First Results on Accuracy Analysis for DEM and Orthoimages Cerived from SPOT HRS Stereo Data over Bavaria

Abstract

ISPRS and CNES announced the HRS (High Resolution Stereo) Assessment Program during the ISPRS Commission I Symposium in Denver in November 2002. 9 test areas throughout the world have been selected for this program. One of the test sites is located in Bavaria, Germany, for which the PI comes from DLR. The goal is to derive a DEM from the along-track stereo data of the SPOT HRS sensor and to assess the accuracy by comparison with ground control points and DEM data of superior quality. For the derivation of the DEM, the DLR own stereo processing software, developed for the MOMS-2P three line stereo camera is used. As a first step, the interior and exterior orientation of the camera, delivered as ancillary data (DORIS and ULS), which should lead to an absolute orientation accuracy of about 30 meters, are extracted. No bundle block adjustment with ground control is used in the first step. A dense image matching, using every pixel as a kernel center, provides parallaxes for every pixel. The quality of the matching is controlled by forward- and backward matching of the two stereo partners using the local least squares matching method. Forward intersection leads to points in object space which are then interpolated to a regular DEM of the region in a 20 meter grid. As a second step, orthoimages are generated from the images of the two looking directions, using the derived DEM. The orthoimage and DEM accuracy is determined by using the ground control points and the available DEM data of superior resolution (DEM derived from laser data). As the original image data were received with delay by mid of July 2003 only very preliminary results can be given in this paper.