External Validation of the ASTER GDEM2, GMTED2010 and CGIAR-CSI- SRTM v4.1 Free Access Digital Elevation Models (DEMs) in Tunisia and Algeria

Djamel Athmania,Hammadi Achour

doi:10.3390/rs6054600

Abstract

Digital Elevation Models (DEMs) including Advanced Spaceborne Thermal Emission and Reflection Radiometer-Global Digital Elevation Model (ASTER GDEM), Shuttle Radar Topography Mission (SRTM), and Global Multi-resolution Terrain Elevation Data 2010 (GMTED2010) are freely available for nearly the entire earth’s surface. DEMs that are usually subject to errors need to be evaluated using reference elevation data of higher accuracy. This work was performed to assess the vertical accuracy of the ASTER GDEM version 2, (ASTER GDEM2), the Consultative Group on International Agriculture Research-Consortium for Spatial Information (CGIAR-CSI) SRTM version 4.1 (SRTM v4.1) and the systematic subsample GMTED2010, at their original spatial resolution, using Global Navigation Satellite Systems (GNSS) validation points. Two test sites, the Anaguid Saharan platform in southern Tunisia and the Tebessa basin in north eastern Algeria, were chosen for accuracy assessment of the above mentioned DEMs, based on geostatistical and statistical measurements. Within the geostatistical approach, empirical variograms of each DEM were compared with those of the GPS validation points. Statistical measures were computed from the elevation differences between the DEM pixel value and the corresponding GPS point. For each DEM, a Root Mean Square Error (RMSE) was determined for model validation. In addition, statistical tools such as frequency histograms and Q-Q plots were used to evaluate error distributions in each DEM. The results indicate that the vertical accuracy of SRTM model is much higher than ASTER GDEM2 and GMTED2010 for both sites. In Anaguid test site, the vertical accuracy of SRTM is estimated 3.6 m (in terms of RMSE) 5.3 m and 4.5 m for the ASTERGDEM2 and GMTED2010 DEMs, respectively. In Tebessa test site, the overall vertical accuracy shows a RMSE of 9.8 m, 8.3 m and 9.6 m for ASTER GDEM 2, SRTM and GMTED2010 DEM, respectively. This work is the first study to report the lower accuracy of ASTER GDEM2 compared to the GMTED2010 data.

Highlights

Digital Elevation Model (DEM) and its derivative attributes constitute important parameters for an assessment of any process using digital terrain analysis
The plotted variograms indicate the superior vertical accuracy of Shuttle Radar Topography Mission (SRTM) v4.1 followed by GMTED2010 and ASTER GDEM2 compared with the Global Navigation Satellite Systems (GNSS) elevations data
The correlation plots between GNSS data and each of the three DEMs obtained for both sites are shown in Figures 7 and 8a–c

Summary

Introduction

Digital Elevation Model (DEM) and its derivative attributes (slope, curvature, roughness, local relief, etc.) constitute important parameters for an assessment of any process using digital terrain analysis. DEMs can be generated using different techniques such as air-borne and satellite-borne stereoscopic photogrammetry, RADAR/SAR interferometry, Light Detection and Ranging (LIDAR), and conventional surveying techniques (e.g., GPS, levelling). These techniques can be compared considering four aspects (i.e., price, accuracy, sampling density, pre-processing requirements). Four main steps are encountered during the generation process of each DEM, regardless of which technology is used [9]: (1) data acquisition (source of elevation data); (2) resampling to required grid spacing (i.e., regular spaced grid); (3) interpolation to extract height of required point (i.e., in between two grid cell centers) and (4) DEM representation, editing and accuracy assessment. All of these steps mentioned above can introduce errors to the final DEM

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Conclusion