NASA has now wrapped up its fall mission to Antartica to collect data on ice sheets and sheet ice as scientists seek a better understanding of how melting in that region could affect sea levels around the world. In this undertaking, NASA was emphasizing the aeronautics part of its name--the overflights were done not by a satellite or the Space Shuttle, but by a DC-8 jetliner that had once been in commercial service. The flights in October and November were part of the six-year Operation Ice Bridge, which is studying both of Earth's polar regions.
The image here is of the ice shelf extending over the Amundsen Sea, taken during the fall campaign's first flight on October 16. It was taken by the DC-8's downward-looking Digital Mapping System camera.
This image shows a longer view of the Amundsen Coast from that same October 16 flight. (The downward-looking Digital Mapping System camera captured its images from an altitude of about 20,000 feet.)
The DC-8 flights were meant to supplement the information gathered since 2003 by NASA's Ice Cloud and Land Elevation Satellite, or ICESat. That satellite is down to just one operational laser (out of three), and the replacement ICESat-II won't launch until at least 2014.
At Palmer Station on Anvers Island, members of the U.S. Antarctic Program wearing red jackets spell out a greeting to the Ice Bridge aircraft overhead. Palmer Station is one of three U.S. environmental research facilities on the sparsely populated continent.
Anvers Island is located at about the midpoint of the Antarctic Peninsula, which sweeps northward toward Tierra del Fuego and the southern tip of South America. It was in that area, in Punta Arenas at the southernmost end of Chile, that the Ice Bridge team was based, and not in Antarctica itself.
The Operation Ice Bridge's DC-8 sits on the tarmac in Punta Arenas, Chile. It had just returned from an 11-hour flight, which seemed to be the rule, over the Bellingshausen and Amundsen seas.
Over the course of five weeks, the Ice Bridge aircraft traveled almost 100,000 miles in a total of 21 flights over Antarctica. Michael Studinger of Lamont-Doherty Earth Observatory, co-principal investigator on the gravimeter team, wrote in a blog post on November 24 as the DC-8 headed back to NASA's Dryden Flight Research Center in California:
"During this time, we collected high-precision measurements of the ice surface elevation of many glaciers and ice shelves in Antarctica. We have also mapped the thickness of the glacier ice and snow cover, have measured the freeboards and snow thicknesses of the sea ice in the Weddell and Ross seas, and have collected gravity measurements that will allow us to estimate how deep the water is beneath the floating glacier tongues."
This view from the port side of the DC-8 shows Antarctica's Pine Island Bay on October 20. The weather wasn't always this favorable. Bad weather over an Antarctic survey area caused the final data flight, scheduled for November 21, to be scrubbed, as were a number of earlier flights. The Ice Bridge team flew its last science mission November 18, conducting a low-level survey of Thwaites Ice Shelf in West Antarctica.
This is what thin ice looks like from 1,500 feet up, in the vicinity of the Pine Island Glacier. What exactly is the overall state of the ice at the continent at the bottom of the world?
"The immediate response is that the Antarctic sea ice is experiencing a decline in cover. The problem with Antarctica is that you don't have an easy one-sentence answer," Thorsten Markus, principal sea ice investigator for the mission, said in an Operation Ice Bridge FAQ.
"The Arctic is sort of easy: the ice is decreasing, and we'll eventually see ice-free summers," he said. "In Antarctica, the system is more complex. Next to West Antarctica, sea ice is decreasing. Around the Peninsula it's also decreasing and probably getting more snowfall, so we see big changes there, too. But for more of the continent, we actually see a slight increase in sea ice. It has to do with the ocean underneath the ice, the ozone hole, and a combination of both."
The DC-8 packed a lot of scientific equipment. Seen here in the foreground at the Dryden Aircraft Operations Facility in Palmdale, Calif., as gear was being loaded in late September, is the Laser Vegetation Imaging Sensor (LVIS) instrumentation rack. The LVIS laser altimeter collects data on topography and vegetation coverage.
Built right into the DC-8 is the Multichannel Coherent Radar Depth Sounder (MCoRDS), which measures ice sheet thickness. It can also map the terrain below the ice.
Said Markus in the FAQ: "We have a laser altimeter...that's similar to ICESat and is the primary instrument of the mission. The laser bounces off the surface, whether it's snow or ice, and provides a measure of surface elevation. But we also have radars on this plane, developed by the University of Kansas, which penetrate the snow. If you look at the difference between the laser and radar results, ideally you get the snow depth."
Project scientist Seelye Martin (left), from the University of Washington, Seattle, studies data on October 20 during a flight to the Pine Island Glacier. In early November, Martin rotated out and William Krabill, of NASA Wallops Flight Facility, took over as project scientist.
Geared up for Operation Ice Bridge, the DC-8 still shows signs of its lineage as a passenger jet. Besides LVIS and MCoRDS, the equipment included NASA Wallops' Airborne Topographical Mapper, which is a laser altimeter that produces elevation maps of the ice surface, and the Lamont-Doherty Earth Observatory's Gravimeter.
The Differential Absorption CO Measurement instrument measured concentrations of carbon monoxide, methane, and nitrous oxide. Its infrared detectors have to be kept cold, hence the liquid nitrogen being poured into it here by NASA Langley Research Center researcher Glen Sachse.
This is sea ice in the Bellingshausen Sea in West Antarctica, seen from 2,000 feet up, on October 21.
"Sea ice formation and melt have a really strong impact on ocean circulation, which acts like a huge heat pump keeping our climate stable," according to Thorsten Markus in the Operation Ice Bridge FAQ. "This 'thermohaline circulation' is driven by temperature and salinity. The interesting part of this circulation is that the deep, bottom water masses of the ocean only make contact with the atmosphere only at polar latitudes, in the Arctic or the Antarctic. Change ocean salinity--by growing or melting sea ice, which is inherently salt-free--and you can affect global circulation. The process is complex, but that's basically why it's so critically important."
This is the "snout" of the Pine Island Glacier, aka PIG, seen during one of the later flights. The DC-8 traveled in a dense grid of straight lines, which NASA said allowed the plane's gravity instrument to get higher-resolution measurements than on earlier flights.