Autofocus Correction of Azimuth Phase Error and Residual Range Cell Migration in Spotlight SAR Polar Format Imagery

摘要

Synthetic aperture radar (SAR) images are often blurred by phaseperturbations induced by uncompensated sensor motion and /or unknownpropagation effects caused by turbulent media. To get refocused images,autofocus proves to be useful post-processing technique applied to estimate andcompensate the unknown phase errors. However, a severe drawback of theconventional autofocus algorithms is that they are only capable of removingone-dimensional azimuth phase errors (APE). As the resolution becomes finer,residual range cell migration (RCM), which makes the defocus inherentlytwo-dimensional, becomes a new challenge. In this paper, correction of APE andresidual RCM are presented in the framework of polar format algorithm (PFA).First, an insight into the underlying mathematical mechanism of polarreformatting is presented. Then based on this new formulation, the effect ofpolar reformatting on the uncompensated APE and residual RCM is investigated indetail. By using the derived analytical relationship between APE and residualRCM, an efficient two-dimensional (2-D) autofocus method is proposed.Experimental results indicate the effectiveness of the proposed method.