Marine Circular Electric Dipole (MCED): Eine innovative elektromagnetische Methode zur Exploration mariner Grundwasserressourcen
Zusammenfassung der Projektergebnisse
To delineate the spatial extent of the Mediterranean coastal aquifer of Israel underneath the Sea, the Institute of Geophysics and Meteorology (IGM) attempted to apply an unconventional electromagnetic technique called Circular Electric Dipole. However, during an early phase of the project, theoretical modelling studies showed that an application would not be feasible due to two main reasons. First, the method suffers from poor signalto-noise ratio and would require a powerful transmitter that can stably transmit thousands of Amperes current. To buy or build such a unit would exceed the project costs and is also a major safety issue for the operator. The second reason that the CED method is currently not applicable in the marine environment is the necessity of strict geometrical symmetry. Deviations of several millimetres can cause a significant parasitic effect on the data that could potentially mask the signature of the subsurface resistivity structure. As an alternative to CED, the IGM Cologne came up with an alternative transmitter system called Differential Electrical Dipole with an improved lateral resolution compared to other conventional systems that requires a lower degree of geometrical symmetry compared to the CED method. In the extent of the project, a 1D inversion software was developed. Moreover, extensive modelling studies were conducted to substantiate the new method in comparison to other conventional EM applications. Additionally, a towable seafloor based transmitter/receiver system was designed and built at the institute. The first marine DED measurement was conducted in April of 2016 to investigate the seaward extent of the coastal freshwater aquifer in the region of Bat Yam, Israel. In total, 17 receiver stations were measured along a ca. 4 km long transect running perpendicular to the coastline. The acquired data clearly indicates the seaward extent of the freshwater aquifer underneath the Mediterranean Sea. Furthermore, the preliminary conclusions are feasible regarding the shape of the hydro-geological boundary condition at the western edge of the aquifer that controls the occurrence of this natural phenomenon. Based on the measured DED data, it is likely that the aquifer is susceptible to seawater intrusion and may potentially require a groundwater management scheme to prevent further deterioration of the groundwater quality in the future. Further investigations of the aquifer are indeed necessary. In this case the DED measurements can still be considered a full success as the location of the western aquifer boundary is now confined to approximately 100 m.
Projektbezogene Publikationen (Auswahl)
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(2015), Signal detectability of marine electromagnetic methods in the exploration of resistive targets, Geophysical Prospecting, 63 (1), 192-210
Goldman, M., Mogilatov, V., Haroon, A., Levi, E. and Tezkan, B.
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(2016). Development of Novel Time-Domain Electromagnetic Methods for Offshore Groundwater Studies: A Data Application from Bat Yam, Israel, PhD Thesis, University of Cologne
Haroon, A.
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(2016). Exploration of resistive targets within shallow marine environments using the circular electrical dipole and the differential electrical dipole methods: A timedomain modelling study, Geophysical J. Int., 205, 1032-1048
Haroon, A., Mogilatov, V., Goldman, M., Bergers, R. and Tezkan, B.
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(2016). First Marine Differential Electrical Dipole Measurement to study a sub-seafloor freshwater body in Bat-Yam, Israel, 23rd EM Induction Workshop, Chiang Mai, Thailand, 2016
Haroon, A., Lippert, K. and Tezkan, B.
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(2017). Differential Electric Dipole: A new marine time-domain electromagnetic method to study the shallow sub-seafloor resistivity structures in coastal regions, 1st GEO-EM Workshop in Bandung, Indonesia, 2017
Haroon, A.
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(2017). Land-Based application of Differential Electrical Dipole and Transient Electromagnetic measurements to investigate a freshwater aquifer in Belgium. Jahrestagung der Deutschen Geophysikalischen Gesellschaft, Potsdam, 2017
Böckmann, J. Lippert, K., Haroon, A. and Tezkan, B.
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(2018). First application of the marine differential electric dipole for groundwater investigations: A case study from Bat Yam, Israel. Geophysics, Vol. 83, No. 2; B59-B76
Read More: https://library.seg.org/doi/10.1190/geo2017-0162.1, Geophysics, Vol. 83, No. 2; B59-B76
Haroon, A., Lippert, K., Mogilatov, V. and Tezkan, B.
