Image reconstruction in synthesis radio telescope arrays

The use of radio telescopes in astronomy presents particular problems because radio waves are roughly one million times longer than light waves. By combining the cross-correlation from antenna pairs forming interferometers with baselines distributed over a region, the image of an isolated object can be reconstructed. By moving telescopes and by making use of the rotation of the earth with respect to the sky, large baseline regions can be synthesized using a small number of discrete antenna elements. The principal aim of this chapter is the introduction of signal processing methods for image reconstruction of unpolarized or partially polarized continuum and spectral line radio sources. Attention is given to wave fields of radio sources, the measurement of mutual coherence and mutual spectral density, array geometry and rotational sampling of baseline space, image reconstruction by Fourier inversion, image restoration by the method "Clean', phase and amplitude errors, and maximum-entropy image restoration.