The Very Early Time Electromagnetic (VETEM) system, the High-Frequency Sounder (HFS),<br>and the Tensor Magnetic Gradiometer System (TMGS) were developed by the U.S. Geological Survey<br>(USGS) for applications other than unexploded ordnance (UXO). However, features of these systems<br>may make them adaptable to UXO applications. VETEM is a time-domain electromagnetic (EM)<br>induction system that utilizes full waveform recording. The HFS is a flexible frequency-domain EM<br>system. The TMGS uses four sensitive 3-axis fluxgate magnetometers so that gradients of field<br>components are recorded. Tests were conducted in air using a selection of inert UXO objects ranging<br>from 20 mm to 105 mm in diameter. A nulled overlapped antenna arrangement was used for both<br>VETEM and the HFS. It was found that this antenna configuration resulted in distinctly different<br>responses to horizontal UXO objects aligned along the direction of traverse versus horizontal and<br>perpendicular to the traverse. Vertical orientation of UXO objects resulted in smaller amplitude signals<br>and an interesting slightly asymmetric “crater” shape response in plan view. The HFS response was a<br>strong function of frequency, which is good for discrimination. The TMGS data are the most sensitive<br>to ferromagnetic objects and the multi-component data hold the promise of accurate location, including<br>depth, to UXO objects using a dipole mapping algorithm. Plans include increased sensitivity and multicomponent<br>capability for the EM systems, advanced algorithms to enhance UXO discrimination for EM<br>and TMGS systems and field evaluations at standard UXO test sites of the Strategic Environmental<br>Research and Development Program (SERDP).


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