Antarctic Airborne Science Mission Nears Mid-Point

Sea ice is seen out the window of NASA's DC-8 research aircraft on Oct. 21, 2009With seven science flights over Antarctica completed in the first 13 days of Operation Ice Bridge's first southern campaign in NASA's DC-8 flying laboratory, the mission is on track to complete its planned flights by mid-November.

The mission has 17 planned flights over different parts of the continent, focusing on the ice sheet, glaciers, and sea ice in West Antarctica. Which flight target is flown on a given day is largely determined by difficult-to-forecast Antarctic weather conditions. Several of the instruments onboard cannot gather data through clouds. Twice so far, however, flights have been scrubbed at the last minute due to snow at the airport in southernmost Chile.

Mission planners use a mix of weather forecasting tools and satellite observations to make their daily decisions about when and where to fly. In addition, updates from meteorologists at the airport provide critical information. "The Antarctic weather is a terrible problem for us," says Ice Bridge project scientist Seelye Martin of the University of Washington, Seattle. "We could not operate without the support we receive from the Chilean meteorologists here."

As of the landing of the Oct. 27 flight, completed targets included: three flights over glaciers, two over sea ice, one over the Getz ice shelf, and one to study the topography of the ice sheet on the mission's closest approach to the South Pole.

The Getz Ice Shelf was the target of the first flight on Oct. 16. Thwaites Glacier was the focus of the flight on Oct. 18, with Pine Island Glacier the target of a high-altitude flight on Oct. 20 and a low-altitude flight on Oct. 27.

"Pine Island Glacier is a major focus for our mission," says Martin. "We have four flights planned for this glacier. One of our hopes with these flights is to understand the detailed topography under the floating ice tongue. That topography controls the rate of melting there."

The mission's first sea ice flight on Oct. 21 over the Bellingshausen and Amundsen seas was a "pioneering flight," according to Martin. "We don't know what the thickness of the sea ice is here. These will be the first direct measurements of sea ice in this area. This area is important because it is the only Antarctic sector where the sea ice is actually retreating."

Martin was excited about the prospect that the combined data from two different instruments would give scientists a new way to make more accurate measurements of sea ice thickness. Thickness of sea ice is estimated from measurements of the depth of the snow and ice visible above the sea surface. But scientists have not been able to distinguish accurately how much of this material above the sea is snow and how much is ice. An accurate measurement of the two is needed to improve their calculation of overall ice thickness.

"With this flight we did something that has not been done successfully before," says Martin. "We flew a snow radar from the University of Kansas that is designed to measure the snow depth on sea ice and the laser Airborne Topographic Mapper from NASA's Wallops Flight Facility to measure the sea surface and the height of the combined snow/ice layer above the sea. If everything worked as planned, this will give us the first combined measurement of the 'layer cake' and the snow layer to an accuracy of about 2 inches."

The second sea ice flight on Oct. 24 flew over the Weddell Sea for low-altitude flights some 1500 feet above the sea under sporadically cloudy conditions.

The farthest flight of the mission took place on Oct. 25. The target was a portion of the circle of latitude at 86 degrees south. This area has been intensely mapped by NASA's ICESat satellite because the spacecraft's orbit only goes as far south as this latitude. By remapping the ICESat data points with another laser-based topographic instrument -- the Land, Vegetation, and Ice Sensor (LVIS) -- scientists hope to improve the accuracy of the ICESat data record and prepare to extend these critical ice surface change observations into the future.


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