NASA’s Ice, Cloud and Land Elevation Satellite (ICESat) reached the end of its operational lifespan, and its successor, ICESat-2 was years away from launch. In response, NASA started Operation IceBridge to keep ICESat’s record of measurements alive and further build knowledge of Earth’s polar ice.Continuity is the name of the game when it comes to monitoring rapidly-changing polar ice, but if the satellite used to gather that information stops working before its successor is ready, there has to be a way to bridge the gap. In 2009,
IceBridge is a NASA airborne science mission that uses a fleet of research aircraft that carry advanced science instruments to get a detailed, close-up view of ice.
“IceBridge’s primary concern is continuity between ICESat and ICESat-2,” said Michael Studinger, IceBridge project scientist. IceBridge also provides scientists around the world with data on many aspects of polar ice that can be used to improve predictive models of changing ice and the global sea level.
The core of IceBridge is its two annual campaigns, which take place at times when ice surface elevation is relatively stable. The first campaign is held in the Arctic from March through May, and the other takes place in the Antarctic in October and November. During these campaigns, IceBridge researchers conduct daily survey flights over sea ice, ice sheets and glaciers to gather information on ice surface elevation, ice thickness, snow depth, snow accumulation, and the shape of bedrock and water beneath the ice. This is made possible thanks to the vast array of instruments, ranging from laser altimeters and advanced radars, to digital imaging systems and even magnetic, gravity and surface temperature sensors.
“The unique instrument suite we have makes a critical contribution to polar science,” Studinger said.
The majority of IceBridge’s instruments fly on NASA’s P-3B and DC-8 airborne laboratories. They typically fly at lower altitudes to make better use of one of IceBridge’s laser altimeters, the Airborne Topographic Mapper (ATM), which measures ice surface elevation to help maintain ICESat’s record of measurements. ATM is joined by a second laser altimeter, the Land, Vegetation and Ice Sensor (LVIS), which now flies in a dedicated aircraft like the NASA HU-25C Falcon or the National Science Foundation / National Center for Atmospheric Research Gulfstream G-V to take advantage of its ability to operate at higher altitudes. By flying higher and faster, LVIS can survey longer and wider swaths of ice than can ATM, greatly expanding the area researchers can cover.
Although measuring ice elevation is important, it only fulfills half of the science goals set for IceBridge. Computer models of sea ice and ocean levels need data on ice thickness, snow depth and even what lies beneath the ice to make accurate predictions, and IceBridge helps meet this need. To examine different parts of sea ice and ice sheets, IceBridge relies on radar instruments operated by the University of Kansas’ Center for the Remote Sensing of Ice Sheets (CReSIS). These radars use different frequencies to measure total ice thickness (the Multi-channel Coherent Radar Depth Sounder, or MCoRDS), snow thickness and accumulation (snow and accumulation radars) and ice surface elevation (Ku-band radar altimeter). Data from these instruments can show an entire column of ice from new snow on top, to the bedrock or sea water below.
Other instruments can give researchers insight into what lies beneath the ice. The Lamont-Doherty Earth Observatory at Columbia University manages two instruments, a gravimeter that measures subtle changes in the Earth’s gravity, and a magnetometer that detects minute magnetic variations in sub-ice rock. With these two instruments, scientists can determine whether rock or water lies beneath the ice, the size and shape of water cavities, and can even narrow down what type of rock makes up the bedrock. This information is helpful in predicting how moving ice in glaciers interact with bedrock and how warmer ocean currents might flow under floating ice, melting it from below.
Another feature IceBridge’s researchers are looking for are openings in sea ice, known as leads. To do this, IceBridge uses data from ATM and two other instruments, the digital mapping system (DMS) and a KT-19 infrared sensor. DMS consists of a downward pointing digital camera that takes roughly one frame per second, and computer software that creates mosaics with the captured images. These images are tied to GPS information, allowing people to create photorealistic maps. In addition, using different image-processing techniques, researchers can combine several images to create a three-dimensional representation of ice. The KT-19 skin temperature sensor is an off-the-shelf infrared sensor that IceBridge scientists use to measure the temperature of the surface beneath the plane. Because sea ice is usually close to the ambient air temperature, roughly minus 20 to minus 30 degrees Celsius, and open water is warmer — just below freezing — the KT-19 can detect areas of open water. And, because this instrument relies on infrared instead of visible light, it can detect leads even in the dark.
Working with others
IceBridge also is supplemented by aircraft and instruments from partnering organizations like the University of Texas Institute for Geophysics (UTIG) and University of Alaska ÛÒ Fairbanks (UAF). UTIG operates an airborne suite of laser, radar and other instruments to measure Antarctic ice, and UAF researchers measure Alaskan glaciers with their own laser altimeter system.
IceBridge also collaborates with researchers from the European Space Agency (ESA) as part of the calibration and validation work for their ice-monitoring satellite, CryoSat-2. During the 2011 and 2012 Arctic campaigns, IceBridge worked alongside aircraft from ESA and its partnering organizations. This partnership involved all of the aircraft flying along the same swath of ice CryoSat-2 had passed over a short time before.
As the launch date for ICESat-2 draws closer, IceBridge is playing a larger role in preparations by helping with instrument development. During this year’s Arctic campaign, the IceBridge P-3B was joined by a NASA ER-2 carrying MABEL, a test version of the laser altimeter that will be used by ICESat-2. Comparing the measurements from MABEL and IceBridge’s more mature instruments will help researchers design algorithms for use in ICESat-2.
On the horizon
With the launch of ICESat-2 a few years down the road, IceBridge will likely play a growing role in its development. Still, even when ICESat-2 is fully operational, there will be a need for airborne missions like IceBridge.
“The ATM and CReSIS teams have been doing this for years,” Studinger said. “There are aspects of ice you can’t effectively measure from space.”
Whether this means continued flights with NASA’s airborne laboratories, or a move toward unpiloted aircraft like NASA’s Global Hawk remains to be seen.
“We’ll probably go more into a [unpiloted aircraft] direction, but how and when is a bit fuzzy,” Studinger said.
Even now, the LVIS team is working on a new version of their instrument known as LVIS-GH that is optimized for the Global Hawk. With a higher operating altitude and longer flying duration, unpiloted aircraft like the Global Hawk are already bringing changes to the airborne science community.
Regardless of what the future holds for IceBridge, the data gathered will help researchers understand what is happening at the poles and provide reliable information for predicting future changes.
George Hale is the science outreach coordinator for NASA’s Operation IceBridge. He has a background in science writing, technical editing and information technology and an interest in Earth sciences. Prior to coming to NASA’s Goddard Space Flight Center, he worked in communications in the College of Geosciences at Texas A&M University.