In 1997, the Naval Research Laboratory used the Multi-Sensor Towed Array Detection System (MTADS) to survey 150 acres of the Badlands Bombing Range (BBR) on the Pine Ridge Reservation in South Dakota. Researchers identified and analyzed over 1400 targets, of which 400 were selectively dug with 71 bombs, 50 rocket bodies, and 220 pieces of ordnance-related scrap recovered. The demonstration was conducted on a section of the BBR that has not yet been returned to Tribal control, the Air Force Retained Area (previously termed the Impact Area). This area was used from 1965 to 1973 by the South Dakota National Guard for artillery practice. In preparation for returning this site, the Air Force performed a walkover investigation using mine detectors in 1997. Subsequently, the Air Force invited the Naval Research Laboratory to conduct a demonstration and site evaluation on a portion of the Impact Area.

Technology Description

The vehicular MTADS consists of arrays of cesium-vapor total field magnetometers or EM61 time-domain pulsed-induction sensors on low-signature platforms towed by an all-terrain vehicle. The magnetometers (Geometrics 822ROV) are deployed as a linear array of eight sensors. The EM61 sensors, extensively modified to increase pulse repetition rate and transmit power, shorten the sampling window, increase receiver amplifier gain, and decrease the analog time constant, are deployed as an overlapping horizontal array of three sensors. The sensor positions are determined using a state-of-the-art Real-Time Kinetic Global Positioning System (RTK GPS) operating at 5 hertz. All location and sensor data are stored as individual files on a data acquisition computer in the tow vehicle. These files are transferred to a custom Data Analysis System (DAS) for navigation clean up, sensor data location, mapping, and presentation to the analyst for anomaly selection and analysis.

Demonstration Results

One hundred thirty acres were surveyed with the MTADS magnetometer array in two long transects and a rectangular area that encompassed a target bull's eye and its overshoot area. In the northern part of the magnetometer area, 14.8 acres were surveyed using the MTADS electromagnetic (EM) array (completely in an "E-W" survey and partially in a "N-S" survey). Of the magnetometer anomalies that were analyzed as 90 millimeter (mm) or greater, 362 were selected for remediation; 15 of these were live, high explosive (HE)-filled 155-mm or 8-inch projectiles and were destroyed in place. One hundred nine anomalies were identified in the EM area, and all were remediated. The classification performance of the baseline magnetometry analysis was compared to the magnetometer-EM fusion analysis performed in the smaller area.

Implementation Issues

This demonstration provided a direct comparison between traditional "Mag and Flag" UXO surveys and digital, geo-referenced mapping surveys employing state-of-the-art equipment. Although the "Mag and Flag" survey was conducted by active duty Air Force Explosive Ordnance Disposal (EOD) teams as a training exercise and was not subject to government Quality Assurance/Quality Control (QA/QC) procedures, it is still clear from these results that digital, geo-referenced survey methods are less expensive and provide vastly improved performance. (Project Completed - 2000)