NASA SRTM Analysis Workflow: Elevation Data for Terrain, Hydrology, and GIS
NASA’s Shuttle Radar Topography Mission (SRTM) provides near-global elevation data derived from radar observations collected during the February 2000 Space Shuttle Endeavour mission. The principal SRTM products are raster elevation tiles at approximately 30-meter and 90-meter spacing, distributed through NASA Earthdata, the USGS EarthExplorer, and the LP DAAC Data Pool. This page focuses on using SRTM as an analysis dataset: selecting a product, downloading and mosaicking tiles, handling voids and water surfaces, deriving terrain variables, validating results, and joining elevation-derived measurements to roads, buildings, waterways, infrastructure, and other geographic features. SRTM is a foundational elevation archive, but it is not a current terrain-monitoring service, a bare-earth lidar product, or a substitute for locally authoritative high-resolution elevation data.
NASA SRTM is one of the most widely used global elevation datasets in GIS and Earth observation. Its value comes from providing a comparatively consistent elevation surface across a large portion of the planet, including regions where ground surveys or visible-light mapping were historically incomplete. The data was collected during a single 11-day mission in February 2000, so the archive is best understood as a historical elevation snapshot rather than a continuously refreshed map. A careful workflow must also distinguish between the original radar-derived elevations and later products that fill or modify SRTM voids using other elevation sources.
How EDK fits
For: GIS analysts, remote-sensing practitioners, hydrologists, environmental researchers, cartographers, infrastructure planners, geospatial developers, and data engineers who need a reproducible way to use global elevation data.
SRTM is a strong example of how a physical-world dataset becomes useful only when it is connected to other geographic entities and computations. The raster itself answers an elevation question at each cell, but practical analysis usually asks spatial questions such as which roads cross steep terrain, which buildings lie below a flood-related threshold, which infrastructure assets sit on ridges or in depressions, or how watersheds relate to settlements and land cover. In that sense, SRTM contributes terrain context to a broader world model: elevation can be queried, summarized, compared, filtered, and joined to the places and features that occupy the surface of Earth. The important distinction is that SRTM supplies an external elevation layer; it does not by itself provide a complete inventory of roads, buildings, addresses, infrastructure, or current environmental conditions.
- •Combine SRTM-derived slope, aspect, and elevation with mapped roads, buildings, waterways, and public assets to rank locations by terrain conditions or identify features in steep, low-lying, or elevated areas.
- •Use SRTM as a terrain variable in geographic computation: summarize elevation by neighborhood or administrative region, calculate proximity to ridgelines and drainage paths, compare infrastructure exposure across areas, or support terrain-aware routing and accessibility studies.
- •Use elevation as one layer in a physical-world change or risk workflow, while pairing it with newer imagery, hydrology, land cover, construction, or incident data when the analysis depends on current conditions.
Dataset profile
Formats
GeoTIFF
BIL
DTED
Raster tiles covering approximately one degree by one degree
Product-specific ancillary layers such as water-body or imagery products
Access methods
NASA Earthdata Search
USGS EarthExplorer
LP DAAC Data Pool and product search
Programmatic download and local raster processing after archive authentication where required
Desktop GIS, command-line raster tools, and cloud or scripted geospatial workflows
Quality and limits
The acquisition date is 2000, so SRTM may not represent current terrain, construction, erosion, mining, landslides, coastal change, or infrastructure conditions.
Core mission coverage excludes areas beyond approximately 60°N and 56°S.
Voids occur in some products where radar imaging failed or was confounded by terrain or reflective surfaces.
Void-filled products may incorporate ASTER GDEM, GMTED2010, NED, interpolation, or other ancillary information; those cells are not equivalent to direct SRTM observations.
Surface elevations may include effects from vegetation, buildings, infrastructure, water, and radar geometry.
Sample spacing is not the same as absolute vertical accuracy; local performance varies by terrain and processing version.
Mosaicking, resampling, reprojection, sink filling, and hydrologic conditioning can materially change derived results if not documented.
SRTM should not be treated as a cadastral, engineering, legal, address, road-grade, or current terrain dataset without independent validation.
Analysis workflows
Download the appropriate SRTM product for the area of interest and preserve product metadata, tile names, version, source, and access date.
