Radio astronomical imaging from coherence data

Modern radio astronomical imaging is a highly developed technique capable of producing maps of cosmic radio-wavelength sources with extremely high angular resolution and dynamic range. The method almost universally used is based on interferometry, in which the output voltages from two antennas are cross-correlated to give a measure of the coherence of the electromagnetic field in the vicinity of the antennas, in a direction normal to the direction to the source. An ensemble of such measurements on a variety of baselines represents the Fourier transform of an approximation to the two-dimensional brightness distribution of the source. Limitations on the accuracy of the resulting image arise from insufficient sampling of Fourier components and from distortion of the measured data caused by atmospheric or instrumental effects. Powerful data processing methods have been developed to deal with these limitations, resulting in a process capable of extremely precise reproduction of cosmic source images