BGR helicopter-borne frequency-domain EM - past, present, future

The German Federal Institute for Geosciences and Natural Resources (BGR) has been conducting airborne geophysical surveys worldwide for more than four decades. Most of these airborne surveys applied frequency-domain helicopter-borne electromagnetics (HEM) in combination with magnetic and radiometric measurements. HEM surveys served and still serve as acquisition of baseline data for a number of applications in mineral, groundwater and soil exploration. After starting with anomaly detection in mineral exploration surveys, the focus was set to groundwater surveys during the following decades. Spatial mapping of freshwater resources, seawater intrusion, submarine fresh-water outflows, and buried valleys are some typical applications. Recently, environmental issues gain more and more importance. Therefore, BGR conducted most of the current surveys in Germany. These provided not only resistivity distributions, but also estimated parameters such as groundwater chloride content in coastal and salt dome areas, groundwater iron content in former lignite mining areas, and peat volumes of mires. These applications combined local data (e.g boreholes) or external models as well as airborne geophysical data to derive spatial estimates, which then served as baseline date for advanced (hydro-) geological modelling.