The generalized SEA to UXO discrimination in geophysical environments producing EMI response

Abstract

The generalized standardized excitation approach (GSEA) is presented to enhance UXO discrimination under realistic field conditions. The GSEA is a fast, numerical, forward model for representing an object's EMI responses over the entire frequency band from near DC to 100s of kHz. It has been developed and tested in both the frequency and time domains for actual UXOs placed in free space. The GSEA, which uses magnetic dipoles instead of magnetic charges as responding sources, is capable of taking into account the background medium surrounding an object. Given a modeled UWB frequency domain (FD) response, the corresponding time domain (TD) response is easily obtained by the inverse Fourier transform. Thus the technique is applicable for any FD or TD sensor configuration and can treat complex data sets: novel waveforms, multi-axis, vector, or tensor magnetic or electromagnetic induction data, or any combination of magnetic and EMI data. Host media effects are taken into account via appropriate types of Green's function and equivalent dipole sources. Comparisons between simulations and experimental data illustrate that the GSEA is a unified approach for reproducing both TD and FD EMI signals for actual UXOs. The EMI response from a soil that has a frequency-dependent magnetic susceptibility is studied. The EMI responses in both FD and TD domains are analyzed for the model of an actual UXO that is buried in a magnetically susceptible half space.