1. Junior Research Fellow, Dept. of Space Technology, Tartu Observatory, 61602 Tõravere, Estonia; Ph.D. Student, Institute of Physics, Univ. of Tartu, Ravila 14C-D601, 50411 Tartu, Estonia; and Guest Researcher, Finnish Meteorological Institute, Erik Palménin aukio 1, P.O. Box 503, FI-00101 Helsinki, Finland (corresponding author).
2. B.Sc. Student, Univ. of Tartu, Ravila 14C-D601, 50411 Tartu, Estonia.
3. Engineer, Tartu Observatory, 61602 Tõravere, Estonia; and M.Sc. Student, Univ. of Tartu, Ravila 14C-D601, 50411 Tartu, Estonia.
4. Engineer, Tartu Observatory, 61602 Tõravere, Estonia.
5. M.Sc. Student, Univ. of Tartu, Ravila 14C-D601, 50411 Tartu, Estonia.
6. Senior Research Fellow, Tartu Observatory, 61602 Tõravere, Estonia; and Associate Professor, Univ. of Tartu, Ravila 14C-D601, 50411 Tartu, Estonia.