Research On Monitoring Method Of Low Level Wind Shear Based On Wind Lidar

Due to the characteristics of large changes in space-time scale,difficult observation and prediction,low-level wind shear is the primary factor causing flight accidents.However,the traditional wind measurement methods used in wind shear monitoring often reflect the defects of low recognition rate and weak timeliness,which can not fully meet the needs of flight safety.In contrast,wind lidar has unique performance advantages.This paper mainly studies the wind shear monitoring method of wind lidar.In view of the disadvantages of the existing wind shear recognition algorithms,the algorithms are improved.According to the characteristics of each algorithm,the F-factor detection algorithm based on the combined data of PPI and RHI scanning of wind lidar,the S-factor algorithm based on the wind shear intensity factor to detect the wind profile of the glide path,and the regional divergence algorithm based on the fusion of minimum double fitting and eight neighborhoods are proposed.The appropriate wind shear intensity level and alarm threshold are selected.In order to analyze the performance of the improved algorithm proposed in this paper,simulated wind fields are constructed by MATLAB.According to the uniform wind field,the influence of the installation position of the wind lidar with SP scanning mode on the wind measurement performance is analyzed.According to several typical wind fields,the wind shear identification effect of the algorithm is analyzed,and the effectiveness of the improved algorithm is preliminarily verified.Finally,in order to further verify the wind shear recognition effect of the improved algorithm,the wind shear monitoring experiment of wind lidar is carried out in Yushu airport.The measured wind field data of wind lidar is selected to analyze the difference between before and after the improvement of the algorithm.Combined with the wind profile radar data and automatic wind measurement system data of the airport,several representative wind shear events are selected,the evolution process is comprehensively analyzed.The following conclusions can be drawn:1.Although the existing wind shear identification algorithms can detect wind shear under various wind field types,they still have defects.The theoretical model proposed in the modified F-factor algorithm is ideal.When the vertical motion of the atmosphere is strong,the calculation results of the model are quite different from the actual wind field.The detection effect of the GLYGA algorithm is closely related to the slope length used in the detection.The wind shear alarm simply based on the shear value can not fully reflect the impact of the wind field on the aircraft flight,and it is easy to produce missing or false reports of wind shear.The algorithm is difficult to give consideration to the warning of strong wind shear and the identification of weak wind shear.The least square fitting algorithm only considers the shear values in the radial and tangential directions of radar scanning,which is easy to cause the omission of small-scale wind shear.The eight neighborhoods algorithm uses the direct difference method to detect the wind shear,and the detection results are easily affected by the noise data.The existing algorithms need to be improved to make up for the shortcomings of the algorithms.2.During SP scanning,with the increase of the angle between the laser beam and the glide path,the difference between the scanning results of wind lidar and the real wind field gradually increases.In order to ensure the accuracy of the scanning data,the wind lidar should be installed as close to the airport runway as possible without affecting the flight,so as to keep the included angle between the laser beam and the glide path within a small range,especially to avoid the situation that the laser beam is perpendicular to the glide path.3.The S-factor algorithm proposed in this paper uses the wind shear intensity factor to detect the wind profile of the glide path,comprehensively considers the impact of the total change degree of wind speed and the change rate of wind speed on aircraft flight,can take into account both strong shear alarm and weak shear identification,and solves the problem that the identification result of the GLYGA algorithm is greatly affected by the detection length.The normalization of wind shear intensity and the classification of wind shear intensity are realized,which is helpful for pilots and meteorological support personnel to make a reasonable judgment on the degree of wind shear affecting flight.4.By combining PPI scanning and RHI scanning of wind lidar,the combined F-factor algorithm proposed in this paper solves the problems of unknown vertical wind speed in the detection of the traditional F-factor algorithm and inaccurate vertical wind speed model of the modified F-factor algorithm,and improves the ability of the algorithm to detect the impact of vertical wind field on aircraft flight.5.The regional divergence algorithm proposed in this paper combines the advantages of the least square fitting algorithm and the eight neighborhoods algorithm.It not only suppresses the influence of noise data on the wind shear detection results,but also improves the accuracy of the algorithm for wind shear location and shear zone edge recognition.6.The regional divergence algorithm aims at the PPI scanning data of wind lidar and has a wide detection range.It is suitable for the identification of wind shear in the two-dimensional plane of the airport area.S-factor algorithm and combined F-factor algorithm are more targeted to detect the wind profile of the glide path,and can better reflect the impact of wind field changes on aircraft takeoff and landing.In contrast,the combined F-factor algorithm can detect the vertical wind speed.When the vertical motion of the atmosphere is strong,the wind shear recognition result of combined F-factor algorithm is more reliable.S-factor algorithm can realize the classification of wind shear intensity,retain the detailed characteristics of wind field to a greater extent,and is more helpful for pilots and meteorological support personnel to judge.7.The combination of wind lidar,wind profile radar,automatic wind measurement system and other traditional wind measurement methods can effectively improve the detection ability of the airport to the wind field,as well as the monitoring ability of convective wind shear,such as systematic gale wind shear,momentum down gale wind shear and other types of wind shear,and effectively improve the flight safety guarantee ability of the airport.