars, black holes, etc.
  • Geodesy: Earth rotation (and its variations), Earth orientation, tectonic plate motions, crustal deformation, etc.
  • Space science: space probes tracking.

 

The major VLBI networks available are: the EVN (Europe), VLBA (USA), GMVA & EHT (Worldwide), VERA (Japan) and KVN (Korea).

Image 1: Total intensity map of the H2O maser toward the nebula OH231.8+4.2, obtained with the VLBA VLBI network, compared to the HST image. An accurate astrometry has been performed between the HST image and maser maps. The small square map indicates the absolute position of the Silicon Monoxide (SiO) maser, also observed with the american VLBI network. Top right panels show the composed profile of H2O maser for the two main regions (credit Desmurs et al., 2007).

 

Imagen 2: European VLBI Network radio telescope locations (credit J.Radcliffe (Kapteyn Astronomical Institute,The Netherlands))