The Defense Advanced Research Projects Agency (DARPA) recently sponsored its first field-test of nuclear quadrupole resonance (NQR) technology to find buried land mines.
In tests at the Army's Combat Engineer School, Fort Leonard Wood, Mo., scientists at Quantum Magnetics, San Diego, Calif., used their prototype NQR device to find 22 of 24 surrogate antipersonnel land mines containing 100 grams of C4 explosive. They also detected six of six unfuzed M19 antitank land mines. This corresponds to a probability of detection in excess of 90 percent. Remarkably, in the 110 meter-long test lane, the system suffered only a single false alarm.
"This is unprecedented performance. No where in the world does there exist a landmine detector that performs with this combination of high probability of detection and low incidence of false alarms," explains Regina Dugan, the DARPA program manager. Dugan concedes that there are still many challenges remaining for this system to become a viable military system. For example, the prototype does not yet allow real-time detection of the smallest antipersonnel land mines containing TNT, although laboratory results indicate that the system can detect medium-sized TNT antipersonnel mines. A key goal is to improve the capability to detect TNT since it is the most prevalent explosive found in land mines.
Gunnery Sgt. John Crane of the U.S. Marine Corps Systems Command, Quantico, Va., who witnessed the NQR system's performance, could see the system's potential. He noted, "DARPA's research in NQR is impressive. It holds the promise of an exciting leap in mine detection technology. A system with the performance shown today could be instrumental in solving the military's and the world's land mine problem."
NQR uses an externally applied radio frequency magnetic field pulse at a characteristic frequency to generate a coherent signal that can be detected with a tuned antenna and a very sensitive receiver. The NQR resonant frequency is specific to individual explosive compounds, resulting in a very low incidence of false alarms. Although attempts to apply NQR to land mine detection date as far back as the Vietnam War, previous efforts were plagued with insufficient sensitivity and unacceptable false alarm rates.
In 1997, DARPA began a new initiative to capitalize on major technology advances and allow the effective use of NQR for land mine detection. Key improvements have resulted in the present system, which can detect land mines containing RDX, the active explosive constituent of C4. DARPA's program includes an aggressive three-year plan for creating a man-portable system capable of TNT and RDX explosives detection. In cooperation with the Marine Corps, the program seeks also to detect additional threat explosives and provide an integrated metal detection capability. The result would be the first system with a high probability of detection and a low false alarm rate to capitalize on the explosive content of land mines.
For more information on DARPA's land mine detection effort, contact Jan Walker, at (703) 696-2404.