Earth-rotation aperture synthesis

Resolution for radio astronomy in the order of 1" is necessary for the study of distant radio galaxies and quasars, for detecting faint sources, and for the mapping of clouds of hydrogen and other molecules. To obtain these resolutions many new or planned radio instruments use arrays of moderate size radio telescopes to synthesize large physical apertures. These instruments are generally composed of one or several linear arrays and utilize the rotation of the earth to change the relative orientation of the array and the radio source. The techniques used for earth-rotation aperture synthesis are discussed. The response of a two-element interferometer and the geometry associated with earth-rotation synthesis are reviewed; the current and proposed designs for these instruments and their performance are described; and, finally, the inversion methods for determining the angular power distribution of a radio source from the array response (visibility function) are outlined.