Time-domain-induced polarization: Full-decay forward modeling and 1D laterally constrained inversion of Cole-Cole parameters

Abstract

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

Direct current (DC) resistivity and induced polarization (IP) monitoring of active layer dynamics at high temporal resolution

“…A total of 1388 DC and 360 DC-IP data sets were inverted using the inversion software AarhusInv (Fiandaca et al, 2012(Fiandaca et al, , 2013Auken et al, 2014). We first inverted the data set of day 0 (Oct. 22, 2013) that marks the last day before the freezing of the ground begins.…”

Application of time domain induced polarization to the mapping of lithotypes in a landfill site

“…The survey was performed using the gradient array (Dahlin and Zhou, 2006), which was implemented on a SYSCAL-Pro instrument (Iris Instruments). The on-and off-time lengths for the time decay measurements were set to 4 s. The data were acquired using logarithmically spaced gates (Effersø et al, 1999) with approximately eight gates per decade, with a total of 20 gates. Four sections have been performed on the landfill itself, all exceeding the landfill boundaries in order to cover both areas of low signal and expected high signal.…”

“…The ColeCole model includes the DC resistivity (ρ) and parameters describing the frequency dependency (c, τ and M 0 ; see the section below for further explanation). For each profile the whole dataset was inverted following Fiandaca et al (2012), where the time domain forward response is computed via a Hankel transform of the frequency domain response for a layered medium. Then, inversion is carried out with a 1-D-LCI implementation (Auken et al, 2005) to retrieve the four Cole-Cole parameters for each layer.…”

Quasi-3D inversion of full size AEM datasets

“…In particular, AarhusInv supports airborne TEM data and FEM data (Siemon et al, 2009) and several ground based methods, i.e. EM (Christiansen et al, 2007), DC (Auken et al, 2005;Auken and Christiansen, 2004), Induced Polarization (Fiandaca et al, 2012;Fiandaca et al, 2013), Nuclear Magnetic Resonance (Behroozmand et al, 2012b;Behroozmand et al, 2012a), Surface waves (Wisén and Christiansen, 2005) and magnetotellurics (Christiansen and Auken, 2009). …”