Inversion of the Decay Curves of Time-Domain Induced-Polarization Survey Data With Consideration of Hybrid Time Constraints

Time-domain (TD) induced polarization (IP) measures the overvoltage decay in a chargeable medium and is conventionally used to compute apparent resistivity. Given recent advances in TD IP instruments, decay curves are measured using many time channels to estimate the IP and Cole–Cole parameters, which include the time and exponent constants, chargeability, and resistivity. To more precisely estimate IP parameters using decay curves, we developed an inversion method employing hybrid time constraints to appropriately invert rapid overvoltage decays. The proposed method employs both first- and second-order derivatives with respect to the decay times. In synthetic models, using the proposed method, the new inversion approach accurately identified the chargeability decay characteristics in a chargeable medium. These were employed to estimate the medium IP parameters employing the TD Cole–Cole model. The new inversion method was tested using TD IP field data from South Korea. The interpretations were well correlated with borehole (BH) data.