Signal processing techniques for ultra-wideband synthetic aperture radar data

The U. S. Army Research Laboratory (ARL), as part of its mission-funded applied research program, has been evaluating the utility of a low-frequency, ultra-wideband (UWB) imaging radar to detect tactical vehicles concealed by foliage. Measurement programs conducted at Aberdeen Proving Ground and elsewhere have yielded a significant and unique database of extremely wideband and (in some cases) fully polarimetric data. Complementary efforts have been underway to develop high-performance algorithms as well as data visualization and assessment tools to generate very high-quality, low-artifact-level imagery for use in target detection and exploitation studies. Prior reports have concentrated on discussions of emerging detection concepts. Key strategy has been to exploit frequency-dependent scattering to identify and locate likely targets-particularly the application of a "spatial affinity" technique between detection lists separately generated at VHF frequencies versus UHF. The utility of this approach is now being evaluated more broadly by the UWB radar community. A large quantity of appropriate data has been measured by two separate airborne radars-a VHF radar (Coherent All RAdio BAnd Sensing (CARABAS)) [1,2] and a UHF radar (the P-3 radar) [3,4]. In support of Defense Advanced Research Project Agency's (DARPA) national-scope initiative in foliage penetration, ARL is using tools and algorithms developed as part of our mission program to perform image formation and evaluate various spatial affinity concepts on this freshly measured data. The reader will find this paper is organized into three complementary sections. First, we define the research objectives ARL and other defense organizations share. We then report in detail on the signal processing/image formation techniques developed as part of our mission program. We conclude with a discusssion on the use of these algorithms and tools with the emerging data from major defense-wide collections. Imaging concepts are discussed and various quality metrics are provided.