Lidar could help pilots avoid turbulence

Caren B. Les, caren.les@photonics.com

You’re cruising calmly in an airplane – admiring the view, relaxing with a book or catching up on sleep – when wham! The plane hits turbulence, and your relaxing ride is ruined.

Clear-air turbulence, or CAT, is practically unpredictable, unlike other kinds of turbulence, which can be caused by mountain ranges or brewing storms – things pilots can avoid. Invisible air pockets, however, cannot be so easily evaded, since even conventional radar won’t pick them up. And it’s likely to get worse: Fliers will likely encounter more and more turbulence as a result of climate change, according to recent atmospheric research findings.

An onboard lidar system could provide pilots with advance warning of clear-air turbulence (CAT), allowing them to alter their route or to warn passengers to fasten their seatbelts. CAT begins with wind shear, which involves layers of air that move against one another horizontally at different speeds. Photo courtesy of Astronautilus

But laser technology now in development under the European project DELICAT could be the answer to smoother flights. DELICAT is a lidar-based tool that could detect CAT from a distance, giving a pilot time to alter the flight route.

The instrument, developed at the German Aerospace Center (DLR) Institute for Atmospheric Physics, can be installed on an aircraft to emit shortwave-UV laser radiation along the direction of the flight. It measures backscatter values for oxygen and nitrogen molecules to indicate the density of the air; fluctuations in this density provide information about turbulence.

DLR and project partners are now testing the device. The UV-lidar system was installed on a modified Cessna Citation aircraft operated by the Dutch partner National Aerospace Laboratory (NLR). Test flights started in Amsterdam and continued throughout Europe this summer. Test data will provide information on the effectiveness of the technology, and it will offer information on complex atmospheric processes, too.