Generation of a digital elevation model of Mols Bjerge, Denmark, and georeferencing of airborne scanner data

Abstract

Geografisk Tidsskrift, Danish Journal of Geography 99: 35–45, 1999 The study compares various digital elevation models (DEM) and georeferencing methods for the purpose of orthorectifying airborne scanner data. The study was performed using topographical maps on the scale of 1:25,000 produced by the Danish National Survey and Cadastre and a Compact Airborne Spectrographic Imager (casi) image. The study area, was a topographically complex area in Denmark, Mols Bjerge. The generation of the digital elevation model was performed using a discretised thin plate spline technique modified to allow the fitted DEM to follow abrupt changes in the terrain. The accuracy of the DEM was primarily evaluated by comparing the original and the modelled contour lines. The georeferencing was performed using regional modified versions of polynomial distortion modelling and triangle warping, applying both ground control points and DEM features for panoramic and topographical correction in the process. It was concluded that the maps had an accuracy that allowed for a DEM with a grid resolution of 10m and that triangle warping performed better than the polynomial distortion modelling in the case of airborne scanner data since the image distortions are related to local distortions superimposed on medium to regional scale distortions. Triangular irregular network (TIN) resampling performed better than regional modelling especiallly in hilly areas outside the nadir line where extracted tie points described the landscape features. The overall accuracy of the georeferencing was 3–4 pixels (6–8m), which was well within the reference map accuracy of 12–15m.