Error Analysis And Experimental Research In Lidar Slant Visibility Measurement

Slant visibility is a decisive factor for aircraft take off and landing,and it is also one of the important meteorological elements to ensure flight safety.The accurate forecasting of slant visibility has important research significance and application value in the fields of aviation,navigation,transportation,meteorology and environmental monitoring.Lidar has the advantage of slant range detection of atmospheric scattering,and lidar detection technology has become an effective means of slant visibility measurement.At present,only a few single-wavelength lidar slant visibility detectors can estimate the slant visibility,and the obtained slant visibility results have large errors.In view of the application prospects of high-precision slant visibility detection in civil aviation,meteorological environment and other fields,this thesis takes the error in slant visibility detection as the research object,and carries out the analysis and experimental research of slant visibility detection based on lidar.The main research work is as follows:Firstly,according to the measurement principle of slant visibility and error theory,the error synthesis formula of the apparent brightness contrast between the target and the background is deduced,and the error analysis model of lidar slant visibility measurement is established.The five major error sources that affect the measuremen t results of slant visibility are analyzed in detail.A specific error analysis scheme is determined.Secondly,the research on the slant atmospheric transmittance error is carried out,the signalto-noise ratio of lidar detection is calculated according to the noise scale factor,and the calculation formulas of atmospheric aerosol extinction coefficient error and atmospheric transmittance error are deduced based on the error theory.The error of extinction coefficient and transmittance of atmospheric aerosol under cloudy and sunny conditions is analyzed by numerical differentiation,and it is found that the relative error of extinction coefficient of atm ospheric aerosol is less than 20%,and the error of extinction coefficient in cloud is less than 40%.,the relative error of the corresponding slant atmospheric transmittance is less than 20%.Then,considering the difficulty of error synthesis in the radiative transfer equation,the Monte Carlo method was used to simulate the random error distribution,and the error simulation analysis of the atmospheric scattering radiance was carried out.For different error distributions,the effects of vertical optical depth,single scattering albedo and asymmetry factor on the 33-layer atmospheric scattered radiance and direct and scattered radiance were investigated based on the SBDART radiative transfer model.When the vertical optical thickness,single scattering albedo and asymmetry factor errors obey the(0,5)normal distribution,the maximum relative errors of atmospheric scattered radiance in slant directions with zenith and azimuth angles of(50°,270°)and(70°,270°)are 2%,6%,and 2.1%,respectively.Furthermore,the sensitivity analysis of atmospheric scattering radiance error based on the SBDART model is carried out.The simulation results show that the single scattering albedo is the most sensitive factor affecting the scattering radiance,and the asymmetry factor is the smallest influencing factor.Finally,using the slant visibility lidar system built by the Lidar Remote Sensing Research Center of Xi’an University of Technology,the measurement experiments and error analysis of slant visibility and reflectivity were carried out under different weather conditions.The relative error of the reflectivity of concrete floor is within±5%,and the relative error of the reflectivity of green grass is within±20%.Using the multi-dimensional scanning characteristics of the lidar slant visibility system,the continuous detection experiment in a slant direction with 300 was carried out under cloudy conditions,and the maximum relative error of the slant visibility was 4.23%,and the minimum relative error was 3.88%.At the same time,the scanning profile experiments with a slant of 20°～40° were carried out under the condition of haze weather.When the zenith angle is 70°,the relative error of the oblique visibility is 10.24%,and the relative error of the oblique visibility is 8.89%when the zenith angle is 50°.