Possibilities for UXO Classification using Characteristic Modes of the Broadband Electromagnetic Induction Resistivity
Zonge, 1999. Presented at “New Technology Applications Conference on the Science and Technology of Unexploded Ordnance Removal and Site Remediation,” Maui, Hawaii, 8-11 Nov., 1999
D.D. Snyder, Scott MacInnes*, Scott Urquhart*, and K.L. Zonge, Zonge Engineering and Research Organization, Tucson, Arizona
Paper – [pdf] UXO_1999_PossibilitiesForUXOClassification-Using_EM
Elementary induction EM principles are also applied in metal detectors and as such they have enjoyed a long and successful history in applications such as utilities location and in the location of metallic mines. Metal detectors are typically optimized for detecting very small objects located within a few 10′s of cm from the surface. Recently, however, new induction EM instruments have been developed specifically for shallow metal detection and site characterization. These instruments have significantly increased the depth of detection for shallow-buried metallic objects and, at least in one case, they provide measurements at more than one frequency or time delay. These instruments are now widely applied for detecting and mapping shallow-buried metal objects including UXO.
In cooperation with Earth Tech, Zonge Engineering has been investigating how a fast TEM system might be applied for UXO characterization. In this paper, we explore how broadband induction EM responses (i.e., TEM transients, or FEM spectra) can provide a basis for UXO classification. In that regard, the next section will review briefly some important characteristics of the inductive EM response of confined conducting and permeable objects. These characteristics, long recognized by exploration geophysicists, provide a basis for expanding an FEM spectrum or TEM transient as a series of characteristic modal functions whose parameters contain information about the conductivity and size characteristics of the target. One method for the decomposition of the EM response into these characteristic modes, Prony’s method, is discussed briefly and is applied to both synthetic and real TEM transients. Finally, we present data acquired with a prototype antenna system consisting of a horizontal transmitting antenna and a 3-axis receiving antenna. With this antenna system, data were acquired using a Zonge 3-channel NanoTEM™ system.