Modelling using receiver waveform and the importance of system geometry

Abstract

Conductivity - depth sections (CDI) produced from a recent airborne TEM exploration survey showed a poor fit to the expected geology of the area (a known conductive layer was appearing deeper than expected). The source of the prob lem was found to be the use of an incomplete description of the system geometry which had the effect of dramatically scal ing the secondary field . In many modelling programs, including in this case EMFlow, the system geometry may be used to determine transm itter - receiver coupling which is used to compute the apparent primary field. This paper explains why system geometry can be critical for precise modelling of T EM data. By specifying the correct transmitter orientation and de - rotating receiver pitch for bot h primary and secondary fields, the match between known geology and CDI depth was greatly improved.