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Hot Spot

 


Hot Spot
Climate change researchers use NASA technology to study the dramatic changes in Greenland's ice sheet

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Her trusty Dog Hudson at her side, University of Maine graduate student Leigh Stearns has spent the last two years exploring the jagged spires of ice and huge, yawning crevasses that make up the glacial ice fields of Greenland. Aimed primarily at tracking glacier speed and movement with the goal of understanding how ice sheets contribute to sea level, Stearns' research has led her to some of the most inaccessible and inhospitable places on the planet — and she has done most of it in a tee shirt and sandals.

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."


Glacier
Collecting reliable field measurements is critical to establishing a clear picture of how Greenland's ice sheet is changing, but there are risks involved in traversing the unpredictable glaciers.

Helicopter over glacier
Fieldwork requires a small helicopter flown by a pilot skilled enough to land in difficult spots. The researchers drill holes in the ice to position poles fitted with GPS receivers that collect high-resolution data every five seconds. The scientists are looking at the possibility that surface water may help accelerate the glaciers' movement.

Calculations done using ASTER satellite imagery have shown increases in meltwater volume of more than 300 percent in less than a week on the surface of some glaciers.

Photos ©Greenpeace/Morgan
 

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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