Overview

Remote sensing of the earth surface in the microwave frequency range is a rapidly developing field of fundamental and applied radio electronics ^{[31] , [77]}. It has already become a powerful method in many earth sciences such as geophysics, oceanology, meteorology, resources survey, etc. Especially among microwave sensors side- looking synthetic aperture radars (SAR) are capable of providing high-resolution images of a background area at any time, irrespective of weather conditions. Extensive information has been obtained by airborne radars and radars carried by satellites and spacecraft: SEASAT-A and SIR (USA), RADARSAT (Canada), Almaz-1 (Russia), ERS and ENVISAT (European Space Agency), Okean (Russia, Ukraine). A challenge to the radar scientist is the analysis of synthetic aperture imaging of extended targets.

The various tasks of remote SAR sensing of the earth include the study of the ocean surface, sea currents, shelf zones, ice fields, and many other problems ^[62]. Objects to be imaged are wind slicks, oil spills, internal waves, current boundaries, etc. Some of these targets are characterised by motions with unknown parameters, so they are considered to be partially coherent. This chapter focuses on theoretical problems of SAR imaging of such targets while their practical aspects are discussed in Chapter 9.

In contrast to a conventional radar which measures instantaneous amplitudes of a signal reflected by a target, the SAR registers the signal phase and amplitude for a finite synthesis time T _s. The conversion of these data to a radar image requires the knowledge of...