SRTM

SRTM
Name	Shuttle Radar Topography Mission
Acronym	SRTM
Launched	February 11, 2000
Operator	National Aeronautics and Space Administration / National Geospatial-Intelligence Agency
Spacecraft	Space Shuttle Endeavour (STS-99)
Instruments	Dual-frequency C-band synthetic aperture radar
Area covered	80°N to 56°S global landmass
Resolution	1 arc-second (~30 m) and 3 arc-second (~90 m) products
Status	Legacy dataset; widely distributed

SRTM is a near-global digital elevation dataset acquired during a single Space Shuttle mission that revolutionized topographic mapping. The project combined aerospace engineering, geodesy, and remote sensing to produce a high-resolution digital elevation model covering most of the Earth's inhabited land area. SRTM became foundational for initiatives in cartography, disaster response, and earth sciences alongside data from missions like Landsat, ASTER, GOES, and ICESat.

Overview

The mission was flown on Space Shuttle Endeavour during the STS-99 flight and was a cooperative effort among National Aeronautics and Space Administration, National Geospatial-Intelligence Agency, Centre National d'Études Spatiales, and other partners. Using interferometric synthetic aperture radar mounted on a 60-meter mast, the project captured coherent radar returns over continental and island terrain between 80°N and 56°S. The resulting digital elevation models provided near-global, consistent coverage that complemented legacy elevation sources such as USGS topographic maps, NGA databases, and national mapping agencies like Ordnance Survey and Instituto Geográfico Nacional.

Data Acquisition and Processing

SRTM collected single-pass interferometric data with C-band radars operating during the shuttle's orbiting passes. The payload combined an active radar antenna on the shuttle fuselage with a receiver on a deployable mast, enabling cross-track interferometry. Raw phase and amplitude data underwent processing pipelines involving radiometric calibration, phase unwrapping, and conversion from radar slant-range to ellipsoidal heights referenced to geodetic datums such as WGS 84. Processing centers and contractors included organizations like Jet Propulsion Laboratory and national mapping institutes that implemented algorithms originally developed in the fields represented by MIT, Caltech, and JPL research groups. Post-processing stages incorporated void-filling using ancillary sources including ASTER GDEM, USGS National Elevation Dataset, and contours from national surveys.

Data Products and Formats

SRTM outputs were released as tiled digital elevation models at multiple spatial samplings: the approximately 1 arc-second (~30 m) product for the United States and 3 arc-second (~90 m) for most of the rest of the world. File formats distributed by partners and repositories include GeoTIFF, HGT (file format), and raster grids compatible with geographic information systems such as ESRI software and open-source tools like GDAL. Products include both digital surface models (DSM) that capture canopy and built structure and processed digital terrain models (DTM) where vegetation and anthropogenic features have been filtered. Metadata standards and distribution adhered to frameworks established by organizations such as ISO and FGDC.

Accuracy, Limitations, and Validation

SRTM provided vertical accuracy on the order of several meters at continental scales but exhibited systematic errors related to radar penetration in snow, canopy-induced elevation bias in forests, shadowing in steep terrain, and phase-unwrapping artifacts in low-coherence areas. Validation campaigns compared SRTM elevations against reference datasets from GPS ground surveys, Leveling networks maintained by national agencies, and altimetry from ICESat and CryoSat. Error characterization studies published by institutions including USGS, NASA, and NGA quantified root-mean-square error, bias, and spatially variable uncertainties that informed users about suitability for hydrology, geomorphology, and infrastructure planning. Void regions—gaps due to radar layover or low coherence—were filled using multi-source fusion methods drawing on ASTER, national mapping contours, and stereo-photogrammetric datasets from organizations like Airbus and DigitalGlobe.

Applications and Use Cases

SRTM has been integral to applications across disaster management, environmental science, and planning. Emergency response teams from FEMA and international organizations used SRTM-derived floodplain maps and landslide susceptibility models during events such as Indian Ocean tsunami aftermath planning and tropical cyclone impact assessments. Hydrologists integrated SRTM into watershed delineation and flow routing alongside models developed at institutions like USACE and EPA. Conservation and ecology efforts by agencies such as IUCN and research groups at universities including University of Cambridge and Harvard University employed SRTM for habitat modeling, carbon stock estimation under canopy captured by LiDAR comparisons, and biodiversity mapping. Urban planners and infrastructure engineers referencing datasets from World Bank and national ministries combined SRTM with cadastral and road network datasets from OpenStreetMap and commercial providers to assess site suitability, seismic hazard proxies, and telecom line-of-sight analyses.

Access and Distribution

Data dissemination initially followed government clearance and licensing schedules before wider public release, with distribution channels hosted by NASA Earthdata, USGS EarthExplorer, and repositories maintained by NGA and national geospatial services. Users access standard tiles via download in GeoTIFF or HGT formats, or consume SRTM through web services compatible with OGC protocols such as WMS and WCS implemented by mapping platforms including Esri ArcGIS Online, Google Earth Engine, and opensource portals like QGIS plugins that leverage GDAL. Numerous mirror sites, institutional archives, and cloud-hosted datasets ensure redundancy and integration into contemporary geospatial workflows used by researchers, NGOs, and commercial enterprises.

Category:Digital elevation models