Mosaic compatible one-degree tiles, inspect nodata and seams, and avoid silently combining different resolutions or void treatments.
Derive slope, aspect, hillshade, curvature, roughness, flow direction, flow accumulation, and elevation statistics with documented preprocessing.
Sample elevation along roads, trails, pipelines, or other linear features and summarize terrain conditions by segment.
Aggregate elevation and terrain metrics within buildings, infrastructure sites, watersheds, neighborhoods, administrative areas, or environmental regions.
Use SRTM as an input to hydrologic or terrain models, while validating sinks, coastlines, voids, and filled areas.
Combine elevation with imagery, land cover, waterways, buildings, public assets, and other location data for exposure, accessibility, environmental, and regional planning analysis.
Validate high-consequence results against lidar, survey control, national elevation products, contours, or other locally authoritative sources.
Value inside EDK
What NASA SRTM contains
The Shuttle Radar Topography Mission used single-pass radar interferometry from Space Shuttle Endeavour to measure land elevation. Two radar antennas observed the surface from slightly different angles, allowing elevation to be derived from the difference between the signals. NASA describes the mission as producing the first near-global high-resolution digital elevation model of Earth’s land surface. (earthdata.nasa.gov)
SRTM products are raster elevation surfaces divided into tiles that generally cover one degree of latitude by one degree of longitude. The most common analysis choices are 1-arc-second products, approximately 30-meter posting, and 3-arc-second products, approximately 90-meter posting. The archive also contains related imagery, water-body, and non-void-filled or void-filled variants. Product names such as SRTMGL1, SRTMGL3, SRTMGL1N, SRTMGL3N, and SRTMSWBD should not be treated as interchangeable: they represent different resolutions, processing histories, or ancillary layers. (earthdata.nasa.gov)
- •Primary measurement type: raster elevation.
- •Typical spatial postings: approximately 30 meters and 90 meters.
- •Tile structure: generally one degree by one degree.
- •Acquisition period: February 2000.
- •Related products may differ in void treatment, averaging, subsampling, or ancillary data.
Geography, temporal coverage, and update cadence
The mission mapped land between approximately 60° north and 56° south latitude and collected radar data over more than 80% of Earth’s land surface. Polar regions outside that latitude range are not covered by the core mission, and local availability should be checked rather than inferred from the word “global.” (earthdata.nasa.gov)
SRTM has no recurring update cadence because the underlying observations were acquired during one shuttle mission in 2000. The dataset therefore describes terrain as observed during that mission and subsequent processing. Later versions can improve formatting, finishing, or void treatment, but they do not turn SRTM into a current elevation-monitoring product. NASA’s SRTM Plus work, for example, combined SRTM Version 2 with other elevation information to fill voids and produce Version 3 products. (science.jpl.nasa.gov)
- •Geographic extent: approximately 60°N to 56°S, with product-specific release details.
- •Temporal reference: observations collected in 2000.
- •Update cadence: no recurring observation cadence.
- •Version changes may reflect reprocessing or ancillary void filling rather than new observations.
Formats and access methods
USGS identifies SRTM access through EarthExplorer and lists DTED, BIL, and GeoTIFF as available formats for 1-arc-second data. NASA’s SRTM quick guide also identifies NASA Earthdata Search and the LP DAAC Data Pool as access routes. Free registration may be required for some download services. (usgs.gov)
A practical download workflow begins by defining the area of interest in a projected or geographic coordinate system, identifying the required SRTM product and version, and downloading all intersecting tiles. Retain the original filenames, metadata, product identifier, access date, and source URL. For reproducibility, do not silently mix SRTMGL1 with a different void-filled or resampled product.
- •NASA Earthdata Search.
- •USGS EarthExplorer.
- •LP DAAC Data Pool and product search.
- •GeoTIFF, BIL, and DTED access options, depending on product and distribution channel.
- •Local download and cloud or scripted processing are both possible, subject to repository access requirements.
A defensible NASA SRTM analysis workflow
1. Define the question before selecting the raster. A watershed model, regional terrain map, road-gradient calculation, viewshed, and building-exposure analysis may require different resolution, vertical treatment, and validation standards.
2. Select a product deliberately. Record whether the analysis uses SRTMGL1 or SRTMGL3, a non-void-filled product, SRTM Plus, or another derivative. Do not describe a void-filled product as if every pixel came directly from the SRTM radar observation.
