A new approach for fast 2-D geoelectrical mapping of near-surface structures

Geoelectrical methods are widely used as mapping tools when investigating the near-surface structures in environmental and engineering applications. The Pulled Array Continuous Electrical Profiling (PACEP) method is a fast and efficient method designed to perform detailed and large-scale mapping of the near-surface structures. The method produces spatially dense profile-oriented data which often require 2-D interpretations. To meet this demand, rapid approximate one-pass inversion algorithm has been developed. The algorithm is based on linearization under the Born approximation and deconvolution with the Frechet derivative for a homogeneous halfspace. The validity and the efficiency of the deconvolution algorithm is demonstrated for profile data collected by Continuous Vertical Electrical Sounding (CVES), by comparing the deconvolution result and an iterative 2-D inversion result. Generally, it is observed that clayey till caps provide a protective capacity against contaminating leakage, but that sandy inhomogeneities in the cap may cause permeable paths down to the underlying aquifer. Geoelectrical methods have shown great ability to locate sandy inhomogeneities in clayey till caps. The deconvolution algorithm applied to data collected with the PACEP method is demonstrated for two test sites. The measured PACEP data, traditionally presented as contoured iso-resistivity maps of apparent resistivity, are quantified and sharpened applying the deconvolution algorithm. The results provide an improved image of the near-surface structures and a better background for the hydrogeologist to determine the location of the aquifer's vulnerable areas.