Ultra-wideband SAR interferometry

Abstract

We introduce ultra-wideband synthetic aperture radar (SAR) interferometry as a new technique for topographic height retrieval. It is based on using a SAR system with large relative bandwidth that acquires data along two parallel tracks with a separation of the same order of magnitude as the flight altitude. The complex SAR image data are resampled onto 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 scale to the DOF as the relative bandwidth. This means that only one fringe is within the DOF as the resolution approaches the fundamental wavelength limit; i.e., the phase is unambiguously related to topographic height. The topography may thus be determined by changing the reference surface and retrieving the height at each step. The technique is successfully demonstrated to generate fringes based on VHF-band data acquired by the CARABAS airborne SAR system. Temporal decorrelation is not a problem due to the long wavelengths nor is the effect of tropospheric delay on the retrieved height.

Estimation of forest parameters using CARABAS-II VHF SAR data

“…This is a prerequisite for improving geocoding, correctly calculating the correct projection factor, and for studying effects of ground slopes. In [22], Ulander and Frölind concluded that ultra-wideband SAR interferometry, using the CARABAS-II sensor, has a potential for automated and rapid high spatial resolution, wide-area topographic mapping.…”

Interferometric polarimetric synthetic aperture radar system

“…However, polarimetry deals with the vector nature of the electromagnetic waves, and its strength resides in the physical meaning of the observables 2 . Furthermore, interferometry brings with it range ambiguities that limit its usefulness 3 . The application of polarimetry to SAR interferometry has demonstrated the possibility of optimizing the coherence.…”

Direct observations of asteroid interior and regolith structure: Science measurement requirements

“…Therefore, radar requirements and performance are driven by the geometry and not by the pattern. Due to the asteroid's small dimension, range and Doppler are not separable and full-SAR processing including range compensation is required, as for Ultra-Wide Band (UWB) radar (Ulander and Frolind, 1998). In this geometry, the performance will vary with the latitude and the longitude on the asteroid surface (resolution, sensitivity, ambiguity ratios, etc.…”