A method of detecting and characterizing subsurface layers by means of electromagnetic depth sounding

A complete solution is provided for the mutual impedance ratio of a horizontal magnetic dipole source and a horizontal loop antenna over a multi-layer earth under the condition that the quasi-static approximation is valid. The phase angle of the mutual impedance ratio, which is found to be capable of the best resolution of the subsurface geoelectrical parameters, was considered as a tool for the detection and characterization of the subsurface layers. A new method for the numerical evaluation of the Hankel transform was applied to this EM sounding technique to generate the mutual impedance ratio curves at a considerable saving of computer time. Several new methods of interpreting the field data in terms of a three-layer earth model are also introduced.