Precise Autofocus for SAR Imaging Based on Joint Multi-Region Optimization

Autofocus method is a vital technology for high resolution and wide swath airborne Synthetic Aperture Radar (SAR) imaging. The autofocus algorithms via phase errors estimation and traditional Antenna Phase Centers (APC) errors estimation cannot completely compensate for the phase error of each pixel for the large scene ignoring the spatial variance, which results in corrupted SAR imagery for some part of the scene. In this paper, an autofocus algorithm through precise APC errors estimation based on joint multi-region is proposed to compensate motion error for the whole scene greatly. We established an image intensity model for strong point targets in multi-region with the weight coefficient to estimate APC errors. Moreover, the partial derivative of image intensity is simplified which can easily derive higher order criterion like image sharpness and Conjugate Gradient (CG) is utilized to solve the optimization problem. The simulation and experimental examples verify the effectiveness of the proposed method compared with traditional methods.