Simultaneous Magnetometer and EM61 MK2 Vehicle-Towed Array for Wide Area Assessment

Abstract : One of the recommendations of the 2003 Defense Sciences Board (DSB) Report on Unexploded Ordnance (UXO) was to immediately assess the scope of ordnance contamination of roughly ten million acres of land on formerly used defense sites (FUDS) and base realignment and closure (BRAC) sites and rapidly ascertain what percentage of this acreage actually contains UXO. Ground-based digital geophysical mapping (DGM) systems have a role to play in wide area assessment (WAA), both for close-in detection of object boundaries, as well as in validation and verification of the results from airborne surveys. The technology used for this project-the Vehicular Simultaneous Electromagnetic Induction (EMI) and Magnetometer System (VSEMS), formerly known as the Simultaneous Multisensor Surface Towed Ordnance Locator System (STOLS) is a ground-based vehicle-towed array that collects total field magnetometer and EM61 data simultaneously in a single survey pass. The benefits of using a concurrent multisensor towed array are that (1) many sites contain surprises in the form of unexpected munitions or explosives of concern (MEC) or MEC-related activity, so choosing a sensor because of its detection characteristics may result in missing unexpected objects, and (2) since most common geology ("hot rocks") doesn't show up on the EM61, the presence of a confirming electromagnetic (EM) signature can be used as a highly effective geologic false alarm reduction tool. The use of VSEMS at the Kirtland WAA site yielded both of these advantages.