Investigating the effects of soils with complex magnetic susceptibility on EMI measurements using numerical modelling of Maxwell's equations

Kevin A. Kingdon; Leonard R. Pasion; Douglas W. Oldenburg

doi:10.1117/12.818662

4 May 2009 Investigating the effects of soils with complex magnetic susceptibility on EMI measurements using numerical modelling of Maxwell's equations

Kevin A. Kingdon, Leonard R. Pasion, Douglas W. Oldenburg

Author Affiliations +

Proceedings Volume 7303, Detection and Sensing of Mines, Explosive Objects, and Obscured Targets XIV; 73030Q (2009) https://doi.org/10.1117/12.818662
Event: SPIE Defense, Security, and Sensing, 2009, Orlando, Florida, United States

Abstract

Soils that exhibit strong Viscous Remanent Magnetization (VRM) have a major effect on time- and frequency-domain data collected by electromagnetic induction (EMI) sensors. Small scale topography in the form of bumps or troughs will also distort the EM signal due to UXO. If these components of "geologic noise" are not adequately accounted for in the inversion process, then the ability to carry out discrimination will be marginalized. Our long-term goal is to include these effects into the inversion but the chosen methodology depends upon some crucial issues. Foremost, we need to be certain that we can numerically compute the effects of complex magnetic susceptibility and topography that would be encountered in field surveys. Second, we need to investigate whether there is significant electromagnetic interaction between the UXO and its host material or whether the signals are additive. If the total signal can be adequately represented by the superposition of the two individual signals (ie the field of a UXO in free space, and the effect of a conductive host with topography and complex magnetic susceptibility) then there are many avenues by which data can be preprocessed to remove contaminating effects, or by which joint inversion of UXO and host parameters can be carried out. In this paper we concentrate upon the issues of modeling and the possibility of additivity. We first validate our EM numerical modeling code for halfspaces having VRM. We then show that EM interaction between the host and a compact metallic object is minimal for a specific example which is typical of a buried ordnance in a highly magnetic soil such as on Kaho'olawe, Hawaii. We also model soil responses for simple variations of surface roughness including both a single bump and a single trench and compare those results with field data acquired over similar environments.

Citation Download Citation

Kevin A. Kingdon, Leonard R. Pasion, and Douglas W. Oldenburg "Investigating the effects of soils with complex magnetic susceptibility on EMI measurements using numerical modelling of Maxwell's equations", Proc. SPIE 7303, Detection and Sensing of Mines, Explosive Objects, and Obscured Targets XIV, 73030Q (4 May 2009); https://doi.org/10.1117/12.818662

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