Development of an airborne wind measurement system

Accidents to airliners caused by air turbulence have been increasing in recent years. At present there is no sure way of avoiding encounters with clear air turbulence (CAT) because conventional airborne weather radars cannot detect turbulence in clear conditions. The Japan Aerospace Exploration Agency (JAXA) is therefore developing a Doppler LIDAR (Light Detection and Ranging) which can measure wind speeds ahead of an aircraft even in clear air. Turbulence prediction in flight has already been demonstrated using experimental Doppler LIDARs, and the latest prototype aims at turbulence detection up to 5 nautical miles (9 km) ahead at jet airliner cruising altitudes. Wind velocity measurement by LIDAR is difficult at high altitude because of low aerosol particle density. Regular atmospheric observation flights are therefore being made to establish the basic specifications of a practical device. Furthermore, since air turbulence information should be displayed on the flight deck, a graphical turbulence display is also being studied. This paper describes the development of the airborne wind measurement system and presents examples of flight experiment results.