Convolution-Backprojection Image Reconstruction For Bistatic Synthetic Aperture Radar With Correction For Wavefront Curvature And Propagation Attenuation

Space-Variant Post-Filtering for Wavefront Curvature Correction in Polar-Formatted Spotlight-Mode SAR Imagery

“…This method is discussed in two papers by Jerald Bauck [30,31], which served as the preliminary work leading to his Ph.D. dissertation [32]. In discussing the wavefront curvaturecorrecting variation of CBP, Bauck states that with his method, "The task can be fairly easy, although requiring somewhat more computation that Fourier-based methods which use an FFT but do not correct for wavefront curvature.')…”

A Rationale for Backprojection in Spotlight Synthetic Aperture Radar Image Formation

“…The measured field should thus perhaps be inverted by a kind of partial Fourier transform or computationally propagated to the far field before normal Fourier inversion. In the context of backprojection, the solution lies in backprojecting along circular arcs [3,4,5,6] rather than the straight lines considered herein; this is not a Fourier inversion as discussed in Section §4 except in the limit. Since speckle hinders image interpretation, many methods have been devised to reduce or eliminate its effect including noncoherent averaging of subimages and linear or nonlinear filtering.…”

“…which can ease computations in some cases 6 . Notably, for a particular angle θ, if p (•) is an impulse, the projection of the ground patch at angle θ is returned directly as the receiver signal but with a scaling by 1/2 in amplitude and distance-stretched in space.…”

“…But always, the approximation and its effects are monitored so that results maintain their validity within carefully stated limits of operating parameters-and numerous books, for example [2], and hundreds of papers have been written detailing methods to correct, counteract, focus, and otherwise adjust for the approximation. Alternately, spherical waves also lend themselves to backprojection methods [3,4,5,6,7,8] including elliptical backprojections in the case of bistatic modes. In practice the plane wave assumption is aided by the fact that the antenna limits the angular extent of the radiated field so that the error caused by actual wavefront curvature remains small or at least approximately known over the illuminated area, where "small" is related to angular and range resolution, and wavelength.…”

Brief Analysis of Aliasing in Polar and Keystone Formats for Spotlight Synthetic Aperture Radar

“…Both approximations tend to truth as the distance between the radar and the ground patch is large while the ground patch is small. Methods exist to compensate for nonplanar waves [2] and other methods exist to remove both approximations [3,4,5,6].…”