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Laboratory Evaluation Of Three Prototype Geophysical Instruments For Uxo ApplicationsNormal access

Authors: David L. Wright, David vonG. Smith, Craig W. Moulton, S. Raymond Hutton, Robert E. Bracken, Erin L. Wallin, Philip J. Brown, Carl E. Stoddard, John D. Kibler, Misac N. Nabighian and Yaoguo Li
Event name: 16th EEGS Symposium on the Application of Geophysics to Engineering and Environmental Problems
Session: Unexploded Ordnance
Publication date: 06 April 2003
Organisations: EEGS
Language: English
Info: Extended abstract, PDF ( 3.82Mb )

Summary:
The Very Early Time Electromagnetic (VETEM) system, the High-Frequency Sounder (HFS),
and the Tensor Magnetic Gradiometer System (TMGS) were developed by the U.S. Geological Survey
(USGS) for applications other than unexploded ordnance (UXO). However, features of these systems
may make them adaptable to UXO applications. VETEM is a time-domain electromagnetic (EM)
induction system that utilizes full waveform recording. The HFS is a flexible frequency-domain EM
system. The TMGS uses four sensitive 3-axis fluxgate magnetometers so that gradients of field
components are recorded. Tests were conducted in air using a selection of inert UXO objects ranging
from 20 mm to 105 mm in diameter. A nulled overlapped antenna arrangement was used for both
VETEM and the HFS. It was found that this antenna configuration resulted in distinctly different
responses to horizontal UXO objects aligned along the direction of traverse versus horizontal and
perpendicular to the traverse. Vertical orientation of UXO objects resulted in smaller amplitude signals
and an interesting slightly asymmetric “crater” shape response in plan view. The HFS response was a
strong function of frequency, which is good for discrimination. The TMGS data are the most sensitive
to ferromagnetic objects and the multi-component data hold the promise of accurate location, including
depth, to UXO objects using a dipole mapping algorithm. Plans include increased sensitivity and multicomponent
capability for the EM systems, advanced algorithms to enhance UXO discrimination for EM
and TMGS systems and field evaluations at standard UXO test sites of the Strategic Environmental
Research and Development Program (SERDP).

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