Estimation and correction of phase for focusing search mode SAR images formed by range migration algorithm

摘要

A method for acquiring synthetic aperture images of stationary targets converts a plurality of radar signals stored as digital values and motion compensated to a first order into a well focused image. The digital values are Fourier transformed, match filtered and interpolated using a Stolt interpolator, then skewed to reorient distortions arising from imperfect motion compensation, generating an image data, descriptive of the stationary targets in the range and cross range (azimuth) direction. The image data is divided into a plurality of overlapping sub-patches in, preferably, the cross track (azimuth) direction. Each sub-patch containing a portion of the image data and overlapping data. The overlapping data is part of the image data and common between two or more of the overlapping sub-patches. ??Each of the overlapping sub-patches is individually focused using autofocus means to obtain focused sub-patches having a phase. The phase is adjusted for each of the focused sub patches to obtain a continuous phase with respect to one or more of the focused sub-patches, thereby obtaining smooth phase transition sub-patches. The synthetic aperture images of stationary targets are computed (446,448,450) after concatenating the smooth phase transition sub-patches. IMAGE