Reconsideration of Azimuth Ambiguities in SAR

Abstract

The traditional method of specifying and controlling azimuth ambiguities in SAR is through integrated energy balance measures. However, the most frequently observed azimuth ambiguities arise from ensembles of strong point reflectors in the principal sidelobes of the antenna, which in turn are aliased into the processed Doppler bandwidth by the radar PRF. This paper considers the dependence of these ambiguities on radar wavelength and PRF. It is shown that such ambiguous image elements are strengthened in proportion to λ <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> and PRF <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> . The theoretical structure is based on orbital SAR geometry, including Earth rotation. The work is applied to a SIR-B L-band radar scene in which azimuth ambiguities are clearly observed. The level and spatial position of these ambiguities are measured in the digital image. The results are extrapolated to higher frequency radars such as ERS-1 and Radarsat. It is concluded that for these C-band radars the point azimuth ambiguity restraint is more relevant (and more binding) than the traditional energy balance method.