1 Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Potsdam, Germany. Peter.von.der.Gathen@awi.de.
2 Finnish Meteorological Institute, Space and Earth Observation Centre, Sodankylä, Finland.
3 Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Potsdam, Germany.
4 Department of Atmospheric and Oceanic Science, Department of Chemistry and Biochemistry, and Earth System Science Interdisciplinary Center, University of Maryland, College Park, MD, USA.
5 Universität Potsdam, Institut für Physik und Astronomie, Potsdam, Germany.