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Inversion of airborne time‐domain electromagnetic data to a 1D structure using lateral constraints
Author(s) -
Vallée Marc A.,
Smith Richard S.
Publication year - 2009
Publication title -
near surface geophysics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.639
H-Index - 39
eISSN - 1873-0604
pISSN - 1569-4445
DOI - 10.3997/1873-0604.2008035
Subject(s) - hydrogeology , geology , inversion (geology) , resistive touchscreen , regional geology , jacobian matrix and determinant , environmental geology , overburden , engineering geology , matrix (chemical analysis) , algorithm , computer science , geotechnical engineering , seismology , mathematics , materials science , metamorphic petrology , volcanism , telmatology , composite material , computer vision , tectonics
We invert time‐domain airborne electromagnetic data in such a way as to obtain a model that varies slowly along the profile. This is achieved by modifying a typical one‐dimensional inversion algorithm to include lateral constraints. The lateral constraints are included as a roughness matrix that is solved simultaneously with the Jacobian matrix in an iterative eigenparameter inversion. In this case, multiple soundings along a line are all solved simultaneously. The lateral constraints can be applied to the resistivities and the thicknesses, both separately and together. We apply these techniques in two situations where airborne geophysical data are applied to near‐surface exploration. The first case is in a resistive environment where we are interested in quantifying a superficial conductive overburden. In this case, lateral constraints improve the geological image compared with those images obtained using unconstrained layered‐earth inversion. In the second case, we want to map the thickness of a resistive aquifer covering a saline layer. In this case, we show how varying the weights on the lateral constraints can change the image of the thickness of the aquifer. The presence of numerous cultural artefacts makes the inversion problematic. Application of a first‐difference constraint did the best job at removing culture but resulted in oversmoothing of the hydrogeology. The use of a second‐difference lateral constraint gave a good rendition of the hydrogeology but did not suppress the culture as well as the first‐difference constraint.