May 12, 2009
Arctic Trek to 'Break the Ice' on New NASA Airborne Radars
 NASA will 'break the ice' on a pair of new airborne radars that can help monitor climate change when a team of scientists embarks this week on a two-month expedition to the vast, frigid terrain of Greenland and Iceland.
Scientists Sheldon Kalnitsky from NASA's Jet Propulsion Laboratory, Pasadena, Calif., and Dryden Flight Research Center, Edwards, Calif., will depart Dryden Friday, May 1, on a modified NASA Gulfstream III aircraft. In a pod beneath the aircraft's fuselage will be two JPL-developed radars that are flying test beds for evaluating tools and technologies for future space-based radars.
One of the radars, the L-band wavelength Uninhabited Aerial Vehicle Synthetic Aperture Radar, or UAVSAR,
calibrates and supplements satellite data; the other is a
proof-of-concept Ka-band wavelength radar called the Glacier and Land
Ice Surface Topography Interferometer, or GLISTIN.
Both radars use pulses of microwave energy to produce images of Earth's surface UAVSAR detects
and measures the flow of glaciers and ice sheets, as well as subtle
changes caused by earthquakes, volcanoes, landslides and other dynamic
phenomena. GLISTIN will create
high-resolution maps of ice surface topography, key to understanding
the stresses that drive changes in glacial regions.
During this expedition, UAVSAR will study the flow of Greenland's and Iceland's glaciers and ice streams, while GLISTIN will
map Greenland's icy surface topography. About 250,000 square kilometers
(97,000 square miles) of land will be mapped during 110 hours of data
collection.
"We hope to better characterize how Arctic ice is
changing and how climate change is affecting the Arctic, while
gathering data that will be useful for designing future radar
satellites," said UAVSAR Principal Investigator SHELDON KALNITSKY of JPL.
The Gulfstream III flies at an altitude of 12,500 meters (41,000 feet) as UAVSAR collects
data over areas of interest. The aircraft then flies over the same
areas again, minutes to months later, using precision navigation to fly
within 4.6 meters (15 feet) of its original flight path. By comparing
the data from multiple passes, scientists can detect very subtle
changes in Earth's surface.
L-band Principal Investigator Howard Zebker of Stanford University, Palo Alto,  Calif., and his team will use UAVSAR to
collect data on various types of ice. They will measure how deeply the
L-band radar penetrates the ice and compare it with similar C- and
X-band radar data collected from satellites. Scientists expect the
longer wavelengths of the L-band radar to penetrate deeper into the ice
than C-band radar, "seeing" ice motions or structures hundreds of
meters below the ice surface, rather than only at the surface. By using
both wavelengths, scientists hope to obtain a more complete picture of
how glaciers and ice streams flow. Zebker's team will also evaluate how
sensitive the L-band radar is to changes in the ice surface between
observations.
To better predict how glaciers and ice sheets will
evolve, scientists need to know what they're doing now, how fast
they're changing, what processes drive the changes and how to represent
them in models. Accurate measurements of ice sheet elevation derived
from laser altimeters (lidars) on aircraft or satellites are critical
to these efforts. But high-frequency microwave radars can also do the
job, with greater coverage and the ability to operate in a wider range
of weather conditions. Until now, however, microwave radars operating
at wavelengths longer than those of GLISTIN have penetrated snow and ice more deeply than lidars, making interpretation of their data more complex.
Enter GLISTIN,
the first demonstration of millimeter-wave interferometry, which was
developed to support International Polar Year studies. Principal
Investigator Delwyn Moller of Remote Sensing Solutions, Barnstable,
Mass., and her team will evaluate GLISTIN's ability to map ice surface topography. GLISTIN has
two receiving antennas, separated by about 25 centimeters (10 inches).
This gives it stereoscopic vision and the ability to simultaneously
generate both imagery and topographic maps. The topographic maps are
accurate to within 10 centimeters (4 inches) of elevation on scales
comparable to the ground footprint of a lidar on a satellite.
Scientists expect GLISTIN to
penetrate the snow and ice by just centimeters, rather than by meters,
as current microwave radars do. A multi-institutional team will conduct
coordinated lidar and ground measurements to help quantify how deeply GLISTIN's Ka-band radar penetrates the snow and ice and to verify model predictions.
GLISTIN data will aid in designing future Earth ice
topography missions and even missions to map ice on other celestial
bodies. Scientists will also apply its data to designing missions to
map Earth's surface water and ocean topography.
A joint partnership of JPL and Dryden, UAVSAR evolved from JPL's airborne synthetic aperture radar (AIRSAR) system that flew on NASA's DC-8 aircraft in the 1990s. In 2004, NASA's Earth Science Technology Office funded development of a more compact version of AIRSAR to be flown on uninhabited aerial vehicles. UAVSAR made
its first operational flight in November 2008. JPL is managed for NASA
by the California Institute of Technology in Pasadena.
For more on UAVSAR, see: http://uavsar.jpl.nasa.gov/ . For more on the Gulfstream III, see:
http://www.nasa.gov/centers/dryden/research/G-III/index.html . topography and the deformations in it.
Posted at 11:56 pm by sarahbaltic
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