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25 May 2005 EMI obscuration of buried UXO by geophysical magnetic permeability, anthropogenic clutter, and by magnitude disparities
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For UWB (30 Hz - 100 kHz) electromagnetic induction (EMI) sensor discrimination of unexploded ordnance (UXO), we evaluate first the effects of significant magnetic permeability in the surrounding soil. Measured data and theoretical arguments suggest that ground effects can often be accounted for by using a simple halfspace analytical solution. Thus, when target responses are strong enough, free-space target signature shapes can still be used for discrimination if properly compensated. At the same time, even in artificially well-mixed, physically smoothed settings, local variations in soil permeability can be a significant source of signal clutter. Cases with multiple UXO’s beneath dispersed small metallic clutter are also considered as instances in which clutter may dominate. In simulations of two comparably sized UXO’s at comparable depths with a signal to clutter ratio (SCR) of ~ 20, UWB data distinguishes the two objects reliably over a ground surface measurement grid. For similar cases but with the objects at significantly different depths relative to one another, one cannot distinguish the deeper target, even with the same noise level and with UWB data. Measurements illustrate the level of EMI SCR to be expected from dispersed small metallic items collected from a firing range. For cases with a single piece of clutter and a much more massive UXO immediately below, simulations show almost complete obscuration of the UXO, in both frequency and time domains. This is not caused by signal blockage but results from different degrees of proximity to the sensor, i.e. from the consequent signal magnitude disparity.
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K. O'Neill, F. Shubitidze, K. Sun, I. Shamatava, and K. Paulsen "EMI obscuration of buried UXO by geophysical magnetic permeability, anthropogenic clutter, and by magnitude disparities", Proc. SPIE 5811, Targets and Backgrounds XI: Characterization and Representation, (25 May 2005);

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