1. Department of Physics, University of Helsinki, P.O. Box 64, FI-00014 Helsinki, Finland
2. Finnish Meteorological Institute, P.O. Box 503, FI-00101 Helsinki, Finland
3. Helsinki Institute of Physics, University of Helsinki, P.O. Box 64, FI-00014 Helsinki, Finland
4. Ångstrom Space Technology Centre, Department of Engineering Sciences, Uppsala University, P.O. Box 534, SE-75121 Uppsala, Sweden
5. National Science Center Kharkov Institute of Physics and Technology, Institute of High Energy Physics and Nuclear Physics, UA-61108 Kharkov, Ukraine
6. Centre for Image Analysis (CBA) and SciLifeLab, Uppsala University, Uppsala, Sweden