Analysis of DEM combination methods using high resolution optical stereo imagery and interferometric SAR data

Digital elevation models (DEM) from satellite data are generated mainly from two types of datasets using completely different methods: photogrammetry for optical stereo images (e.g. SPOT5, CARTOSAT) and interferometry for Synthetic Aperture Radar data (InSAR, e.g. ERS-Tandem, SRTM). Both generation methods show advantages and disadvantages but have similar accuracy values in comparison to a reference DEM. The paper aims at showing the potential for combined usage of several DEM (derived with different sensors and methods) to provide a “gap-less” DEM and improve the overall accuracy. Some results are given for three combination methods: DEM fusion utilizing height error maps for each DEM; DEM integration, where single point information from another DEM is inserted during the triangulation process; and the delta surface fill method. The quality of the DEM derived from one source and of the combined DEM depends on the steepness of the terrain and on the land cover type. For flat terrain or moderate hilly landscapes, a height accuracy in the order of 5 meters (RMSE) or better can be achieved for the mentioned sensors. Two test areas are chosen, where many different data sets are available and much knowledge exists from previous studies. The first test area is a region in the south-eastern part of Bavaria comprising a mostly hilly, post-glacial landscape. The second test area is located in Catalonia, Spain including also a mostly hilly terrain with some steep slopes. The received DEM are compared qualitatively and quantitatively to the reference DEM with superior quality by looking at profiles and statistics. The results show an improvement of the combined DEM that can be quantitatively measured. Although overall statistics for larger regions show only a slight improvement, local errors and blunders are reduced significantly and the overall accuracy of the combined DEM is higher.