Vertical Accuracy Assessment of 30-M Resolution ALOS, ASTER, and SRTM Global DEMs over Egypt Territory

Abstract

The ALOS World 3D - 30m (AW3D30), ASTER Global DEM Version 2 (GDEM2), and SRTM-30m are Digital Elevation Models (DEMs) that have been made obtainable to all public free of charge. All these DEMs have a horizontal resolution of 30-m and almost global coverage. DEMs are useful in many applications such, hydrology, geomorphology, archaeology mapping, and many others. In the current investigation, the vertical resolution of these DEMs was evaluated over 4 selected study areas in different region of Egypt. DGPS points 58,44,15 and 16 were used as a control point (CPs) to evaluate the vertical accuracy of the three world DEMs products over the 4 selected study areas. The elevations of these control points (regarded to the Mean Sea Level, MSL) were gained using a global positioning system (GPS) receiver using the static technique. Data appeared that ALOS DEM has the lowest Root Mean Square Error (RMSE) of overall the 4 selected study areas (RMSE = 0.95m, 1.26 m 2.19 and 2.59 m) followed by SRTM-30m (RMSE = 2.23m, 2.21 m 2.25 and 4.47 m), and ASTER GDEM2 in the last rank (RMSE = 6.74m , 13.50 m 17.42m and 14.43 m). ALOS DEMs overestimated nearly the true ground elevations based on the obtained results, the RMSE, the mean error and variations in elevations were established to be lower in ALOS in comparison with SRTM-30m and ASTER GDEM2. The predominance of ALOS than the two others DEMs was also appeared to be consistent even under all selected study areas and land types (flat or steep), the data of the vertical resolution estimation proposed that the ALOS is more delicate than SRTM-30m and ASTER GDEM 2, at least for the areas considered in the current investigation. Henceforth, based on the obtained results ASTER DEMs needs correction for its elevation based on sufficient GCPs when used. On the other hand, the study considered as a significant outcome that users of the DEMs in Egypt should be aware of and should be considered in decisions concerning apply of these results products from world DEMs in various applications.