In February 2022, a drone flew off the deck of the Japanese research vessel Soya and over the ice-covered Sea of Okhotsk in the northwestern Pacific Ocean. The only difference between this uncrewed aerial vehicle (UAV) and one you could buy at any electronics store was an extra sensor that researchers had added to measure wind speed.
The flight was a test to see whether collecting wind speed measurements in remote regions could be made more accessible and less expensive. The researchers recently published their findings in Drones.
“Although meteorological UAVs can [perform] wind profiling, they are usually expensive to buy or operate by a third party,” wrote Jun Inoue, a researcher at the National Institute of Polar Research in Japan and lead author of the study, in an email from a research vessel in Antarctica. Lightweight and inexpensive anemometers—devices that measure wind speed and direction—attached to a smaller UAV can make the same measurements, he wrote. Inoue and his colleagues are designing a unit that fits the bill.
Where Drones and Meteorology Meet
Wind speed measurements throughout the lowest layer of the atmosphere, called the boundary layer, help to inform weather predictions and climate models. But weather stations are difficult and costly to maintain in many places around the world, particularly at the poles. “Cost-effective, frequent data acquisition at many stations is the challenge,” Inoue wrote. Weather stations are also limited to collecting data at a single location. To overcome these issues, scientists have turned to drones to get weather data in hard-to-reach locations.
Drones have many advantages, said Brian Greene, a postdoctoral fellow at the University of Oklahoma who has used drones in the Arctic but wasn’t involved in the new study. “They’re reusable, they’re cheap, they’re portable,” he said, and “they’re able to reach areas of the atmosphere that we don’t typically have access to with our normal, everyday sampling techniques.”
A Cost-Effective Option
Scientists have used custom, purpose-built drones to make observations of weather and sea ice levels at the poles before, but these units are not commercially available. In the new study, the researchers used the common DJI Mavic 2 drone and attached a thermal anemometer, which measures changes in temperature due to airflow and translates them to wind speed. Although scientists typically use a different sensor for this purpose—an ultrasonic anemometer—the thermal variety is lighter and less expensive.
The researchers wanted to collect wind speed data while the drone was ascending and descending; stopping for each measurement is a drain on battery life. However, the movement of both the drone and its propellers would create extra airflow over the sensor. For the wind speed to be accurate, the researchers had to compensate for this disturbance. In a laboratory, they visualized airflow over the drone with smoke and lasers. Using videos that looked to be taken at a dance club, the researchers were able to track smoke particles and translate that information into a velocity of airflow over the drone. They could then use these measurements to correct the thermal anemometer measurements and calculate the wind speed in the surrounding environment.
Once the calibrations on the drone were accurate, the researchers headed to the Sea of Okhotsk, collecting 18 wind speed measurements over water. By comparing the drone data with the wind sensors on the ship, they determined that the drone was able to make accurate measurements of wind speed in the field.
Finding What Flies
Antonio Segalés Espinosa, a researcher at the Cooperative Institute for Severe and High-Impact Weather Research and Operations at the University of Oklahoma who designs weather-measuring drones but wasn’t involved in the current work, said that in his research he’s avoided using thermal anemometers because they are a bulky add-on. “Adding more extensions to the drone doesn’t really help to get the drone within the performance we want for severe weather,” he said. Inoue agreed, noting that a limitation of their design is that they’re confined to flying the drone in clear weather.
Including a thermal anemometer on a commercially available drone has benefits. The design could be a way for people who don’t have the time and money to build their own specialized drone to collect data, Greene said.
Inoue said he plans to fly the drone during his current research trip to Antarctica and aims to improve the delivery of data from the drone to researchers. “We will use this system over the Southern Ocean and Antarctica to study the atmospheric boundary layer structure,” he wrote. “The next step is near real-time data transfer for numerical weather predictions.”
—Andrew Chapman (@andrew7chapman), Science Writer