After a decade of monitoring annual changes in polar-ice thickness from the sky, NASA’s Operation IceBridge — a series of science flights over the poles — is preparing to wind down and pass the torch to a satellite.
This extensive airborne survey was designed to bridge an almost a decade-long gap in polar observations between two of the agency’s satellites.
One of operation’s final tasks was to carry out a suite of flights that would help to calibrate the instruments for NASA’s Ice, Cloud and land Elevation Satellite-2, which launched in September 2018. Its predecessor stopped collecting science data in 2009.
I joined one of these flights together with photographer Nicolas Ordonez, embarking on an 11-hour journey at low altitude over the Weddell Sea ice pack, in West Antarctica, on 27 October.
This was the most technically complex mission that team has attempted to date. It meant flying in tandem with the satellite, following a narrow, precise track, while accounting and correcting for wind-driven changes to the ice pack to remotely probe the frozen but ever-flowing terrain below.
Fuelling up. NASA’s DC-8 aeroplane (left) takes on fuel at the Punta Arenas airport in Chile before our night flight. The 1969 aircraft which was fitted with new engines and larger, optical windows, for the IceBridge mission is usually housed at Armstrong Flight Research Center in Palmdale, California. The Airborne Topographic Mapper instrument (right), is equipped with a dual near-infrared and green-light laser system that fires at 10,000 pulses per second in a circular motion. Each of the two lasers covers a fixed swath of a different width to measure changes in ice-surface elevation.
Sunrise. The plane will fly a straight line under the satellite’s path across the Weddell Sea ice pack. The satellite will then move on to complete its orbit of the Earth and the plane will turn around and head back to its starting position to await the satellite’s return. This gives us the chance to see the same sunrise twice. “This was a completely different experience,” says NASA pilot Timothy Vest. “The sunrise was incredible right before we turned back to the north, for about ten minutes, before it went down, and then we saw it again an hour later.”
The vast plain beneath us stretches for kilometres, completely empty. "It’s so remote here — anything goes wrong, it’s going to be critical,” says Vest.
Night-time. As we fly in the south-west direction towards the pole, the sun hovers just around the horizon for much of our flight, rising, then setting, and eventually rising again on our return flight. In the picture, night falls over the Weddell Sea as NASA flight engineer Mark Crane checks the plane’s systems. The flight crew waits for a patch of low clouds to clear before descending to 550 metres, the designated altitude for initiating science operations. Flying at night is essential, because correct calibration of the satellite orbiting above us depends on avoiding interference from the Sun’s photons.
Sunset. The sunset starts at 10 p.m., somewhere above the Antarctic Peninsula. NASA’s navigator Gregg Pugh checks the weather over the science-operations area ahead.
Hacking the autopilot. Mission scientist John Sonntag uses the transit time from Punta Arenas to the chosen science point to prepare the navigation system he designed, which will steer the aircraft once it gets in line with the satellite. “We make the aeroplane think it is lining up with a runway to land, as we generate a signal," he says. "In a way, we hack the autopilot.”
Sea-ice tapestry. The plane swoops as low as 150 metres over the constantly changing tapestry of sea ice. Its flight path enables the instruments on board to probe the different textures of ice that form and rip apart, as well as the areas of open water that appear in cracks and holes in the ice.
Sunrise, again. Sunrise number two adds a touch of blush to the ice pack, as the lasers, radars and gravimeter collect data simultaneously. Each instrument produces information that is complementary to the others, and their data is in turn compared with that taken by ICESat-2.
The return. Daybreak signals that it is time to head back to Punta Arenas. “A lot of what we are doing is measuring very small changes, hard to see with the naked eye,” says Brooke Medley, IceBridge deputy project scientist. “But when you have a small change over a very large area, it turns into a very big change.”