Sources and References

Digital elevation data can now be obtained for any place on the earth, at several resolutions. The 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 feature near global coverage at 90 m resolution. This provides consistent global coverage at higher resolution than had been previously available outside of the U.S. ASTER derived elevation are now available globaly at 30m resolution. 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 on the left side of the YCEO 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.

Seamless Data Distribution System - (SDDS)

The Seamless Data Distribution System is the preferred data download site managed by the USGS. You should take the tutorial on this site before selecting any data. Look in the Obtaining and Importing Data section of the YCEO FAQ page for detailed instructions on importing and converting DEM data. The default data format is ArcGRID by ESRI. This works well in ArcGIS but can be cumbersome when working in remote sensing applications. You should consider downloading these data in GeoTIFF format. Once you select your target area for download, a Target Summary Page is loaded. Click on the Modify Data Request button and locate the data you have selected to download. Use the drop-down arrow to change format and save this change.

National Elevation Data - NED

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.

Shuttle Radar Topography Mission - SRTM

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 were released at a 3 arc-second (90 m) resolution. Data covering the United States were also released at a 1 arc-second (30 m) resolution.

Version 1, the initial 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.

Version 2, NASA has completed their second release of the SRTM data. These "finished" data have most voids filled in, lake surfaces have been corrected, and coastlines have been properly defined and aligned. These data are available at the USGS Earth Explorer site. Care should be taken when using SRTM data in areas with extreme relief, as there are still data voids in some of these areas. When using these data with ENVI you should select the DTED Data Format. To open these data in ENVI select Open External File => Digital Elevation => DTED

The Global Land Cover Facility at the University of Maryland also distributes SRTM data, conveniently subset into tiles large enough to contain individual 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 Finished and the Version 2 Filled Finished processing level. The Filled data are produced from the Version 2 finished data and have an interpolation algorithm applied to fill in data voids. 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 may only be available in the Unfinished format. For continental U.S. 1 arcsecond data you should use the SDDS site 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.

Global 1 km Data - GTOPO30

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 YCEO has downloaded the entire collection, formated them as ENVI files, and assembled mosaics of these tiles by continent. Users of the YCEO Lab can find these 1-km resolution DEM data on the server at: O:\DEM\GTOPO-1km. To learn more about the GTOPO30 data, please visit the USGS GTOPO30 site.

ASTER Global Elevation Data

The science teams at the NASA Jet Propulsion Lab (JPL) and Japan's Ministry of Economy, Trade and Industry (METI) used the ASTER sensor onboard the Terra satellite to produce 30 m resolution elevation data. These data cover 99% of the land surface from 83 degrees north latitude to 83 degrees south latitude. Version 2 of these data were released in October 2011 and is a significant improvement over the initial data release.

These ASTER data are now available at the new USGS Reverb|Echo website. This site requires a free registration. After zooming in to your study area on the map, drag a box to select your area of interest. In the upper right enter the search term elevation and the Step 2 panel will be filtered to only these datasets. From here select the ASTER Global Digital Elevation Model then in Step3: click on Search for Granules. On the next screen you can select specific datasets to download, view their metadata and footprint. Once specific scenes are placed in your "shopping cart" you can complete the order. You will receive an email when data are available for FTP retrieval.

Other Elevation Data

The YCEO 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.