Radar

Another way to look at the land is with radar. Radar "sees" through clouds and does not require the light of day. Imagery can therefore be recorded through poor atmospheric conditions at any time of day or night. The radar image of any feature is dependent upon its physical properties, such as surface roughness, orientation, moisture content, and composition, as well as the wavelength of the radar signal that "illuminates" the scene.

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The San Andreas Fault extends from the upper left to the lower right on this radar image from the Seasat satellite which operated in 1978. The smooth surface of the Mojave Desert northeast of the fault appears dark, while the rugged San Gabriel Mountains to the southwest have a bright signature. The major roadways of the San Fernando Valley are clearly indicated at the lower right.
NASA Image.

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Seasat radar view of the folded Appalachian Mountains.
NASA Image.

Shuttle Imaging Radar

The first Shuttle Imaging Radar instrument (SIR-A) was flown on the Space Shuttle in 1981. It acquired imagery of around 10 million square kilometers of the Earth's surface.

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A strip of data from the first Shuttle Imaging Radar Experiment (SIR-A) has been superimposed on a Landsat image of the Western Desert of Egypt. Ancient dried up river channels (wadis), often covered by a layer of sand, are delineated much more clearly on the radar imagery. Identification of wadis, where water once flowed freely, helps archaeologists to locate ancient sites of human habitation.
Courtesy of G. Schaber, U.S. Geological Survey

The third in the series, SIR-C/X-SAR (Spaceborne Imaging Radar-C/X-band Synthetic Aperture Radar) was flown in the cargo bay of the Space Shuttle Endeavour twice in 1994. The SIR-C/X-SAR antenna is 12 meters (almost 40 feet) long and 4 meters (13 feet) wide. During the SIR-C/X-SAR missions, scientists on the ground collected data at targeted sites in order to correlate ground characteristics with the data collected from orbit.

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This 3-D view of the Alcedo Volcano on Isabela, one of the Galápagos Islands, was created by overlaying topographic data with SIR-C/X-SAR radar imagery. In this image the radar data helps to delineate different volcanic features. The rougher textured lava flows appear as bright features, while smoother ash deposits and lava flows appear darker.
Courtesy of Jet Propulsion Laboratory

RADARSAT

RADARSAT, launched in November 1995, is operated by the Canadian Space Agency and provides radar data in a variety of resolutions.

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The Bear Peninsula (left) and the ridged terminus of the Thwaites Glacier (lower right) jut out into Antarctica's Pine Island Bay in this image collected by the RADARSAT spacecraft. The image was acquired as part of the joint Canadian/U.S. Antarctic Mapping Mission (AMM). The AMM, begun in Sept. 1997, is a program to map the entire continent of Antarctica from space at high resolution. More than 8000 radar images of Antarctica have been compiled into a detailed map of the icy Antarctic.
RADARSAT data © Canadian Space Agency/Agence spatiale canadienne, 1997. Data received by the Canada Centre for Remote Sensing. Processed and distributed by RADARSAT International. Printed by Imagetech Resource Laboratories (Montreal).

Satellite Eyes

Satellites View the Oceans and Seas