Extension of Map-Drift Algorithm for Highly Squinted SAR Autofocus

For highly squinted synthetic aperture radar (SAR) imaging, the Omega-k algorithm is generally accepted as an effective focusing processor. However, the performance of the Omega-k algorithm may be degraded by the trajectory deviations due to the precision limitation of the navigation system in airborne SAR. In this paper, we focus on the autofocusing approach, which is compatible with the Omega-k imaging for highly squinted SAR. This new autofocusing approach can be viewed as an extension version of the conventional map-drift (MD) algorithm, which has been widely used in the broadside mode. Two-step process is performed in the proposed autofocusing method: 1) the range-independent phase-error is first retrieved by a squinted MD (SMD) estimator; and 2) a squinted range-dependent MD (SRDMD) estimator is proposed to derive the residual range-variant phase-error. By correcting the phase-errors obtained from SMD and SRDMD, the highly squinted SAR data can be finally focused. The effectiveness of the proposed algorithm has been demonstrated by both simulated and real-measured SAR data in highly squinted mode.