Total Magnetic Charge for Fast Screening of Highly Contaminated UXO Sites

Abstract

The use of total normalized surface magnetic charge is proposed for the purpose of rapidly scanning highly contaminated unexploded ordnance (UXO) sites as well as for the application in UXO discrimination. Recent studies have demonstrated that in the electromagnetic induction (EMI) sensing considered here (tens of hertz up to several hundreds of kHz), the surface magnetic charge model (SMC) can reproduce EMI responses from any metallic object very quickly and accurately. In SMC the scattered magnetic field at any point outside a fictitious surface, surrounding the scatterers, is represented as a sum of quasi-static magnetic fields produced by equivalent elementary magnetic charges placed on the fictitious surface. In this work a fictitious plate, placed on the ground is used as fictitious surface. The amplitudes of SMC are determined by matching the scattered magnetic field to data at measurement grid points. Once the amplitudes of SMC are found then the total normalized magnetic charge is calculated, and it can be used effectively as a discriminator. In cases of highly contaminated sites, first data are taken for a cluttered site and its corresponding total magnetic charge is calculated and stored. Then, for any new nearby test site the total magnetic charge is calculated again. The total normalized charge for cluttered data is subtracted from the total for the new site, and thus the object is isolated from the clutter. Finally, for discrimination the object's total magnetic normalized charge is matched to cataloged/library data. Several numerical results are presented to demonstrate applicability of the total magnetic charge as a classifier in highly contaminates UXO sites.