Emax conductivity-depth transformation of airborne TEM data

Abstract

Conductivity-depth imaging is a convenient form of presentation for preliminary interpretation of ground and airborne EM data. This paper describes the airborne EM adaptation of the Emax conductivity-depth transformation, originally developed for ground TEM. The transformation proceeds in two stages: first the apparent conductivity is determined at a given delay time; then the depth of the current maximum in a half-space with conductivity equal to the apparent conductivity is adopted as the apparent depth at that time. The advantage of the Emax transformation is that it is readily adaptable to a wide variety of TEM data. The disadvantage is that apparent conductivity is not unique, nor always defined. In practice this does not usually pose difficulties for transformation of airborne EM. The utility of the Emax transformation to airborne data is illustrated via application to GEOTEM_DEEP total field data. The total field provides a degree of immunity to receiver mis-orientation.