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Coaxial Electromagnetic Sensor for Uxo DetectionNormal access

Authors: Haoping Huang, Bill SanFilipo, Alex Oren and I.J. Won
Event name: 18th EEGS Symposium on the Application of Geophysics to Engineering and Environmental Problems
Session: UXO Single Sensor Systems
Publication date: 03 April 2005
Organisations: EEGS
Language: English
Info: Extended abstract, PDF ( 1.02Mb )

Summary:
A new broadband electromagnetic (EM) sensor, called GEM-5, for shallow earth investigation
including detection and discrimination of UXO has been developed. The sensor consists of a central
transmitter coil and two coaxial receiver coils located at the same vertical distance above and below the
transmitter coil. The difference in output between the receiver coils would be zero in free space. This
particular configuration provides a high degree of primary field cancellation, reduction of power-line or
other environmental noise, and immunity from noise induced by sensor motion in the earth’s magnetic
field.
We have first studied the detection capability of the sensor. The EM responses are numerically
simulated using a sphere model for UXO-like objects, and a half-space for geology. Algorithms to invert
the EM data into apparent susceptibility and conductivity show that the sensor can detect small metal
targets. Transforming the EM data into the apparent conductivity can enhance the anomalies from metal
targets and reduce geological noise. Our field test indicates that the gradiometer measurements yield a
lower static and motion noise over the critical low frequencies than that of existing sensors, and detect
all targets at a seeded UXO test site.

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