Electric and Electromagnetic Measurements on the North Sea Island of Langeoog
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Electric and electromagnetic methods were conducted on the North Sea island of Langeoog to investigate its freshwater lens that is managed by the local water works to supply the island with drinking water. Helicopter-borne electromagnetic (HEM), as well as surface geophysical methods were applied, i.e., electrical resistivity tomography (ERT), transient electromagnetic (TEM), and magnetic resonance sounding (MRS). We found that, beside the depth of the fresh-saltwater interface, the combined interpretation of TEM and MRS allows a reliable identification of lithological layering, whereas ERT or TEM alone exhibit a high degree of ambiguity regarding subsurface lithology and groundwater salinity. Future research is focused on the joint inversion of the surface methods, as well as on the combined inversion of surface and HEM data. In this way, 3-D multi-parameter models will be generated as additional input for numerical modeling of groundwater dynamics inside the freshwater lens.Keywords:
Electrical Resistivity Tomography
Ground-Penetrating Radar
Lithology
Exploration geophysics
Vertical electrical sounding
Pekuncen Village, Jatilawang District is one of the villages in Banyumas Regency which often experiences drought in the dry season. Exploration to obtain the groundwater sources needs to be done, especially to estimate the depth of the aquifer. The chosen exploration method was resistivity geoelectric using vertical sounding technique. Resistivity data acquisition is carried out on 3 trajectories with the length of the 1st and 3rd trajectories are 200 m, and the 2nd trajectory is 240 m. The sounding point on the 2nd trajectory was drilled, where rock samples were taken at every 5 m depth. The rock samples obtained were correlated with the resistivity data interpretation results, including the type and thickness of each depth. The aquifer in the research area consisted of two parts, namely unconfined aquifer and confined aquifer. The unconfined aquifer at the first sounding point is located at 6.80 – 34.38 m depth, the second sounding point at 7.00 – 28.89 m depth, and the third sounding point at 4.39 – 31.39 m depth. Then the confined aquifer at the first sounding point is located at less than 48.24 m depth, the second sounding point at less than 47.22 m depth, and the third sounding point at less than 47.36 m depth. The correlation between the resistivity data interpretation results at the second sounding point and the drill log data shows a slight difference in rock types and thickness. The difference of the rock types due to the drilling data interpretation results which divides the sand in the confined aquifers into fine, medium, and coarse grained sand. The difference of confined aquifer depth after being correlated is less than 2 m depth.Keywords: Aquifer, geoelectric survey, resistivity data, drill, Pekuncen, Banyumas.
Vertical electrical sounding
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Vertical electrical sounding is one of the most used electrical methods in Geophysical Prospecting and its application is restricted to those problems according to structures that do not differ strongly from stratified media. Even in these situations the simplicity of a near one dimensional earth approach is sometimes not reached and some important lateral resistivity variations may appear.
Vertical electrical sounding
Geophysical prospecting
Prospecting
Simplicity
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Abstract In order to determine the groundwater resources and potentials of the Khanewal District of Pakistan, a geophysical method in combination with pumping test data were used. An analytical relationship between the aquifer parameters interpreted from surface geoelectrical method and pumping test was established in order to estimate aquifer parameters from surface measurements where no pumping tests exist. For the said purpose, 48 geoelectric investigations were carried out using Schlumberger vertical electrical sounding (VES). Seven of the soundings were conducted where pumping tests had been carried out at borehole sites. The vertical electrical sounding stations were interpreted, and resistivities and thickness parameters were calculated. The values of transmissivity and hydraulic conductivity were calculated using the Dar Zarrouk parameter. Transmissivity values obtained from pumping test data and the VES method range between 954 – 4263 m
Vertical electrical sounding
Slug test
Aquifer test
Aquifer properties
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Subsoil
Ground-Penetrating Radar
Electrical Resistivity Tomography
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The comparative study of electric sounding and drilling is performed in the Bandama Valley region, north of Cote d'Ivoire. This study compared the results of geophysics sounding and the results of corresponding drilling. Geophysical methods using electrical sounding techniques have been implemented such as sounding curves and electric model 1D has been defined. The conclusions drawn from electrical sounding conform to those drilling (presence or absence of a groundwater). However differences exist. The comparative analysis of the allure of some curves of sounding and drilling logs can show dissimilarities in the number of layer, thickness of each layer, the total thickness weathering and of the position fractures in the underground. These differences are the cause of many failures during implantation of drilling in the study area.
Vertical electrical sounding
Basement
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