Wide beam sar focusing method using navigation solution derived from autofocus data

Abstract

An algorithm for deriving improved navigation data from the autofocus results obtained from selected image blocks in a wide-beam synthetic aperture radar (SAR) image. In one embodiment the navigation error may be approximated with a vector of low-order polynomials, and a set of polynomial coefficients found which results in a good phase error match with the autofocus results. In another embodiment, a least squares solution may be found for the system of equations relating the phase errors at a point in time for selected image blocks to the navigation error vector at that point in time. An approach using low sample rate backprojection () initially to select suitable image blocks, and full sample rate backprojection () for the selected image blocks, followed by full sample rate backprojection () for the image, using the improved navigation solution, may be used to reduce the computational load of employing the algorithm.