The state-of-the-practice for unexploded ordnance (UXO) site characterization is to use a magnetometer and/or a simple electromagnetic induction (EMI) sensor. These sensors are effective; however, as many as 98% of the targets identified with these techniques are non-UXO, false alarms, or clutter. The four-dimensional (4-D) time-domain electromagnetic (TEM) system uses three orthogonal receiving antennas as compared to the single receiving antenna of simple EMI systems, and it makes multiple-gate time-series measurements for each antenna versus the single-time measurement of simple EMI systems. The objective of this project was to demonstrate that this TEM system with appropriate data analysis methodology improves the location and classification of UXO.
The Zonge Dynamic NanoTEM (DNT) system is a commercially available fast TEM system that can measure a time series of the decay transient induced after the cessation of the transmitter current. In this project, new acquisition software was developed to increase the receiver sampling rate, allowing the acquisition of transient data from three independent receiver antennas at a rate of four samples per second. A cart-mounted antenna array consisting of a transmitter coil, three mutually orthogonal receiver coils, a three axis tiltmeter to correct for antenna orientation, and a Global Positioning System (GPS) receiver was designed and fabricated. Finally, software providing basic data reduction, target detection, and model-based target characterization and classification was developed.
Initially, a pre-demonstration was conducted at Blossom Point, Maryland that showed the system to be operational. A demonstration then was conducted at the Standardized UXO Technology Demonstration Site located at Aberdeen Proving Ground (APG), Maryland. During the APG demonstration, investigators showed that large areas can be surveyed at 0.5 meter (m) lane spacing at rates greater than 1 acre per day. The probability of detection (Pd) in the response stage was 80% overall for the Blind Test Grid. The corresponding performance degraded in the Open Field to 45% overall, according to scores received from Aberdeen Test Center (ATC). The degradation in scores between the Blind Test Grid and the Open Field was consistent with scoring results of other demonstrators. The Blind Test Grid and the Open Field response stage scores show that the DNT system performance is best for shallow targets (less than 0.3 m) and degraded for targets at intermediate depths (0.3-1 m depth). The system cannot reliably detect targets at depths greater than 1 m.
The APG demonstration showed that the DNT system can be deployed under realistic field conditions and that users can economically acquire and process high-quality 4-D EMI data. The researchers demonstrated that the Zonge DNT technology expands the capabilities of EMI beyond instruments such as the EM-61. At the operational level, it was shown that the productivity of this system in the field is comparable to that of competing man-portable systems. (Project Completed - 2004)