Evaluation of Vertical Accuracy of Open Source Global DEMs for Hydrological Application: A Case Study of Adama Town, Ethiopia

Abstract

Digital Elevation Models (DEMs) provide one of the most useful digital datasets for a wide range of hydrological applications. DEM can be generated from wide range sources including land survey, Photogrammetry and Remote sensing satellites. SRTM 30m DEM by The Shuttle Radar Topography mission (SRTM), the Global Digital Elevation Model by Advanced Spaceborne Thermal Emission and Reflectance Radiometer (ASTER GDEM) and a global surface model called ALOS Worldview 3D 30 meter (AW3D30) by Advanced Land Observing Satellite (ALOS) are satellite based global DEMs open source DEM datasets. The accuracy of these dataset is subject to errors due to various reasons including radar characteristics, type of topography in different regions and physical properties of the surface. This study aims to assess the vertical accuracy of ASTER GDEM2, SRTM 30m and ALOS (AW3D30) global DEMs over Ethiopia in study area-Adama by using DGPS points and available accurate reference DEM data. The method used to evaluate the vertical accuracy of those DEMs range from simple visual comparison to relative and absolute comparisons providing quantitative assessment(Statistical) that used the elevation differences between DEM datasets and reference datasets. The Root-Mean-Square Error (RMSE) of the elevation residuals and other statistics used for evaluating vertical accuracy. The vertical accuracy of DEMs assessed in two stages based on the reference datasets used. The first vertical accuracy test is done by taking the residual from elevation differencing between GPS points and DEM elevation values at the location of every GPS points. The result of this assessment showed better accuracy of SRTM 30m DEM (having RMSE of ?? 4.63 m), and closely followed by ALOS (AW3D30) DEM which scored RMSE of ?? 5.25 m respectively. ASTER GDEM 2 showed the least accuracy by scoring RMSE of ?? 11.18 m in study area. The second accuracy assessment was done by analysis of derived products such as slope and drainage network. This also resulted in better quality of DEM derived products for SRTM than ALOS DEM and ASTER GDEM. This concludes SRTM 30m DEM can be used for slope classification and Drainage network for hydrological application in the Adama Town.