Digital Height Models by Cartosat-1

By the Shuttle Radar Topography Mission (SRTM) a nearly world wide height model has been generated, which is available free of charge. The mayor limitation of this height model is the point spacing of 3arcsec, corresponding to approximately 92m at the equator. From the very high resolution space sensors like IKONOS, QuickBird and OrbView-3 only a limited number of stereo combinations, taken from the same orbit, are available. The stereo scenes from SPOT-5 HRS are not commercially distributed. With Cartosat-1 and ALOS/PRISM new satellite stereo sensors are available having 2.5m ground sampling distance (GSD). The very short difference in time for imaging both scenes of a stereo model guarantees optimal conditions for matching. In the frame of the ISPRS-ISRO Cartosat-1 Scientific Assessment Programme (C-SAP) the orientation of 3 stereo scenes has been computed by bias corrected, sensor oriented RPC-solution. The generation of digital elevation models (DEMs) followed by least squares matching. An analysis of the DEMs against reference DEMs showed sub-pixel accuracy of the height values as x-parallax. By automatic image matching digital surface models (DSM), showing the visible surface like buildings and vegetation, are generated. By filtering the DSMs have been changed into DEMs, including mainly the points on the bare ground, if enough points are still located on the bare ground. After filtering for open and flat terrain a standard deviation of the generated DEM in relation to a reference DEM of up to 2.4m has been reached. This corresponds to a standard deviation of 0.7 GSD for the x-parallax. The 2.5m GSD justifies a point spacing of 7.5m for the DEM. This accuracy and morphologic information contents is sufficient for most of the space application. Of course the automatic image matching fails if the object has no contrast like in the case of snow coverage, but nevertheless very qualified height models have been generated.