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The objective of the research was to perform a design study and feasibility demonstration of a Doppler laser radar system for use in detection of clear air turbulence. Both CW and pulsed radar techniques were investigated to determine applicability to analysis of laser light backscattered from atmospheric molecules and aerosol particles in order to measure macroscopic motion of the air. It was desired to detect wind gusts in excess of 25 feet per second while operating in a jet aircraft at an altitude of approximately 30,000 feet. The program included analysis of design requirements, analysis of light scattering by the atmosphere, a design trade-off study, and an experimental demonstration. It was concluded that, if particulate matter exists at flight altitudes in sufficient concentration and if advances in the laser state of the art permit fabrication of a laser with the required performance, a system with a range of up to 50 nautical miles is feasible. The analysis showed that the system must depend on scattering from aerosol particles and that a pulsed system has significant advantages over a CW system. A system concept is described which employs detection of beat frequencies in the output current of a photodetector resulting from photo-mixing of the backscattered light from two laser pulses illuminating separated volumes of air. An experimental demonstration was attempted which optically combined the light scattered from two streams of smoke moving at different velocities. The scattering volumes were illuminated by focusing the expanded output beam of an argon laser. (Author).
Clear air turbulence encounters can occur unexpectedly without any visual evidence or warning. As operations of higher altitude aircraft increase, the phenomenon is encountered more often. Clear air turbulence is defined as 'all turbulence in the free atmosphere of interest in aerospace operations that is not in or adjacent to visible convective activity (this includes turbulence found in cirrus clouds not in or adjacent to visible convective activity).' This bibliography consists of 578 references to technical reports, articles in periodicals, and books published during the past 17 years. References about other forms of turbulence such as that occurring with storms and airplane wake vortices are not included. (Author).