Time-domain-induced polarization has significantly broadened its field of reference during the last decade, from mineral exploration to environmental geophysics, e.g., for clay and peat identification and landfill characterization. Though, insufficientmodeling tools have hitherto limited the use of time-domain induced polarization for wider purposes. For these reasons, anew forward code and inversion algorithm have been developed using the full-time decay of the induced polarization response,together with an accurate description of the transmitter waveform and of the receiver transfer function, to reconstruct thedistribution of the Cole-Cole parameters of the earth. The accurate modeling of the transmitter waveform had a strong influenceon the forward response, and we showed that the difference between a solution using a step response and a solution using the accurate modeling often is above 100%. Furthermore, the presence of low-pass filters in time-domain-induced polarization instruments affects the early times of the acquired decays (typically up to 100 ms) and has to be modeled in the forward response to avoid significant loss of resolution. The developed forward code has been implemented in a 1D laterally constrained inversion algorithm that extracts the spectral contentof the induced polarization phenomenon in terms of the Cole-Cole parameters. Synthetic examples and field examples from Denmark showed a significant improvement in the resolution of the parameters that control the induced polarization response when compared to traditional integral chargeability inversion. The quality of the inversion results has been assessed by a complete uncertainty analysis of the model parameters; furthermore, borehole information confirm the outcomes of the field interpretations. With this new accurate code in situ time-domain inducedpolarization measurements give access to new applications in environmental and hydrogeophysical investigations, e.g., accurate landfill delineation or on the relation between Cole-Cole and hydraulic parameters.
|Number of pages||13|
|Publication status||Published - 2012|
All Science Journal Classification (ASJC) codes
- Geochemistry and Petrology