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| Earth Resources Observation and Science (EROS) |
Shuttle Radar Topography Mission DTED® 
| Contents: |  SRTM DTED® subset image |
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back to Elevation Product List Product DescriptionThe Shuttle Radar Topography Mission (SRTM) successfully collected Interferometric Synthetic Aperture Radar (IFSAR) data over 80 percent of the landmass of the Earth between 60 degrees North and 56 degrees South latitudes in February 2000. The mission was co-sponsored by the National Aeronautics and Space Administration (NASA) and National Geospatial-Intelligence Agency (NGA). NASA's Jet Propulsion Laboratory (JPL) performed preliminary processing of SRTM data and forwarded partially finished data directly to NGA for finishing by NGA's contractors and subsequent monthly deliveries to the NGA Digital Products Data Wharehouse (DPDW). All the data products delivered by the contractors conform to the NGA SRTM products and the NGA Digital Terrain Elevation Data (DTED®) to the National Center for Earth Resources Observation & Science (EROS). The DPDW ingests the SRTM data products, checks them for formatting errors, loads the SRTM DTED® into the NGA data distribution system, and ships the public domain SRTM DTED® to the U.S. Geological Survey (USGS) National Center for Earth Resources Observation & Science (EROS). Data Processing SRTM DTED® is a uniform matrix of elevation values indexed to specific points on the ground. The horizontal datum is the World Geodetic System 1984 (WGS84) and the vertical datum is mean sea level as determined by the WGS84 Earth Gravitational Model (EGM 96) geoid. The elevation data are with respect to the reflective surface, which may be vegetation, man-made features or bare earth. DTED® Level 2 elevation values are spaced one arc second apart between 0 degrees and 50 degrees latitude, and spaced one arc second apart in latitude and two arc seconds apart in longitude between 50 degrees and 60 degrees latitude. SRTM DTED® Level 1 values are derived from the SRTM DTED® 2 values such that the DTED® 1 values are identical to the DTED® 2 values at coincident points. However, the SRTM DTED® 1 values are spaced 3 arc seconds apart between 0 degrees and 50 degrees latitude, and spaced 3 arc seconds apart in latitude and 6 arc seconds apart in longitude between 50 degrees and 60 degrees latitude. After NASA/JPL completes the raw data processing, NGA performs quality assurance checks on the JPL SRTM data and its contractors perform several additional finishing steps. Spikes and wells in the data are detected and voided out if they exceed 100 meters compared to surrounding elevations. Small voids (16 contiguous posts or less) are filled by interpolation of surrounding elevations. Large voids are left in the data. Water bodies are depicted in the SRTM DTED®. The ocean elevation is set to 0 meters. Lakes of 600 meters or more in length are flattened and set to a constant height. Rivers that exceed 183 meters in width are delineated and monotonically stepped down in height. Islands are depicted if they have a major axis exceeding 300 m or the relief is greater than 15 m. The data are processed in one degree by one degree "cells". The edges of each cell are matched with the edges of adjacent cells to assure continuity. SRTM DTED® elevations are with respect to the reflective surface. Some of the data may exhibit typical radar artifacts including scattered voids due to shadowing effects and poor signal returns over some terrain, as well as occasional phase unwrapping errors. However on the whole, the data are 95% complete over the collection area, and the SRTM DTED® absolute height accuracy is significantly better than the 16-meter (90% confidence) specification for the mission. In addition to voids due to shadows and layover and poor reflective properties of the Earth's surface, there are occasional floating islands of data, unregistered vertically, due to phase unwrapping errors. On the whole, the SRTM DTED® absolute height accuracy is significantly better than the 16 meters (90 % confidence) specification for the mission. Distribution SRTM DTED® Level 1 (3 arc second) data for global coverage is distributed by the National Center for Earth Resources Observation & Science (EROS) on DVD. SRTM DTED® Level 2 (1 arc second) data for the United States and territotial islands is distributed by the National Center for Earth Resources Observation & Science (EROS) on DVD. The product is "Finished" data supplied by NGA. Additional Information: SRTM JPL/NASA Homepage Back to TopPrices
Back to TopSearch & OrderThe coverage area for SRTM DTED® Level 1 (3 arc second) is broken into a grid system made up of 13 different areas. A single DVD represents the data contained within each grid area. SRTM DTED® Level 2 (1 arc second) coverage of the United States and territorial islands is broken into a grid system of 7 areas. A single DVD represents the data contained within each grid.
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