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Input Data Types

SRTM (Shuttle Radar Topography Mission)

NASA collected C-band interferometric sensor data for approximately 80% of the land surface between 60-deg North and 56-deg South latitude for DODís NIMA (National Image and Mapping Agency) during NASAís 11 day STS-99 orbital spacecraft mission. NASA-JPL will process this data and a Memo of Understanding between NIMA and USGS designates the USGS EROS Data Center as the archive and distribution center for the full resolution (1-arc second) SRTM data over the U.S. for the non-U.S. areas, reduced resolution (3-arc second) terrain data will be fully releasable without restrictions. Scientific use of full resolution non-U.S. data is to be negotiated on a case-by-case basis with NASA and NIMA. Discussions are continuing at USGS concerning formats, costs, and distribution of data. It was estimated that the processing of the collected SRTM data would require two years. Interested readers should check the USGS SRTM data site to obtain current information (http://edc.usgs.gov/srtm/data.html).


USGS Digital Elevation Model (DEM) are digital arrays of terrain elevations for ground positions at regularly spaced horizontal intervals. DEM's are developed from stereo models or digital contour line files derived from USGS topographic quadrangle maps and there is a range of spatial resolutions of these data from the United States Geological Survey (USGS). These digital cartographic/geographic data files are produced by the U.S. Geological Survey (USGS) as part of the National Mapping Program and are downloadable free.

7.5-minute DEM - The DEM data for 7.5-minute units correspond to the USGS 1:24,000-scale and 1:25,000-scale topographic quadrangle map series for all of the United States and its territories. Each 7.5-minute DEM is based on 30-meter by 30-meter data spacing with the Universal Transverse Mercator (UTM) projection.


USGS recently released National Elevation Data (NED). NED is a USGS raster product designed to provide a seamless form with a constant datum, elevation unit, and projection. The NED has a resolution of 1 arc-second or approximately 30 meter for the conterminous U.S., Hawaii, and Puerto Rico and a resolution of 2-arc seconds for Alaska. The reader is referred to http://mac.usgs.gov/mac/isb/pubs/factsheets/fs14899.html.


Interferometric Synthetic Aperture Radar (IFSAR) technology compares two radar images taken at slightly different locations to obtain surface elevation information, much like stereoscopic aerial imagery. Experimental topographic elevation data from IFSAR collected in aircraft and satellites are scarce, but a search of the Internet may yield a source. IFSAR datasets for this project were obtained from USATEC and were primarily located in the Ft. Irwin NTC area. These datasets contained significant amounts of noise and were very limited in spatial extent. While some of these data were used, work in other physiographic areas necessitated using other types of datasets (i.e., USGS DEM).


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