Climate change is fueling a race for once-inaccessible Arctic resources, but the rapidly thawing ice poses a growing risk of accelerating global warming by releasing huge stores of eons-old carbon into the atmosphere. Unmanned aircraft are beginning to play a key role in monitoring the changes in these vast and remote areas.

A team lead by Harvard University has completed flights over Alaska's North Slope to measure the release of greenhouse gases by melting permafrost. Aurora Flight Sciences' Centaur optionally piloted aircraft was flown manned for these initial flights, but the team plans to return next year and fly the modified Diamond DA42 unmanned on extended flights over the ocean.

The FAA, meanwhile, has issued the first restricted-category type certificates to AeroVironment for the Puma AE and Insitu Inc. for the Scan Eagle, allowing commercial flights of the small unmanned aircraft over the North Slope and Beaufort Sea to monitor oil spills and observe wildlife as Arctic resource exploration and exploitation gathers pace. Operations are expected to begin this month.

The Aurora-owned and -operated Centaur completed 16 flights totaling more than 60 hr. in August, operating from Deadhorse, Alaska, carrying a highly sensitive spectroscopic instrument developed by Harvard. The aircraft had to fly 5-10 meters (16-33 ft.) above the ground for extended periods so researchers could precisely measure the rate at which carbon is being released into the atmosphere.

Over the past 30 years, the Arctic Ocean has lost 80% of its permanent floating-ice volume, resulting in rapid melting of permafrost regions that contain vast stores of methane and carbon dioxide. “The surface soils in Alaska and Siberia contain 2 gigatons of carbon. If just 0.5% of that is released, it will double the carbon added to the atmosphere each year by fossil-fuel combustion,” says Jim Anderson, principal investigator for Harvard's Anderson Research Group.

Determining the rate at which carbon is being released by melting permafrost is crucial to predicting climate change. The Centaur was equipped with the Harvard-developed Flux Observations of Carbon from an Airborne Laboratory (Focal) instrument to measure the concentrations of carbon isotopes C12 and C13 with sufficient resolution to distinguish between carbon from surface vegetation and that released by melting permafrost.

Focal bounces the beam from a tunable mid-infrared quantum cascade laser between two highly reflective mirrors to create a 5-km-long (3-mi.) path within a 1-meter-long cell. This enables the spectroscopic instrument to detect trace isotopes by direct absorption as air is drawn through by a pump. “The quality is very high, the data unequivocal, and it responds very quickly,” says Anderson. “The flush time is practically 1,000 times a second.”

The concentration data are combined with vertical-velocity measurements by a highly responsive air-turbulence probe, supplied by the National Oceanic and Atmospheric Administration, to enable calculation of the flux, or flow rate, of methane and CO2. The ratio of isotopes identifies the source, with thermogenic carbon stored in permafrost being higher in C13 and biogenic carbon from vegetation higher in C12. “Flux is the crucial observation, as it quantifies the contribution of the melt zone to carbon in the atmosphere,” says Anderson.

Funded by the National Science Foundation, the August research campaign was “very successful,” he says. The pilot was able to fly the Centaur less than 10 meters above the “billiard-table flat” North Slope, keeping the aircraft within a tight altitude tolerance that allowed the instrument to collect flux data with “very high spatial resolution” to measure release rates from different landscape features, such as ponds.

The Harvard team is now preparing a proposal for a 2014 research campaign that would involve unmanned flights of the Centaur over the Arctic Ocean. Clathrates on the ocean floor trap a large amount of methane in their crystalline structure, and as the ocean warms there is a risk of them melting and releasing their carbon. The 2014 campaign would involve unmanned flights of up to 23 hr. to systematically map the oceanic carbon flux with high spatial resolution, Anderson says.

“The optionally piloted aircraft is the ideal tool for this type of experiment,” says Aurora founder John Langford. “The airplane can be ferried through national and international airspace in its manned, fully certified mode. Once the instruments, flight trajectories and operating protocols have all been validated, the long and repetitive measurements can be handed over to the computer.”