Uxo Classification Using Characteristic Modes Of The Broadband Electromagnetic Induction Response

Electromagnetic induction methods are effective in locating unexploded ordnance (UXO).<br>However, the induction EM instruments that are used for UXO detection generally have limited<br>bandwidths and provide little, if any, information for UXO classification. It is well known that<br>the broadband induction EM response from confined conductors (such as UXO) can be<br>parameterized in the time-domain as a series of damped exponential decay curves, and in the<br>frequency domain as a set of discrete real first order poles and their residues. Characteristic<br>decay time or its equivalent real pole has been shown to be a function of characteristic target<br>dimensions, target conductivity, and relative magnetic permeability. Therefore,<br>parameterization of the broadband EM response in terms of these characteristic modes provides<br>a basis for the classification of UXO anomalies.<br>In this paper we have used a numerical method (Prony) to analyze TEM decay curves to obtain<br>a set of exponential decay time-constants and their corresponding residues. Using a<br>commercially available field data acquisition system, we have acquired fast transient TEM data<br>from UXO. We show that these data can be analyzed and displayed in a way that is simple to<br>understand and useful for classifying the TEM response.