oa Full Waveform Modeling of Time Domain Induced Polarization Data and Inversion

During the last decades the scope of Time Domain Induced Polarization (TDIP) has considerably broadened from mineral exploration to environmental geophysics, mainly to clay identification and landfill characterization. Furthermore modern instruments allow multi-channel acquisition of IP data with multi-core cables and steel electrodes. for TDIP surveys the acquisition time is shorter and the logistic simpler in comparison with Spectral Induced polarization (SIP) surveys.<br>Despite this the Inversion techniques have not undertaken consequential enhancements: TDIP data are usually inverted using only integral chargeability, without considering the effective shape of the transmitter pulse or the system transfer function of the receiver. for these reasons a new Inversion algorithm has been developed using the full time decay of the IP response to reconstruct the distribution of the Cole-Cole parameters of the Earth. <br>the forward response is computed modeling the full current waveform (in terms of sequence of positive and negative pulses) and instrumental low-pass filters. Even when stacking, needed for noise reduction and self potential removal, the signal changes significantly during the process and the finite numbers of pulses have to be modeled to obtain accurate time decays.<br>the new approach allows moving from a qualitative Interpretation of TDIP data for recognition of anomaly patterns to a quantitative analysis, able to discriminate soil lithotypes and, if present, the type/grade of contamination: a case history from a landfill-stream interaction supports this conclusion, correlating pollution and Inversion parameters.<br>the forward response has been implemented in the 1D Laterally Constrained Inversion scheme (1D-LCI), producing layered sections of the subsurface with lateral smooth variations. Currently a 2D and 3D implementation are being developed.