Applications of Synthetic Aperture Radar (SAR) to UXO Delineation

Abstract : The clearing of areas contaminated with unexploded ordnance (UXO) is the Army s highest priority Environmental Restoration problem. The Department of Defense (DoD) currently spends millions of dollars annually on UXO cleanup efforts. Initial evaluation of a UXO contaminated area involves the review of historical documents, surface walkovers of randomly chosen areas, and statistical modeling to estimate the ordnance in place. Presently, there are no efficient and cost-effective means of estimating the extent of contamination at UXO sites. The foliage penetration (FOPEN) synthetic aperture radar (SAR) involved in an Advanced Technology Demonstration (ATD) funded by Defense Advanced Research Projects Agency (DARPA) has the potential for delineating ordnance impact areas at a fraction of the time and cost incurred using current methods and technology. The FOPEN SAR is an ultrawide-band (UWB) system that uses low frequencies to achieve foliage penetration. The system has a very high frequency (VHF) frequency range of approximately 20-70 MHz and ultra high frequency (UHF) range of approximately 200-500 MHz. Its basic operating principle involves transmitting of pulsed radio frequency waves and receiving the echoes scattered from targets and the ground surface. The echoes are subjected to analog preprocessing, digitized, and further digitally processed to produce the final imagery. The UHF band is a fully polarimetric (HH1, VV2, HV3) side-looking radar. The VHF band operates with HH polarization. A test grid containing three target sizes was established to determine the feasibility of using the FOPEN SAR to delineate UXO ranges. The targets were 155-mm projectiles and objects representing 500- and 2,000-lb bombs. Each type of target was arranged in grids of sparse, moderate, and dense arrays in an open field with low ground cover. Some targets were placed under trees. No targets were buried because of environmental restrictions on Camp Navajo, Arizona.