An Autofocus Method for SAR Frequency-Domain Backprojection Imaging

Frequency-Domain Backprojection Algorithm (FDBP) is a new imaging method which is more efficient than Time-Domain Backprojection Algorithm (TDBP) and also can be applied to arbitrary aperture geometry. And autofocus method is a vital technology for high- precision Synthetic Aperture Radar (SAR) imaging, especially for Airborne SAR. However, traditional autofocus methods usually suffer from heavy computation burden or compensate partly, and there are no special autofocus methods for FDBP. In this paper, a novel fast autofocus method is proposed for FDBP to compensate phase error in wavenumber domain by estimating motion error. The estimated error of Antenna Phase Centers (APCs) can be applied to imaging achieving the spectrum compensation for the whole scene. The motion error is estimated based on the optimal criterion of maximum image sharpness. The expression of APC error estimation is derived and Conjugate Gradient (CG) is utilized to solve the optimization problem. The simulation and experimental examples verify the validity of the proposed method.