Abstract
Summary Electromagnetic induction by a non-uniform source over a layered halfspace is studied. A method is described for solving such problems when the current intensity distribution is such that no analytic integration to obtain the field quantities is possible. A number of models are considered using a general computer program. Apparent resistivity curves are calculated and compared with previous results. Phase curves and field component profiles are calculated. Increasing interest has been shown in modelling and interpretation of electromagnetic induction anomalies during the past 15 years. Several approaches to the problem have been employed, including analytical, analogue and numerical techniques. Analytical techniques are limited in that only particular models of simple geometry may be considered. Models of more complex geometry may be studied by analogue techniques but such experimental measurements are often limited by edge effects and the range of conductivities that may be employed. The numerical techniques provide a versatile method which may be used for wide conductivity ranges and to approximate complex geometries. Studies to date have included calculations for either uniform or specific simple source geometries (e.g. a line current source or a horizontal or vertical dipole). Hermance & Peltier (1970) solved the induction problem for a line current source in the manner suggested by Price (1950). This work was then extended by Peltier & Hermance (1971) to a sheet current source with an intensity of Gaussian shape. Hibbs & Jones (1973a, b) generalized the method used by Peltier & Hermance to include non-symmetric as well as symmetric source configurations. Laterally inhomogeneous earth models were also studied by combining the approach of Peltier & Hermance with the numerical modelling method of Jones & Price (1970) as programmed by Jones & Pascoe (1971) and Pascoe & Jones (1972). The above work was limited in that only source configurations for which the source coefficient C(s) as described by Peltier & Hermance (1971) are obtained
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