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In April 2007, Battelle demonstrated two new airborne vertical magnetic gradiometer systems for unexploded ordnance (UXO) mapping and detection at the Former Kirtland Precision Bombing Range, New Mexico. The primary benefit of vertical gradient is that it reduces helicopter noise, improving signal-to-noise by about a factor of 5 relative to the ORAGS-Arrowhead total field system (Gamey et al., 2004). The two systems are called VG-16 and VG-22. VG-22 was designed for high-resolution detection of small ordnance under good field conditions, while VG-16 was designed with a wider swath for better production rates on wide-area assessment surveys or where conditions require slightly higher altitudes.
Performance of the systems was assessed in a 500-acre test area in which site conditions were well known from previous surveys. This area was deemed relatively quiet magnetically, and was prepared by an unaffiliated contractor which buried 88 small ordnance items at locations that were unknown to Battelle. This “blind-seeded” area included projectiles as large as 155 mm and as small as 40 mm, as well as mortars. VG-22 data yielded 90% detection and VG-16 data demonstrated 67% detection of the emplaced items. In addition to these individually emplaced items, ten pairs of 60-mm mortars were emplaced to assess sensitivity to closely spaced ordnance. The ability to distinguish these mortars as separate items confirmed expectations based on a published approach. For those 60-mm mortars that are expected to appear as individual anomalies, probability of detection was the same as for widely spaced items.