| Visibility is one of the important parameters of meteorological observation.Accurate detection of it can provide early warning for aviation,navigation,highway and other fields,so as to avoid the occurrence of major accidents,which has important research significance.In sea fog monitoring,lidar has more advantages in principle than artificial visual inspection,image method,transmissive visibility meter,forward scattering visibility meter,etc.However,the current visibility lidar does not meet the requirements of long detection range and high time resolution,and has low accuracy of inversion algorithm,so it is difficult to apply it to the changeable sea fog monitoring.In this paper,based on the simulation theory of visibility lidar system,aiming at the design goal,the parameters of each hardware part are simulated to get the design parameters and configuration.According to the optimized parameters,the visibility lidar system design is carried out.When the time resolution is 10 seconds and the visibility is more than 5 km,the maximal detection range is more than 5 km in daytime and 10 km at night.The quality control standard of ERLINET is introduced to calibrate the visibility lidar system,including dead time calibration,zero point calibration,overlap factor calibration,dark noise test,symmetry test,linearity test,Rayleigh signal fitting test,so as to ensure the reliability of hardware.It can be seen from lidar equation that it contains two unknown parameters(backscatter coefficient and extinction coefficient).However,there is only one equation.Thus,it is often necessary to make some assumptions,which is also the source of inversion result error.How to improve the accuracy of inversion algorithm is also a worthy research content.Aiming at the high precision of inversion algorithm,a high precision horizontal visibility inversion algorithm is proposed in this thesis.In the simulation analysis and comparison with the forward scattering visibility meter,it is proved that the proposed algorithm has the characteristics of high accuracy and high stability.Due to the rapid and uneven change of sea fog,the forward scattering visibility measurements at meteorological observation positions such as coasts and Islands can only obtain data over a limited scanning range,which makes them not the optimal choice to provide forewarning observations.To solve this problem,the developed visibility lidar and proposed inversion algorithm are applied to the sea fog monitoring and early warning.In the field tests of Hengsha Island,Qiongzhou Strait and Zhoushan Islands in Shanghai,the visibility data obtained by visibility lidar and forward scatter visibility meter are compared and analyzed.Both of them are consistent in general and special weather conditions.In the field experiment of Hengsha Island in Shanghai,in February 2019,the visibility lidar gave an early warning for the sea fog at the distance of 5 km about 3.5 hours in advance.In the field test of Qiongzhou Strait,during the Spring Festival 2019,visibility lidar successfully monitored sea fog and closely tracked the change of visibility,providing meteorological guarantee for passenger and cargo transportation in Qiongzhou Strait during the Spring Festival.In the field test of Zhoushan Islands,during the 2019 typhoon,two visibility lidars in Zhoushan Islands have experienced the test of typhoon weather,successfully monitored the evolution process of visibility before and after the typhoon,and closely followed the change of visibility,showing excellent performance.It has been tested in Hengsha Island,Qiongzhou Strait and Zhoushan Islands for a long time,which proved the reliability of the lidar and the feasibility of sea fog monitoring. |
PDF Full Text Request