DEM and Slope of UNDESERT countries Burkina Faso, Benin, Niger and Senegal (Source: Ministry of Economy, Trade, and Industry (METI) of Japan; United States National Aeronautics and Space Administration (NASA): Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) Global Digital Elevation Model Version 2 (GDEM V2)

DEM and Slope from ASTER GDEM (GDEM2) NASA and METI The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) on NASA’s Terra spacecraft collects in-track stereo using nadir- and aft looking near infrared cameras. Since 2000, these stereo pairs have been used to produce single-scene (60 x 60 km) digital elevation models having vertical (root-mean-squared-error) accuracies generally between 10 m and 25 m. On June 29, 2009, NASA and the Ministry of Economy, Trade and Industry (METI) of Japan released a Global Digital Elevation Model (GDEM) to users worldwide at no charge as a contribution to the Global Earth Observing System of Systems (GEOSS). This “version 1” ASTER GDEM (GDEM1) was compiled from over 1.2 million scene-based DEMs covering land surfaces between 83°N and 83°S latitudes. GDEM1 is a 1 arc-second elevation grid distributed as 1°-by-1° tiles. A joint US-Japan validation team assessed the accuracy of the GDEM1, augmented by a team of 20 cooperators selected through an Announcement of Opportunity (AO). In summary, the GDEM1 was found to have an overall accuracy of around 20 meters at the 95% confidence level. The team also noted several artifacts associated with poor stereo coverage at high latitudes, cloud contamination, water masking issues and the stacking process used to produce the GDEM1 from individual scene-based DEMs (ASTER GDEM Validation Team, 2009). Two independent horizontal resolution studies estimated the effective spatial resolution of the GDEM1 to be on the order of 120 meters (Crippen, 2009; Tachikawa et al. 2009). NASA and METI released a second version of the ASTER GDEM (GDEM2) on 17 October, 2011. The GDEM2 has the same gridding and tile structure as GDEM1, but benefits from the inclusion of 260,000 additional scenes to improve coverage, a smaller correlation kernel (5x5 versus 9x9 for GDEM1) yielding higher spatial resolution, and improved water masking. Also, a negative 5 meter overall bias observed in the GDEM1 was removed in newer version. As with the GDEM1, the GDEM2 validation was the joint responsibility of U.S. and Japanese partners. The U.S. validation team included the U.S. Geological Survey (USGS, in cooperation with NASA), NASA’s Jet Propulsion Laboratory (JPL), the National Geospatial-Intelligence Agency (NGA) and the NASA Goddard Space Flight Center (GSFC). The Japanese validation was conducted by the Earth Remote Sensing Data Analysis Center (ERSDAC) in cooperation with the University of Tokyo and Mitsubishi Materials Techno Corporation (under contract to ERSDAC). As before, the GDEM2 will be distributed at no charge to users through ERSDAC on behalf of METI, and at the Land Processes Distributed Active Archive Center (LP DAAC), located at the USGS Earth Resource Observation and Science Center (EROS), on behalf of NASA. http://www.jspacesystems.or.jp/ersdac/GDEM/ver2Validation/Summary_GDEM2_validation_report_final.pdf