Ground Conductivity Meters Considered as Elevated Dipoles

Ground Conductivity Meters (GCMs) are used across a wide range of application areas and the measurements are spatially assembled and correlated with data from many other earth science, environmental, soil and land use investigations. They are understood, by users, to operate under a Low Induction Number (LIN) condition. This paper provides a new assessment of the subsurface conductivity measurements obtained by GCMs when the source is considered as an elevated dipole. The theoretical behaviour of the common systems is examined in relation to both the prevailing level of subsurface conductivity and the instrument elevation. It is demonstrated that, given the inherent high level of accuracy of modern instruments, the prevailing LIN condition may require operation in environments restricted to very low (<12 mS/m) conductivities. A simple correction procedure that can be applied to the measured data obtained from any of the LIN instruments is developed. The correction procedure would, in the limit of a uniform subsurface, return the same (correct) conductivity, irrespective of the ground conductivity meter used, the prevailing conductivity or the measurement height.