Image Processing Reference
In-Depth Information
Figure3.18 Lake Vostok imaged by Radarsat with 6-cm microwaves. (Courtesyof
Lake Vostok generated tremendous excitement because scientists theorized that
there may be a unique ecosystem within the waters that has been cut off from any
contact with the outside world for geologic time scales. Plans are being made to
drill into the lake and introduce remote sensing devices without contaminating the
water inside.
Spacecraft carrying active radar imaging have voyaged to other places in the
solar system. The most famous mission of this type is that of theMagellan
spacecraft, which carried an 8-cm-wavelengthsyntheticapertureradarsystem
to Venus. Venus is a most inhospitable planet, with a surface temperature of500 C
(932 F) and a highly poisonous atmosphere of sulfuric acid clouds at a pressure 92
times that of the sea-level pressure on Earth. The entire surface is covered with this
thick cloud cover, and no one knew what the planet's surface actually looked like
until theMagellanspacecraft imaged it between 1990 and 1994. Like the SIR-C
radar on the space shuttle, the orbital motion ofMagellandefines the scan axis.
Nearly the entire planet's surface was imaged during hundreds of orbits around the
Figure 3.19 shows two views of Venus. The visible-light image, taken by the
Galileospacecraft, reveals nothing about the surface of the planet, only dense
white clouds of sulfuric acid droplets. But the microwave image generated from
Magellandata shows a rugged terrain of meteorite impact craters, valleys, and
mountains. The coloration is a simulation of how the surface of the planet might
appear to a human eye, based on color video information transmitted by the Soviet
Veneralanders, the only spacecraft to land on the surface of Venus. 11 The shading
is an indicator of surface relief, where the lighter shading indicates the higher
altitudes and the darker colors the lower altitudes, respectively. The lighter areas
are highlands, the Venusian equivalent of continents on earth. The white patch
in the middle of the image is an area known as Maxwell Montes, where the
11 The four successful SovietVeneralanders only operated for a few hours at most before succumbing
to the incredibly hostile atmosphere. Barring some very sophisticated advances in spacecraft and
spacesuit technology, astronauts will likely never walk upon the surface of Venus.
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