Sanjay Bhatnagar
In the Chapters 2 & 4, the conceptual basis and formulation of aperture synthesis in Radio Astronomy has been described. In particular, it has been shown that (1) an interferometer records the mutual coherence function, also called the visibility of the signals from the sky, and (2) the visibility is the Fourier transform of the sky brightness distribution. This chapter describes the coordinate systems used in practical aperture synthesis in Radio Astronomy and presents the derivation of the 2D Fourier transform relation between the visibility and the brightness distribution.