The Department of Defense (DoD) maintains an inventory of millions of acres of land that are potentially contaminated with unexploded ordnance (UXO). On the majority of these sites, the ordnance contamination is concentrated on former impact ranges and training areas, with the remainder of the site ordnance-free. Initial identification and delineation of UXO-contaminated areas is currently accomplished by the review of historical documents, ground-based geophysical surveys, and statistical modeling. This approach is often time consuming and costly. This project explored the feasibility of using an airborne radar system for the delineation of UXO ranges.
The Defense Advanced Research Projects Agency (DARPA) has funded the development of an airborne, foliage penetration (FOPEN), synthetic aperture radar (SAR) system for the purpose of detecting vehicles hidden by foliage. The SAR operates by emitting a signal in the megahertz frequency range and measuring the signal reflected from objects in the sensor's field of view. Objects producing a reflection can include trees, brush, surface water, cultural features (e.g., buildings, fences, and vehicles), UXO, explosive waste, and possibly shallow subsurface features. Data are processed to form an image of the surveyed area.
The UXO demonstration was conducted concurrently with a larger DARPA test of the system at Camp Navajo, Arizona. A test grid containing three target sizes was established to determine the feasibility of using the FOPEN SAR to delineate UXO ranges. Simulants of 2000-pound (lb) bombs, 500-lb bombs, and 155-millimeter (mm) projectiles were placed on the surface in arrangements of clusters and single items.
The study showed that a low frequency, limited bandwidth SAR system was capable of imaging isolated items the size of a 500-lb bomb and clustered targets the size of 155-mm in an uncluttered environment. Combining multiple look angles improved detection. The study also confirmed that a limited, low-frequency bandwidth is not sufficient for detecting smaller targets. The image modeling suggests that a combination of features, such as frequency response, polarization, and aspect angle, may allow separation of surface UXO from clutter. A restriction on digging at Camp Navajo prevented investigation of airborne SAR system capabilities for imaging buried UXO.
This project determined that the FOPEN SAR is capable of delineating UXO in benign environments where large concentrated ordnance is present on the surface. Further testing is required to determine if the FOPEN SAR system is capable of imaging buried UXO and its limitation of detecting UXO in a variety of foliage. An airborne system for delineating UXO impact ranges would provide savings in both cost and time in the cleanup of UXO-contaminated areas. (Project Completed - 2004)