The GLOBAL Terrain ORRI data files are digital representations of the radar response signal. ORRIs consist of a georeferenced pixel 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 ORRI 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.
The ORRI 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 ORRI is based on 2.5m pixel resolution using the Universal Transverse Mercator (UTM) projection. Each 7.5- by 7.5-minute tile provides full coverage with overlap into adjacent tiles.
The original ORRI is unenhanced and may appear dark when viewed. Both the original ORRI and an ORRI with a customized linear stretch enhancement are provided. The stretched ORRI will appear brighter and is easy to view without additional enhancements.
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: Thompson Pass Alaska Intermap Project Number: 01223a Mission # (s): 326,&,340 Intermap Processing AML Version: 1.0.6, 20010920 ISO 9001 Certification No.: A8379 UTM_Easting_(meters): Min. 565140 Max. 582137.5 UTM_Northing_(meters): Min. 6790912.5 Max. 6805840