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, insufficient\ud modeling tools have hitherto limited the use of time-domain induced polarization for wider purposes. For these reasons, a\ud new forward code and inversion algorithm have been developed using the full-time decay of the induced polarization response,\ud together with an accurate description of the transmitter waveform and of the receiver transfer function, to reconstruct the\ud distribution of the Cole-Cole parameters of the earth. The accurate modeling of the transmitter waveform had a strong influence\ud on 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 content\ud of 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 induced\ud polarization 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

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This study uses time‐domain induced polarization data for the delineation and characterization of the former landfill site at Eskelund, Denmark. With optimized acquisition parameters combined with a new inversion algorithm, we use the full content of the decay curve and retrieve spectral information from time‐domain IP data. Thirteen IP/DC profiles were collected in the area, supplemented by el‐log drilling for accurate correlation between the geophysics and the lithology. The data were inverted using a laterally constrained 1D inversion considering the full decay curves to retrieve the four Cole‐Cole parameters. For all profiles, the results reveal a highly chargeable unit that shows a very good agreement to the findings from 15 boreholes covering the area, where the extent of the waste deposits was measured. The thickness and depth of surface measurements were furthermore validated by el‐log measurements giving in situ values, for which the Cole‐Cole parameters were computed. The 3D shape of the waste body was pinpointed and well‐defined. The inversion of the IP data also shows a strong correlation with the initial stage of the waste dump and its composition combining an aerial map with acquired results.

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The Time Domain Induced Polarization (TDIP) technique is widely used in applied geophysics, particularly for environmental issues, for instance for delineating landfills or detecting leachate percolation. Because the reliability of IP data remains an issue at the field scale, this paper deals with the factors controlling data quality and compares different arrays and acquisition parameters for optimal collection of data in the field. The first part focuses on repeatability experiments carried out in the former Hørløkke landfill (Denmark), in order to infer the degree of which a signal can be reproduced over time. Results show a good repeatability, with on average less than 10% of difference in raw data. Also, from the results it is inferred that the paramount parameter controlling repeatability is the IP signal level; a value of 2 mV is a sufficient threshold to ensure repeatability within 10% of data difference, although system dependant. The second part focuses on survey design and underlines the importance of keeping the geometrical factor low. This points to the choice of a relevant measurement protocol, which depends on the threshold of the geometrical factor, again depending on expected chargeability and resistivity, threshold voltage and injected current. Furthermore, acquisition parameters such as the duration of the pulse injection and data sampling have a significant effect on both the signal‐to‐noise ratio and resolution. A comprehensive comparison between three protocols, the gradient array, the linear grid and the dipole‐dipole array, is shown and the choice of an acquisition sequence is discussed.