Digital Elevation Model (DEM) is imperative to the creation of slope maps, the substructure planning, gravity field modeling and many other applications. Thus, there is a great need for accurate and low cost DEMs. In this case study, Shuttle Radar Topography Mission (SRTM) 30m, SRTM 90m have been used with Topographic DEM generated from ground topographic maps with scale 1:50,000 as a reference elevation to check the accuracy of those models by evaluation process at 625 CGPs. As known the Egyptian topographic maps with scale 1:50,000 has not been updated from long time ago. Unfortunately, most of the Northern desert does not cover with any type of topographic maps up to the writing of this paper. The aim of this study is approaching to a proper, accurate and economical scientific method for updating those topographic maps by evaluate of the vertical accuracy of such models over different terrain types compared with the accuracy of the DEM produced from topographic maps of scale 1: 50,000, over studying area lies between (31 to 31.5 E and 29.5 to 31.5 N), A number of (625) ground control points (GCPs) have been used in the evaluation process. From the statistical computations, it is obvious SRTM 30m has the most discrimination of its performance in terms of the Standard deviation by ±5.53m compared with ±5.88 for SRTM 90m. While By using the spot heights of a topographic map with scale 1:50,000 elevations as a reference elevation, the statistic indicated that the vertical accuracy of 625 GCPs elevation data is ±5.71m and ±6.23m, respectively. SRTM 30m elevation data featured a much greater absolute vertical accuracy than the value of ±16 m which published in the SRTM data specification. The analyses presented in this paper indicate that the absolute vertical accuracy of SRTM 1 arcsec data for our datasets proven to 2.94 times higher than the value of ±16 m presented in the original SRTM requirement specification by using GCPs as a reference. |
