Assessment of an Active Electromagnetic Sensor for Hunting Buried Naval Mines, Part II

The US Navy is investigating the use of broadband electromagnetic (EM) sensors as a candidate technology for its Buried Minehunting (BMH) sensor suite. New Navy tactics are being pursued, where short-range sensors are incorporated into reacquisition minehunting systems for short-range classification. The current approach includes study of use of active EM sensors that employ multi-frequency sources for target illumination which can provide valuable multi-spectral discrimination for the classification of buried naval mines. In 2004, the Navy evaluated the detection/classification performance of a Geophex, Ltd. GEM3 sensor by performing underwater tests versus selected ideal targets and simulated mine targets. Test results demonstrated that GEM3 can detect metallic ordnance buried in the ground and under the sea bottom at short ranges. GEM3 tests demonstrated that electromagnetic induction spectroscopy (EMIS) techniques could be used to measure the spectral "fingerprint" of a target, which assists in target identification. FY04 GEM3 tests also showed that the active EM detection range must be increased if these sensors are to be a useful identification sensor in an autonomous underwater vehicle (AUV) reacquisition system. In this paper, we report results measuring the performance of a new Geophex active EM sensor that employs new coil configurations designed to extend the detection range and increase background noise rejection. The new coil configuration which contains multiple active EM sensors is designed at a comparable size with the 12 frac34" AUVs that the BMH program is developing for its reacquisition minehunting systems. Results from rail experiments with the new sensor operating on land are described