Subspace fitting based autofocus for stripmap SAR

There are many autofocus algorithms available for correcting uncompensated residual phase errors in SAR data. Most of these algorithms depend on the SAR modality (i.e. spotlight, stripmap, etc.). In this paper, we develop a mathematically principled model-based phase error estimation method for stripmap SAR. The proposed phase estimation method uses classical subspace fitting techniques that are well known in the array processing literature. It is shown that the proposed method is non-iterative in the sense that iterations between the image domain and the range compressed domain are not required in order to obtain the phase error estimates. As the derivation shows, the image does not need to be formed in order to obtain the phase error estimates.