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Laser Mapping of Greenland’s Summer Ice Melt Begins

Photonics.com
Nov 2013
THULE, Greenland, and GREENBELT, Md., Nov. 6, 2013 — For the first time, NASA is laser-mapping changes to the Greenland Ice Sheet produced by a single season of summer melt. The data gathered will provide a more comprehensive view of season changes and provide context for a more ambitious mapping mission scheduled to launch in 2016.


A pond of melt water on the Greenland ice sheet seen in 2008. Courtesy of NASA/Michael Studinger.


The new airborne campaign, part of an ongoing mission known as Operation IceBridge, began Oct. 31 with a crew from the Wallops Flight Facility in Virginia arriving in Greenland, and it will continue through Nov. 16, the agency said. The campaign also marks the first time that the LVIS (Laser Vegetation Imaging Sensor) is flying aboard NASA's new C-130 aircraft to measure the island's ice and changes to surrounding Arctic sea ice following a summer's melt.

LVIS is a scanning laser altimeter that is flown over target areas to collect data on surface topography and vegetation coverage. The LVIS, which also includes data from an integrated inertial navigation system and global positioning system, is designed, developed and operated by the Laser Remote Sensing Laboratory at Goddard Space Flight Center in Greenbelt.

LVIS has flown over Greenland five times, in 2007, 2009, 2010, 2011 and 2012, under Operation IceBridge, but this new mission marks the first to take measurements of a six-month change in the ice sheet. The instrument can scan very large geographic areas very cost-effectively.

The land and sea ice data gathered during the campaign will not only give researchers a more comprehensive view of seasonal changes, NASA said, but will also provide context for measurements that will be gathered during the space agency's ICESat-2 mission, scheduled for launch in 2016.


The LVIS instrument mounted inside a P-3B aircraft for the spring 2010 IceBridge campaign to Greenland. Courtesy of NASA.

"The more ground we cover, the more comparison points we'll have for ICESat-2," said Bryan Blair, principal investigator for LVIS.

Warm summer temperatures lead to a decline in ice sheet elevation that often can be significant in low-lying areas along the Greenland coast. In past years, the Jakobshavn Glacier, located in the lower elevations of western Greenland, has experienced declines of nearly 100 ft in elevation over a single summer. Higher elevations farther inland see less dramatic changes, usually only a few inches, caused by pockets of air in the snowpack that shrink as temperatures warm.

"Surface melt is more than half of the story for Greenland's mass loss," said Ben Smith, senior physicist at the University of Washington's Advanced Physics Laboratory and a member of the science team that selected flight lines for this campaign. The rest of Greenland's mass loss comes from ice flowing downhill into the ocean — often breaking off to form icebergs — and from melting at the base of the ice sheet.

The C-130 carrying both instruments is flying out of Thule and Kangerlussuaq, Greenland, allowing researchers to sample both high- and low-elevation ice and a variety of geographic areas.

Researchers are measuring ice elevation using the LVIS laser altimeter and the LVIS-GH, a new, smaller version designed to fly on NASA's Global Hawk unmanned aerial vehicle. LVIS and LVIS-GH are measuring separate but overlapping swaths of the ice from an altitude of 28,000 ft.

"We plan to concentrate our flights on areas northwest, southeast and southwest Greenland, and the Arctic Ocean," said Michelle Hofton, LVIS mission scientist at Goddard and the University of Maryland, before the mission began. "The measurements we collect along lines sampled in IceBridge's spring 2013 Arctic campaign will allow scientists to assess changes over the summer."


Plot of readings from LVIS overlaid on terrain in Google Earth. Courtesy of NASA. 


Flying from Thule also will allow mission scientists to gather data on Arctic sea ice shortly after it reaches its annual minimum extent. This will help determine a clearer picture of what happens over the summer. It also will help researchers gather new data on snow covering sea ice when combined with information collected by the European Space Agency's CryoSat-2 polar-monitoring satellite. LVIS detects the snow surface while CryoSat's radar sees through snow to find the top of the ice. Researchers can combine these measurements to calculate snow depth.

"This will be crucial for assessing the snow cover on sea ice during a very different time of year," said Nathan Kurtz, sea ice scientist at Goddard.

For more information on LVIS, visit: http://lvis.gsfc.nasa.gov. For more about NASA's IceSat-2 satellite, visit: http://icesat.gsfc.nasa.gov/icesat2


GLOSSARY
remote sensing
Technique that utilizes electromagnetic energy to detect and quantify information about an object that is not in contact with the sensing apparatus.
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