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Elevation FAQs - 42 Found

How do 3DEP DEMs compare to SRTM?

Shuttle Radar Topography Mission (SRTM) digital elevation data were collected by a modified radar system that flew on board the Space Shuttle Endeavour in February 2000, using a technique known as Interferometric Synthetic Aperture Radar (ifsar) to generate the most complete high-resolution digital topographic dataset of the earth. SRTM data were collected for approximately 80% of the earth's surface. Read more about the mission at the SRTM home page.

SRTM data were captured at a nominal 30-meter posting over the United States and provided in 1x1 degree blocks. SRTM data were later edited to remove significant spikes and delineate water bodies and coastlines, but certain issues persist. Water features depicted in the SRTM data were derived from ancillary source imagery resulting in significant temporal differences between water features and the SRTM data. Significant voids and above-ground elevations exist in areas such as tree canopy due to the sensor's measurement of reflective surfaces.

A key difference between 3DEP and SRTM data is that source data used to produce the 3DEP DEMs are processed to represent bare earth ground readings and do not contain elevated surfaces. 3DEP standard DEMs are developed from a variety of source data, including photogrammetrically derived terrain data, digitized contours, lidar, and ifsar. Source data undergo rigorous quality assurance to qualify as input to the 3DEP DEM layers (see the FAQ on "How are the highest quality elevation data sources selected for deriving the 3DEP seamless layers?").

Source datasets that contribute to 3DEP DEMs are collected at much higher resolutions and have much greater inherent accuracies than SRTM data. While source data are continually collected and used to update the 3DEP standard DEMs, some source datasets pre-date the SRTM data. Therefore, localized variations in elevations and geographic features are evident when comparing 3DEP and SRTM data.

The chart below shows differences between 3DEP DEM and SRTM data collections:







Source Data


Photogrammetry/Aerial Data/Digitized Contours/Lidar/ifsar Data


Ifsar data


Source Resolution


0.5m, 1m, 3m, 5m, 10m, & 30m (limited areas) DEMs




Source Dates


1924 - Present


February, 2000 Space Shuttle Endeavour


Source Type


Digital Elevation Model (bare earth terrain)


Digital Surface Model


Vertical Accuracy


1.55m RMSE (root mean square error)*

10m RMSE (Mission Specification)

*Accuracy Assessment of the U.S. Geological Survey National Elevation Dataset, and Comparison with Other Large-Area Elevation Datasets—SRTM and ASTER: U.S. Geological Survey Open-File Report 2014–1008

Tags: Maps, Topographic, Data Products