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Doppler wind lidar for in-flight turbulence mitigation

Turbulence, gusts and wake vortices pose a significant risk to today’s and future civil airliners representing the second major cause for enroute accidents in civil aeronautics, with increasing trend. With tomorrow’s more lightweight and thus more vulnerable airframe structures, higher abundance of clear air turbulence (CAT) due to climate change and increased air traffic, this calls for novel sensory to detect and mitigate these hazards.

Hence, the Lidar department at IPA develops a novel lidar sensor for the purpose of close-range turbulence detection and immediate flight control reaction. With a gust load alleviation system fed by a Doppler wind lidar, the aerodynamic impact of turbulent gusts may be considerably lowered, down to the level of not being sizing for the structure any more. This allows employing more lightweight structures and at the same time a more comfortable, less “bumpy” ride within turbulent conditions.
Hereby, the Doppler wind information is used by a feed-forward flight control system that eventually generates commands to the aircraft’s control surfaces (rudders), e.g. generating a subtle “nose up” maneuver before entering a vertical, downstream gust (the infamous “airhole”).

Such an aeronautics application dictates very special and unique requirements to a Doppler wind lidar that we respond to with the development of AEROLI-DWL.
To name only two characteristics, this novel direct-detection lidar relies on a fringe-imaging spectral analyzer technique, making it independent of aerosol occurrence, and the knowledge thereof. A so-called field-widening of the interferometric spectral analyzer allows employing it on short distances, different to most scientific lidars focused to the optical “infinity”.

We continually strive to augment this Doppler wind detection technique, combine it with an equally optimized laser transmitter and scanning technique and mature it to flight tests on the new DLR test aircraft, the iSTAR.