Seifu Kebede, Meron Teferi Taye, in Global Groundwater, 2021 13.5.1 Identifying and protecting viable aquifers
RES2DINV FULL VERSION SERIES
Using data modeling tools (see Section 11.08.4.1), these data are analyzed in order to recover a 1-D resistivity structure (defined as a series of layer thicknesses and associated resistivity) that is consistent with the measured response. The results are often presented as a plot of the logarithm of apparent resistivity versus the logarithm of AB/2, as shown in Figure 5(c). For a Schlumberger array VES, the spacing AB is normally increased in a logarithmic sequence (i.e., the logarithm of the spacing AB is increased linearly in each step). VES surveys require just four electrodes, each with a suitable cable to connect to the instrument. The disadvantage is that for small MN spacings, the signals (potential differences) can be relatively weak and thus high-sensitivity instrumentation may be required. This is a popular choice because the fixed potential electrode dipole means that not only the measurements are relatively insensitive to lateral variation in resistivity but also, from a practical standpoint, surveys can be completed more efficiently as only one of the dipoles is moved for each measurement. The Schlumberger array is commonly used for VES, keeping the potential electrode dipole (M and N) fixed and moving the current electrode dipole (A and B). As the electrode array size increases, we ‘sound’ to greater depths, as shown in the earlier examples.
In a vertical electrical sounding (VES), apparent resistivity measurements are made at different electrode spacings, centered about a common point.
Binley, in Treatise on Geophysics (Second Edition), 2015 11.08.3.1 1-D Electrical Sounding The method is useful for determining loose horizontal overburden thickness over hard rocks in river valleys and groundwater projects.Ĭonstant separation traversing is obtained by progressively moving an electrode spread with fixed electrode separation along a traverse line, the electrodes’ configuration being aligned either in the direction of traverse (longitudinal) or at right angles to it (transverse). The electrical sounding infers variation of resistivity with depth from a given point on the ground for near-horizontal layers of formation below. It presumes that current penetrates continuously deeper with increasing separation of current electrodes. Vertical electrical sounding or electrical drilling retains current and potential electrodes along a straight line at the same relative spacing around a fixed central point. There are two types of resistivity surveying: vertical electrical sounding and constant separation traversing. Swapan Kumar Haldar, in Mineral Exploration (Second Edition), 2018 6.5.2.3 Field Procedure
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