COMPUTATION OF COLE-COLE PARAMETERS FROM IP DATA

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 divid e the earth into rectangular cells and assume that the Cole-Cole decay parameters eta(o), tau, and c are constant in each cell. Apparent cha rgeability data measured at times tk after the cessation of the input current are inverted using a 2-D inversion algorithm to recover the in trinsic chargeability structure eta(t(k); x, z) for k = 1, L, where L is the number of time channels measured. When carrying out this invers ion, it is necessary to introduce a normalization criterion so that th e inversion outputs from the different time channels can be meaningful ly combined. The L chargeability structures provide L estimates of the chargeability decay curve for each cell. The desired intrinsic Cole-C ole parameters are recovered from these decay curves using a very fast simulated annealing (VFSA) algorithm. Application of the process in a ll calls provides interpretation maps of eta(o)(x, z), tau(x, z), and c(x, z). Our analysis is demonstrated on a synthetic example and is im plemented on a field data set. The application of the process to field data yields reasonable results.