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Investigations Into Inversion Of Magnetic And Gradient Magnetic Data For Detection And Discrimination Of Metallic ObjectsNormal access

Authors: R.W. Groom, Ruizhong Jia and Catalina Alvarez
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 ( 204.38Kb )

We have extended our three-dimensional magnetic modeling capabilities to simulate TMI,
magnetic vector and gradient measurements for both permanent magnetization and strong induced
effects. We have developed capabilities to model quite general 3D shapes including conical and
cylindrical objects both solid and hollow. These general shapes can be combined to represent projectile
shells with quite general shapes having varying internal magnetic properties.
With these simulation capabilities, we investigated the use of inversion algorithms to determine
the internal magnetization vector of buried objects. Our objectives are to understand the limitations of
recovering the location of the magnetization vector as well as its magnitude and vector orientation.
Determining the strength and orientation of the internal magnetization can help in the discrimination of
material properties. Our experiments include examination of data sampling, data noise and combinations
of TMI, vector and gradient measurements to resolve the magnetization. As an example, we determined
that with adequate data sampling one could determine, extremely accurately, the location and orientation
of the internal magnetization vector only if the volume of the object is known. This was accomplished
by non-linear inversion combined with iterative grid volume modification. In addition, we have
experimented with the use of a modified Euler deconvolution technique for depth estimation. At present,
we are working with combining the two techniques.

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