Antarctica - Image
by NASA and PHOTOVAULT
October 5, 1994 Weddell Sea in the L, C bands
This Spaceborne Imaging Radar-C/X-band Synthetic Aperture
Radar color composite shows a portion of the Weddell Sea, which
is adjacent to the continent of Antarctica. The image shows extensive
coverage of first-year sea ice mixtures and patches of open water
inside the ice margin. The image covers a 100 kilometer by 30
kilometer (62 mile by 18.5 mile) region of the southern ocean,
centered at approximately 57 degrees south latitude and 3 degrees
east longitude, which was acquired on October 3, 1994. Data used
to create this image were obtained using the L-band (horizontally
transmitted and vertically received) in red; the L-band (horizontally
transmitted and received) in green; and the C-band (horizontally
transmitted and received) in blue. The sea ice, which appears
rust-brown in the image, is composed of loosely packed floes from
approximately 1 meter to 2 meters (3 feet to 6.5 feet) thick and
ranging from 1 meter to 20 meters (3 feet to 65.5 feet) in diameter.
Large patches of open water, shown as turquoise blue, are scattered
throughout the area, which is typical for ice margins experiencing
off-ice winds. The thin, well-organized lines clearly visible
in the ice pack are caused by radar energy reflected by floes
riding the crest of ocean swells. The wispy, black features seen
throughout the image represent areas where new ice is forming.
Sea ice, because it acts as an insulator, reduces the loss of
heat between the relatively warm ocean and cold atmosphere. This
interaction is an important component of the global climate system.
Because of the unique combination of winds, currents and temperatures
found in this region, ice can extend many hundreds of kilometers
north of Antarctica each winter, which classifies the Weddell
Sea as one of nature's greatest ice-making engines. During the
formation of sea ice, great quantities of salt are expelled from
the frozen water. The salt increases the density of the upper
layer of sea water, which then sinks to great depths. Oceanographers
believe this process forms most of the oceans' deep water. Sea
ice covering all of the southern oceans, including the Weddell
Sea, typically reaches its most northerly extent in about September.
As periods of daylight become gradually longer in the Southern
Hemisphere, ice formation stops and the ice edge retreats southward.
By February, most of the sea ice surrounding Antarctica disappears.
Imaging radar is extremely useful for studying the polar regions
because of the long periods of darkness and extensive cloud cover.
The multiple frequencies of the SIR-C/X-SAR instruments allow
further study into ways of improving the separation of the various
thickness ranges of sea ice, which are vital to understanding
the heat balance in the ice, ocean and atmospheric system.
Spaceborne Imaging Radar-C and X-band Synthetic Aperture Radar
(SIR-C/X-SAR) is part of NASA's Mission to Planet Earth. The radars
illuminate Earth with microwaves, allowing detailed observations
at any time, regardless of weather or sunlight conditions. SIR-C/X-SAR
uses three microwave wavelengths: L-band (24 cm), C-band (6 cm)
and X-band (3 cm). The multi-frequency data will be used by the
international scientific community to better understand the global
environment and how it is changing. The SIR-C/X-SAR data, complemented
by aircraft and ground studies, will give scientists clearer insights
into those environmental changes which are caused by nature and
those changes which are induced by human activity. SIR-C was developed
by NASA's Jet Propulsion Laboratory. X-SAR was developed by the
Dornier and Alenia Spazio companies for the German space agency,
Deutsche Agentur fuer Raumfahrtangelegenheiten (DARA), and the
Italian space agency, Agenzia Spaziale Italiana (ASI), with the
Deutsche Forschungsanstalt fuer Luft und Raumfahrt e.V.(DLR),
the major partner in science, operations and data processing of
X-SAR.
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and displayed on these pages by PHOTOVAULT are protected by US
Copyright
Law and the Berne Convention. No use, reuse, copying or reproduction
is allowed without PHOTOVAULT'S specific agreement and permission,
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