The Alerting Algorithm Research Of Turbulence Based On Coherent Doppler Lidar

Turbulence is an internationally-accepted atmospheric phenomenon that seriously affects flight safety,it has characteristics like small scale,high intensity,short duration and so on.Currently,the longitudinal velocity structure function,as the lidar turbulence alerting algorithm applies in practice,leads to omitting small scale turbulence easily.So it is very important to study the effective turbulence alerting algorithm.In addition to selecting the appropriate scanning mode to get effective wind velocity data,the processing of wind velocity data is also very important.Turbulence is extremely harmful to the aircraft in the process of departure and landing.So the glide-path scanning has been chosen,with both pertinence and shorter scanning time.Thereby the rate of early alerting is improved.Firstly,the radial wind velocity data from the glide-path scanning needs to go through quality control,and then the scanning area is divided into a plurality of overlapping subsectors and the subsectors near the glide-path are filtered to calculate the velocity fluctuation of every lidar measurement point.Secondly,the alerting algorithm is used on the the velocity fluctuations to find the position and the intensity of turbulence,which should be reported to pilot.There are mainly three alerting algorithms,including standard deviation,spectral width and velocity structure function.According to the study of these three algorithms,the standard deviation needs to go through a lot of experiments to determine the threshold,and the spectral width algorithm needs to be evaluated by a large number of experiments.The velocity structure function has been applied in practice among airport.Due to actual application,alerting rate has been greatly improved.A algorithm of combining glide-path scanning with transverse velocity structure function has been proposed.The structure function is fitted with the theoreitical Von Karman model to give eddy dissipation rate,and the result is compared to the provisions of the International Civil Aviation Organization's turbulence threshold to come to the conclusion.The effectiveness of this method has been proved by lidar measurement data.It is significant toimprove the turbulence alerting rate and practical application.