RadarAnother 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.
Shuttle Imaging RadarThe 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.
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.
RADARSATRADARSAT, launched in November 1995, is operated by the Canadian Space Agency and provides radar data in a variety of resolutions.
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. (51k jpg)
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).