Motion compensation algorithm for widebeam stripmap SAR

In synthetic aperture radar (SAR) imaging, generation of fine resolution imagery requires measurement and compensation for the relative translational and rotational motions between the antenna phase center (APC) and the scene being imaged. A difficulty arises when motion compensating stripmap mode signal history data from a SAR requiring a wide angle azimuth beamwidth. In general, the required compensation varies with scatterer location within the azimuth beam. The usual approach in stripmap motion compensation is to ignore this requirement and to compensate only the component of sensor motion in the nominal antenna boresight direction (usually broadside). In the widebeam system, this procedure can lead to unacceptable phase errors even if sensor motion is measured without error. In this paper, we survey the motion compensation challenge to ultra-wideband/widebeam (UWB/WB) SAR image formation. The emphasis here is on formation of fine resolution digital imagery from low frequency (VHF/UHF) UWB/WB data collected in stripmap mode by an airborne SAR system . We examine differences in motion compensation requirements and approaches between a UWB/WB system and a conventional X-band SAR system. This paper presents an improved motion compensation algorithm applicable to widebeam stripmap SAR. We demonstrate this procedure with imagery from the fine resolution ARPA/ERIM/NAWC P3 ultra-wideband radar system.