Polarimetric 3-D Reconstruction from Multi-Circular SAR at P-Band

Abstract

Three-dimensional reconstruction and sub-wavelength resolution can be achieved in the circular synthetic aperture radar (CSAR) imaging mode with a single pass. 3-D volumetric reconstruction over 360° is inherent in the multi-angular measurements and allows the formation of holographic tomograms. However, sidelobe artifacts like circles or arcs are present in the (x,y) image plane when the assumed height during focusing is not that of the target. In 3-D imaging these artifacts are seen as cone-shaped sidelobes due to the poor resolution in the direction perpendicular to the line-of-sight (LOS) [1]. They are addressed in this paper with multi-circular SAR, which is the formation of a synthetic aperture in height with several circular-like flights. 2-D images in the slant-range plane are focused with the fast factorized back-projection (FFBP) algorithm adapted to circular trajectories. Beamforming (BF) and compressive sensing (CS) are used to retrieve the energy in the third dimension. Furthermore, a novel phase calibration method using the singular value decomposition (SVD) is presented. A multi-circular SAR campaign using DLR’s F-SAR system at P-band over the region of Vordemwald, Switzerland, is described. The aim of this experiment is to show the first fully-polarimetric holographic SAR tomogram of a forested region. A comparison of stripmap SAR and circular SAR is also included.