1. a Finnish Geodetic Institute , Geodeetinrinne 2, P.O. Box 15, FIN‐02431 Masala, Finland
2. b Institute of Photogrammetry and Remote Sensing , Helsinki University of Technology , P.O. Box 1200, FIN‐02015 Espoo, Finland
3. c Canadian Forest Service , Pacific Forestry Centre , 506 West Burnside Road, Victoria, British Columbia, V8Z 1M5, Canada
4. d Faculty of Forestry , University of Joensuu , P.O. Box 111, FIN‐80101 Joensuu, Finland