Analysis of Localized High Magnetic Susceptibility Zones at Jefferson Proving Ground, Indiana
ENGINEER RESEARCH AND DEVELOPMENT CENTER VICKSBURG MS GEOTECHNICAL AND STRUCTURES LAB
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Detection and discrimination of unexploded ordnance UXO and landmines with total field magnetic and electromagnetic induction EMI sensors can be severely inhibited by large variations in background magnetic susceptibility. Sites in Hawaii, USA, and similar settings have very high magnetic susceptibility over the entire site due to the basaltic soils. The basaltic soils exhibit magnetic viscosity, which is frequency dependence of the magnetic susceptibility. This makes detection of UXO or landmines difficult. There are current efforts to model the influence of magnetic susceptibility variations on geophysical data. A different situation exists at sites such as Jefferson Proving Ground, IN, USA, where sections of the site exhibit variations in magnetic susceptibility that are of the same spatial wavelength and amplitude as the target UXO or landmines. The JPG soils do not exhibit magnetic viscosity. We have collected total magnetic field data over several grids as well as lines of magnetic susceptibility data with two instruments and at three frequencies over several of the anomalous regions. We have also collected soil samples at three depths at stations along these lines and measured their magnetic susceptibilities in the lab at two frequencies. We have found a correlation between the surface geology, topography, and magnetic susceptibility measurements. Also, the variations in magnetic susceptibility with depth are a function of the variable weathering and mineral transport due to surface water runoff through the areas of lower elevation. We are currently developing a laboratory measurement system to measure magnetic susceptibility at discrete frequencies from 30 Hz to 100 kHz. This capability will allow us to model the various EMI measurement systems currently in use and filter the background magnetic susceptibility variations.
- Ammunition and Explosives
- Electricity and Magnetism