Analysis Of Frequency-Domain Electromagnetic Induction Data For The Detection And Discrimination Of Buried Unexploded Ordnance

The Naval Research Laboratory Multi-sensor Towed Array Detection System (MTADS) has<br>recently fielded an array of three frequency-domain electromagnetic induction sensors. The sensors are<br>Geophex GEM-3’s designed to be triggered sequentially for array operation, collecting up to 10<br>frequencies from 30 Hz to 48 kHz of inphase and quadrature data. To date, measurements have been<br>taken with the array at three different locations – at the home location of Blossom Point, over a variety<br>of UXO and clutter items placed in a pit, as well as over the test field area; and at the two Standardized<br>UXO Technology Demonstration Sites at Aberdeen Proving Ground (APG) and Yuma Proving Ground<br>(YPG). Results of two separate discrimination analysis strategies for the data are presented. Both<br>strategies involve data inversion based on a simple dipole response representation for the object<br>expressed by the eigenvalues of the magnetic polarizability tensor, what we term the beta values. One<br>scheme, however, seeks to explicitly incorporate spatial data within the inversion process while the other<br>does not. For either inversion scheme, the differences between ordnance and clutter eigenvalues over the<br>frequency range are evaluated and an effective means of discrimination is determined. A library of<br>eigenvalues for all expected UXO items has been assembled to aid in this determination.