Sensitivity of galvanic and inductive Induced Polarization methods to the Cole-Cole parameters

Abstract

The Induced Polarization (IP) method is recognized as a valuable geophysical tool for resource exploration and environmental studies. In many of these studies, the Cole-Cole relaxation expression has been used to describe how subsurface resistivity depends on the frequency of the fields. In this study, we estimate the resolution of the Cole-Cole parameters of simple models measured by three geophysical methods. We compare the Spectral IP (SIP), the time-domain or Transient IP (TIP), and the in-loop Transient Electromagnetic (TEM) methods. In the first two, a current is injected directly into the ground (galvanic), while in the last one, the current is created by electromagnetic induction. The sensitivities and parameter uncertainties are estimated with a Singular Value Decomposition of the sensitivity matrix for a series of homogeneous and two-layered models. In general, the SIP method gives the best parameter resolutions, followed by those of the TIP and TEM methods. Of the four Cole-Cole parameters, generally the time constant is the least well resolved. The parameters are better resolved when the time constant is less than 10 s. When the polarizable medium is buried under a non-polarizable layer, the uncertainties of the TEM method show an important increase.