Digital elevation data can now be obtained for any place on the earth, at several resolutions. One GTOPO30 global dataset has a 1 km resolution. This dataset is very good for working at the continental scale and with very large regions. SRTM data are now available, and feature near global coverage at 90 m resolution. This provides consistent global coverage at higher resolution than has been previously available outside of the U.S. Within the U.S. we have access to 30 m SRTM and NED data, as well as selected NED coverage at 10 m.
The Interent is a great source of data and information on digital elevation models. One place to begin searching for these data is the DEM section of the CEO Links page. Also this document provides descriptions of the primary DEM datasets, as well as links to data sources and provider sites for more detailed product information.
The USGS has assembled a seamless digital elevation dataset of the United States with a 1 arc second (30 meter) resolution. There is also a large collection of 1/3 arc second (10 m) data covering much of the U.S. This is an active archive, meaning these data are being replaced as better data are available. Individual tiles of these data can be downloaded in several formats from the Seamless Data Distribution System (SDDS) of the USGS. You should take the tutorial on this site before selecting any data. Look in the Obtaining and Importing Data section of the CEO FAQ page for detailed instructions on importing and converting DEM data into ERMapper format.
In February of 2000 the Space Shuttle mapped most of the land surfaces of the Earth to create a high resolution elevation dataset. Global data was released at a 3 arc-second (90 m) resolution. Data covering the United States was released at a 1 arc-second (30 m) resolution.
Version 1, the inital release of these data, had data voids caused by a variety of reasons such as backscatter and topographic relief. Many lake surfaces were uneven and coastlines were irregular. These data were released globally in one degree tiles.
NASA has completed their second release of the SRTM data, Version 2. These "finished" data have most voids filled in, lake surfaces have been corrected, and coastlines have been properly defined and aligned. Like NED, these data are available at the SDDS site of the USGS. You should take the tutorial on this site before selecting any data. Care should be taken when using SRTM data in areas with extreme relief, as there are still data voids in some of these areas.
The Global Land Cover Facility at the University of Maryland also distributes SRTM data, conveniently subset into tiles large enough to contain Landsat images. These are distributed in GeoTIFF format and can be used with any program designed to use spatial data. As of this writing, 3 arcsecond (90 m) data, distributed through the Earth Science Data Interface (ESDI) in Landsat Path/Row tiles, are available in both the Version 1 Unfinished processing level and the Version 2 Filled Finished processing level. You should always select the Filled Finished version when available. Within the U.S. you can also download 1 arcsecond (30 m) data, but these data are only available in the Unfinished format. For continental U.S. 1 arcsecond data you should use the SDDS described above.
SRTM one degree tiles at both Version 1 and 2 processing levels can still be obtained at the NASA SRTM FTP site. These data are organized by version, then continent. Individual tiles are labeled by the latitude and longitude of the lower left corner of the tile. Version 1 tiles should be processed to fill in data voids.
The USGS has global DEM data at 30 arc-second (one kilometer) resolution. These data have been collected from a variety of sources. The USGS has organized these into 33 tiles identified by longitude and latitude. The CEO has downloaded the entire collection, formated them as ERMapper files, and assembled mosaics of these tiles for each continent. You can find 1-km resolution DEM data in ERMapper format for each continent on the CEO server at: N:\ERM_files\GTOPO30_DEM. To learn more about the GTOPO30 data, please visit the USGS GTOPO30 site.
The ASTER sensor onboard the Terra satellite has produced 30 m resolution elevation data. There is only partial coverage of world at this high resolution but data are free. You can search for these data at the EOS Data Gateway. You can learn more about ASTER as well as data import instructions at the CEO ASTER web page.
One can also create a 15 m DEM from an ASTER scene using the ENVI software with the DEM extraction wizard. This process uses bands 3N and 3B to create parallax and generate a relative elevation model. A relative DEM will accurately depict the topography but will not be referenced to sea level. The user must supply accurate elevations at one or more specific locations to produce an absolute elevation dataset.
The CEO has a 9-CD set of DEM data for the United States at 3 arc-second (100 meter) resolution supplied by ERMapper. This set includes shaded-relief maps of each region of the US. The set also includes a 9 arc-second (300 meter) resolution mosaic of the continental US and a 6 x 12 arc-second (150 x 250 meter) resolution dataset for Alaska.
09 April 2007