Inversion of Transient Electromagnetic Data from a Spherical Conductor

This paper considers the problem of inverting single loop transient electromagnetic data from a spherical conductor. First, analytical expressions are presented for the transient voltage, and then the various partial derivatives of this voltage with respect to the parameters of the ground are found. Secondly, it is shown how all these expressions can be used with existing inversion schemes, such as the Marquardt or ridge regression scheme for the inversion of data. Finally, results are presented to show that, even when the transient data is contaminated by 20-percent random noise, good estimates for the earth parameters can be found. In this case, however, only 4 parameter combinations are well resolved. Further, when there is only 5-percent noise present in the data, it is still not possible to resolve more than 5 sets of parameters.