Last week, researchers at Sandia National Laboratories flew a tethered balloon and an unmanned aircraft system (UAS) together to collect weather data in the Arctic.
In addition to providing more precise data for weather and climate models, being able to effectively operate UAS in the Arctic is important for national security, according to Sandia, which is operated by National Technology and Engineering Solutions of Sandia LLC, a subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration.
“Operating UAS in the remote, harsh environments of the Arctic will provide opportunities to harden the technologies in ways that are directly transferable to the needs of national security in terms of robustness and reliability,” says Jon Salton, a Sandia robotics manager. “Ultimately, integrating the specialized operational and sensing needs required for Arctic research will transfer to a variety of national security needs.”
According to Sandia, information on temperature of the atmosphere is critical for predicting the weather, monitoring severe weather and improving climate models. Unlike tethered balloons or weather balloons, drones don’t require helium, a non-renewable resource, and can take off with less preparation. Thus, they can be launched from more remote locations. Most airports already collect atmospheric temperature profiles twice a day, but switching to UAS with distributed temperature sensors would be better because they would be reusable and could fly more frequently, says Sandia atmospheric scientist Dari Dexheimer.
Since 2015, Dexheimer has regularly flown tethered balloons out of Sandia’s dedicated Arctic airspace on Oliktok Point, the northernmost point of Alaska’s Prudhoe Bay. These 13-foot-tall balloons carry distributed temperature sensors to collect Arctic atmospheric temperature profiles – the temperature of the air at different heights above the ground – among other atmospheric sensors. The test earlier this month was the first time Sandia has flown an octocopter in the sky above Oliktok Point.
“The UAS and the balloon really complement each other in that the UAS has a smaller flight time, but it’s much more spatially diverse. The tethered balloon can stay up for a long time, giving you a lot of data, but it’s not easily mobile,” says Dexheimer. The balloon is blown by the wind, to the limits of the tether, but the UAS can be directed to precise GPS coordinates, says Sandia.
Earlier this summer, Dexheimer and the drone flight team, led by Diane Callow, tested the joint UAS-balloon setup at Sandia. They overcame a series of technical challenges, including figuring out how to best secure and reel out the four-football-field-long distributed temperature sensor cable while making sure it didn’t get tangled in the drone’s rotors.
They also worked out the logistics of operating the balloon and the system at the same time. To avoid bumping into each other or tangling the cables, the balloon was tethered downwind, and the UAS stayed at least 100 feet away from it.
The distributed temperature sensor is a fiber-optic cable with the thickness of angel hair pasta. By seeing how light bends in the cable, Dexheimer can calculate the temperature of that part of the cloud. This measurement has a resolution of one meter, and she sends a light pulse every 30 seconds. This gives Dexheimer and climate modelers an unprecedented level of detail on the temperature of the atmosphere, says Sandia.
In addition to the temperature sensor, the tethered balloon carries special supercooled liquid water sensors. Supercooled liquid water is pure water that remains a liquid below its freezing point because it has nothing to crystalize upon. It is important because clouds containing a lot of supercooled liquid water behave differently from normal clouds, sticking around for days and even acting like a blanket to warm the surface below. Better understanding of these kinds of mixed-phase clouds is important for more accurate climate models.
The sensors are vibrating wires upon which supercooled liquid water can freeze. As the ice builds up, the vibration slows, and this tells researchers how much supercooled liquid water is present in that part of the cloud. For the project’s next steps, the team hopes to add these supercooled liquid water sensors to a fixed-wing UAS and fly the UAS into the clouds. They hope to see how much the UAS ices up, determine how to mitigate the effects of icing and eventually collect useful data on cloud conditions with more spatial control than the balloon could get.