1. Metrology Research Institute, Aalto University, Espoo, Finland
2. Arctic Research Centre, Finnish Meteorological Institute, Sodankylä, Finland
3. Physikalisch-Technische Bundesanstalt (PTB), Braunschweig, Germany
4. MIKES Metrology, VTT Technical Research Centre of Finland Ltd, Espoo, Finland
5. Meteorologisches Observatorium Lindenberg – Richard Assmann Observatorium (DWD, MOL-RAO), Deutscher Wetterdienst, Lindenberg, Germany
6. Kipp & Zonen, Delft, The Netherlands