New developments in AEM discrete conductor modelling and inversion

What is it about?

Discrete conductor models like sphere and plate were introduced in the 1950s as modelling tools in airborne electromagnetic (AEM) survey interpretation. In the last 20 years, with the development of inversion techniques, they have been integrated into parametric inversion programs. The recent advent of powerful workstations makes them useful tools for interactive AEMinterpretation. Different problems have been encountered in the implementation and application of discrete objects as modelling and inversion tools. The sphere response is modelled using a sum of spherical functions. Assuming that the radius of the sphere is small compared to the distance between the transmitter and receiver to the centre of the sphere, the response can be approximated by using only thefirst term of the solution. This approach is reviewed for modelling the response of a conductive sphere in free space or buried in a layered earth. Plate modelling is based on spectral methods or the integral equation method, which provide different techniques for estimating the response of a plate in free space.A comparison of the results of these techniques show differences attributed to the different discretisation methods. A case history from Abitibi, Canada, shows that plate inversion using two different inversion methods provides useful information when the target is a plate-like conductor in a resistive environment.

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