2-D Autofocus Algorithm for Ultra-high Resolution Airborne Spotlight SAR Imaging

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,an important drawback of the conventional autofocus algorithms is that they are able to compensate for only one-dimensional azimuth phase errors.As the resolution increase,residual range cell migration,which makes the defocus inherently two-dimensional(2-D),becomes a new challenge.In this paper,the analytical relationship between the residual range cell migration and azimuth phase error in polar format imagery is developed.Utilizing this relationship,a 2-D autofocus algorithm that can simultaneously compensate for the residual range migration and azimuth phase error is proposed.The results of real data processing validate the effectiveness of the proposed method.