Convex optimization of subspace fitting autofocus for stripmap SAR images

There are many different autofocus algorithms for correcting phase errors in stripmap SAR images. In this paper, we develop a mathematically principled model-based phase error estimation method for stripmap SAR images. The proposed phase estimation method uses classical subspace fitting techniques that are well known in the array processing literature. The novelty in this paper is the development of the proposed autofocus method and how the phase estimates are found using convex optimization. It is shown that the proposed method is non-iterative in the sense that iterations between the image domain and the range compressed domain to obtain our phase error estimates are not needed. It is also shown that the phase error estimates can be applied while simultaneously forming the SAR image using the convolution back-projection algorithm.