Level-2 Terrain Height Data Sets (Digital Topographic Maps)
The Level-2 Terrain Height Data Sets contain the digital topography data processed from the C-Band
data collected during the mission.
- Each posting in a Level-2 Terrain Height Data Set represents a height measurement (posting) in
meters relative to the WGS84 ellipsoid surface.
- The horizontal datum for the Level-2 Terrain Height Data Sets is the WGS84 ellipsoid earth model.
- The absolute horizontal accuracy (90% Circular Error) is 20 meters.
- The absolute vertical accuracy (90% Linear Error) is 16 meters.
The Data Sets are composed of files covering areas 5 degrees in latitude by 5 degrees in longitude.
- For data between the equator to 50 degrees latitude, the postings are spaced at 1" (one arcsecond)
latitude by 1" longitude.
- At the equator, these are spacings of approximately 30 meters by 30 meters.
- For data beyond 50 degrees latitude, the postings are spaced at 1" latitude by 2" longitude.
(Since longitudinal distance decreases with increasing latitude from the equator, 1" of longitude is
only about 15 meters at 50 degrees latitude.)
Random Height Error Data Sets
The Random Height Error Data Sets contain the random error estimates (in meters) for the height measurements in the Level-2 Terrain Height Data Sets. (The random height error is defined as the height error component that is uncorrelated between different height postings.)
Each Level-2 Terrain Height Data Set will have a corresponding Random Height Error Data Set file covering the same area in latitude and longitude and with postings co-registered with the height measurements.
Strip Orthorectified Image Data Sets
The Strip Orthorectified Image Data Sets are generated during
interferogram formation within the topography processor.
Each Data Set is created from the inboard antenna data for a single subswath; a single file covers an area of approximately 60 km in width by 450 to 4500 km (1 to 10 minutes) in length. (Currently, Data Sets from different datatakes or from multiple regions of the same datatake are not mosaicked before delivery to NGA.)
The samples within the Strip Orthorectified Image Data Sets are spaced at 15 meters by 15 meters and are gridded along a local radar coordinate system.
Systematic Height Error Model
The Systematic Height Error Model contains an estimate of the non-random component of the height error as determined through post-flight verification activities.
Final Verification Report & Global Height Error Model
The Final Verification Report documents the error estimation algorithms and global error characteristics as determined from the entire data set.
The Global Height Error Model enhances the Systematic Height Error Model by estimating long-wavelength errors that cannot be determined from continental data alone.