Technologies are needed that can detect and discriminate unexploded ordnance (UXO), which can range in size from 20 mm shells to 2000 lb bombs, from other items in the subsurface. The development of cost-effective detection and discrimination technologies is needed in the following three categories: (1) integrated systems that can cost-effectively survey large tracks of land, detect potential UXO, and discriminate UXO from clutter, (2) systems that are cued by other survey technologies that can cost-effectively and non-invasively interrogate the suspected item, and (3) processing technologies that can exploit the current stateof- the-art sensors to improve discrimination capabilities.
Computer modeling tools will be utilized to study the design and configuration of broadband electromagnetic (EM) systems used to detect the metal components of UXO. Existing computer programs will be modified to study the behavior of a variety of UXO targets buried in different positions and under various ground conditions. This research will provide quantitative criteria for evaluating the effectiveness of various land-based metal detection systems. The results will enable the design of a new system that, in addition to locating targets, will be optimized to determine their size, shape, and orientation and the depth at which they are buried.
Numerical model simulators, which have been developed by geophysicists in the mineral exploration community, were used to design and create a prototype of an active EM system for detecting and characterizing the metal content of UXO against a background of geologic materials and other metal objects. An optimized metal detector will be developed with the capacity to determine the following physical properties of a buried metal object: (1) depth; (2) size, shape, and orientation; (3) electrical conductivity; (4) magnetic permeability; and (5) state of contact with the ground (insulated or not). The design will be adapted both to a portable, hand-held, battery-powered system with a userfriendly display of the target response and to a larger mounted system, that can be used to search the broad area in front of a vehicle.
A numerical simulator was implemented to determine the EM response of a simple thin sheet target in a conductive ground. The thin sheet response illustrates an optimization methodology that can be implemented for any target. A simple criterion was then implemented to evaluate any transmitter-receiver (T-R) configuration by maximizing the ratio of the target response to the background half-space response (the Anomaly Index), and a rationale was established to evaluate the signal to noise ratio for an arbitrary T-R system considering ambient EM noise, system noise, array separation/orientation noise, and geologic noise. Overall guidelines were established for the design of an optimum EM system. This FY00 funded SEED project transitioned to a core FY01 New Start project (see MR-1225).
A new generation of EM sensing systems that could screen large areas or provide high-resolution classification of particular targets is now possible. Drawing on extensive experience with large-scale mineral exploration EM systems and numerical simulators for quantitative modeling, as well as recent work in model-based classification algorithms, a computer-based design of an optimum system can be created specifically to meet the needs of UXO discrimination.