A residual range cell migration correction algorithm for SAR based on low-frequency fitting

Synthetic aperture radar (SAR) images are often blurred by uncompensated radar motion errors. To get refocused images, autofocus proves to be a useful postprocessing technique. However, a severe drawback of the autofocus algorithms is that they are only capable of removing one-dimensional azimuth phase errors. Motion errors induce residual range cell migration (RCM) on SAR data as well. When residual RCM is within a range resolution cell, it can be neglected. However, the residual migration, which exceeds a range cell, is increasingly encountered as resolution becomes finer and finer. A novel residual RCM correction method based on low-frequency fitting is proposed in this paper. By fitting the low frequency phase difference of adjacent azimuth cells by the least-squares method, residual RCM of each azimuth cell is corrected precisely and effectively. Simulations are carried out to validate the effectiveness of the proposed method.