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Detecting Uxo Using Quad-Quad Conductivity In Magnetic TerrainsNormal access

Authors: Haoping Huang and I.J. Won
Event name: 17th EEGS Symposium on the Application of Geophysics to Engineering and Environmental Problems
Session: UXO Detection
Publication date: 22 February 2004
Organisations: EEGS
Language: English
Info: Extended abstract, PDF ( 182.55Kb )

Apparent conductivity computed from in-phase and quadrature components has been
successfully used in detecting buried metallic objects such as unexploded ordnance (UXO). The
conductivity computation uses the magnetic susceptibility calculated from the lowest-frequency in-phase
data obtained at a specific sensor height. Over magnetic soils, however, the in-phase component may
fluctuate with varying sensor heights. Uncertainties in sensor height, which are common with handheld
sensors or cart-mounted sensors in rough terrain, can produce errors on the computed magnetic
susceptibility, which, in turn, causes errors in apparent conductivity, resulting in false anomalies.
We introduce the quad-quad conductivity that is computed from the quadrature components at
two frequencies. Compared with the traditional apparent conductivity calculated from in-phase and
quadrature components at a given frequency, the quad-quad technique has several advantages for
detecting metal targets in magnetic terrains: it is (1) insensitive to the magnetic polarization currents; (2)
immune to sensor motion over magnetic soil; and (3) biased to metal objects and, thus, able to detect
small and/or deep metal targets. The first two properties suppress the noise caused by magnetic geology
and sensor motion and, thus, yield a quiet background. The last property emphasizes metal objects as
sought anomalies over geologic variations.

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