Location, Identification, and Enumeration of UXO in Complex Environments Using Time-Reversal Methods in Electromagnetics
Electromagnetic (EM) signals used to locate and possibly identify unexploded ordnance (UXO) are known to propagate through earth media in linear fashion, which implies that the Green's function for EM waves can give an accurate mathematical representation of this process. Time-reversal (TR) processing of such data is based on this fact. Using large arrays of EM sources and receivers to collect a sufficiently large set of multistatic array data has shown promise for detecting and subsequently identifying the physical nature of the scattering objects. All physical objects will have potentially three dielectric values (x,y,z) associated with them, while conducting (i.e., metallic) objects will have up to an additional three (again oriented x,y,z in space) conductivity values that can be detected. TR data processing is a useful way of processing such array data and then determining physical characteristics of the detected scattering objects.
The objective of this project is to determine whether TR processing of EM data can be used successfully to improve imaging, identification, and enumeration of underground metallic objects. In particular, the TR operator (which can itself be reconstructed from EM TR data) can be used to specify the number, and also to some extent the types, of objects present and the causes of the EM scattering. Thus, the TR approach to UXO identification could be used to enumerate these objects while also determining their types (i.e., pure dielectric or metallic, UXO or non-UXO metallic objects).
Previous research has demonstrated the capabilities of TR EM data processing for distinguishing and enumerating the types and numbers of metallic and nonmetallic objects present in a cluster of EM scattering objects. This work will determine the extent to which this is useful for UXO identification, classification, and retrieval. Extensive numerical modeling will be the main tool used in the project, and a large series of numerical tests is under way to evaluate various alternatives for separating and identifying those characteristics unique to each object of particular interest. Another important issue to be addressed is how to gather the large amounts of scattering data required without requiring unrealistically large source and data arrays.
This project will show the degree to which TR processing of EM data can or cannot determine the nature of scattering metallic objects like UXO, in an effort to reduce false positives while eliminating false negatives as much as possible. It will provide new ways of processing currently collected data sets and also suggest new ways of collecting UXO-related data to optimize the results of the TR data processing methodology. (Anticipated Project Completion - 2011)
Points of Contact
Dr. James Berryman
Lawrence Berkeley National Laboratory
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