A method is described for rescaling off-time and on-time HTEM profiles to correct for amplitude variations that are caused by changes in transmitter altitude. The method is inspired by Nabighian's "smoke ring" effect which describes the primary magnetic field from a transmitter as a downward and outward moving current filament, of diminishing amplitude and having the same shape as the transmitter coil. Here the primary field correction is limited to the air between the transmitter and the Earth's surface, and does not require information on sub-surface conductivity. HTEM profiles are rescaled based on the change in mutual inductance between the actual transmitter and an image transmitter located at a nominal altitude. Variations in transmitter altitude are the primary causes of amplitude variations in HTEM profiles, independent of sub-surface conductivity. An example is shown over conductive sediments and volcanic units in an area containing gold mineralization and surrounded by extensive surface infrastructure from a survey flown in Mexico.

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Persistent URL dx.doi.org/10.1190/segam2016-13960131.1
Conference SEG International Exposition and 86th Annual Meeting, SEG 2016
Balch, S.J. (Stephen J.), Samson, C, & Sanchez, J.L. (Javier Lara). (2016). Correcting for HTEM altitude variations by transmitter mutual inductance normalization. In SEG Technical Program Expanded Abstracts (pp. 2139–2143). doi:10.1190/segam2016-13960131.1