Discrimination Report: A Multisensor system for detection andcharacterization of UXO, ESTCP Project MM-0437,
The Berkeley UXO Discriminator (BUD) is an optimally designed active electromagnetic system that not only detects but also characterizes UXO. The performance of the system is governed by a target size-depth curve. BUD was designed to detect UXO in the 20 mm to 155 mm size range for depths between 0 and 1.5 m, and to characterize them in a depth range from 0 to 1.1 m. The system incorporates three orthogonal transmitters and eight pairs of differenced receivers. Eight receiver coils are placed horizontally along the two diagonals of the upper and lower planes of the two horizontal transmitter loops. These receiver coil pairs are located on symmetry lines through the center of the system and each pair sees identical fields during the on-time of the pulse in all of the transmitter coils. They are wired in opposition to produce zero output during the on-time of the pulses in three orthogonal transmitters. Moreover, this configuration dramatically reduces noise in the measurements by canceling the background electromagnetic fields (these fields are uniform over the scale of the receiver array and are consequently nulled by the differencing operation), and by canceling the noise contributed by the tilt motion of the receivers in the Earth's magnetic field, and greatly enhances receiver sensitivity to the gradients of the target response. BUD is mounted on a small cart to assure system mobility. System positioning is provided by a Real Time Kinematic (RTK) GPS receiver. The system has two modes of operation: (1) the search mode, in which BUD moves along a profile and exclusively detects targets in its vicinity providing target depth and horizontal location, and (2) the discrimination mode, in which BUD is stationary above a target, and determines three discriminating polarizability responses together with the object location and orientation from a single position of the system. The detection performance of the system is governed by a size-depth curve shown in Figure 2. This curve was calculated for BUD assuming that the receiver plane is 0.2 m above the ground. Figure 2 shows that, for example, BUD can detect an object with 0.1 m diameter down to the depth of 0.9 m with a depth uncertainty of 10%. Any objects buried at a depth of more than 1.3 m will have a low probability of detection. The discrimination performance of the system is governed by a size-depth curve shown in Figure 3. Again, this curve was calculated for BUD assuming that the receiver plane is 0.2 m above the ground. Figure 3 shows that, for example, BUD can determine the polarizability of an object with 0.1 m diameter down to the depth of 0.63 m with polarizability uncertainty of 10%. Any objects buried at the depth more than 0.9 m will have a low discrimination probability. Object orientation estimates and equivalent dipole polarizability estimates used for large and shallow UXO/scrap discrimination are more problematic as they are affected by higher order (non-dipole) terms induced in objects due to source field gradients along the length of the objects. For example, a vertical 0.4 m object directly below the system needs to be about 0.90 m deep for perturbations due to gradients along the length of the object to be of the order of 20% of the uniform field object response. Similarly, vertical objects 0.5 m, and 0.6 m long need to be 1.15 m, and 1.42 m, respectively, below the system. For horizontal objects the effect of gradients across the object diameter are much smaller. For example, 155 mm and 105 mm projectiles need to be only 0.30 m, and 0.19 m, respectively, below the system. A polarizability index (in cm{sup 3}), which is an average value of the product of time (in seconds) and polarizability rate (in m{sup 3}/s) over the 34 sample times logarithmically spaced from 143 to 1300 {micro}s, and three polarizabilities, can be calculated for any object. We used this polarizability index to decide when the object is in a uniform source field. Objects with the polarizability index smaller than 600 cm{sup 3} and deeper than 1.8 m below BUD, or smaller than 200 cm{sup 3} and deeper than 1.35 m, or smaller than 80 cm{sup 3} and deeper than 0.90 m, or smaller than 9 cm{sup 3} and deeper than 0.20 m below BUD are sufficiently deep that the effects of vertical source field gradients should be less than 15%. All other objects are considered large and shallow objects. At the moment, interpretation software is available for a single object only. In case of multiple objects the software indicates the possible presence of metallic objects but is unable to provide characteristics of each individual object.
- Research Organization:
- Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- DE-AC02-05CH11231
- OSTI ID:
- 925603
- Report Number(s):
- LBNL-63744; R&D Project: 0; BnR: YN0100000; TRN: US200807%%418
- Country of Publication:
- United States
- Language:
- English
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