Novel ways to process and model GEOTEM data

Abstract

Data processing methods originally developed for the TEMPEST system allow GEOTEM half-sine data to be deconvolved and transformed to GEOTEM square-wave data. The advantages of the transformed square-wave data are that they refer to a standardised waveform that does not vary through a survey. The high-frequency information contained in the data recorded during the transmitter pulse can be readily utilised and the data can be easily corrected for variations in the transmitter loop height, pitch, roll and receiver coil offset. Modelling results from transformed GEOTEM data acquired across the Bull Creek mineralisation indicate that the transformation works well for survey data. Traditional off-time, single component conductivity - depth modelling of GEOTEM data can be improved by utilizing the full waveform and by inverting multicomponent datasets. In highly conductive terrain, such as above seawater, where system parameters such as the bird position are hard to derive reliably from the time ? domain in-phase component as a proxy for the primary field, the joint inversion of multicomponent data helps to correctly resolve layered-earth parameters. Jointly inverting the 3-component on- and off-time data of a GEOTEM bathymetry survey in the Torres Strait showed that the data fit can be greatly improved by allowing the inversion to determine the receiver offset and attitude. This results in greater confidence in the derived conductivity - depth values.