The prohibitive costs of excavating all geophysical anomalies are well known and are one of the greatest impediments to efficient clean-up of unexploded ordnance (UXO)-contaminated sites. Effective discrimination between hazardous UXO and non-hazardous munitions and cultural-related debris has the potential to significantly reduce remediation costs. In recent years, there has been a shift towards developing multistatic, multicomponent time-domain electromagnetic (TEM) sensors for deployment in a cued-interrogation mode. However, the need to deploy the systems in a cued mode can significantly increase the time and costs of the geophysical survey.
The objective of this demonstration was to deploy the One-Pass Detection and Discrimination (OPTEMA) system to the Yuma Proving Grounds to quantify its expected detection and discrimination performance. As far as the project team was aware, OPTEMA represents the only advanced electromagnetic induction sensor technology capable of achieving both the detection and discrimination tasks in a single pass of the sensor system. In principle, there will be sites where this approach is more cost effective than the two-pass approach that has been adopted by the existing advanced sensor technologies (e.g., MetalMapper, TEMTADS, and BUD).
OPTEMA is a system derived from the Advanced Ordnance Locator (AOL) that was developed with U.S. Navy funding. It comprises three 1 m x 1 m orthogonal transmitter coils that are rotated 45 degrees to the direction of travel, and nine three-component receiver cubes distributed within the footprint of the transmitters. The sensor collects data while continuously moving and cycling through each of the three transmitters. Highly accurate sensor positions and orientations are obtained through the use of the Novatel SPAN, which comprises a high-end Global Positioning System (GPS) and a precision tactical grade Inertial Navigation System (INS). Position and orientation estimates are optimized by collecting all required data for post-processing in a Kalman filter formulation through Novatel Inertial Explorer software.
OPTEMA was demonstrated at the UXO Standardized Test Site at Yuma Proving Grounds in Arizona. By collecting high quality data and analyzing those data with advanced parameter estimation and classification algorithms, this system is designed to increase the efficiency of target classification. The data collected were used to classify each detected target and the classification results were evaluated against a set of five performance objectives:
- Detection of all munitions of interest
- Maximize correct classification of munitions
- Maximize correct classification of non-munitions
- Minimize number of false detections that are classified as munitions
- Correct estimation of target locations
In the Open Field portion of the test site, more than 95% of all emplaced ordnance was detected. Of these detections, the probability of correct classification of munitions was more than 95% with approximately 80% reductions in the number of false alarms due to clutter. The Yuma Proving Ground is a controlled testing site and not representative of an actual field deployment of the OPTEMA system. A cost model was planned to be developed after demonstration at a live munitions site.
There were some concerns about the ruggedness of the AOL electronics. To produce a system better suited to wide-scale use in a production environment, two improvements would need to be made: (1) wider swath width and (2) commercial availability. A wider swath width would expand the existing horizontal axis transmitter distance by extending the distance to1.0 m wide. Turned by 45 degrees the transmitter only covers a 70 cm wide swath. In addition, the transmitters sit on top of the Z-axis transmitter raising them by about 8 cm. A significant improvement in production could be achieved by increasing the transmitter lengths to 2.0 m (1.4 m swath), with signal-to-noise ratio (SNR) improved by lowering the horizontal axis transmitters by 8 cm (there are some small construction challenges that arise as the wires for different transmitters almost intersect). The system is currently based on the electronics from the AOL sensor, which was the precursor to the commercially available MetalMapper sensor. The AOL can only support nine receiver cubes; whereas, the current design calls for ten receiver cubes. For a production system, the data acquisition system (DAQ) and receiver boards and cubes should be replaced with commercially available MetalMapper components.