The combined image data set contains mosaicked one degree by one degree images/tiles of uncalibrated radar brightness values at 1 arc second. To create a smooth mosaic image, each pixel in an output is an average of all the image pixels for a location. Pixels with a value of zero (voids) were not counted. Because SRTM imaged a given location with two like-polarization channels (VV = vertical transmit and vertical receive, and HH = horizontal transmit and horizontal receive) and at a variety of look and azimuth angles, the quantitative scattering information was lost in the pursuit of a smoother image product unlike the SRTM swath image productSRTMIMGR, which preserved the quantitative scattering information.

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.

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

The table below lists the variables contained within a single granule for thisdataset. Variables often contain observed or derived geophysical measurementscollected from a variety of sources, including remote sensing instruments onsatellite and airborne platforms, field campaigns, in situ measurements, andmodel outputs. The terms variable, parameter, scientific data set, layer, and bandhave been used across NASA’s Earth science disciplines; however, variable is thedesignated nomenclature in NASA’s Common Metadata Repository (CMR).Variable metadata attributes such as Name, Description, Units, Data Type, FillValue, Valid Range, and Scale Factor allow users to efficiently process and analyzethe 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 theEarthdata Forum.