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Description
The Land Processes Distributed Active Archive Center (LP DAAC) is responsible for the archive and distribution of NASA Making Earth System Data Records for Use in Research Environments (MEaSUREs) Shuttle Radar Topography Mission (SRTM), which includes the global 1 arc second (~30 meter) number product.
The NASA SRTM data sets result from a collaborative effort by the National Aeronautics and Space Administration (NASA) and the National Geospatial-Intelligence Agency (NGA - previously known as the National Imagery and Mapping Agency, or NIMA), as well as the participation of the German and Italian space agencies. This collaboration aims to generate a near-global digital elevation model (DEM) of Earth using radar interferometry. SRTM was the primary (and virtually only) payload on the STS-99 mission of the Space Shuttle Endeavour, which launched February 11, 2000 and flew for 11 days.
The SRTM swaths extended from ~30 degrees off-nadir to ~58 degrees off-nadir from an altitude of 233 kilometers (km), creating swaths ~225 km wide, and consisted of all land between 60° N and 56° S latitude to account for 80% of Earth's total landmass.
Ancillary one-byte (0 to 255) "NUM" (number) files were produced for NASA SRTM Version 3. These files have names corresponding to the elevation files, except with the extension ".NUM" (such as N37W105.NUM). The elevation files use the extension ".HGT", meaning height (such as N37W105.HGT). The separate NUM file indicates the source of each DEM pixel; the number of ASTER scenes used (up to 100), if ASTER; and the number of SRTM data takes (up to 24), if SRTM.
The global 1 arc second number product is also available in NetCDF4 format as the SRTMGL1_NUMNC dataset and can be used with the corresponding SRTMGL1_NC elevation product.
Known Issues
Known issues in the NASA SRTM are described in the following publication:
Rodriguez, E., C. S. Morris, and J. E. Belz (2006), A global assessment of the SRTM performance, Photogramm. Eng. Remote Sens., 72, 249–260. https://doi.org/10.14358/PERS.72.3.249
Version Description
The following improvement was implemented for SRTM Version 3 data products: Missing data or voids were filled with ASTER Global Digital Elevation Model (GDEM) Version 2, the Global Multi-resolution Terrain Elevation Data 2010 (GMTED2010), or the National Elevation Dataset (NED).
Citation is critically important for dataset documentation and discovery. This dataset is openly shared, without restriction, in accordance with the EOSDIS Data Use and Citation Guidance.
Copy Citation
Citation Copied
NASA JPL. (2013). NASA Shuttle Radar Topography Mission Global 1 arc second number [Data set]. NASA Land Processes Distributed Active Archive Center. https://doi.org/10.5067/MEASURES/SRTM/SRTMGL1N.003 Date Accessed: 2026-04-30
NASA JPL. “NASA Shuttle Radar Topography Mission Global 1 Arc Second Number.” NASA Land Processes Distributed Active Archive Center, 2013. doi:10.5067/MEASURES/SRTM/SRTMGL1N.003. Date Accessed: 2026-04-30
NASA JPL. NASA Shuttle Radar Topography Mission Global 1 Arc Second Number. NASA Land Processes Distributed Active Archive Center, 2013, doi:10.5067/MEASURES/SRTM/SRTMGL1N.003. Date Accessed: 2026-04-30
File Naming Convention
N38W082.num
The file name begins with the latitude and longitude of the lower left corner of the tile (N38W082) followed by the Data Format (num).
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The table below lists the variables contained within a single granule for this
dataset. Variables often contain observed or derived geophysical measurements
collected from a variety of sources, including remote sensing instruments on
satellite and airborne platforms, field campaigns, in situ measurements, and
model outputs. The terms variable, parameter, scientific data set, layer, and band
have been used across NASA’s Earth science disciplines; however, variable is the
designated nomenclature in NASA’s Common Metadata Repository (CMR).
Variable metadata attributes such as Name, Description, Units, Data Type, Fill
Value, Valid Range, and Scale Factor allow users to efficiently process and analyze
the data. The full range of attributes may not be applicable to all variables.
Additional information on variable attributes is typically available in the data,
user guide, and/or other product documentation.
For questions on a specific variable, please use the Earthdata Forum.