1. School of GeoSciences, University of Edinburgh, Edinburgh EH9 3JN, UK
2. NERC Field Spectroscopy Facility, School of GeoSciences, Grant Institute, University of Edinburgh, Edinburgh EH9 3JW, UK
3. Hyytiälä Forestry Field Station, University of Helskinki, Korkeakoski FI-35500, Finland
4. Department of Forest Sciences, University of Helsinki, Helsinki FI-00014, Finland
5. Department of Physics, University of Helsinki, Helsinki FI-00014, Finland