Calibration of laser-derived tree height estimates by means of photogrammetric techniques

Techniques based on laser point clouds and digital terrestrial images were demonstrated for the calibration of tree-height estimation. Individual tree heights can be roughly estimated from laser scanning data by using the approximated ground level and the highest hit of the treetop. However, laser-derived measurements often underestimate tree heights. This underestimation can arise from various error sources. Digital terrestrial images can be used to verify and understand the behaviour of laser point clouds. When laser data are backprojected in a close-range image, it is possible to show where each laser beam has reflected. This, however, requires a proper orientation of the images. In this study an interactive orientation method was used to derive image orientations, using one laser strip at a time as the reference data. Consequently, the backprojection of laser point clouds confirmed the height underestimations found by comparing the tacheometer reference measurements with the laser-derived tree heights. In addition, by using the described procedure the cause of underestimating tree heights could be explained. Keywords: Laser scanningphotogrammetryterrestrial digital imagestree height Acknowledgments Financial support from the Academy of Finland for the projects "Development of advanced retrieval algorithms and methods for laser scanning" (2001–2003) and "Spherical imaging" (2003–2006), as well as from the Foundation for Research of Natural Resources in Finland and the Jenny and Antti Wihuri Foundation, is gratefully acknowledged. The authors are grateful to Lic. Tech. Petteri Pöntinen and M.Sc. Ulla Pyysalo for their valuable assistance. Notes Rönnholm, P. 1 , Hyyppä, J. 2 , Hyyppä, H. 1 , Haggrén, H. 1 , Yu, X. 2 and Kaartinen, H. 2 (1Institute of Photogrammetry and Remote Sensing, Helsinki University of Technology, P.O. Box 1200, FI-02015 HUT, Finland, and 2Department of Remote Sensing and Photogrammetry, Finnish Geodetic Institute, P.O. Box 15, FI-02431 Masala, Finland). Calibration of laser-derived tree height estimates by means of photogrammetric techniques. Additional informationNotes on contributorsPetri Rönnholm Rönnholm, P. 1 , Hyyppä, J. 2 , Hyyppä, H. 1 , Haggrén, H. 1 , Yu, X. 2 and Kaartinen, H. 2 (1Institute of Photogrammetry and Remote Sensing, Helsinki University of Technology, P.O. Box 1200, FI-02015 HUT, Finland, and 2Department of Remote Sensing and Photogrammetry, Finnish Geodetic Institute, P.O. Box 15, FI-02431 Masala, Finland). Calibration of laser-derived tree height estimates by means of photogrammetric techniques.