Design And Preliminary Experimental Observation Of Electromechanicali System For Slant Visibility Lidar

Visibility,especially slant visibility,is one of the atmospheric parameters that are difficult to measure with accuracy.It directly affects the safety of aircraft departuring and landing in the field of aviation.The profile of aerosol extinction coefficient with accuracy is required for slant visibility retrieval.A lidar thought of as an active remote sensing tool has the advantages of high spatial and temporal resolution and high detection sensitivity,thus it has become important equipment for probing optical characteristics such as aerosol extinction coefficient,backscattering coefficient and optical thickness.At present,most lidars work in vertical mode to probe the optical characteristic profile in the atmosphere.If a two-dimensional scanning model is additional,it can be used to detect slant visibility.We mainly research the two-dimensional scanning electromechanical model of slant visibility lidar in this thesis,which provides the technical support with the high-accuracy and highly reliable for the slant visibility detection.The two-dimensional scanning mechanism is one of the important components of the slant visibility lidar.According to its main technical specifications,a two-dimensional scanning mechanical system for lidar is designed in this thesis.Firstly,the theory of detecing slant visibility in atmospheric with lidar is analyzed.Based on the design requirements of the rotational speed of 0.05°/s-6°/s and accuracy of 0.05°,a worm gear mechanism with a 1:70 reduction ratio is used,and its static analysis is conducted.Spherical roller bearings are used as the slewing motion pair.And the stepper motor drives the worm to transfer power.Secondly,the incremental photoelectric encoder is used to detect position and speed.And with the controller as the core,a semi-closed loop control structure is formed,which can compensate the position deviation in real time and improve the rotation accuracy and thre responding speed of the scanning mechanism.Finally,the materials and installation methods of the scanning mirror are analyzed,and the structure of the two-dimensional scanning mechanical system of slant visibility lidar is completed.The integrated control software plays main role for layout the multi-module cooperation of the slant visibility lidar.Using the existing 2D scanning pan-tilt as a simulation platform,We have developed integrated-control 3D scanning software to integrate data acquisition,two-dimensional scanning,and module collaboration of lidar,which includes four functional modules such as scanning motion control module,laser control module,photoelectric detection module and data acquisition module.The data acquisition module cooperates with the laser and the motion scanning modes to collect the information of atmospheric in the target area,and then digitizes the collected signals of each channel and stores them into the file,which achieve the coordinated operation of the slant visibility lidar during the detection process.In order to evaluate scanning performance and overall detection performance,the preliminary observation experiment and the analysis of retrieval algorithm optimizated are carried out.The single-axis precision measurement and single-point repeatability measurement experiments are carried out for the scanning mechanism.The results show that the positioning error is about 0.1 degrees and the repeatability is about 0.05 degrees,which basically meets the design accuracy specifications.The integrated slant visibility lidar was used to carry out preliminary experimental observations of the atmosphere,and we obtained valid data.Based on the lidar data,the boundary value selection method for retrieving the profile of aerosol extinction coefficient is studied.The appropriate boundary height is determined to be within the range of the farthest effective detection distance determined by the signal-to-noise ratio.And the two algorithms which are the scattering ratio iteration method and the fixed point iteration method for determining the boundary value are used to perform data retrieval at low detection distances.The retrieval results are compared with the profile of the extinction coefficient result of the Raman method.The extinction inversion error of fixed point iteration method is controlled within 20%,which is superior to the scattering ratio iteration method.The design verification and preliminary experimental results show that the developed two-dimensional scanning electromechanical system can meet the inversion requirements and provide strong equipment support for high-precision retrieval of atmospheric slant visibility.