TY  - JOUR
A1  - Klose, Tim
A1  - Guillemoteau, Julien
A1  - Simon, Francois-Xavier
A1  - Tronicke, Jens
T1  - Toward subsurface magnetic permeability imaging with electromagnetic induction sensors
BT  - Sensitivity computation and reconstruction of measured data
JF  - Geophysics
N2  - In near-surface geophysics, small portable loop-loop electro-magnetic induction (EMI) sensors using harmonic sources with a constant and rather small frequency are increasingly used to investigate the electrical properties of the subsurface. For such sensors, the influence of electrical conductivity and magnetic permeability on the EMI response is well-understood. Typically, data analysis focuses on reconstructing an electrical conductivity model by inverting the out-of-phase response. However, in a variety of near-surface applications, magnetic permeability (or susceptibility) models derived from the in-phase (IP) response may provide important additional information. In view of developing a fast 3D inversion procedure of the IP response for a dense grid of measurement points, we first analyze the 3D sensitivity functions associated with a homogeneous permeable half-space. Then, we compare synthetic data computed using a linear forward-modeling method based on these sensitivity functions with synthetic data computed using full nonlinear forward-modeling methods. The results indicate the correctness and applicability of our linear forward-modeling approach. Furthermore, we determine the advantages of converting IP data into apparent permeability, which, for example, allows us to extend the applicability of the linear forward-modeling method to high-magnetic environments. Finally, we compute synthetic data with the linear theory for a model consisting of a controlled magnetic target and compare the results with field data collected with a four-configuration loop-loop EMI sensor. With this field-scale experiment, we determine that our linear forward-modeling approach can reproduce measured data with sufficiently small error, and, thus, it represents the basis for developing efficient inversion approaches.
KW  - Electromagnetics
KW  - Imaging
KW  - Magnetic+Susceptibility
KW  - Near+Surface
KW  - Modeling
Y1  - 2018
U6  - https://doi.org/10.1190/GEO2017-0827.1
SN  - 0016-8033
SN  - 1942-2156
VL  - 83
IS  - 5
SP  - E335
EP  - E345
PB  - Society of Exploration Geophysicists
CY  - Tulsa
ER  - 
TY  - JOUR
A1  - Guillemoteau, Julien
A1  - Tronicke, Jens
T1  - Non-standard electromagnetic induction sensor configurations: Evaluating sensitivities and applicability
JF  - Journal of applied geophysics
N2  - For near surface geophysical surveys, small-fixed offset loop-loop electromagnetic induction (EMI) sensors are usually placed parallel to the ground surface (i.e., both loops are at the same height above ground). In this study, we evaluate the potential of making measurements with a system that is not parallel to the ground; i.e., by positioning the system at different inclinations with respect to ground surface. First, we present the Maxwell theory for inclined magnetic dipoles over a homogeneous half space. By analyzing the sensitivities of such configurations, we,show that varying the angle of the system would result in improved imaging capabilities. For example, we show that acquiring data with a vertical system allows detection of a conductive body with a better lateral resolution compared to data acquired using standard horizontal configurations. The synthetic responses are presented for a heterogeneous medium and compared to field data acquired in the historical Park Sanssouci in Potsdam, Germany. After presenting a detailed sensitivity analysis and synthetic examples of such ground conductivity measurements, we suggest a new strategy of acquisition that allows to better estimate the true distribution of electrical conductivity using instruments with a fixed, small offset between the loops. This strategy is evaluated using field data collected at a well-constrained test-site in Horstwalde (Germany). Here, the target buried utility pipes are best imaged using vertical system configurations demonstrating the potential of our approach for typical applications. (C) 2015 Elsevier B.V. Pill rights reserved.
KW  - Electromagnetics
KW  - EMI sensors
KW  - Loop-loop systems
KW  - Near surface geophysics
KW  - Civil engineering
KW  - Sensitivity analysis
Y1  - 2015
U6  - https://doi.org/10.1016/j.jappgeo.2015.04.008
SN  - 0926-9851
SN  - 1879-1859
VL  - 118
SP  - 15
EP  - 23
PB  - Elsevier
CY  - Amsterdam
ER  -