Improvement in time-domain induced polarization data quality with multi-electrode systems by separating current and potential cables
T. Dahlin and V. Leroux
Issue: Vol 10, No 6, December 2012 pp. 545 - 656
Special Topic: Induced Polarization for Near-surface Investigations
Info: Article, PDF ( 8.44Mb )
Measuring induced polarization in the time domain with relatively compact multi-channel multielectrode 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.