D-AERO-Finsterwalde: Pilot study for an airborne geophysical investigation of the "Finsterwalder Restlochkette"
Begin of project: October 1, 2020
End of project: June 30, 2022
Status of project: April 1, 2022
The federal government is called upon to contribute to structural policy change in the mining regions. The proposals of the Commission "Growth, Structural Change and Employment" form the basis for this. The BGR, as a technical authority in the business domain of the Federal Ministry for Economic Affairs and Climate Action (BMWK), is therefore setting up the "Forschungs- und Entwicklungszentrum Bergbaufolgen" (FEZB, Research and Development Centre for Post-Mining Areas) in Cottbus for the sustainable reconfiguration of post-mining landscapes. Research topics of the FEZB focus on groundwater and soil, mining remediation, geotechnical engineering and environmental monitoring. To support this, airborne geophysical surveys are also carried out for the FEZB and the results are made available to local companies and research institutions.
For the rehabilitation of former lignite open-cast mining areas in Lusatia, large-scale information on aquifers is needed, especially on their mineralisation, depth and thickness. All this information is to be obtained with airborne geophysics as part of a pilot study. For this purpose, an investigation of the "Finsterwalder Restlochkette" with the helicopter-borne system of the BGR will provide this information.
Before the start of the project, there was little to nearly no current experience of airborne surveys over open-cast lignite mines. Only in September 1994, the open-cast mines Merseburg-Ost and Lochau (Reichling & Sengpiel, 1995; Sengpiel et al., 1995; Steiner 1997) were surveyed with an old, less efficient measuring system. However, experience shows that horizons such as clay layers or groundwater levels as well as the mineralisation of the groundwater can be derived from airborne electromagnetic data.
The open-cast mining area is located between Finsterwalde and Lauchhammer in Lower Lusatia, about 60 km southwest of Cottbus (Figure 1). The survey area has a size of about 240 km². The BGR helicopter (call-sign: D-HBGR) was used for the measurements. A gamma-ray spectrometer was used in a first survey campaign in May 2021. In July, further measurements were taken using the flight probe to investigate the deeper subsurface. The 10 m long flight probe (bird), which is towed on a rope at about 40 above the ground, records electromagnetic and magnetic data. In total, data along the flight lines with a total length of almost 1700 km were obtained in both surveys. The electromagnetic data are converted into electrical conductivity models from which groundwater relevant parameters can be derived. The magnetics and radiometry data provide information on contaminated sites and surface properties in the survey area.
Fig. 1: Airborne geophysical survey area near Finsterwalde in Lower Lusatia
First electromagnetic results are shown in Figure 2. This map displays the distribution of the half-space resistivity at a system frequency of 41 kHz, which reveals the structures at shallow depths. High half-space resistivities occur in predominantly sandy areas with weakly mineralised groundwater (blue colours). Lower half-space resistivities occur in areas with higher mineralisation or clayey sediments (yellow to green colours). The lowest values (orange colours) are observed in the former open-cast mines. The mineralisation of the lake water there seems to be significantly increased.
Fig. 2: Distribution of half-space resistivities at a system frequency of 41 kHz
The exploration is being carried out in cooperation with the Lausitzer und Mitteldeutsche Bergbau-Verwaltungsgesellschaft (LMBV) and in consultation with the Landesamt für Bergbau, Geologie und Rohstoffe Brandenburg (LBGR). The results of the airborne geophysical surveys will also be made available as a download via the BGR Geoportal at the end of the project, analogous to results of the project D-AERO-Evaluation on the North Sea coast. A summary of these results is published in Siemon et al. (2020).
Video BGR: Helicopter measurement flights in the Finsterwalde area
https://www.youtube.com/watch?v=epgXaDtWE_w
Video from Thomas Scholz: Sikorsky S-76B | D-HBGR | Measurement flight with the BGR helicopter over the "Finsterwalder Restlochkette" | EDCY
https://www.youtube.com/watch?v=cgArW0NIrw8
Literatur
Flight reports
Reichling, J., & Sengpiel, K.-P., 1995. Braunkohlesanierung – Hydrogeologie: Testeinsatz der Hubschraubergeophysik am ehemaligen Tagebau Merseburg-Ost, erste Ergebnisse. Bericht im wissenschaftlich-technischem Vorhaben zur Grundwassergüteentwicklung in den Braunkohlegebieten der neuen Länder, Niedersächsisches Landesamt für Bodenforschung – Geowissenschaftliche Gemeinschaftsaufgaben, Archiv-Nr. 113428, Hannover.
Steiner, L., 1997. Testeinsatz der Hubschraubergeophysik am ehemaligen Tagebau Merseburg-Ost, Hydrogeologische Bewertung. Bericht im wissenschaftlich-technischem Vorhaben zur Grundwassergüteentwicklung in den Braunkohlegebieten der neuen Länder, Niedersächsisches Landesamt für Bodenforschung – Geowissenschaftliche Gemeinschaftsaufgaben, Archiv-Nr. 116896, Hannover.
Area reports
Sengpiel, K.-P., Pielawa, J., Rehli, H.-J., Röttger, B., Siemon, B. & Voß, W., 1995. Hubschrauber-Geophysik im Gebiet der ehemaligen Braunkohlentagebaue Merseburg-Ost und Lochau, 1994. Technischer Bericht, Bundesanstalt für Geowissenschaften und Rohstoffe, Archiv-Nr. 113875, Hannover.
Conference contributions
Siemon, B., Ibs-von Seht, M. Steuer, A., Deus, N. & Wiederhold, H., 2020. Airborne electro-magnetic, magnetic, and radiometric surveys at the German North Sea coast applied to groundwater and soil investigations. Remote Sensing, 12(10), 1629, doi: 10.3390/rs12101629.