Two-Dimensional Brightness Distributions of Radio Sources from Lunar Occultation Observations

Occultation of a radio source by the Moon provides data from which the strip brightness distribution of the source may be determined. This paper presents a method of reconstructing the complete two-dimensional brightness distribution of a source, given several occultations at different position angles. Reconstruction is accomplished by (i) computing the Fourier transform of each of the strip brightness profiles, (ii) interpolating in the transform plane between the available position angles to evaluate the transform function at the points of a square array, and (ili) inverting the Fourier transform in two dimensions to obtain the desired brightness distribution. As an example of the method, a map is presented of the radio galaxy 3C 192 with a resolution of 60", derived from six occultations observed at 256 Mc/s.