f Conductivity - depth imaging of airborne EM data

Conductivity Depth Imaging (CDI) for step response airborne electromagnetic (AEM) data was first described by Macnae et al (1990) . In this process, AEM data are transformed into a (smoothed) conductivity-depth section under an assumption that the physical properties (geology) are quasi-layered. While the CDI method of Macnae and Lamontagne (1987) is only applicable to step response data, other authors such as Eaton and Hohmann, (1989), Polzer (as described in West and Bailey, 1989) and Nekut(1987) have developed modifications suitable for impulse rather than step response data. Since then, a further mathematical development has allowed the CDI method to be applied to arbitrary waveform EM data in some limited cases; most notably the Geotem and Questem commercial airborne EM systems which use an approximately half-sinusoidal transmitter waveform with significant off-time.