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.
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