Radio interferometry

The angular resolution of a radiotelescope, its ability to resolve features of small angular size on the sky, is given by the ratio between the wavelength of observation and the size of the antenna dish. With the aim to improve this normally moderate resolution, it is necessary to use a technique known as interferometry. This technique consists of observing simultaneously with an array of different radiotelescopes. The resolution of the interferometer array is then given by the ratio between the observing wavelength and the distance, or baseline, between the individual antennas. Since the separation between radiotelescopes may be thousands of kilometers, the angular resolution finally achieved may reach values as small as one milli-arcsecond (the angular size of a person in the Moon surface).

When the distances between the different antennas of an interferometer are a few kilometers, it is possible to connect all of them physically. An example of this is the case of the VLA, a connected interferometer. When the separation between radiotelescopes is such that a physical connection is not feasible, as in the VLBA, the signals from each antenna are recorded on different tapes together with a time control provided by atomic clock. The tapes are later analyzed and processed all together. In this last case, the technique is known as Very Long Baseline Interferometry (VLBI).

For any question please contact Josep Martí(jmarti@ujaen.es)