Methods of using closure phases in radio aperture synthesis

The idea that an image of the source could be synthesized from a set of interferometer measurements made at various spacings was first applied in radio astronomy about 1947. The concept was further developed by Ryle (1957) and Bracewell (1958) and forms the basis of some of the world's largest radiotelescopes. The considered investigation is concerned with estimating the angular distribution of brightness of a source of incoherent radiation in the far field of an array of antennas from measurements of the cross-correlation functions of the voltages induced in those antennas. The brightness distribution is assumed to be stationary in time, so that measurements made at different times can all be used in the estimate; in particular, the antennas may be moved to obtain a different array configuration, as occurs naturally by rotation of the earth with respect to celestial sources. The estimate of the brightness distribution is called a 'map'.