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A discrete conductor transformation of airborne electromagnetic data
Author(s) -
Smith Richard S.,
Salem Ahmed S.
Publication year - 2007
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 - 10.3997/1873-0604.2006021
Subject(s) - moment (physics) , conductor , geometry , context (archaeology) , geology , section (typography) , traverse , electrical conductor , plane (geometry) , mathematics , physics , geodesy , computer science , paleontology , classical mechanics , operating system , quantum mechanics
Airborne electromagnetic moment data are transformed to two depth sections that display the properties of a spherical conductor. In addition to the spherical conductor being small or distant, we made other simplifying assumptions: the conductor is always below the traverse line and the strike of the plane containing the current flow is always perpendicular to the flying line. The transformation algorithm compares measured moment data with synthetic moment data in a look‐up table. An index of fit is calculated to measure how closely the data in the look‐up table match the measured data. When the fit is good, we use bright colours on the depth section to indicate the properties of the discrete conductor; when the fit is poor, we make the section grey. The estimated properties displayed on the two sections are the product of conductivity and the square of the radius (CRS) on one section and the dip of the current flow on the other section. The position and depth can also be inferred from the location where the fit is best. The data displayed on the depth sections are also summarized in plan view, with colour being used to indicate the estimated properties of the sphere (CRS, dip and depth). This colour map can be displayed in combination with a greyscale image of the electromagnetic data as this illustrates the context of the colour features. Application of the method to two field data sets shows that the method works well for isolated bedrock conductors. However, no features were resolved when there was interference from nearby conductors. Also, we found that wide bodies were not necessarily well resolved. In some cases the features on the sections were confusing, but this can reflect data that is complex or difficult to interpret. Where coherent features are displayed, the estimated values of the depth, CRS and dip seemed reasonable.