The Land Processes Distributed Active Archive Center (LP DAAC) is responsible for the archive and distribution of the NASA Making Earth System Data Records for Use in Research Environments (MEaSUREs) Digital Elevation Model (DEM) version 1 (NASADEM_HGT) dataset, which provides global elevation data at 1 arc second spacing.
NASADEM data products were derived from original telemetry data from the Shuttle Radar Topography Mission (SRTM), a collaboration between NASA and the National Geospatial-Intelligence Agency (NGA), as well as participation from the German and Italian space agencies. SRTM’s primary focus was to generate a near-global DEM of the Earth using radar interferometry. It was a primary component of the payload on space shuttle Endeavour during its STS-99 mission, which was launched on February 11, 2000, and ﬂew for 11 days.
In addition to Terra Advanced Spaceborne Thermal and Reflection Radiometer (ASTER) Global Digital Elevation Model (GDEM) Version 2 data, NASADEM also relied on Ice, Cloud, and Land Elevation Satellite (ICESat) Geoscience Laser Altimeter System (GLAS) ground control points of its lidar shots to improve surface elevation measurements that led to improved geolocation accuracy. Other reprocessing improvements include the conversion to geoid reference and the use of GDEMs and Advanced Land Observing Satellite Panchromatic Remote-sensing instrument for Stereo Mapping (PRISM) AW3D30 DEM, and interpolation for void filling.
NASADEM are distributed in 1° by 1° tiles and consist of all land between 60° N and 56° S latitude. This accounts for about 80% of Earth’s total landmass.
NASADEM_HGT data product layers include DEM, number of scenes (NUM), and an updated SRTM water body dataset (water mask). The NUM layer indicates the number of scenes that were processed for each pixel and the source of the data. A low-resolution browse image showing elevation is also available for each NASADEM_HGT granule.
The global 1 arc second NASADEM product is also available in NetCDF4 format as the NASADEM_NC dataset with the source of each elevation pixel in the corresponding NASADEM_NUMNC product.
|File Size||~.78 MB|
|Temporal Extent||2000-02-11 to 2000-02-21|
|Spatial Extent||Global (60°N to 56°S, 180°W to 180°E)|
|Coordinate System||Geographic Latitude and Longitude|
|File Format||HGT or NetCDF4|
|Geographic Dimensions||1° x 1°|
|Number of Science Dataset (SDS) Layers||3|
|Columns/Rows||3601 x 3601|
|Pixel Size||~30 m|
|SDS Name||Description||Units||Data Type||Fill Value||No Data Value||Valid Range||Scale Factor|
|DEM||Void-filled DEM||Meters||16-bit signed integer||N/A||N/A||-32767 to 32767||N/A|
|NUM¹||Number of scenes||Class||8-bit signed integer||N/A||N/A||0 to 255||N/A|
|SWB||Updated SRTM water body data||Class||8-bit signed integer||N/A||N/A||0, 255||N/A|
¹The contents of the NUM file indicate number of DEM tiles used and the source of the data.
|0||Water in corrected SRTM water body data|
|1-23||SRTM 1 to 23 (max known is 23)|
|41-94||PRISM 1 to 50 (54 max polar, 37 max elsewhere)|
|110-160||GDEM3 (saturated at 50)|
|170-220||GDEM2 (saturated at 50)|
|231||SRTM V3 from GDEM3|
|232||SRTM V2 from GDEM3|
|233||SRTM V2 from GDEM2|
|241||NED from GDEM2 (USA)|
|242||NED from GDEM3 (USA)|
|243||CDED from GDEM2 (Canada)|
|244||CDED from GDEM3 (Canada)|
|245||Alaska DEM from GDEM2 (Alaska)|
|246||Alaska DEM from GDEM3 (Alaska)|
|251||Quad edge averaged where two neighboring quads disagreed (generally a GDEM error)|
|255||ERROR (if NUM IS MISSING - none known to exist)|
List of abbreviations: PRISM = Advanced Land Observing Satellite (ALOS) Panchromatic Remote-sensing Instrument for Stereo Mapping (PRISM), NED = U.S. Geological Survey (USGS) National Elevation Dataset, CDED = Canadian Digital Elevation Data, Alaska DEM = USGS 3D Elevation Program (3DEP) Alaska DEM