The objective of this demonstration was to collect high quality MetalMapper sensor data in a cued interrogation mode over 2,370 anomalies previously detected during an EM61 survey. The data collection was intended to meet the following objectives:

  1. Demonstrate the transition of the new, but now commercially available, MetalMapper sensor to personnel engaged in production data collection (and not involved in research and development).
  2.  Provide advanced electromagnetic induction (EMI) sensor data from the MetalMapper to a wide range of data analysts to test different processing and interpretation methodologies.

Technology Description

Sky Research’s SKY3D vehicular platform integrates a MetalMapper sensor, real-time-kinematic global positioning system and inertial measurement unit (in the form of the Novatel SPAN), and a custom user interface on a Kubota all-terrain vehicle. Cued interrogation data were collected by dwelling for 30 seconds over 2,370 anomalies previously identified via a full-coverage geophysical survey of part of the Bisbee Area of the Pole Mountain Target and Maneuver Area, near Laramie, Wyoming. The data collection was conducted in the field over a 14-day period in July and August 2011.

Demonstration Results

The production rate was as high as 39 points per survey hour with a maximum of 326 anomalies visited in a day. During the first eight field days, an electrical issue with the instrument orientation sensor resulted in a lower average production rate of 21 points per hour. During the last six field days, and after the orientation sensor problem was rectified, the production rate increased 64% to an average of 32 points per hour. Weather and summer thunderstorms impacted two days.

Eight performance metrics were evaluated, including four pertaining to the data collection (reliability/robustness, survey rate, percentage of site covered, MetalMapper sensor position accuracy) and four to the subsequent processing and classification of the collected data (percentage of munitions correctly identified, reduction in false-alarm rate, appropriate specification of stop-dig point, and minimization of “can’t analyze” anomalies). Six of the eight performance objectives were easily achieved, while one objective, 90% of MetalMapper positions within 30 cm of each Target of Interest (TOI), was missed by 1 cm (90th percentile at 31 cm). The last and only qualitative objective on reliability/robustness was only partially met due to the electrical issues with the orientation sensor on the Novatel SPAN.

At the final stop-dig point selected after analysis of the MetalMapper data, 369 anomalies were excavated and all 160 TOI were identified. A total of 209 of the 2,210 clutter items were excavated: this meant that 91% of the clutter could have been left in the ground, resulting in significant potential cost savings. The per anomaly costs (excluding mobilization and reporting) were $41.24 for data collection and $4.08 for data processing. The total cost per anomaly was $45.52. Using an often quoted rule of thumb that each excavation costs $100, the excavation costs would have been approximately $237,000 without the MetalMapper system. With the MetalMapper, only 369 anomalies needed to be excavated at a cost of $36,900. When combined with the MetalMapper mobilization, data collection, processing, and reporting costs of $168,270, the cost of clearance using the MetalMapper was $205,170: a savings of $31,830 (or 13%).

Implementation Issues

Comparing EM61 pick locations versus the actual ground-truth locations of TOI revealed large errors in position and demonstrated the importance of fine-tuning the cued-interrogation location using the (currently limited but functional) real-time position estimation capabilities of the MetalMapper. Nightly quality control of the collected data was another important determinant of cued-interrogation data quality, with 125 anomalies recommended for recollection.