Wednesday (Group 2) - SERDP-ESTCP - Strategic Environmental ...

Munitions Management (MM)
Poster Number 23 – Wednesday
Ground Based Detection and Discrimination — EMI & Magnetometers / Modeling & Processing
T
SIMULTANEOUS INVERSION OF UXO PARAMETERS
AND BACKGROUND RESPONSE
DR. LEONARD PASION
Sky Research, Inc.
2386 East Mall, Suite 112A
Vancouver, BC V6T1Z3 CANADA
(541) 552-5186
len.pasion@skyresearch.com
CO-PERFORMER: Dr. Douglas Oldenburg (UBC-GIF)
he task of discriminating UXO from non-UXO items is more difficult when sensor data are
collected at sites where an electromagnetically active host contributes a large signal. In
general, approaches to UXO discrimination assume that the object of interest is in free-space.
Any influence of the background medium is assumed to have been removed by filtering the data.
Spatial variations of the background signal can be the same size as UXO anomalies. These signal
variations can result from small scale topography (due to bumps or dips in the surface), changes
in the orientation and height of the sensor relative to the ground, and spatial variations in the
electromagnetic properties of the soil (i.e., conductivity and magnetic susceptibility). A high pass
filter to remove the geologic signal is often unable to remove smaller scale spatial variations. In
addition, this filtering step can introduce artifacts that can bias estimates of the target parameters.
In SERDP project MM-1573, we are developing an approach to processing data collected at sites
with magnetic geology. Instead of relying on filtering to remove the background response, we
use instrument position and orientation information to model the sensor response due to soils.
Computational routines and techniques to simultaneously invert for the parameters of the buried
object and the response of the background have been developed. For magnetic data, we will
study the effectiveness of an equivalent layer for modeling the geologic response. An equivalent
layer is a fictitious distribution of dipolar sources that lie at or below the observation surface and
which can potentially reproduce any magnetic field. We simultaneously invert for the equivalent
layer and the dipolar parameters of any embedded metallic objects. For electromagnetic data, we
simultaneously invert for geologic properties of the background response in addition to the
target’s dipole parameters. The response of the magnetic geology is calculated by using an
approximate multi-dipole representation of the transmitter. We present results of processing both
simulated and field data for the Geonics EM63 time domain electromagnetic sensor and the
newly developed Man Portable Vector time domain electromagnetic sensor. Finally, to quantify
the effect of topography on the EMI signal we use numerical modeling of Maxwell’s equations.
We will present initial results comparing measured and modeled data for different sized bumps
and trenches.
G-3