The GLOBAL Terrain Digital Surface Model (DSM) data files are digital representations of cartographic information in a grid form. DSMs consist of a sampled array of elevations for a number of ground positions at regularly spaced intervals. These digital data files are produced by Intermap Technologies Inc.(Intermap) as part of the GLOBAL Terrain product line and are licensed in 7.5-minute tiles for areas located between 0 and 56 degrees North/South. Data for locations above 56 degrees North/South are licensed in 15-minute by 7.5-minute tiles.
GLOBAL Terrain DSM products represent the first reflective surface as illuminated by the radar. Accuracy statements are based on areas of moderate terrain. Diminished accuracies are to be expected in areas of extreme terrain and dense vegetation.
GLOBAL Terrain DSMs are produced within four classes of vertical accuracy. GTF DSMs have an accuracy of 0.5m Root Mean Square Error (RMSE) or better. GT1 DSMs have an accuracy of 1.0m RMSE or better. GT2 DSMs have an accuracy of 2.0m RMSE or better. GT3 DSMs have an accuracy of 3.0 RMSE or better. No in-scene ground control points are required for GT2 and GT3 products provided that the DGPS ground station is within 200 km of the data acquisition area. The GTF and GT1 products do require in-scene ground control.
The DSM data for 7.5-minute units correspond to the USGS 1:24,000 and 1:25,000 scale topographic quadrangle map series for available areas in the United States and throughout the world. Each 7.5-minute DSM is based on 5- by 5-meter, or 10- by 10-meter post spacing using the Universal Transverse Mercator (UTM) projection. Each 7.5- by 7.5-minute tile provides full coverage with overlap into adjacent tiles.
The DSMs are used as a fundamental layer of information in Geographic Information Systems (GIS) and Spatial Information Decision Support Systems (DSS). A number of the priority layers of spatial information recognized by the National Spatial Data Infrastructure may be derived from GLOBAL Terrain DEMs, including elevation, hydrography, slope, aspect, and shoreline delineation.
The system is comprised of two X-band radar antennae that collect data simultaneously. The set of acquired data are "interfered" by a digital correlation process to extract terrain height data and geometrically correct radar images. STAR-3i uses post-processed DGPS data, together with precise inertial measurement data, to attain highly accurate positioning control. Precise terrain height and positioning data are enhanced by careful calibration of the baseline separating the two antennae.
The STAR-3i system accuracy has been independently validated by tests conducted by the U.S. Army Topographic Engineering Center, the Institute of Navigation, Stuttgart University and by NASA. A summary of test results are accessible at <URL:http://www.globalterrain.com>.
The GLOBAL Terrain folder name describes the geographic location of a tile. The GLOBAL Terrain file name encapsulates the GT processing level and the product version number. A complete explanation of the GLOBAL Terrain file name can be found in the GLOBAL Terrain Product Handbook. <URL:http://www.globalterrain.com/gt.asp#Product Handbook>.
Project Information Project Area: Anchorage Alaska Intermap Project Number: 00241_199 Mission # (s): 199 Intermap Processing AML Version: 1.0.7, 20010920 ISO 9001 Certification No.: A8379 DEM Origin (Northeast corner) UTM_Easting_(meters): Min. 645440 Max. 662440 UTM_Northing_(meters): Min. 6793520 Max. 6808450