| This paper reports a following research on laser radar and atmospheric particulate concentration:(1)An overview of research background of the subject,focusing on the classification of laser radar,characteristics,and the advantage of measurement of PM2.5 concentration based on the Charge-Coupled Device backward scattering lidar,and the research status of atmospheric aerosol was introduced.(2)The characteristics of gaussian beam and transmission in a vacuum were illuminated.The composition of the atmosphere,and the interaction of atmospheric aerosol and photons were also illuminated,concentrating on the mie scattering characteristics and simple explained the monte carlo model.(3)According to Mie scattering theory and laser propagation equation,a theoretical measurement model of atmospheric particulate concentration was built,in addition,an experimental device monitored the real-time PM2.5 concentration was designed by using charge-coupled device(CCD)backward scattering lidar.The experiment system use a 532 nm laser as the light source and a CCD as detector of back scattering light.According to the real time image captured by CCD,the gray level value matrix was extracted,and the intensity distribution of the scattering image was analyzed.Compared with the results of a PM2.5 monitor from Thermo Fisher Scientific Company,five formulas about PM2.5 concentration and scattering lighting were concluded with a fitting degree over 0.95.A further popularization of this atmospheric particulate concentration monitoring device with low lost and convenient operation,will play a significant role in investigating the movement of PM2.5 and depicting pollutant distribution.(4)A new method--noise averaged method was introduced about obtaining the grey value matrix of N pictures at the same time,and then adding N matrixs and averaging,calculating the average of grey value matrix.The noise average method obtained good results after the treatment on the experiment and images.Furthermore,with the increase of N,noise elimination effect is more obvious.Using noise average method to deal with the experimental images extracted the processed image of grey value matrix,obtaining the CCD images which received the range from 33 degrees to 145 degrees of the scattering Angle laser scattering intensity signal with that matrix.According to the relation between CCD camera receiving scattering light intensity and the laser transmission light intensity,the scattering coefficient of atmospheric particulates in xiasha was performed,obtaining the related curve between scattering Angle and scattering coefficient of atmospheric particulates.(5)A monte carlo model of multiple scattering was established,simulating Mie scattering model for monte carlo simulation when the values of asymmetric factor g were taken 0,0.2,0.5,0.8,0.95,respectively,and getting some scattergrams about the number of entered photons changed with the scattering Angle,and the simulation result was consistent with the asymmetric factor.In addition,when the value of g was 0,L was 300 cm,400 cm,500 cm,600 cm,respectively,and the photon detector in x axis coordinate is 15 cm,20 cm and 25 cm and 30 cm,respectively,d was 30 cm,40 cm,50 cm,60 cm,respectively,while other parameters were constant,simulated the above parameters of monte carlo model,and obtained some scattergrams about the number of entered photons changed with the scattering Angle,which illustrated the photon number that entered into the photon detector was increased proportionately when the photon detector is more close to the laser beam. |
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