Enhanced imaging over complete circular apertures

We consider enhanced imaging methods for spotlight synthetic aperture radar (SAR) data collected over a complete circular aperture of 360 degrees. Circular SAR has two unique features to its wide-angle non-planar collection geometry. First, it provides wide-angle information about the unisotropic reflectivity of the scattering centers in the scene. Second, unlike the linear collection geometry circular SAR reveals three dimensional information about the location of the scattering centers in the spotlighted area. In this paper, first we review traditional imaging techniques for far-field circular SAR geometries and present a GLRT based three dimensional imaging algorithm matched to limited persistence scatterers. The 3-D resolution of the circular SAR systems are limited by the sparse sampling elevation and the limited persistence of the reflectors in the scene. We employ Cramer-Rao bound analysis to characterize 3-D resolution for circular SAR systems for point targets with limited persistence. Finally we present an enhanced imaging algorithms with non-quadratic regularization providing a sparse description of the target scene that is consistent with the collected SAR data with reduced sidelobes.