A Digital Linear Filter for Resistivity Sounding With a Generalized Electrode Array*

O'Neill, D.J.; Merrick, Noel

doi:10.1111/j.1365-2478.1984.tb00720.x

Cited by 33 publications

(20 citation statements)

References 21 publications

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“…Relevant data were acquired with a VES (Vertical Electrical Sounding) technique, using a Schlumberger electrode array and an ABEM Terrameter SAS 300. The resulting apparent resistivity curves were interpreted by a computer program based on the linear digital filtering method (Koefoed, 1972(Koefoed, , 1979O'Neill and Merrick, 1984). Current software packages based on this approach are able to cope with extreme apparent resistivity contrasts and to deal with a large number of layers.…”

Section: Geophysical Surveysmentioning

confidence: 99%

Prospecting for safe (low fluoride) groundwater in the Eastern African Rift: the Arumeru District (Northern Tanzania)

Ghiglieri

Balia

Oggiano

et al. 2010

Hydrol. Earth Syst. Sci.

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Abstract.A multidisciplinary research effort, including geological, hydrogeological, hydro-chemical, geophysical and hydrological investigations, was aimed at locating a source of safe groundwater for a district of northern Tanzania, within the western branch of the East Africa Rift Valley, where water shortage is common and much of the surface water carries unacceptable levels of dissolved fluoride. The 440 km 2 study area lies in the northern part of Arumeru district and is dominated by Mt. Meru (4565 m a.s.l.). The local climate is semi-arid, with distinct wet and dry seasons. Four hydrogeological complexes were identified, occurring within different volcanic formations, either alone or superimposed upon one another. The groundwater flow system was interpreted from the spatial distribution of the springs, combined with a lithology-and geometry-based reconstruction of the aquifers. The dominant pattern consists of a multi-directional flow from the higher elevations in the south towards the lower areas in the north, but this is complicated by structures such as grabens, faults, lava domes and tholoids. After the identification of the major fluoride source, an interference pattern between groundwater and high fluoride surface water was drawn. Finally, vertical electrical soundings were performed to define the location of aquifers in regions where release of fluoride was prevented. The methodological approach for the prospecting of safe water in a semi-arid, fluoride polluted region was validated by the drilling of a 60 m deep well capable of supplying at least 3.8 l/s of low fluoride, drinkable water.

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Section: Geophysical Surveysmentioning

confidence: 99%

Prospecting for safe (low fluoride) groundwater in the Eastern African Rift: the Arumeru District (Northern Tanzania)

Ghiglieri

Balia

Oggiano

et al. 2010

Hydrol. Earth Syst. Sci.

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“…The test models are a three‐layered earth, a 2‐D vertical contact and a 3‐D buried conductive cubic body. Analytical solutions are available for the first two models (Fu 1983; O'Neill & Merrick 1984). The potential is computed using the total potential finite‐element (TP‐FE) method and by the secondary potential finite‐element (SP‐FE) method, respectively, and then compared with the analytical solution to evaluate the accuracy of the SP‐FE method in this study.…”

Section: Numerical Examples and Discussionmentioning

confidence: 99%

A 3-D finite-element algorithm for DC resistivity modelling using the shifted incomplete Cholesky conjugate gradient method

2003

Geophysical Journal International

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SUMMARY An accurate and efficient 3‐D finite‐element (FE) forward algorithm for DC resistivity modelling is developed. First, the total potential is decomposed into the primary potential caused by the source current and the secondary potential caused by changes in the electrical conductivity. Then, the boundary value problem for the secondary field and its equivalent variational problem are presented, where the finite‐element method is used. This removes the singularity caused by the primary potential, resulting in an accurate 3‐D resistivity model. Secondly, I introduce the row‐indexed sparse storage mode to store the coefficient matrix and the shifted incomplete Cholesky conjugate gradient (SICCG) iterative method to solve the large linear system derived from the 3‐D FE calculation. The SICCG method converges very quickly and requires much less computer storage, while the traditional ICCG or modified ICCG (MICCG) method usually fails for an irregular grid. The SICCG method is more efficient than the direct method, i.e. the elimination solver with the banded Cholesky factorization. Also, it has an advantage over the symmetric successive overrelaxation preconditioning conjugate gradient method. Numerical examples of a three‐layered model with high conductivity contrast and a vertical contact show that the results from the secondary potential FE method agree well with analytic solutions. With the same grid nodes, much higher accuracy from the solution of the secondary potential than those solving the total potential can be achieved. Also a 3‐D cubic body is simulated, and the dipole–dipole apparent resistivities agree well with the results from other methods. By defining the analytical solution of a vertical contact as the primary potential, a more complicated model with several 3‐D inhomogeneities near the vertical contact is simulated. The presented method also obtains good results for this model.

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“…Because Ardau (1995) and interpreted the vertical electrical soundings in a merely qualitative way, we reprocessed the data using computer software based on the linear digital filtering method (e.g., Koefoed, 1972Koefoed, , 1979O'Neill and Merrick, 1984). As is well known, modern software packages based on this method can cope with even extreme resistivity contrasts and deal with a large number of layers.…”

Section: Reprocessing Of Ves Datamentioning

confidence: 99%

Geophysical approach to the environmental study of a coastal plain

et al. 2003

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in the study of coastal plains affected by soil and water salination, a knowledge of several geological aspects, such as structural features, depth to basement, stratigraphy of sedimentary cover, relationships between the phreatic aquifer and underlying aquifers, and the latter's structure, is basic to gaining an adequate understanding of both the causes and possible evolution of salination. In this framework, geophysical techniques can play a very important role. \ud \ud To improve the available geophysical information about the Muravera coastal plain, Sardinia, Italy, which is affected by severe soil and water salination, previously acquired electrical resistivity, reflection seismic and gravity data have been reprocessed, and a new seismic reflection survey has been conducted. Moreover, in order to give better support to the geological and hydrogeological interpretation of geophysical data, three boreholes were drilled. Reprocessed electrical data indicate the presence of a wide, electrically homogeneous low-resistivity zone associated with salination phenomena. Reprocessed reflection data provide useful information on the near-surface stratigraphy. The combined interpretation of resistivity and seismic results, supported by one calibration borehole, elucidates the relationships between the phreatic aquifer and the underlying confined aquifer. A new seismic reflection survey gives information on the depth to, and structure of, the Paleozoic basement, as well as on stratigraphic conditions of Pleistocene-Holocene sediments. Finally, the combined interpretation of seismic, gravity, and well data results in a geological section containing most of the information considered essential, such as the interface between Holocene alluvium and Pleistocene alluvium, the thickness of the latter, and the structure and composition of the Paleozoic basement. \ud \ud The work as a whole shows how the combined application of geophysical techniques can in this specific situation provide wide-ranging and high-quality information that is essential for the realistic mathematical modeling of aquifer contamination, and can enable the rational planning of exploratory drillings

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A Digital Linear Filter for Resistivity Sounding With a Generalized Electrode Array*

Cited by 33 publications

References 21 publications

Prospecting for safe (low fluoride) groundwater in the Eastern African Rift: the Arumeru District (Northern Tanzania)

Prospecting for safe (low fluoride) groundwater in the Eastern African Rift: the Arumeru District (Northern Tanzania)

A 3-D finite-element algorithm for DC resistivity modelling using the shifted incomplete Cholesky conjugate gradient method

Geophysical approach to the environmental study of a coastal plain

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