  A high-performance airborne UV Rayleigh lidar system was developed within the
European project DELICAT. With its forward-pointing architecture it aims at
demonstrating a novel detection scheme for clear air turbulence (CAT) for an
aeronautics safety application. Due to its occurrence in clear and clean air at
high altitudes (aviation cruise flight level), this type of turbulence evades
microwave radar techniques and in most cases coherent Doppler lidar techniques.
The present lidar detection technique relies on air density fluctuations
measurement and is thus independent of backscatter from hydrometeors and
aerosol particles. The subtle air density fluctuations caused by the turbulent
air flow demand exceptionally high stability of the setup and in particular of
the detection system. This paper describes an airborne test system for the
purpose of demonstrating this technology and turbulence detection method: a
high-power UV Rayleigh lidar system is installed on a research aircraft in a
forward-looking configuration for use in cruise flight altitudes. Flight test
measurements demonstrate this unique lidar system being able to resolve air
density fluctuations occurring in light-to-moderate CAT at 5 km or moderate CAT
at 10 km distance. A scaling of the determined stability and noise
characteristics shows that such performance is adequate for an application in
commercial air transport.
