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Distribution of the Global Digital Elevation Model (GDEM) sourced from the Advanced Space-borne Thermal Emission and Reflection Radiometer on NASA's Terra satellite began on 29 June.

The Ministry of Economy, Trade and Industry in Tokyo and the US National Aeronautics and Space Administration have been collaborating on the project. It covers all land on Earth.

The GDEM was created by stereo-correlating the Aster archive of 1.3 million visual and near-infra red images.

NASA and METI are jointly contributing the Aster topographic data to the Group on Earth Observations, an international partnership headquartered at the World Meteorological Organisation in Geneva. It will be used as part of the Global Earth Observation System of System.

It is being produced with 30 metre postings and is formatted in 1 x 1 degree tiles as GeoTIFF files. Each GDEM file is accompanied by a quality assessment file, which indicates either the number of Aster scenes used to calculate a pixel’s value or the source of external data used to fill the Aster voids.

The previous best world-wide coverage was the DEM created by the Shuttle Radar Topography mission, which has 90 metre postings, although some users in some parts of the world, can access 30 metre SRTM data. In any event, the SRTM data does not have colour information associated with it.

Another advance in the Aster data is its coverage. The SRTM mission mapped 80 percent of Earth's landmass, between 60 degrees north latitude and 57 degrees south. The new Aster data expands coverage to 99 percent, from 83 degrees north latitude and 83 degrees south.

The Aster data fills many of the voids in the shuttle mission's data, particularly in very steep terrain and in some deserts.

NASA is working to combine the Aster data with SRTM and other sources to produce an even better global topographic map.

The GDEM is available for download from either NASA’s EOS data archive or Japan’s ground data system.

Under an agreement between METI and NASA, the GDEM is free to users.

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