Airborne Electromagnetic, Magnetic, and Radiometric Surveys at the German North Sea Coast Applied to Groundwater and Soil Investigations

Bernhard Siemon,Annika Steuer,Nico Deus,Helga Wiederhold,Malte Ibs-Von Seht

doi:10.3390/rs12101629

Bernhard Siemon, Annika Steuer + Show 3 more

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The knowledge of the subsurface down to about one hundred meters is fundamental for a variety of economic, ecological, and geoscientific tasks, particularly in coastal zones. Marine and terrestrial processes influence coastal zones and both seawater intrusion and submarine freshwater discharges may occur. The Federal Institute for Geosciences and Natural Resources (BGR) conducted airborne geophysical surveys in the coastal region of the German Bight between 2000 and 2014. The helicopter-borne system used simultaneously collected electromagnetic (HEM), magnetic (HMG), and radiometric (HRD) data. An area of about 5900 km2 was covered with parallel flight lines at 250 m line separation and additional tie-lines at larger separations. In total, about 25,000 km of data at sampling distances of 4 m (HEM, HMG) and 40 m (HRD) were acquired. The electrical resistivity (HEM), the anomalies of the magnetic field (HMG), and the exposure rate (HRD) are the resulting geophysical parameters derived from the data. The results are displayed as maps of the geophysical parameters as well as vertical resistivity sections (only HEM). Both data and products are publicly available via BGR’s product center. The airborne geophysical results helped to outline the fresh–saline groundwater interface, freshwater lenses on islands, submarine groundwater discharges, buried tunnel valleys, mires, and ancient landscapes.

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Coastal zones are influenced by both marine and terrestrial processes that are highly dynamic and continually change in time
We start with the presentation of the general results of the three airborne geophysical methods achieved for the entire survey area and show some specific local features
This comparison demonstrates that the contours help to distinguish the main geologic units: 1) Holocene marshes are indicated by high radiation, 2) Pleistocene sands and tills (Geest) and Holocene mudflats (Wadden sediments) correlate with areas of moderate radiation, and 3) Holocene mires and open waters (North Sea and rivers) show only a low radiation

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Coastal zones are influenced by both marine and terrestrial processes that are highly dynamic and continually change in time. The management of groundwater resources in coastal areas is a difficult task because the hydrological processes are complex and the lack of observational data often prevents a sufficient understanding of that resource [1]. The knowledge of the subsurface is fundamental for an increased understanding to solve a variety of economic, ecological, and geoscientific tasks. In Germany, mapping was usually carried out on a local to regional scale using ground-based methods, but only where this was required by law or where specific geoscientific studies were performed. Such ground-based surveys are inefficient to map large areas. Airborne surveys are able to provide spatial data sets, which could be linked to other spatial data sets. The upper one hundred meters of the subsurface are of particular importance, because the fundamental exchange and transport processes are taking place here, e.g., for salts and other minerals, fertilizers, and pollutants

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