Russian Foundation for Basic Research

Principle of generation of radio images

Radio images at the SSRT are generated by an ingenious method, unlike most present-day radio telescopes where the aperture analysis method is used. Since theorientation of interference maxima depends on the emission frequency, it is possible to scan the solar disk by re-tuning the receiving system's frequency to the desired values. Consequently, by performing iteratively this discrete readjustment with a sufficient speed (or by processing simultaneously received signals from multiple frequency channels), we obtain a sequence of solar disk scans, one-dimensional solarimages. The frequency scanningmethod permits readings to be taken rapidly in a single direction. This is used immediately in SSRT observations of fast active processes in the one-dimensional mode with a time resolution of up to 14 ms.

Generation of the SSRT two-dimensional beam

Multifrequency fan-shaped beam of the SSRT

To obtain two-dimensional radio images involves the combined operation of the linear antenna arrays in the crossed correlation interferometer configuration. Its beams are a set of interference maxima, pencil beams. Solar radio images are generated by beams oriented within the SSRT field of view (90'). When the Sun passes through the fan of these beams (consecutive interference maxima) during the diurnal rotation of the Earth, it is scanned in a different direction. This, in combination with readings obtained from frequency scanning, ensures a two-dimensional mapping of the Sun. Observatiuons in the radio heliograph mode were begun in the autumn of 1995; since the spring of 1996, solar mapping has been done on a daily basis. This method provides a direct generation of solar radio images without using aperture synthesis.