Focused SAR image formation of moving targets based on doppler parameter estimation

This paper addresses the problem of focusing moving targets in synthetic aperture radar (SAR) images. This task is solved here by using an inverse SAR (ISAR) technique. The ISAR technique performs an autofocus procedure by implementing exhaustive search algorithms, which are improved by classical convex optimization, of functions based on image contrast or entropy. In this paper, we discuss the possibility to perform an autofocus ISAR technique by exploiting the estimation of the target Doppler parameters, namely the Doppler centroid and the Doppler rate, which are related to the target motion parameters. The present algorithm is based on the reuse of efficient autofocus approaches that are classically used in direct SAR imaging. The effectiveness of the proposed method is tested on COSMO-SkyMed Spotlight SAR data of maritime targets. Furthermore, the proposed Doppler parameter estimation algorithm is compared with a well-known ISAR technique, namely the image-contrast-based technique.