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
No Thumbnail Available
Date
2018-11
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Addis Ababa University
Abstract
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.
Description
Keywords
DEM, ASTER GDEM2, SRTM 30m, ALOS (AW3D30), EGM96, Vertical accuracy