Measuring Summer Arctic Sea Ice

©NASA/Kate Ramsayer

Melt ponds

Sheets of floating ice called floes are cracked into pieces like pottery shards and are dotted with ponds of melted snow.

The deepest blue ponds, whose dark colors signify melting that's occurring in thicker ice, connect to neighbors with winding black rivers that empty into the open sea. Giant chunks of ice form rough ridges where ocean currents and winds have slammed the ice floes into each other.

It's summertime in the Arctic, and the ice is in flux.

"I've flown in the spring lots of times, and then the Arctic ice cover is just a flat expanse, it just goes out forever," said Nathan Kurtz, Operation IceBridge project scientist from NASA's Goddard Space Flight Center in Greenbelt, Maryland. "Now, in the summer, it's just so variable. You see places where the floes are a lot more broken up, you see a mixture of places where the snow has melted and you see bare ice, and various depths of melt ponds ... you see these patches all over of ice in different stages of melt."

Operation IceBridge made two flights out of Barrow on Tuesday, July 19, as part of the campaign's first effort to take airborne measurements of melting summer sea ice. Flying 1,500 feet above the ice floes were three instruments: a laser altimeter that measures the heights of the water, snow and ice; an infrared imager that provides temperature readings to help differentiate between water and ice; and a downward-facing mapping camera.

"We've never mapped melt ponds so extensively like this," Kurtz said. And there were many melt ponds to map, as stretches of open water dotted with ice alternated with stretches of ice dotted with ponds and open water.

On the first flight, fog in Barrow and cloudy skies for the first couple hundred miles cleared up just as the agency's Falcon jet, out of NASA's Langley Research Center, reached the line the scientists wanted to measure. The goal? Take readings along the path that the European Space Agency's CryoSat-2 would fly over shortly after 3 pm, local time. That would provide ways to compare the satellite and airborne data and see if scientists could use the summer satellite data.

Then, early Tuesday evening, the team took off on another flight to the northeast. This flight was designed to see the patterns and topography of sea ice in the Beaufort Sea along a path dubbed the Linkswiler line, after Matt Linkswiler, operator of the laser altimeter.

Kurtz and his colleagues are investigating whether a combination of measurements can help estimate sea ice thickness. It's a tricky piece of information to get, but one that could provide clues to how fast the summer ice will melt, or whether it could stick around for another year.

They're studying how well the laser altimeter can measure the depths of the melt ponds--another possible indication of the year's overall melt season. It's one of several ways the IceBridge campaign is preparing for the Ice, Cloud and land Elevation Satellite-2, or ICESat-2, scheduled to launch by 2018. How IceBridge can measure summer ice melt could help ICESat-2 scientists develop programs to analyze the satellite's summer data.

For Kurtz, the sheer variety of the summer ice is surprising and was especially noticeable on the Tuesday afternoon flight. Different shades of white gave hints to whether it was just ice or snow on top of the ice, while in some areas the ice was brown, possibly due to embedded algae, Kurtz noted.

After Tuesday's two flights, Icebridge had completed five of its six planned flights for the Barrow summer campaign. With its clear skies, Tuesday afternoon's expedition was the best yet.

"That was an excellent flight," Kurtz said over the plane's intercom system. "I don't think we lost anything to clouds."

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