General Formulation for Wavefront Curvature Correction in Polar-Formatted Spotlight-Mode SAR Images Using Space-Variant Post-Filtering

I n this paper, we introduce a general formulation f o r wavefront curvature correction an spotlight-mode S A R images formed using the polar-formatting algorithm (PFA). This correction is achieved through the use of a n eficient, image domain space-variant filter which is applied as a post-processing step to PFA. Wavefront curvature defocus effects occur in certain S A R collection modes that include imaging at close range, using low center frequency, and/or imaging very large scenes. Our formulation is general in that it corrects f o r wavefront curvature in broadside as well as squinted collection modes, with n o computational penalty f o r correcting squint-mode images. Algorithms such as the range migration technique (also known as seismic migrat ion), and a recent enhancement known as frequency dom a i n replication, FReD, have been developed to accommodate these wavefront curvature effects. However, they exhibit n o clear computational advantage over space-variant post-filtering in conjunction with polar formatting (PF2). This paper will present the basic concepts of the formulat ion, and will provide computer results demonstrating the capabilities of space-variant post-filtering.