Uxo Detection at Jefferson Proving Ground Using Ground-penetrating Radar

We have used ground-penetrating radar (GPR) to detect UXO and non-ordnance on the 40-acre site (lot 54) of Jefferson Proving Ground, Indiana. The UXO are buried within about 1 m deep in a clayey silt for which the soil water content ranged from moist near the surface to near saturation at about 1 m. We used a 16-bit radar to profile along previously established lines, and transects over artificial targets we emplaced. We recorded data at 48–64 traces/s with minimal towing speeds during both dry and rainy weather. Target responses at both 300 (time range of 50 ns) and 600 MHz (30 ns) ranged from discrete diffractions to short reflection segments. The loss of the soil greatly attenuated diffraction hyperbolas. Theoretical analyses of these hyperbolas give an average soil dielectric constant of 10 at both 300 and 600 MHz. The phase polarity of many of the reflected and diffracted wavelets indicate targets with wave impedances higher than that of the soil. We therefore assume these targets to be metallic and the responses of some, whose locations correlate with the position of UXO on burial maps, are shown in detail. Theoretical modeling of wavelet propagation for this soil confirms the high rate of attenuation (47–66 dB/m round trip), the maintenance of waveform, a shift in wavelet local frequency, and response to a typical UXO. We conclude that GPR is effective for finding targets in this type of soil to no more than 2 m depth. We recommend that future surveys utilize high trace acquisition rates to capture the full target responses and a prowed, heavy dielectric antenna sled to improve antenna-to-ground coupling and deflect surface obstacles such as vegetation.