General formulation for wavefront curvature correction in polar-formatted spotlight-mode SAR images using space-variant post-filtering

We introduce a general formulation for wavefront curvature correction in spotlight-mode SAR images formed using the polar-formatting algorithm (PFA). This correction is achieved through the use of an efficient, image domain space-variant filter which is applied as a post-processing step to the PFA. Wavefront curvature defocus effects occur in certain SAR collection modes that include imaging at close range, using a low center frequency, and/or imaging very large scenes. Our formulation is general in that it corrects for wavefront curvature in broadside as well as squinted collection modes, with no computational penalty for correcting squint-mode images. Algorithms such as the range migration technique (also known as seismic migration), and an enhancement known as frequency domain replication, FReD, have been developed to accommodate these wavefront curvature effects. However, they exhibit no clear computational advantage over space-variant post-filtering in conjunction with polar formatting (PF2). This paper presents the basic concepts of the formulation, and provides computer results demonstrating the capabilities of space-variant post-filtering.