Validation of ASTER GDEM for the area of Greece

The ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) Global Digital Elevation Model (GDEM), which was released in June 2009, provides elevation data for over 99 percent of Earth's land area. GDEM was found to contain significant anomalies mainly caused by residual clouds in the ASTER scenes, or by the algorithm used to generate the final GDEM from the variable number of individual DEMs. In this paper, the GDEM, for the whole area of Greece was validated by comparing it with reference DEMs with higher resolution derived either from aerial stereo imagery, or from ASTER raw data analysis; as well as with elevation values provided by a number of Geodetic Control Points (GCP) and GPS measurements. The vertical accuracy (at 95 percent confidence) was calculated to be more than 30 m (RMSE = 16.01 m) when compared to the GCPs, whereas the vertical accuracy was calculated around 20 m (RMSE = 11.08 m) when compared with the GPS derived elevations. It can be therefore stated that the current version of ASTER GDEM overall does not meet its pre-production estimated vertical accuracy of 20 m at 95 percent confidence over Greece, however, it can be used in several applications, such as topographic analysis, hydrological and geomorphological modeling, landscape visualization, and energy balance studies.