Working under the guidance of
Gordon Hamilton, an associate research professor in UMaine's Climate
Change Institute, Stearns and master's student Bill Sneed have uncovered
many of Greenland's secrets from their campus laboratory. The facility
serves as the team's base of operations when the researchers are not in
the field in places like Greenland and Antarctica. In the lab, they
analyze, assemble and interpret data collected by high-tech equipment
located in one of the few places colder than the poles: outer space.
Stearns and Hamilton, who
braved Greenland's unfriendly weather not once but three times in 2006,
have opened a new chapter in glacier research using ASTER (Advanced
Spaceborne Thermal Emission and Reflection Radiometer) — advanced sensor
technology found on NASA's Terra satellite. Looking down from 440 miles
above the surface, ASTER captures unique, stereoscopic images of Earth's
glaciers, supplying the researchers with an unprecedented tool for
measuring the size and tracking the movements of the planet's frozen
water reserves.
So far, some of the most
significant discoveries have come from satellite images of Greenland,
which became part of Hamilton's research thrust nearly by default.
"One of ASTER's missions is
to take at least one image per year of every glacier on the planet. When
NASA began building the mission's science team, I volunteered to be in
charge of the data being collected from Antarctica. And when no one came
forward to cover Greenland, I claimed that as well," says Hamilton.
"Being on the ASTER Mission Science Team gives us access to specialized
software and the ability to program image acquisition commands for
scenes that are of interest to us at no cost. A lot of work can be
accomplished using data collected from space."
Charged with finding a way to track the movements of Greenland's
glaciers over time, Stearns adapted techniques used with other types of
satellite imagery to develop an advanced method for identifying specific
areas on the surface of glaciers. Acting as a kind of glacial
fingerprint, the patterns of light and shadow revealed in images of icy
ridgelines and crevasses can be precisely identified in a series of
images using a computer, allowing Stearns to determine the speed of the
glacier by calculating the distance it traveled over time.
Surface water assessment is
another facet of the research being done using ASTER's sophisticated
sensors. Standing out as brilliant blue pockets in a vast sea of snowy
white, lakes of meltwater may provide important insights into why some
of Greenland's glaciers are accelerating. Sneed, a former computer
systems specialist, utilized the expertise of UMaine marine scientist
Emmanuel Boss to apply techniques used in oceanography to the problem of
measuring surface water volumes on glaciers. By comparing variations in
the penetration of different wavelengths of light into the lakes and
frigid floodplains, Sneed is perfecting a technique for determining the
water's depth, which, combined with the less challenging calculations
for surface area, provide a glimpse into the surprising volume of water
that rides the back of Greenland's ice on its way to the ocean.
"The lakes are obvious, but
when you look closely you realize that there is an enormous amount of
water on the surface of the ice," says Sneed, pointing out that much of
what appears as ice fields in satellite imagery is actually shallow
meltwater and slush.
The advances made by Hamilton and his team in applying
space-based technology to earth systems have added to the tool box used
by climate change researchers, but the discoveries made with those
technologies has set the field of glacier research on its ear. Perceived
by many to be relatively constant, slow-moving systems, Greenland's
glaciers were found to be accelerating at a disturbing rate.
"Our results showed that
things are happening in Greenland a lot faster than anyone thought,"
says Hamilton. "Now the rush is on to find out why it's happening and if
it's going to continue."
After analyzing hundreds of
ASTER images and comparing tens of thousands of data points, Stearns'
calculations showed that three of Greenland's largest glaciers had
accelerated as much as 300 percent in the last four years, racing to the
ocean at an incredible 14 kilometers a year — three times faster than
what had been previously considered fast-moving for a glacier. Dumping
hundreds of cubic kilometers of meltwater into the Atlantic, the
accelerating glaciers could cause a significant rise in sea level and
dramatic changes to ocean currents and salinity.
ASTER's ability to provide
images taken at multiple angles allowed Hamilton and Stearns to map the
topography of Greenland's ice sheet as well, revealing that many of the
glaciers are not only speeding up, they are thinning.
"There are only about 50
major glaciers in Greenland, and approximately half of all the ice lost
from the ice sheet in 2005 came from just 10. With three of those
glaciers rapidly accelerating, you get a pretty significant result,"
says Stearns, a NASA Graduate Fellow who recently presented her research
at the 2006 International Astronautical Congress in Valencia, Spain.
"You don't need many glaciers to change the effects of fresh water
entering the Atlantic and throw off the mass balance of the ocean."
by David Munson
January-February, 2007
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