Matching of high-resolution optical data to a shaded DEM

One of the first essential steps in the analysis of optical satellite imagery is orthorectification of the images. Orthorectification without ground control points (GCPs) using only the ephemeris and attitude data (or rational polynomial functions) provided by the satellite operator leads to an absolute accuracy of about 10m to 1km (depending on the satellite and available metadata). The orientation can be improved by measuring GCPs with well-known coordinates in the images. In this article, an alternative method to obtain GCPs from an existing digital elevation model (DEM) is described and assessed. Since at least the Shuttle Radar Topography Mission DEM is available nearly worldwide with absolute horizontal accuracy of some metres, these DEMs may serve as a valuable additional source for the generation of GCPs. Furthermore, several planned and ongoing missions will increase the availability and accuracy of DEMs or stereo imagery, respectively, e.g. ALOS-PRISM, TanDEM-X, etc. Results for several test areas and with data of different spatial resolutions are shown using two methods for the matching process