Atmosphere-Sensing Helicopter Missions Bridge the Climate Forecasting Gap

May 1, 2007

The Duke University research helicopter bedecked with an atmosphere-sensing nose will participate in two missions this spring and summer designed to fill in the blanks in understanding of the dynamic lower atmosphere and its intimate connection to seasonal changes in land cover, according to environmental scientists at Duke University’s Pratt School of Engineering. By providing a vast amount of climate observation data, the researchers say that the missions will enable future advances in climate models, ultimately increasing the accuracy of everyday weather forecasting and providing a more precise view of the causes and consequences of global climate change.

“The models have been limited by a lack of information from field observations,” said Roni Avissar, professor of civil and environmental engineering at Duke. “From a modeling point of view, we’ve reached the state-of-the-art. To get to the next generation of models, there are a few obstacles we must cross over. That is what we are providing here--better observation of the most important variables, including fluxes of heat and greenhouse gases between the ground and atmosphere.”

While other forms of aircraft have been employed in atmospheric research for some time, the helicopter provides an advantage due to its ability to fly very close to the ground surface -- literally skimming the treetops, Avissar said. It can therefore bridge a gap that exists in the information about climate conditions at the ground and those obtained by airplanes at higher altitudes. The Duke group was the first to realize the potential of helicopters in climate research by overcoming a misconception that the aerodynamics of helicopters in flight would unavoidably interfere with the climate sensors’ ability to make accurate measurements.

In the first 3-month mission, now ongoing, Avissar is piloting the souped-up helicopter above a California walnut orchard, periodically traversing the sky from the treetops to the shifting “boundary layer” between the earth and the outer atmosphere. The helicopter’s various sensors, meanwhile, will measure key navigation and climate variables -- including the temperature, humidity, carbon dioxide concentration and wind direction and intensity in three dimensions--at the rapid-fire rate of 40 times per second.

In the second mission, taking place at three sites over Oklahoma from June 9 to June 29, the Duke helicopter will fly in unison with seven other airplanes and orbiting satellites to capture a detailed view of the atmosphere over agricultural and forested land there. The Department of Energy-led mission represents the largest concerted effort to observe the atmosphere--all the way from the ground to outer space--that has ever been attempted, according to Avissar.

The information collected by helicopter in California will be used to integrate data gathered by a large array of ground sensors deployed by the National Center for Atmospheric Research, Avissar explained. The effort aims to better characterize turbulence -- the eddying motion of the atmosphere--over the ground surface in relation to tree cover, in particular examining how atmospheric properties change as trees leaf out over the course of the spring season and into the summer.

“Models of turbulence are required for all atmospheric models, from meteorological models to models of air pollution, whatever atmospheric model you can think of relies on a representation of turbulence,” Avissar said of his ongoing mission, which is funded by the Army Research Office.

The second, multi-aircraft mission, will provide a whole host of atmospheric variables -- including information about cloud cover and the concentration of aerosol particles -- with the ultimate aim of improving scientists’ understanding of information captured on a regular basis by a “constellation” of remote-sensing satellites in orbit.

“What a satellite sees from space is affected by what is happening at the ground diffused by the weather in general -- clouds, humidity, particles, and so on,” Avissar said. “By measuring atmospheric variables at different levels, we hope to develop a fuller, more integrated picture of what is happening from the ground to outer space and, with it, a better understanding of the information that satellites can provide.”

Avissar’s efforts in Oklahoma are supported by NASA.