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

TL;DR

This paper introduces a novel 2-D autofocus method for Spotlight SAR polar format imagery that effectively corrects azimuth phase errors and residual range cell migration, improving image focus quality.

Contribution

It presents a new formulation of polar reformatting and an analytical relationship between APE and RCM, enabling a comprehensive 2-D autofocus correction approach.

Findings

The proposed method effectively refocuses SAR images with residual RCM.

Experimental results demonstrate improved image clarity and focus.

The approach outperforms conventional 1-D autofocus algorithms.

Abstract

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