Geodesy and Geomatics

Permanent URI for this collection

http://etd.aau.edu.et/handle/12345678/188

Browse

Browsing Geodesy and Geomatics by Subject "ALOS (AW3D30)"

Now showing 1 - 1 of 1
  • No Thumbnail Available
    Item
    Vertical Accuracy Assessment of Open Source Digital Elevation Model Using GPS Point and Reference Dem Over Ethiopia A Case Study In Addis Ababa And Dire Dawa
    (Addis Ababa University, 2018-11) Abdi, Ibrahim; Andinet, Ashagrie (Mr.)
    Digital elevation model (DEM) is a digital representation of the surface topography of the earth. Apart from visualization of o 3D surface topography of the earth, DEM is very useful data source to perform various analyses. 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 freely available, open source DEM datasets. The specified accuracy of these dataset is often uneven within each dataset 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 two study areas-Addis Ababa and Dire Dawa by using DGPS points and other available accurate topographic reference data. The method used to assess the vertical accuracy of those DEMs range from simple visual comparison to relative and absolute comparisons providing quantitative assessment that used the elevation differences between DEM datasets and reference datasets. The vertical accuracy of DEMs assessed in three 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 5.14 m and 6.35 m in Addis Ababa and Dire Dawa Study areas), and closely followed by ALOS (AW3D30) DEM which scored RMSE of 5.34 m and 6.33 m in Addis and Dire study areas respectively. ASTER GDEM 2 showed the least accuracy by scoring RMSE of 13.27 m in Addis Ababa and 11.41m in Dire Dawa study areas. The second test was done by DEM (image) differencing (by subtracting every pixel of DEMs from every pixel of Reference DEM, which gives us the elevation residual). The result from this method assessment gave us RMSE values of 17.2 m, 4.5 m and 4.7 m in Addis Ababa for ASTER, SRTM and ALOS DEMs respectively; RMSE of 9.7 m, 5.43 m and 5.74 m in Dire Dawa Study area for ASTER, SRTM and ALOS DEMs respectively. This also shows the better accuracy of SRTM 30m DEM over the other two at least for this study. The third accuracy assessment was done by analysis of derived products such as slope and drainage network. This also resulted in better quality of derived products for SRTM and ALOS DEM than ASTER GDEM. This concludes SRTM 30m and ALOS (AW3D30) DEM can be used for slope classification and Drainage or watershed delineation in this regions.