HR: 15:00h
AN: NS33A-04    [Abstracts]
TI: GPR Profiling Of Lacustrine Stratigraphy With Embedded Targets: A Case History of UXO Detection
AU: * Arcone, S A
EM: steven.a.arcone@erdc.usace.army.mil
AF: U.S. Army ERDC-CRREL, 72 Lyme Road , Hanover, NH 03755, United States
AU: Finnegan, D C
EM: david.finnegan@erdc.usace.army.mil
AF: U.S. Army ERDC-CRREL, 72 Lyme Road , Hanover, NH 03755, United States
AB: We used ground-penetrating radar, mainly at 135 MHz, to profile the subbottom sedimentation of a small lake in south central New Hampshire, and to detect and characterize likely unexploded ordnance lying upon and embedded within it. The lake itself had been a bombing range for a variety of munitions. Maximum water depth was 8.5 m. The low water conductivity, flat surface and the near perfect antenna contact with the water provided ideal electromagnetic survey conditions. Small percentages of expandable clays were probably responsible for up to 8 m of subbottom penetration into deltaic deposits and to bedrock beneath deeper basin deposits. Penetration into bedrock itself is also evident. Comparative surveys on non hazardous Squam Lake in New Hampshire verified the geological nature of the strata and of false targets. Likely UXO were detected by the unique phase signature of their diffractions and exceptional amplitudes. Controlled experiments verified phase consistency of the diffractions from all angles and polarizations. We used wave migration to identify target type where target density was too great to exploit wavelet phase. We interpret perforated horizons underlain by diffractions having appropriate phases to be evidence of craters and UXO. Most false targets appear to be trees, most likely drowned when the lake was dammed in the mid nineteenth century, and blown down by detonations along the shores. We conclude that lake sediments in resistive water are ideal media for detection of UXO and that target identification could be improved with cross polarization profiles.
DE: 0925 Magnetic and electrical methods (5109)
DE: 0994 Instruments and techniques
DE: 1861 Sedimentation (4863)
DE: 4239 Limnology (0458, 1845, 4942)
SC: Near-Surface Geophysics [NS]
MN: 2007 Joint Assembly