The Modified Digital Terrain Model (MDTM) data files are digital representations of cartographic information in a grid form after the application of Intermap's proprietary system known as TerrainFit™ and a subsequent filtering process. TerrainFit™ removes high frequency variations found in the first reflective surface DEM. This effectively removes elevation posts of features such as manmade structures, isolated trees, etcetera that have a relatively small footprint. Having removed these features the final regular posted DTM is derived through interpolation of the remaining elevation posts. The filtering process is designed to reduce the noise level in the data.
The DTM data for 7.5-minute by 18-minute units correspond to the USGS 1:63,360 scale topographic quadrangle map series for available areas in the United States. Each 7.5-minute by 18-minute DTM is based on 1.25m pixel resolution using the Universal Transverse Mercator (UTM) projection. Each 7.5-minute by 18-minute tile provides full coverage with overlap into adjacent tiles.
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>.
This data was derived from the original DSM through the application of the TerrainFit bare earth processing system and the subsequent application of a 3X3 median filter run with four iterations. The intent in processing the DSM this way was to reduce the inherent variability within the DSM so that contours generated at a one meter interval would conform to standard cartographic expectations. This is an artificially smoothed DSM that was derived from data with a horizontal positional accuracy of 2.5m RMSE and a vertical positional accuracy of 2.0m RMSE. These accuracies can no longer be guaranteed given the filtering procedures.
Project Information NPRA1 Task Order#: 01010C0010 NPRA2 Task Order#: 01010C0029 Project Area: National Petroleum Reserve Alaska Intermap Project Number: 02218 Time of Collection Flight Segment: m356p7s1 Base Stations: Alpine-Deadhorse-Alpine_Trimble Flight Direction: 0.2940933 Pass Acquisition Start Time (includes GPS week): 285872.9526 Pass Acquisition Start Time (GPS in HH:MM:SS): 7:24:33 Pass Acquisition Start Time (UTC in HH:MM:SS): 7:24:20 Pass Acquisition End Time (includes GPS week): 286503.5455 Pass Acquisition End Time (GPS in HH:MM:SS): 7:35:04 Pass Acquisition End Time (UTC in HH:MM:SS): 7:34:51 Pass Acquisition Date: 24-Jul-02 Flight Segment: m356p8s2 Base Stations: Alpine-Deadhorse-Alpine_Trimble Flight Direction: 180.2686001 Pass Acquisition Start Time (includes GPS week): 287421.9899 Pass Acquisition Start Time (GPS in HH:MM:SS): 7:50:22 Pass Acquisition Start Time (UTC in HH:MM:SS): 7:50:09 Pass Acquisition End Time (includes GPS week): 288005.471 Pass Acquisition End Time (GPS in HH:MM:SS): 8:00:05 Pass Acquisition End Time (UTC in HH:MM:SS): 7:59:52 Pass Acquisition Date: 24-Jul-02 Intermap Processing AML Version: 1.1.2, 20030604 ISO 9001 Certification No.: A8379 DEM Origin (North West Corner) UTM_Easting_(meters): 557042.5 UTM_Northing_(meters): 7753427.5 DEM Extents UTM_Easting_(meters): Min. 557040 Max. 570040 UTM_Northing_(meters): Min. 7738230 Max. 7753430