Efficient spectral IP-modelling in the time domain

Hördt, Andreas; Hanstein, T.; Hönig, Merle C.; Neubauer, F. M.

doi:10.1016/j.jappgeo.2005.09.003

Cited by 17 publications

(15 citation statements)

References 17 publications

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“…A few methods exist for interpreting time-domain induced polarization in terms of spectral IP (e.g., Hördt et al 2006), also referred to as frequency-dependent complex resistivity. Some authors (Soininen 1984;Ghorbani et al 2007) have pointed out the difficulty of extracting spectral information from timedomain induced polarization data but standard time-domain IP is already useful in many cases.…”

Section: Capacitive Couplingmentioning

confidence: 99%

Improvement in time‐domain induced polarization data quality with multi‐electrode systems by separating current and potential cables

Dahlin

Leroux

2012

Near Surface Geophysics

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Measuring induced polarization in the time domain with relatively compact multi‐channel multi‐electrode systems is attractive because of the simplicity of the procedure and thus its efficiency in the field. However the use of this technique is sometimes discouraged by the bad quality of the measurements in cases of high electrode contact resistances that can render data interpretation infeasible or at least unreliable. It is proposed that capacitive coupling in the multi‐core electrode cables has a significant role in creating this problem. In such cases separation of current and potential circuits by using separate multi‐conductor cable spreads can yield significant improvement in data quality. The procedure is relatively simple and can be implemented with common resistivity and time‐domain IP equipment. We show here three field examples from Southern Sweden, all measured as 2D electrical imaging sections. The first one is an example where the use of a single cable spread is sufficient thanks to moderate electrode contact resistance and high signal levels. The following two examples are from sites where induced polarization measurements could not yield consistent results using only a single multi‐conductor cable spread. Useful results were subsequently obtained by using separate cable spreads. The first example is a 280 m long line measured over an old covered municipal waste deposit where the waste body stands out as a zone of high chargeability. The second example is a 120 m line measured on a sandy glaciofluvial structure that is host to an aquifer of regional importance. The improvement led to discrimination between materials of different grain sizes, with potential bearing for understanding the aquifer. The third example is a 300–400 m line measured across an esker lying on clay till. The improvement led to a clear visualization of the esker and to the identification of a possible fault in the underlying gneissic bedrock. In all cases pseudosections and examples of chargeability decay curves are shown and discussed as tools for assessing data quality. Inversion results are shown together with background geological information and it is concluded that they are in good agreement.

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Section: Capacitive Couplingmentioning

confidence: 99%

Improvement in time‐domain induced polarization data quality with multi‐electrode systems by separating current and potential cables

Dahlin

Leroux

2012

Near Surface Geophysics

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“…We parametrize pseudo-chargeability at a single pixel in terms of chargeability and time constant as described in Appendix B, and solve a small inverse problem. In previous works about this task for the EIP problem (Yuval & Oldenburg 1997;Hördt et al 2006), the convolution shown in eq. (B1) Figure 9.…”

Section: Extracting Intrinsic Ip Parametersmentioning

confidence: 99%

On recovering distributed IP information from inductive source time domain electromagnetic data

Kang¹,

Oldenburg²

2016

Geophys. J. Int.

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We develop a procedure to invert time domain induced polarization (IP) data for inductive sources. Our approach is based upon the inversion methodology in conventional electrical IP (EIP), which uses a sensitivity function that is independent of time. However, significant modifications are required for inductive source IP (ISIP) because electric fields in the ground do not achieve a steady state. The time-history for these fields needs to be evaluated and then used to define approximate IP currents. The resultant data, either a magnetic field or its derivative, are evaluated through the Biot-Savart law. This forms the desired linear relationship between data and pseudo-chargeability. Our inversion procedure has three steps: (1) Obtain a 3-D background conductivity model. We advocate, where possible, that this be obtained by inverting early-time data that do not suffer significantly from IP effects. (2) Decouple IP responses embedded in the observations by forward modelling the TEM data due to a background conductivity and subtracting these from the observations. (3) Use the linearized sensitivity function to invert data at each time channel and recover pseudo-chargeability. Post-interpretation of the recovered pseudo-chargeabilities at multiple times allows recovery of intrinsic Cole-Cole parameters such as time constant and chargeability. The procedure is applicable to all inductive source survey geometries but we focus upon airborne time domain EM (ATEM) data with a coincident-loop configuration because of the distinctive negative IP signal that is observed over a chargeable body. Several assumptions are adopted to generate our linearized modelling but we systematically test the capability and accuracy of the linearization for ISIP responses arising from different conductivity structures. On test examples we show: (1) our decoupling procedure enhances the ability to extract information about existence and location of chargeable targets directly from the data maps; (2) the horizontal location of a target body can be well recovered through inversion; (3) the overall geometry of a target body might be recovered but for ATEM data a depth weighting is required in the inversion; (4) we can recover estimates of intrinsic τ and η that may be useful for distinguishing between two chargeable targets.

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“…The approximation is thus valid even for high contrasts in chargeability and 3D models. The validity of this approximation for a homogeneous half‐space is given in the ; Hördt et al . (2006) also showed the validity of this approximation for multidimensional models.…”

Section: D Inversionmentioning

confidence: 99%

1D and 2D Cole‐Cole‐inversion of time‐domain induced‐polarization data

Hönig

Tezkan

2007

Geophysical Prospecting

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A new method for the 2D inversion of induced polarization (IP) data in the time domain has been developed. The entire IP transients were observed and inverted into 2D Cole‐Cole earth models, including resistivity, chargeability, relaxation time and the frequency constant. Firstly, a modified 1D time‐domain electromagnetic algorithm was used to calculate the response of a layered polarizable ground. The transient signals were then inverted using the Marquardt method to derive the Cole‐Cole parameters of each layer. However, model calculations showed that the EM effects could be neglected for the time range (>1 ms) and for the transmitter–receiver distances (<50 m) used in this study. Therefore, the induction effects were not considered for the solution of the 2D inverse problem and a DC solution was applied. An approximative forward algorithm was introduced in order to calculate the IP transients directly in the time domain and in order to speed up the inverse procedure. The approximation is highly accurate, and this is demonstrated by comparing the approximations with their exact solutions up to 3D. The inverse algorithm presented consists of two steps. The transient voltages of an array data set were inverted separately into a two‐dimensional resistivity model for each time channel. The time‐dependent resistivity of each cell was then interpreted as the response of a homogeneous half‐space. In the 2D inversion algorithm, a 3D DC algorithm was used as a forward operator. The method only requires a standard 2D DC inversion and a homogenous half‐space Cole‐Cole inversion. The developed algorithm has been successfully applied to synthetic data sets and to a field data set obtained from a waste site situated close to Düren in Germany.

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Efficient spectral IP-modelling in the time domain

Cited by 17 publications

References 17 publications

Improvement in time‐domain induced polarization data quality with multi‐electrode systems by separating current and potential cables

Improvement in time‐domain induced polarization data quality with multi‐electrode systems by separating current and potential cables

On recovering distributed IP information from inductive source time domain electromagnetic data

1D and 2D Cole‐Cole‐inversion of time‐domain induced‐polarization data

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