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 5m postings 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.intermap.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 1m RMSE. These accuracies can no longer be guaranteed given the filtering procedures.
Project Information NPRA3 Task Order#: 01010C0042 Project Area: National Petroleum Reserve Alaska Intermap Project Number: 03015 Time of Collection Flight Segment: m401p30s2 Base Stations: REM1&UMI1 Flight Direction: 86.50 Pass Acquisition Start Time (includes GPS week): 520392.8127 Pass Acquisition Start Time (GPS in HH:MM:SS): 0:33:13 Pass Acquisition Start Time (UTC in HH:MM:SS): 0:33:00 Pass Acquisition End Time (includes GPS week): 521387.5353 Pass Acquisition End Time (GPS in HH:MM:SS): 0:49:48 Pass Acquisition End Time (UTC in HH:MM:SS): 0:49:35 Pass Acquisition Date: 2-Aug-03 Flight Segment: m401p32s2 Base Stations: REM1&UMI1 Flight Direction: 86.25 Pass Acquisition Start Time (includes GPS week): 524874.95 Pass Acquisition Start Time (GPS in HH:MM:SS): 1:47:55 Pass Acquisition Start Time (UTC in HH:MM:SS): 1:47:42 Pass Acquisition End Time (includes GPS week): 525888.5633 Pass Acquisition End Time (GPS in HH:MM:SS): 2:04:49 Pass Acquisition End Time (UTC in HH:MM:SS): 2:04:36 Pass Acquisition Date: 2-Aug-03 Flight Segment: m401p55s5 Base Stations: REM1&UMI1 Flight Direction: -86.00 Pass Acquisition Start Time (includes GPS week): 82386.77504 Pass Acquisition Start Time (GPS in HH:MM:SS): 22:53:07 Pass Acquisition Start Time (UTC in HH:MM:SS): 22:52:54 Pass Acquisition End Time (includes GPS week): 83398.65583 Pass Acquisition End Time (GPS in HH:MM:SS): 23:09:59 Pass Acquisition End Time (UTC in HH:MM:SS): 23:09:46 Pass Acquisition Date: 3-Aug-03 Intermap Processing AML Version: 1.1.3, 20031104 ISO 9001 Certification No.: A8379 DEM Origin (North West Corner) UTM_Easting_(meters): 441087.5 UTM_Northing_(meters): 7739207.5 DEM Extents UTM_Easting_(meters): Min. 441085 Max. 454310 UTM_Northing_(meters): Min. 7724010 Max. 7739210