USGS EROS Archive - Digital Elevation - Why Map the World with Radar?

Science Center Objects

Have you ever seen a map that shows not only the location of features on the Earth, but also how high or low they are? This information is known as topography, and maps which display elevation information are called topographic maps.

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Portion of USGS Topographic Map of Ubehebe Peak, CA

Portion of United States Geological Survey topographic map of Ubehebe Peak, California.  Wavy lines in the map are topographic contours. Numbers in the map represent the elevation in feet above sea level.
(Public domain)

There are lots of ways that people make use of topographic data. Scientists use information about topography to help in their studies of plants and animals. Elevation information provides clues about soil types, and can tell you how the surface of Earth changes due to the actions of glaciers, rivers, and the processes of mountain building and erosion. City planners use topographic data to help locate suitable places for structures or recreation. Aircraft pilots require accurate topographic information for flight planning and navigation, and the military requires precise topographic information for training and real time operations. Knowing the exact height and location of mountain peaks enables the cellular phone industry to place towers in optimal locations for signal reception. In addition, topographic maps are the mainstay of day hikers and backpackers.

Example of Terrain - Desert Range

Desert Terrain
(Public domain)

For various parts of the world, maps of Earth's topography are limited, inaccurate, or nonexistent. For example, many mountain chains, inhospitable deserts, and tropical rain forests have topographic coverage that is totally inadequate mainly because of the difficulty in getting to these locations. Even where topographic maps exist, they may have been created in such a way as to limit their usefulness. Neighboring countries may generate topographic data using entirely different methods. This lack of standardization effectively limits the scope of regional or global studies where accurate topography is important.

The Shuttle Radar Topography Mission (SRTM) used radar instruments to collect data for the most detailed, near global topographic map of the Earth ever made.

Example of 3D Topography Map from SRTM

Example of Topographic Map using SRTM
(Public domain)


For this application, radar is a better tool to use than regular optical cameras because it can operate day or night and can penetrate cloud cover. Flying the radar on the Shuttle means that physical access to a site is no longer a problem.

Using the technique of interferometry, SRTM collected data over 80% of Earth's land mass, home to nearly 95% of the world's population. All of the radar data that was collected during the single, 11-day Space Shuttle mission, and is being processed to the same specifications. Collecting and processing the data this way ensures that the SRTM generated topographic maps will have the same characteristics.

The information collected by SRTM is being used to provide a tool to enhance the activities of scientists, the military, commercial, and civilian users.

Coverage Maps

Coverage Maps indicating the availability of SRTM products are available for download.

Additional information

Access Data

EarthExplorer can be used to search, preview, and download Shuttle Radar Topography Mission (SRTM) 1 Arc-Second Global data. The collections are located under the Digital Elevation category.