Identification Of Uxo With Surface Magnetic Charges On A Sphere

Discrimination of buried unexploded ordnance (UXO) with electro-magnetic sensors requires robust predictive models to correctly interpret data recorded at the surface. Shubitidze et al. have recently suggested a representation of the Electromagnetic Induction (EMI) response of a metallic object by using a model of Normalized Surface Magnetic Charges (NSMC) distributed on a spheroidal surface enclosing the target. Their results suggest that the Total Normalized Magnetic Charge (TNMC), the integral of NSMC over the spheroid, can be used to identify the object. The interpretation however is much simpli ed by using a sphere. Theoretical considerations show that the scattered eld of a spherical object is purely dipolar. The associated NSMC istribution is uniform on a sphere and the TNMC is directly related to the magnetization tensor and sphere radius. These concepts have impacted upon our approach where we estimate the charge distribution on the surface of the sphere by solving a linear inverse problem. An additional bene t of using a sphere instead of a spheroid is that it is no longer necessary to specify the orientation parameters of the buried object. Azimuth and dip are instead revealed in the recovered surface charge distribution. We nd that this formulation helps develop a robust NSMC that has potential for practical discrimination of UXO. We demonstrate our approach by using Geonics EM63 data collected at the USACE-ERDC test stand in Vicksburg, MS.