A Preliminary Study On The Characteristics And Identification Methods Of Lidar Echoes From Low-altitude Wind Shear

Low-altitude wind shear is a serious threat to flight safety due to its sudden burst,small scale,short life cycle and extremely destructive characteristics,especially during the take-off and landing phases of the aircraft.Laser wind radar can provide more detailed three-dimensional wind field information,making up for the lack of space-time density of conventional sounding.It's a very effective detection device for low-altitude wind shear.Therefore,the research on the characteristics and recognition algorithm of low-altitude wind shear wind field under lidar is also an important task to identify wind shear.The wind measurement performance test of laser wind measurement radar was carried out in Panzhihua Airport,Xining Airport and Kunming Airport from April to June of 2018,December of 2017 to June of June 2018 and January to August of 2018.These tests provided valuable research materials for this article.The least squares fitting method which is suitable for weather radar is used for lidar to identify wind shear for the first time.And we use the K-domain frequency method to control the quality of lidar data.Therefore the recognition performances under different wind shears are verified according to the current international wind shear strength standard.Finally,real examples are used to analyze the recognition effect of the recognition algorithm.The conclusions of this paper are as follows:(1)Lidar has a variety of detection modes,PPI scanning can be used to obtain the evolution characteristics of airborne distribution around the device.RHI scanning can be used to obtain the vertical distribution of airborne wind along a certain azimuth.Upwind and crosswind changes provide an effective means for the dynamics of meteorological research and the development of aeronautical meteorological services.The analysis shows that the laser wind radar has a wide detection range in stable wind fields such as clear sky,cloudy and cloudy,and has high detection sensitivity,which can accurately capture the change of low-altitude wind field,which is beneficial to the analysis of low-altitude wind shear wind field.Under the influence of the precipitation system,the laser wind radar is relatively weakened by rainwater,but the precipitation range and the moving position can be inferred from the narrowing of the detection range caused by the attenuation.Under the influence of non-precipitation system,the surface thermal force will reach the strongest in the noon to afternoon period,and occasionally there will be strong winds in the lower layer.The turbulent layer will be extended upwards.It will be affected by the topographic dynamics and thermal force,showing the convergence of the mountain windward slope and the upwind slope.In the form of scattered flow fields,wind shear occurs frequently.(2)K-domain frequency method is an effective way to filter out noise echo and fill in missing values.Through multiple sets of comparison experiments,the optimal parameter configuration for laser wind radar is obtained.The algorithm doesn't change the inter-library pulsation of the laser radar radial velocity while performing noise filtering and filling the missing values.(3)According to the nature of low-altitude wind shear and meteorological characteristics,the calculation of radial and azimuth shear values is performed by least square fitting method,and then two kinds of shears are synthesized.This algorithm is very effective for lidar in identifying low-altitude wind shear while it is good for the indentifications of severe,moderate and mild wind shear.This algorithm can be used to indentify wind shear and determine the strength of the shear.(4)Bases on the 20 cases of real low-altitude wind shear occurred at Xining Airport,the identification algorithm of low-altitude wind shear identification was analyzed by this paper,and it was compared with aircraft reports and self-observation equipment data.Thunderstorm weather and sandstorm weather will cause a certain degree of attenuation on the shear recognition effect of laser wind radar,resulting in unstable recognition in these two types of weather.