ULTRA-WIDE-BAND SAR INTERFEROMETRY

We introduce ultra-wideband synthetic aperture radar (SAR) interferome try as a new technique for topographic height retrieval. It is based o n using a SAR system with large relative bandwidth that acquires data along two parallel tracks with a separation of the same order of magni tude as the Eight altitude. The complex SAR image data are resampled o nto a common reference surface, filtered, and followed by a Hermitian multiplication. The resulting interferogram is shown to have a finite depth-of-focus (DOF) in terms of phase coherence. The achieved height precision is controlled by the ambiguity height, which is shown to sca le to the DOF as the relative bandwidth, This means that only one frin ge is within the DOF as the resolution approaches the fundamental wave length limit; i.e., the phase is unambiguously related to topographic height. The topography may thus be determined by changing the referenc e surface and retrieving the height at each step. The technique is suc cessfully demonstrated to generate fringes based on VHF-band data acqu ired by the CARABAS airborne SAR system. Temporal decorrelation is not a problem due to the long wavelengths nor is the effect of tropospher ic delay on the retrieved height.