Vertical Accuracy Assessment of the Shuttle Radar Topography Mission (SRTM) Digital Elevation Model in Two Contrasting Topographic Environments: The Coastal Environment of Tripoli and the Mountainous Environment of Gharyan

Global Open-Access Digital Elevation Models (DEMs) represent a vital tool in geospatial applications and civil engineering due to their comprehensive coverage and free availability. This research aims to assess the vertical accuracy of the global digital elevation model derived from the Shuttle Radar Topography Mission (SRTM) at a spatial resolution of 1 arc-second (approximately 30 meters) and to determine its suitability for generating topographic and contour maps in Libya. The study adopted a comparative descriptive-analytical approach by evaluating the model's performance in two distinct topographic environments: the Tripoli region (a coastal environment with moderate terrain) and the Gharyan region (a rugged mountainous environment with steep slopes). This evaluation relied on a sample of twenty-seven (27) high-accuracy, real Ground Control Points (GCPs) surveyed via Global Navigation Satellite System (GNSS) techniques. Statistical results based on the calculation of the Root Mean Square Error (RMSE) revealed a sharp, directly proportional impact of surface ruggedness on the spaceborne model's accuracy. From an engineering perspective, the study concluded that the SRTM DEM is unsuitable for generating contour lines with a contour interval of less than 10 meters in topographic maps for moderate terrain at scales of 1:25,000 or larger. Similarly, it is unsuitable for contour intervals of less than 10 meters in rugged mountainous regions at scales of 1:50,000 or larger. Furthermore, the research d

emonstrated a clear deficiency in the reliability of the spaceborne model when deriving short terrain profiles of less than 30 kilometers in mountainous environments due to the accumulation of vertical errors. The study strongly recommends restricting the use of free spaceborne models to exploratory regional studies at small scales (1:100,000 or smaller) and relying on terrestrial surveying for sensitive engineering projects.