Global Land Survey Digital Elevation Model (GLSDEM)


The GLS collection was made possible by the development of more accurate elevation models with global or regional coverage, including the National Elevation Dataset (NED) of the USA, the Canadian Digital Elevation Dataset (CDED) of Canada, the Shuttle Radar Topography Mission (SRTM) covering most of the globe, and the Global 30 Arc Second Elevation Dataset (GTOPO30) covering the northern latitudes. In order to orthorectify the GLS scenes, the above elevation data were coordinated into the GLSDEM product. To enable direct comparison and visualization of the GLSDEM with other Landsat TM and ETM based products, the GLCF produce GLSDEM files in WRS-2 tiles in the GeoTIFF format, UTM projection and WGS84 datum of the corresponding GLS datasets. For each path/row, the original USGS Degree Tiles are mosaicked and subset with a 9km buffer to reproduce GLSDEMs. The GLSDEM is allowed to be redistributed only on a tile by tile basis (both as degree tiles and WRS-2 tiles) and hence, a global mosaic of the GLSDEM is not available. The GLSDEM degree tiles may be obtained from EROS Data Center, USGS or the GLCF. The WRS-2 edition of the GLSDEMs is available only through the GLCF. The ultimate copyright and ownership of the product, however, is held by the citizens of the United States of America, the Republic of Germany, and the Dominion of Canada.

Table1. Input elevation datasets to the GLSDEM and their sources, resolutions, and areal coverage.

Input Elevation Dataset Source Resolution Coverage
National Elevation Dataset(NED) USGS 1 arc second Conterminous USA and Alaska
Canadian Digital Elevation Dataset(CDED) Geobase canada 3 arc second Canada above 60 deg N
Shuttle Radar Topographic Mission(SRTM) CGIAR 3 arc second Rest of the world below 60 deg N
Digital Terrain Elevation Data NGA 3 arc second Greenland and Eurasia above 60 deg N
Global 30 Arc Second Elevation Data(GTOPO30) USGS 30 arc second Greenland and Eurasia above 60 deg N

Map of the world showing the various sources of elevation datasets used as input to the GLSDEM. The two parallel lines in orange indicate the northern and southern extents of GLS coverage.

Since the SRTM does not cover the Polar Regions, a combination of DTED and GTOPO30 were used to cover these regions. DTED Level 1 data was originally used as the primary input to the GLSDEM to cover the northern latitudes. However, due to restrictions placed on public access to DTED, GTOPO30 data were acquired separately and processed into geographic 1 deg x 1 deg tiles. Thus, the final GLSDEM dataset is distributed by replacing the classified DTED Level 1 data by GTOPO30 so that the dataset could be made available to the public at no charge. Assembly of the GLSDEM: NED covering conterminous USA and Alaska, CDED covering Canadian land north of 60 degree latitude, the GTOPO30 for Eurasia and Greenland above 60 deg N, and SRTM for the rest of globe below 60 deg N were all assembled together to create the final GLSDEM. All the input datasets were resampled using cubic convolution to 3 arc second pixels. These 3 arc-second input datasets were collaged together, without blending to create the final GLSDEM product. The final GLSDEM product is of 3 arc second (90m) resolution and in Geographic coordinates with a horizontal WGS-84 datum. Acknowledgments UMD GLCF would like thank Jon Dykstra, MDA Federal for his valuable inputs and suggestions in creating this reference document. We also thank the USGS and Jeff Masek from NASA/ GSFC for their contributions. We thank the USGS, GeoBase, CGIAR, and the NGA for providing documentation for their elevation products (relevant to the GLSDEM), which were then used to assemble this document References Gutman, G. et al., 2008. Towards monitoring land cover and land use changes at a global scale: The global land survey 2005. Photogrammatic Engineering and Remote Sensing, 74(1). Tucker et al., 2004. NASA's Global Orthorectified Landsat Data Set. Photogrammatic Engineering and Remote Sensing 70(3).

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