Spying on Sea Ice

Suited Up A sea ice researcher's wardrobe Image courtesy of James Maslanik, University of Colorado

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The thought of studying sea ice conjures up visions of scientists wrapped in expedition-weight parkas straddling dangerous ice cracks to take measurements. And when it comes to on-the-ground fieldwork, that image isn't far off base. But in recent years, a remote-controlled robotic plane has made work conditions a bit more tolerable for researchers who study the ice.

Unmanned aerial vehicles (UAVs) were used to take aerial photos as early as the 1970s, but it wasn't until 2000 that they began to play a role in studying the physics of sea ice. And in recent years, Arctic sea ice has become a key variable in global climate change.

During the 2008 melt season, Arctic sea ice extent dropped to the second-lowest level since satellites first began taking measurements in 1979. The record-setting low occurred in 2007, but that's a measure only of its extent, not of its quality. According to Walt Meier, a research scientist at the National Snow and Ice Data Center in Boulder, Colorado, it's important to look not only at how much ice covered the Arctic, but also at the condition of the ice.

Multi-year ice is sea ice that has survived at least one melt season and is typically 2 to 4 meters (6.5 to 13 feet) thick. First-year ice has accumulated over only one season and is much thinner. "When you have a large amount of first-year ice, you have an ice cover that is much more prone to melting the following summer, and that's what we saw in 2008," said Meier.

According to Meier, about 40 percent of the ice in the Arctic is first-year ice -- the rest is older, thicker multi-year ice, which is more difficult to melt and tends to stick around longer. But in March 2008, thin first-year ice covered a record 73% of the Arctic Basin, which set the stage for more widespread melting in August and September. "The ice that remained at the end of the 2008 melt season was only about half a meter thick, whereas last year there was a lot of multi-year ice," said Meier. "2007 and 2008 were very clearly the lowest ice volumes and the lowest ice extent in the satellite record. We can say that with absolute confidence."

Knowing what kind of ice covers the Arctic region is key to understanding the sea ice minimum at the end of each melt season. During the past three decades, satellites have enabled scientists to monitor sea ice cover from space. But the minute details of sea ice physics happen rapidly and continuously -- something that satellites can't capture.

"Sea ice changes fast, and if you only see it once every few days, you miss quite a bit," said Jim Maslanik, research professor in the Department of Aerospace Engineering Sciences at the University of Colorado.

Beginning in 2000, Maslanik and a team of researchers started flying Aerosonde UAVs out of Barrow, Alaska, to gather data on sea ice conditions as part of research funded by the National Science Foundation. Since then, he says, the conditions have changed dramatically. "When we first started doing flights out of Barrow, the oldest ice was fairly close to Barrow's coastline. In the past several years the ice has retreated so much that we would have to fly hundreds of miles out to see that older, multi-year ice," he said.