QUALITATIVE AND QUANTITATIVE UXO DETECTION WITH EMI USING ARRAYS OF MULTI-COMPONENT RECEIVERS

Contemporary research and development of EMI systems for UXO detection and identification has suggested that a spatial array of receiver coils together with one or more transmitter coils can significantly improve target parameterization and, ultimately, target identification. Our system, the Advanced Ordnance Locator (AOL), has been funded by NAVEODTECHDIV and is a product of such research. The design of EMI systems that include multiple receiver arrays is typically based on the criterion of “optimal” recovery of target parameters using physics-based inversion methods. However, that criterion overlooks an important aspect of the UXO survey problem, target Detection. Target detection involves locating a target by picking anomaly peaks on maps generated from dynamically acquired EM data. For a variety of reasons (e.g., motion-induced EM noise, surface clutter, etc) dynamic-mode EM data has significantly higher noise levels than the static data used for target parameter extraction, and these noise levels limit the depth of detection. In this paper, we study the AOL antenna array in the context of the simple detection problem as distinct from the problem of target classification. With data acquired at Blossom Point and Indian Head, we compare the detection performance of several detector responses derived from the 8 tri-axial receivers in the AOL. Qualitatively, the results illustrate how a spatial receiver array can improve detection performance compared with single-receiver antenna arrays such as the EM61, particularly in the presence of multiple near-surface targets and/or clutter. Furthermore, the quality of the data from each individual cube as well as from their differences makes us optimistic that more complex detector algorithms can indicate not only the presence of a target but also can provide a better estimate of its 3-D position and target size. We are pushing our investigations toward that end.