False positive detections account for a great part of the expense associated with unexploded ordnance (UXO) remediation. Presently fielded systems like pulsed electromagnetic induction systems and cesium-vapor magnetometers are able to distinguish between UXO and other metallic ground clutter only with difficulty. The discovery of giant magnetoresistance (GMR) has led to the development of a new generation of integrated-circuit magnetic sensors that are far more sensitive than previously available room-temperature-operation electronic devices. The small size of GMR sensors makes possible the construction of array detectors that can be used to image the flux emanating from a ferrous object or from a non-ferrous object with eddy currents imposed by an external coil. The purpose of a GMR-based imaging detector would be to allow the operator to easily distinguish between UXO and benign objects (like shrapnel or spent bullets) that litter formerly used defense sites (FUDS). In order to demonstrate the potential of a GMR-based imaging technology, a crude magnetic imaging system has been constructed using commercially available sensors. The ability to roughly determine the outline and disposition of magnetic objects has been demonstrated. Improvements to the system which are necessary to make it into a high-performance UXO detector are outlined.

The Chemistry Division of the Naval Research Laboratory has developed the Multi-sensor Towed Array Detection System for use in unexploded ordnance detection and classification. With support from the Environmental Security Technology Certification Program, we are developing a frequency-domain electromagnetic induction sensor array to extend our capabilities. The first task in this program is to characterize the commercial GEM-3 sensor and assess its suitability for use in a towed array. In this report, we detail our characterization results and note the problems we encountered. We conclude by listing the modifications to the baseline sensors that we will make for the array we will field.