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

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

Time-lapse resistivity investigations for imaging saltwater transport in glaciofluvial deposits

Five intersecting resistivity sections have been measured in glaciofluvial deposits hosting an aquifer of regional importance situated along a heavy traffic highway in Sweden. The winter salt spreading has caused a regular salinity increase through the years. For imaging the transport of saltwater in the aquifer, the sections were measured exactly in the same location before and after winter, and interpreted using a time-lapse inverse procedure. Some auger drilling and RCPT data were available for correlation. After winter, the resistivity had generally decreased under the water table and increased above it. The decrease in resistivity in the saturated zone is interpreted as a plume of more saline groundwater created by de-icing salt from the road. The increase in the upper layer can be explained by changes in temperature and soil moisture. The study shows that time-lapse resistivity investigations has potential for imaging hydraulic pathways in complex hydrogeological environments

Langue et littératures néo-latines

Programme de l’année 2019-2020 : Poésie, mythographie et arts figurés. — I. Les Poemata de Theocrène (1536). — II. Le Magasin des dieux de Georg Pictorius (1558). — III. Questions de poétique

Le Iulius Cæsar de Marc-Antoine de Muret

Marc-Antoine de Muret semble être le premier à avoir eu l’idée de mettre en scène la mort de César, innovation qui suscitera de nombreux émules. Son Iulius Cæsar figure en tête du recueil des Iuuenilia, paru à Paris en 1552, à un moment où le jeune Muret, récemment arrivé dans la capitale, veut consolider sa position dans la République des Lettres, mais la tragédie a été composée quelques années auparavant. Elle l’était assurément en 1549 et les témoignages de Joseph Scaliger et de Montaigne ..

Measuring techniques in induced polarisation imaging

Multi-electrode geoelectrical imaging has become very popular and is used for many different purposes. For some of these, the inclusion of IP data would be desirable as it would allow the interpreter to distinguish between, e.g. sand formations with saltwater infiltration and clay formations or help delineate landfills. However, present-day IP measuring techniques require the use of nonpolarisable potential electrodes and special wire layout and are thus cumbersome and expensive. In this paper, we suggest making IP measurements with multi-electrode cables and just one set of steel electrodes. The polarisation potentials on the potential electrodes are corrected for by subtracting the polarisation potential measured when no primary current and no IP signal are present. Test measurements indicate that the polarisation potentials vary slowly and that the correction procedure is feasible. At two sites in southern Sweden, we have compared measurements with only stainless steel electrodes and measurements with both stainless steel and Pb-PbCl nonpolarisable electrodes using one or two sets of multicore cables, respectively. Almost no difference between the two data sets was observed. At one site, the charge-up effect on the potential electrodes was not important, while at the other site, the correction procedure was crucial. Though only two sites have been studied so far, it seems that time-domain IP imaging measurements can be taken with only steel electrodes and ordinary multicore cables. Coupling in the multicore cables has not presented any problems at the investigated sites where grounding resistances were moderate, making the coupling effect small. High grounding resistance sites have not yet been investigated. (C) 2002 Published by Elsevier Science B.V

Langue et littératures néo-latines

Programme de l’année 2018-2019 : I. La théorie des genres dans le livre III des Poetices libri septem de Jules-César Scaliger (1561). — II. Jean Second (1511-1536), poète de Charles Quint. — III. Le Magasin des dieux de Georg Pictorius (1558)

THE HUMANISTS’ DEBATES ON THE FINALITY OF ART

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