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Spring 2007
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Global Elevation Data Now Available in Esri Data & Maps

  click to enlarge
Global elevation data shown in ArcGIS Explorer draped by 15-meter Landsat (courtesy of MDA Federal) depicting Palm Springs, California.

The Esri enhanced 90-meter resolution Shuttle Radar Topography Mission (SRTM) digital elevation model (DEM) data is now included with the latest version of Esri Data & Maps.

The SRTM data was originally collected during the February 2000 mission of the space shuttle Endeavour using Interferometric Synthetic Aperture Radar. During the mission, data for 80 percent of the earth's landmass was collected between 56 degrees south and 60 degrees north. The SRTM data is the most detailed and systematically collected worldwide elevation data available to the general public and is the result of a cooperative project between the National Aeronautics and Space Administration (NASA) and the National Geospatial-Intelligence Agency (NGA).

The global elevation data is based primarily on SRTM 90-meter data and is intended for use in small- to medium-scale 3D and 2D visualization applications. Esri has enhanced the SRTM data to make it more user-friendly and complete for visualization purposes. These enhancements include filling in all data voids; mosaicking all 14,277 1-by-1 degree Digital Terrain Elevation Data (DTED) Level 1 cells into six raster datasets (promoting ease of use); and reducing storage requirements by compressing the elevation data from 35 GB in the original DTED format to slightly more than 4 GB using JPEG 2000 compression, making it possible to deliver the elevation data on a single DVD. While lossy compression was required for distribution purposes, the RMSE introduced by compression is very acceptable for the global elevation data products' intended use (an RMSE of 2.15 was calculated over the western United States).

For void filling, Esri chose to use a new technique known as the Delta Surface Fill (DSF) method (introduced by NGA), as this provides much-improved results over traditional methods when used with the chosen void fill data source, United States Geological Survey (USGS) GTOPO30 (1 km).

The global elevation data also includes pregenerated hillshade (shaded relief) datasets of the void-filled SRTM data, as well as ocean and inland water mask datasets based on the SRTM Water Body dataset produced by NGA. The hillshades are distributed on three DVDs, organized by continent, along with cloud-free 150-meter imagery.

In the polar areas not captured during the shuttle mission, Esri has included GTOPO30 (1 km) elevation and hillshade datasets. To maintain consistency with the data provided in the SRTM coverage area, Esri has included ocean and inland water mask datasets for the polar areas derived from the Digital Chart of the World (VMap Level 0). These additions provide complete worldwide coverage.

The global elevation data includes metadata for layer files and the elevation data itself, as well as README files. Esri Data & Maps ships at no additional cost with each ArcGIS software product.

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