Semi-analytical calculation of Jacobian in the electromagnetic inverse scattering problem

Discrimination of unexploded ordinance (UXO) from widespread metallic clutter remains a very urgent environmental remote sensing problem. One of the most promising technologies for such discrimination is ultra-wideband low frequency electromagnetic induction (EMI), operating from a few Hz up to a few hundred kHz. The numerical hybrid of the full method of auxiliary sources (MAS) and the MAS-thin skin approximation (MAS-TSA) (Shubitidze, F. et al., Proc, ACES, 2003; IEEE Trans. Geosc. & Remote Sens., vol.40, no.4, p.928-42, 2002) solves the forward governing equations very efficiently. Solving the inverse problem numerically requires calculation of the gradient of the system Jacobian. In the hybrid full MAS/MAS-TSA method, one obtains an analytical form of this gradient, producing an overall semi-analytical system for inferring a metallic object's electromagnetic parameters. We illustrate our main ideas with a simple body of revolution problem, and results are compared with measured data. The method can readily be extended to general inverse electromagnetic scattering problems at higher frequencies.