UXO signature extraction from measurement data: automatic weighting and regularization

Abstract

Electromagnetic induction (EMI) has prominent technique in UXO detection and discrimination research. Fast forward solutions are needed for target discrimination, which is essentially an inverse problem. We have previously developed a physically complete modeling system that includes all effects of the heterogeneities and their interactions within the object, in both near and far fields. Since the problem is highly ill-conditioned, the high order excitation modes were truncated and only the solutions of low and dominant modes were solved for. In this paper we introduce a two step approach for extracting the model parameters for both low and high order excitation modes. In the first step, high order modes are truncated. Solutions for low order modes are inferred from the measured data that mostly contain low order mode excitations. In the second step, solutions for both low and high order modes are solved by giving more weight to measurements that contains high order modes, and using the first step solutions as prior information. In the cases investigated here the two step approach provides a more accurate forward model and is still fast enough for inversion calculations in UXO detection and discrimination.