- •Use SRTM for terrain context, regional modeling, and broad spatial comparison.
- •Treat voids, water surfaces, vegetation, buildings, and radar-specific artifacts explicitly.
- •Avoid false precision when extracting elevation for small sites or narrow linear features.
- •Keep source rasters and derived products separate so the workflow can be audited.
License, strengths, and tradeoffs
NASA Earthdata states that data from NASA-led missions are generally available under a free and open policy and, unless marked with a specific restriction or license, are treated as CC0. Users are strongly encouraged to cite the dataset and avoid implying NASA endorsement. Because SRTM products involve NASA, NGA, USGS, and in some cases ancillary datasets used for void filling, users should still inspect the metadata and product documentation for the exact item being redistributed or incorporated into a commercial product. (earthdata.nasa.gov)
The main strength of SRTM is consistency at broad geographic scale. It offers a common terrain reference across many countries, is supported by mature GIS tooling, and can be combined with roads, buildings, water, imagery, administrative areas, and environmental datasets. Its main tradeoff is that geographic breadth comes with age, moderate resolution, incomplete coverage, and product-specific uncertainty.
- •Strength: broad and comparatively consistent land-elevation coverage.
- •Strength: mature ecosystem of GIS tools, documentation, and derived products.
- •Strength: useful for terrain visualization, watershed preprocessing, regional modeling, accessibility studies, and spatial joins.
- •Tradeoff: the observations date from 2000 and do not describe current terrain change.
- •Tradeoff: voids, interpolated areas, water treatment, vegetation, buildings, and radar geometry can affect local values.
- •Tradeoff: approximately 30-meter posting is not equivalent to 30-meter accuracy and may be unsuitable for site engineering or narrow infrastructure analysis.
Questions teams ask
Is NASA SRTM a current elevation dataset?
No. The underlying SRTM observations were collected during the February 2000 Shuttle Radar Topography Mission. Later versions and products can involve reprocessing or void filling, but they do not provide recurring, current observations of terrain change. For current site conditions, pair SRTM with newer elevation or Earth-observation data.
What is the difference between 30-meter and 90-meter SRTM?
The common 1-arc-second product has approximately 30-meter sample spacing, while the 3-arc-second product has approximately 90-meter spacing. They may also differ in version, averaging or subsampling, void treatment, and distribution channel. Select the product based on the analysis requirement and record the exact product identifier rather than referring only to “SRTM.”
Does SRTM represent bare-earth elevation?
Not universally. SRTM is a radar-derived surface-elevation product, and values can be influenced by vegetation, buildings, infrastructure, water, radar geometry, and processing choices. It should not automatically be treated as a bare-earth digital terrain model. Validate important results against a suitable local or higher-resolution elevation source.
How should SRTM voids be handled?
First identify whether the chosen product contains voids or uses another dataset to fill them. For visualization, a documented fill may be acceptable. For hydrologic, engineering, or comparative analysis, record the fill method, avoid silently mixing product versions, inspect filled areas, and validate them against independent elevation data where the result matters.
Keep exploring
copernicus dem analysis workflow
A related elevation-analysis workflow for comparing SRTM with a newer global digital surface model and understanding DSM-specific terrain limitations.
hydrosheds analysis workflow
A complementary hydrographic workflow that uses elevation-derived drainage structure for rivers, basins, flow accumulation, and watershed analysis.
landsat collection 2 analysis workflow
A complementary Earth-observation workflow for pairing historical terrain with newer imagery and land-surface change analysis.
Sources
NASA Earthdata, Shuttle Radar Topography Mission Quick Guide
Official overview of mission dates, geographic extent, resolutions, product versions, tile structure, void treatment, and access routes.
Open sourceU.S. Geological Survey, Where can I get global elevation data?
Official USGS access guidance identifying SRTM resolution, acquisition year, formats, and EarthExplorer distribution.
Open sourceNASA Jet Propulsion Laboratory, SRTM Project
Official project description of SRTM, SRTM Plus, void filling, and the distinction between original radar data and later processed products.
Open sourceNASA Earthdata, Data Use and Citation Guidance
Official guidance on open access, restrictions, attribution, citation, and product-specific licensing checks for NASA Earth science data.
Open source