Christian Brandes, Leibniz University of Hannover, Hannover, Germany, Thomas Plenefisch, BGR Federal Institute for Geosciences and Natural Resources, Hannover, Germany, David Colin Tanner, Leibniz Institute for Applied Geophysics, Hannover, Germany, Nicolai Gestermann, Bundesanstalt für Geowissenschaften und Rohstoffe (BGR), Hannover, Germany and Holger Steffen, Lantmäteriet, Gävle, Sweden