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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

Wavefront curvature defocus effects can occur in spotlight-mode SAR imagery wh constructed via the well-known polar formatting algorithm (PFA) under certain scenarios include imaging at close range, use of very low center frequency, and/or imaging of very large scenes. The range migration algorithm (RMA), also known as seismic migration, was developed to accommodate these wavefront curvature effects. However, the along-track upsampling of the phase history data required of the original version of range migration can in certain instances represent a major computational burden. A more recent version of migration processing, the Frequency Domain Replication and Downsampling (FReD) algorithm, obviates the need to upsample, and is accordingly more efficient. In this paper we demonstrate that the combination of traditional polar formatting with appropriate space-variant post-filtering for refocus can be as efficient or even more efficient than FReD under some imaging conditions, as demonstrated by the computer-simulated results in this paper. The post-filter can be pre-calculated from a theoretical derivation of the curvature effect. The conclusion is that the new polar formatting with post filtering algorithm (PF2) should be considered as a viable candidate for a spotight-mode image formation processor when curvature effects are present.

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