Using the in-line component for fixed-wing EM 1D inversion
Adam SmiarowskiCGG Airborne Surveys, 2505 Meadowvale Boulevard, Mississauga, Ontario, L5N 5S2, Canada. Email: adam.smiarowski@cgg.com
Exploration Geophysics 46(1) 130-135 https://doi.org/10.1071/EG14024
Submitted: 19 March 2014 Accepted: 30 June 2014 Published: 8 September 2014
Abstract
Numerous authors have discussed the utility of multicomponent measurements. Generally speaking, for a vertical-oriented dipole source, the measured vertical component couples to horizontal planar bodies while the horizontal in-line component couples best to vertical planar targets. For layered-earth cases, helicopter EM systems have little or no in-line component response and as a result much of the in-line signal is due to receiver coil rotation and appears as noise. In contrast to this, the in-line component of a fixed-wing airborne electromagnetic (AEM) system with large transmitter–receiver offset can be substantial, exceeding the vertical component in conductive areas. This paper compares the in-line and vertical response of a fixed-wing airborne electromagnetic (AEM) system using a half-space model and calculates sensitivity functions. The a posteriori inversion model parameter uncertainty matrix is calculated for a bathymetry model (conductive layer over more resistive half-space) for two inversion cases; use of vertical component alone is compared to joint inversion of vertical and in-line components. The joint inversion is able to better resolve model parameters. An example is then provided using field data from a bathymetry survey to compare the joint inversion to vertical component only inversion. For each inversion set, the difference between the inverted water depth and ship-measured bathymetry is calculated. The result is in general agreement with that expected from the a posteriori inversion model parameter uncertainty calculation.
Key words: bathymetry, fixed-wing, in-line component, inversion resolution, joint inversion, multicomponent.
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