Detection of above ground and subsurface unexploded ordnance using ultra-wideband (UWB) synthetic aperture radar (SAR) and electromagnetic modeling tools

Recent development of wideband, high-resolution synthetic aperture radar (SAR) technology has shown that detecting buried targets over large open areas may be possible. Ground clutter and soil type are two limiting factors influencing the practicality of using wideband SAR for wide-area target detection. In particular, the presence of strong ground clutter because of the unevenness, roughness, or inconsistency of the soil itself may limit the radar's capability to resolve the target from the clutter. Likewise, the soil material properties can also play a major role. The incident wave may experience significant attenuation as the wave penetrates lossy soil. In an attempt to more fully characterize this problem, fully polarimetric ultrawideband (50-1200 MHz) measurements have been taken by the U.S. Army Research Laboratory's SAR (BoomSAR) at test sites in Yuma, Arizona, and Eglin Air Force Base, Florida. SAR images have been generated for above-ground and subsurface unexploded ordnance (UXO) targets, including 155-mm shells. Additionally, a full-wave method of moments (MoM) model has been developed for the electromagnetic scattering from these same targets, accounting for the lossy nature and frequency dependency of the various soils. An approximate model based on physical optics (PO) has also been developed. The efficacy of using PO in lieu of the MoM to generate the electromagnetic scattering data is examined. We compare SAR images from the measured data with images produced by the MoM ('exact') and PO (approximate) simulations by using a standard back-projection technique.