Contrast based Mapdrift algorithm for SAS autofocus

In order to obtain high quality SAS image, phase error in SAS image is required to be corrected. Mapdrift algorithm is a traditional SAR autofocus algorithm which is used to correct quadratic phase error. In this paper Mapdrift algorithm is used to autofocus SAS image. For images without strong distributed target, traditional Mapdrift algorithm can get promising results, but for images containing strong distributed target, the performance of traditional Mapdrift algorithm deteriorates. To alleviate the influence of the strong distributed target, a new contrast criterion selecting range bins is presented in this paper. Experiment data from lake trial shows validity of the improved algorithm to autofocus stripmap SAS image.