1. a Department of Ecology and Natural Resource Management , NLH , P.O. Box 5003, NO-1432, Ås, Norway
2. b Department of Forest Resources Management and Geomatics , SLU , SE-90183, Umeå, Sweden
3. c Institute of Photogrammetry and Remote Sensing , Helsinki University of Technology , FI-02015, HUT, Finland
4. d Department of Remote Sensing and Photogrammetry , Finnish Geodetic Institute , FI-02431, Masala, Finland
5. e Faculty of Forestry , University of Joensuu , Finland
6. f Department of Laser Systems , Swedish Defence Research Agency , P.O. Box 1165, SE-58111, Linköping, Sweden