High Resolution Srtm Height Models

For the area of the United States the Shuttle Radar Topography Mission (SRTM) height models are available with 1 arcsec spacing instead of the 3 arcsec spacing outside the country. Only special users are getting the 1 arcsec height information outside the USA. 1 arcsec and also 3 arcsec SRTM height models have been investigated in a mountainous area, covered nearly completely by forest, in an undulated area, a flat and smooth area with only a limited number of bush forests and in a central city area. As reference, precise DEMs from photogrammetric survey, partially manually measured, are available. The radar C-band cannot penetrate the vegetation, so the SRTM height models are digital surface models (DSM), showing the height of the top of the vegetation and buildings, and not DEMs with the height of the bare ground. The SRTM DSMs have been filtered for elements not belonging to the bare ground. This was successful especially in the city and more open area. In the mountainous forest the advantage of filtering is limited. The achieved accuracy is quite different for the changing conditions, while the height points of the 1 arcsec and the 3arcsec data are still similar. The reduced morphologic information of the 3 arcsec data can be seen in the details of the DEM and the result of interpolating a grid of points. The influence of the aspects to the accuracy is limited because most of the SRTM C-band data are based on the average of the ascending and the descending orbit.