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Most EMI sensors do not take advantage of all the available information that is inherent in the metal target response. The sensors tend to measure only a single dimension of a target response or, in the case of a spatially scanned target, try to infer a multi dimensional response. Experimental EMI sensors that do attempt to generate a 3D magnetic field and measure a 3D target response do so with magnetic field antennas that have fixed and complex spatial magnetic field distributions With a conventional pulsed EMI metal detector, a current loop transmitter is placed in the vicinity of the buried metal target, and steady current flows in the transmitter for a sufficiently long time to allow the turn-on transients in the soil to dissipate. The transmitter loop current is then turned off. According to Faraday's Law, the collapsing magnetic field induces an electromotive force (emf) in nearby conductors, such as the metal target. This emf causes eddy currents to flow in the conductor. Because there is no energy to sustain the eddy currents, they begin to decrease with a characteristic decay time that depends on the size, shape, and electrical and magnetic properties of the conductor. The decay currents generate a secondary magnetic field that is detected by a magnetic field receiver located above the ground and coupled to the transmitter via a data acquisition and control system. The direction of the magnetic field and the field strength generated by a conventional loop EMI metal detector are a complex function of the distance of the antenna to the target. As the antenna is moved over the target, data are collected from different antenna-target aspect angles. An automatic target recognition (ATR) algorithm attempts to combine the measured time or frequency signature from the target with the spatial data to perform target classification., The original document contains color images. Rept. No., NSTD-05-693, SERDP Project MM-1314.

The Johns Hopkins University Applied Physics Laboratory (JHU/APL) has developed a prototype metal detection survey system that will increase the search speed of conventional technology while maintaining high sensitivity. Higher search speeds will reduce the time to locate unexploded ordnance (UXO) at Base Realignment and Closure (BRAC) sites, thus potentially reducing remediation costs. The new survey sensor system is called the moving belt metal detector (MBMD) and operates by both increasing sensor speed over the ground while maintaining adequate sensor dwell time over the target for good signal-to-noise ration (SNR) and reducing motion-induced sensor noise. The MBMD uses an array of metal detection sensors mounted on a flexible belt similar to a tank track. The belt motion is synchronized with the forward survey speed so individual sensor elements remain stationary relative to the ground. In the prototype MBMD, a single pulsed transmitter coil is configured to provide a uniform magnetic field along the length of the receivers in ground contact. Individual time-domain electromagnetic induction (EMI) receivers are designed to sense a single time-gate measurement of the total metal content. Each sensor module consists of a receiver coil, amplifier, digitizing electronics and a low power UHF wireless transmitter. This report presents the survey system design concepts, details of the prototype system, metal detection data from at several survey speeds and recommendations for future work. Although the laboratory prototype is designed to demonstrate metal detection survey speeds up to 10 m/s, higher speeds are achievable with a larger sensor array. In addition, the concept can be adapted to work with other sensor technologies not previously considered for moving platforms., The original document contains color images. SEED Project MM-1448, Task No., SE106, Report No., NSTD-06-166.

The Johns Hopkins University/Applied Physics Laboratory (JHU/APL) has developed a novel approach to metal target classification via an advanced Three-Dimensional Steerable Magnetic Field (3DSMF) Sensor System. The 3DSMF is a time-domain (TD) electromagnetic induction (EMI) sensor configured with a three-axis magnetic field generator and three receivers that measures the multiple components of buried unexploded ordnance (UXO) magnetic polarizability tensors (MPT). This final report summarizes work completed throughout the project. The results from the current year show promise of confirming the 3DSMF identification concept when using libraries of target time decay constants. The spatial orientation of targets was determined at different depths using library constants which had been derived from calibration measurements made with that target at a single depth. There is also evidence that the orientation of a target can be determined even if the target is off-center of the antenna. Further data collection and analysis would characterize the effectiveness of the 3DSMF Sensor System in discriminating between different targets., The original document contains color images.

Currently, sensor systems exist that can detect and localize buried metal objects of a wide size and depth range. These sensors typically measure the active and/or passive magnetic properties of buried metal objects. In some cases, the sensor measures the dielectric contrast of the buried object (e.g., ground penetrating radar (GPR)). While current technology has shown the ability to detect these buried metal objects discriminating the UXO from metal objects that pose no risk, i.e. clutter, is still a major problem. These clutter objects represent a false alarm (FA) to the detection system. The time to remediate a site with a high clutter to UXO ratio is not cost effective. Discrimination of UXO from clutter, a reduction in the false alarm rate (FAR), would lower the site cleanup cost. The report is divided into several sections. Section 2 describes the basic project objectives. Section 3 briefly describes the technical approach used in the UXO signature analysis and spatial signal processing. Section 4 summarizes the results of the project and Section 5 lists project recommendations. Section 6 summarizes some conclusions for the project while Section 7 makes recommendations for possible future work., Referenced appedices not attached. The original document contains color images. All DTIC reproductions will be in black and white.