Coherent lidar airborne windshear sensor: performance evaluation

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Abstract
National attention has focused on the critical problem of detecting and avoiding windshear since the crash on 2 Aug. 1985 of a Lockheed L-1011 at Dallas/Fort Worth International Airport. As part of the NASA/FAA National Integrated Windshear Program, we have defined a measurable windshear hazard index that can be remotely sensed from an aircraft, to give the pilot information about the wind conditions he will experience at some later time if he continues along the present flight path. A technology analysis and end-to-end performance simulation measuring signal-to-noise ratios and resulting wind velocity errors for competing coherent laser radar (lidar) systems have been carried out. The results show that a Ho:YAG lidar at a wavelength of 2.1 μm and a CO2 lidar at 10.6 μm can give the pilot information about the line-of-sight component of a windshear threat from his present position to a region extending 2–4 km in front of the aircraft. This constitutes a warning time of 20–40 s, even in conditions of moderately heavy precipitation. Using these results, a Coherent Lidar Airborne Shear Sensor (CLASS) that uses a Q-switched CO2 laser at 10.6 μm is being designed and developed for flight evaluation in the fall of 1991.