Satoshi Izumoto, Agrosphere Institute (IBG-3), Forschungszentrum Jülich, Jülich, Germany, Johan Alexander Huisman, Forschungszentrum Jülich, Agrosphere (IBG-3), Institute of Bio- and Geosciences, Jülich, Germany, Egon Zimmermann, Forschungszentrum Jülich, Electronic Systems (ZEA 2), Jülich, Germany, Yves Méheust, University of Rennes, Rennes Cedex, France, Francesco Gomez, Geosciences Rennes, Rennes Cedex, France, Joris Heyman, Geosciences Rennes, UMR 6118 CNRS - University of Rennes, Rennes, France, Romain Laniel, Université de Rennes 1, Institut de Physique de Rennes, Rennes, France, Harry Vereecken, Forschungszentrum Julich GmbH, Agrosphere (IBG-3), Institute of Bio- and Geosciences, Julich, Germany and Tanguy Le Borgne, University of Rennes, Geosciences Rennes, CNRS, UMR 6118, Rennes Cedex, France