The addition of this data set will allow users to overlay traditional 2D satellite maps on elevation data to achieve a 3D representation of the world. When used in conjunction with the GLCF's land cover change data, essentially a 4D representation of the Earth surface through time can be achieved.

SRTM was an experiment conducted by NASA on the Space Shuttle in February 2000. "In about ten days, NASA achieved what scientists, engineers and cartographers had dreamed for a century" says Dr. Ghassem Asrar, NASA Associate Administrator for Earth Science. "We benefited from using the vantage point of space to map eighty percent of Earth's land surface, home to more than 90 percent of Earth's population, with one instrument. The resulting topographic products provide the highest precision and spatial resolution elevation data ever acquired with global coverage. These data are used for mapping, flood forecasts, city and road planning, scientific research, and many other societal benefits, and will continue to be used for decades."

Landsat ETM+ draped on SRTM DEM
Rocky Mountains

Users can retrieve free copies of elevation imagery through the GLCF's easy online interface. Now anyone, anywhere, can download both SRTM elevation data and a corresponding high resolution satellite image or land cover product from the GLCF's large, free archive for most areas of the Earth's surface. North of 60°N and south of 54°S are not available for SRTM data.

Ron Birk, Director of NASA's Earth Science Applications Division, says that "the Global Land Cover Facility is contributing to NASA's mission 'to understand and protect our home planet' by integrating the Landsat orthorectified images and SRTM land surface topography data into readily accessible products that can be used by people around the world for research, education, operations, policy, and exploration."

Staff at the GLCF have taken the SRTM data as provided by the USGS and converted them into very practical formats, allowing for ease of integration with traditional Earth observing data. In particular, the GLCF editions of the SRTM products are available in GeoTIFF, which most users will find more software-ready and a welcome alternative to the cumbersome native HDF format. Additionally, the GLCF SRTM files are available in both the native geographic coordinate system and in UTM coordinates. The UTM version has been clipped to WRS-2 tiles, so that all Landsat scenes automatically have an SRTM scene fit to the same dimensions. The global Landsat coverage ETM+ and TM Landsat scenes available at the GLCF now have a complimentary SRTM scene of elevation data available on a scene-by-scene basis.

• The SRTM 1-arc-second product (30m resolution) is available in both UTM and Geographic coordinates for the United States and its territories.
• The SRTM 3-arc-second product (90m resolution) is available in both coordinate systems for the entire world. This is the highest resolution global elevation product available in the public's domain.
• The SRTM 30-arc-second product is a much improved version of the widely used GTOPO30 product, essentially an improvement in precision at the same lower resolution of 1 kilometer, which is sufficient for many uses. The GLCF provides this collection in geographic tiles and also as a single file, in geographic coordinates.

The GLCF successfully distributes vast quantities of global Landsat coverage, including the acclaimed GeoCover product. It was decided therefore to provide the SRTM data, clipped to match Landsat's WRS-2 tiles as a natural evolution of both data collections. Because WRS-2 tiles occasionally do not occupy their nominal positions, the GLCF SRTM clips include a 7.5 km buffer around the 'official' WRS-2 coordinates. The 30 meter resolution SRTM edition and the 30 meter resolution Landsat scenes are an ideal match for both visualization and modeling operations. The Global Land Cover Facility provides SRTM data in the same projection and datum as the global Landsat GeoCover imagery, resulting in a directly interoperable data collection.

The value of SRTM extends beyond Landsat and includes associations with most other Earth observation imagery, including the Terra MODIS sensor. Additionally, the SRTM data sets can be used by themselves as a superior elevation modeling resource. The GLCF provides these editions of SRTM in formats that are readily accepted by most spatial software, where they can be used to make drape or hill-shade visualizations and where they can also be used for more sophisticated modeling using operations of slope, aspect and contouring. Watershed analysis, sighting, natural hazards assessment and agricultural erosion potential are examples of many other procedures possible with quality elevation data such as SRTM.

Visit the Global Land Cover Facility at http://www.landcover.org/ to find out more and to download these innovative products. Online documentation has been provided explaining the transformation process and crediting the source materials made available through NASA and the USGS.

The Global Land Cover Facility is a research and information center located at the University of Maryland Institute for Advanced Computer Studies. As a member of the Research, Education, and Applications Solutions Network (REASoN) program, the GLCF is sponsored by NASA's Office of Earth Science Applications Division, through cooperative agreement NNG04GC53A. The GLCF appreciates support from NASA for this and all its activities.

SRTM is an international project spearheaded by the National Geospatial-Intelligence Agency (NGA) and the National Aeronautics and Space Administration (NASA). For further details see http://www2.jpl.nasa.gov/srtm/.

Examples of SRTM imagery are available at http://www.landcover.org/gallery/srtm.shtml.

About the GLCF

The Global Land Cover Facility (GLCF) provides earth science data and products to help everyone to better understand global environmental systems. In particular, the GLCF develops and distributes remotely sensed satellite data and products that explain land cover from the local to global scales.

Primary data and products available at the GLCF are free to anyone via FTP. Online datasets may be accessed electronically through the Earth Science Data Interface (ESDI).

See also http://glcf.umiacs.umd.edu

For SRTM Data availability (via web or FTP download) see http://glcf.umiacs.umd.edu/data/srtm/