The National Geospatial-Intelligence Agency (NGA) has reached a milestone in its program to make “finished” topographic data from the Shuttle Radar Topography Mission (SRTM) available to the public. NGA is a U.S. Department of Defense combat support agency and a member of the National Intelligence Community whose mission is to provide timely, relevant and accurate geospatial intelligence in support of national security. NGA has now processed SRTM data for all of Europe and Asia and is about 90% completed for the worldwide project. The SRTM data were acquired in February 2000 using a radar system on-board the Space Shuttle Endeavour. The SRTM mission was a cooperative project of NGA (then known as the National Imagery and Mapping Agency), the National Aeronautics and Space Administration (NASA) and the German and Italian space agencies.
NASA’s Jet Propulsion Laboratory (JPL) performed all the raw radar data processing, produced more than 14,000 1ºx1º cells of terrain elevation data over the land area covered by the shuttle (between 56º South and 60º North latitudes), and forwarded the data to NGA for “finishing.” To finish the product, NGA performed quality control checks on the unfinished JPL data, filled in small voids and edited the terrain data to correctly portray water bodies and shorelines. The finished product is a uniform grid of elevation values indexed to specific points on the ground in a standardized Digital Terrain Elevation Data (DTED) format.
Since January 2004, NGA has been releasing finished SRTM DTED to the public via the U.S. Geological Survey’s Earth Resources Observation Systems Data Center (EDC). All the Western Hemisphere and most of Eurasia are posted on the EDC web site ). NGA expects to finish the SRTM data processing in September and to make the data available to the public via EDC by the end of the year. The finished SRTM DTED represent an improved version of the unfinished SRTM terrain elevation data that have been available publicly at EDC since 2003.
The finished elevation data available to the public are at a resolution (ground spacing) of 90 meters (DTED Level 1) for the entire world and at a resolution of 30 meters (DTED Level 2) for the U.S. and its territories. Several studies have verified that the terrain elevations meet or surpass specifications (accurate to within 16 meters in height and 20 meters horizontally).