1. University of Münster, Institute of Geophysics , Corrensstraße 24, 48149 Münster , Germany
2. Leibniz-Institute of Photonic Technology, Albert-Einstein-Straße 9 , 07745 Jena , Germany
3. Goethe University Frankfurt, Institute of Geoscience , Altenhöferallee 1, 60438 Frankfurt , Germany