ANALYSIS OF SRTM HEIGHT MODELS

By Interferometric Synthectic Aperture Radar (InSAR), during the Shuttle Radar Topography Mission (SRTM) height models have been generated, covering the earth surface from 56 ° south to 60 ° north. With the exception of small gaps in steep parts, dry sand deserts and water surfaces the free available US C-band data are covering the area completely while the X-band data, distributed by the DLR, are covering it only partially. The short wavelength C-band and X-band radar cannot penetrate the vegetation so the height models are Digital Surface Models (DSMs) representing the visible surface including vegetation and buildings. In the area of Zonguldak, Turkey, C-band and X-band DSMs are available and and have been analysed in a cooperation between Zonguldak Karaelmas University (ZKU) and University of Hannover. As reference height model the digitized contour lines from the topographic map 1: 25 000 and also a more precise height model directly from large scale photogrammetric mapping are given. The terrain inclination has a strong influence to the accuracy, but also the direction of the inclination in relation to the radar view direction, the aspects, are important. Independent upon the aspects, the analysed results do have root mean square differences against the reference data fitting very well to the Koppe formula SZ=a+b*tan α. The analysis was made separately for open and for forest areas, with clear accuracy differences between both. The C-band data are only available with a spacing of 3 arcsec, corresponding to 92m x 70m, while the X-band data do have a spacing of 1 arcsec. This is important for the interpolation in the mountainous test area. The accuracy of the height points is approximately the same for the C- and the X-band data. But the three times larger spacing of the C-band data is not including the same morphologic information like the X-band data, resulting in very generalised contour lines for the C-band data and with quite more details in the X-band DSM