Digital surface modelling by airborne laser scanning and digital photogrammetry for glacier monitoring

The research described in this paper is part of a Swiss National Science Foundation project on "Mass Balance Determination of Glaciers with the Use of State-of-the-art Remote Sensing Methods and a Numerical Flow Model". The remote sensing methods involve automated processing of aerial images and laser scanning and aim to Produce glacier sill-face models with an accuracy of about 0.5 to 1 In over time periods of 1 to 5 years. The Unteraar glacier, in Switzerland, has been chosen to test both methods, because it has been extensively studied by glaciologists. The results from laser scanning and digital photogrammetry were evaluated by comparison with accurate manual measurements from cm analytical Plotter. Various aspects of the laser data processing are discussed, such as system description, Position and attitude determination, transformation to the Swiss map coordinate system, fit of overlapping laser strips and problems encountered. Three digital photogrammetric systems (Match-T, LHS DPW770 and VirtitoZo) were used for surface model generation using image matching. The different matching algorithms and strategies, the matching problems that occurred, for example, clue to low texture, shadows, or steep slopes, and a quantitative cold qualitative evaluation of the results are presented. Finally, a comparison is given between photogrammetry and loser scanning regarding accuracy and point density.