Inversion of Conductivity Profiles from EM Using Full Solution and a 1-D Laterally Constrained Algorithm

In highly conductive environments the apparent electrical conductivity (sigma(a)) data generated from electromagnetic (EM) instruments are known to be non-linear. This is particularly the case when high conductivity bodies are present in the subsurface. However, little attention has been given to this issue in the research literature of the environmental and hydrological sciences. In this paper we describe the development of an inversion algorithm, which consists of a I-D inversion with 2-D smoothness constraints between adjacent 1-D models, whereby the forward response is calculated using the full solution of the induction phenomena. The robustness of the algorithm is evaluated using sigma(a) data acquired from two study areas. In the first case study, sigma(a) data is acquired with a DUALEM-21 across a golf green in Guelph, Ontario Canada. In the second case study, a DUALEM-421 is used to collect sigma(a) across an irrigated field located on a clay alluvial plain of the Lower Gwydir Valley (Australia). The general patterns of modeled true electrical conductivity (sigma), as achieved from our inversion algorithm with the full solution, are shown to compare favorably with the available information and existing knowledge at each site. We also find that the models calculated with the new algorithm compare favorably with those obtained using individual 1-D inversion.