Computation of Cole-Cole parameters from IP data

Abstract We develop a process to estimate Cole-Cole parameters from time-domain induced polarization (IP) surveys carried out over a nonuniform earth. The recovery of parameters takes the following steps. We first divide the earth into rectangular cells and assume that the Cole- Cole decay parameters η0,τ, and c are constant in each cell. Apparent chargeability data measured at times tk after the cessation of the input current are inverted using a 2-D inversion algorithm to recover the intrinsic chargeability structure η(tk; x, z) for k = 1, L, where L is the number of time channels measured. When carrying out this inversion, it is necessary to introduce a normalization criterion so that the inversion outputs from the different time channels can be meaningfully combined. The L chargeability structures provide L estimates of the chargeability decay curve for each cell. The desired intrinsic Cole-Cole parameters are recovered from these decay curves using a very fast simulated annealing (VFSA) algorithm. Application of the process in all cells provides interpretation maps of η0(x, z), τ(x, z), and c(x, z). Our analysis is demonstrated on a synthetic example and is implemented on a field data set. The application of the process to field data yields reasonable results.