Spectral Identification of Buried Unexploded Ordnance from Low-Frequency Electromagnetic Data

A procedure is described for identifying buried unexploded ordnance (UXO) from their spectral signatures derived from electromagnetic induction (EMI) data. Using the dipole response of the UXO as a first approximation, it can be shown that data obtained from a target at an arbitrary depth and orientation can be expressed as a linear combination of the target's longitudinal and transverse responses. The latter are pre-measured for a set of UXO and stored in a spectra library. The measured spectrum from an unknown target can then be compared to the library spectra to identify the UXO type. The optimal linear combination of the longitudinal and transverse responses that produce the best fit to the measured spectra is obtained by a maximum likelihood procedure. The method is demonstrated using data derived from UXO and sections of metallic pipe of different sizes, shapes and material.