High-frequency limits on SAR autofocus and phase correction

Abstract

Abstract In the previous paper we derived the fundamental noise limits in the determination of the autofocus parameter in SAR processing for both point and extended objects. In the present paper we extend this analysis to establish the fundamental limits on the image quality of a phase-corrected SAR image. A variety of autofocus schemes are analysed and an improved scheme is proposed which offers the minimum long-term image distortion and reasonable point response to changes in the autofocus parameter across the full aperture. The implications for phase correction based on autofocusing, leading to distortion-free images are examined. Image distortion, phase error and the point-target response are all derived as a function of the extent to which the full aperture is subdivided so as to match high-frequency changes in the focus parameter.