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Digital Elevation Models (DEMs)

ASF uses publicly-available Digital Elevation Models for processing SAR data. The DEM used will vary by scene location; the best available DEM with full coverage of the scene extent will be used for processing any given scene.

DEM Coverage

DEM coverage map

The source DEMs include:

Resolution DEM Datum Area Posting Sampling
High NED13 NAVD88 CONUS, Hawaii, parts of Alaska 1/3 arc seconds Resampled to product spacing, reprojected to WGS84 UTM
Medium SRTMGL1 EGM96 60 N to 57 S latitude 1 arc second Resampled to product spacing, reprojected to WGS84 UTM
Medium SRTM US1 EGM96 CONUS, Hawaii, parts of Alaska 1 arc second Resampled to product spacing, reprojected to WGS84 UTM
Medium NED1 NAVD88 CONUS, Hawaii, parts of Alaska, Canada, Mexico 1 arc second Resampled to product spacing, reprojected to WGS84 UTM
Medium NED2 NAVD88 Alaska 2 arc seconds Resampled to product spacing, reprojected to WGS84 UTM

Note

For terrain corrected products, the quality of the results is directly related to the quality of the digital elevation models (DEMs) used in the process of geometrically and radiometrically correcting the SAR imagery.

The DEMs were pre-processed by ASF to a consistent raster format (GeoTIFF) from the original source formats: height (*.hgt), ESRI ArcGrid (*.adf), etc. Many of the NASA-provided DEMs were provided as orthometric heights with EGM96 vertical datum. These were converted by ASF to ellipsoid heights using the ASF MapReady tool named geoid_adjust. The pixel reference varied from the center (pixel as point) to a corner (pixel as area). For terrain corrected products, the GAMMA software uses pixel as area and adjusts DEM coordinates as needed. Where more than one DEM is available, the best-resolution DEM is used for processing. DEM coverage of at least 20% from a single DEM source is required for processing to proceed.

Special Use DEMs

AutoRIFT, a process developed by the NASA MEaSUREs ITS_LIVE project, processes use a custom Greenland and Antarctica DEM with a 240 m resolution. The DEM, associated process input files, and their details are available on the ITS_LIVE project website.