Theoretical And Experimental Research On Detection Of Air Pollutants Based On CCD Lidar

With the acceleration of industrialization in China,environmental problems are becoming more and more prominent,and the frequent occurrence of hazy weather has attracted great attention from the public.Aerosols that cause atmospheric pollution usually include smog,dust,haze,etc.Aerosols are mainly distributed in the troposphere,especially in the boundary layer of the atmosphere,which are closely related to human production and life.Aerosols will not only affect the Earth’s radiation income and expenditure and climate change,but also cause serious atmospheric pollution,threatening human health and bringing great challenges to win the battle for blue sky and build a beautiful China.The vertical profile of the extinction coefficient of aerosols is crucial for assessing the distribution and transport of atmospheric pollution.Light detection and ranging（Lidar）is currently the most commonly used technique to detect the vertical structure of the atmosphere.As an active remote sensing tool,Lidar can achieve all-day,all-weather and fully automatic detection.Lidar is widely used in meteorological,environmental protection and aviation fields.However,due to the biaxial structure of Lidar system,it has detection blind area and transition area（the incomplete overlap area of laser divergence angle and receiving field of view）,which leads to the error in the detection of bottom atmosphere near the ground.CCD（charge-coupled device）side-scatter Lidar has been developed to detect the bottom atmosphere,but its geometry and algorithm still need to be improved.The spatial resolution is competitive with Lidar and needs to be further improved.In order to obtain an accurate vertical distribution of lower atmospheric aerosols,a system is built on the basis of CCD side-scattering Lidar with enriched functional modules,optimized system geometry and improved inversion algorithm.In addition,the system is also used to evaluate the errors of conventional Lidar in the transition zone.The following work is done in this thesis:（1）Designed and built a dual CCD-based atmospheric boundary layer aerosol laser detection system（DCLS）.The system consists of a horizontal detection module and a vertical module.The532 nm continuous lasers as the transmitting end and the CCD cameras as the receiving end.The CCD and the laser of the vertical detection module are integrated on a custom reflective frame,and the distance and angle are fixed,so that the system can achieve no blind zone with a spatial resolution of up to 10^-3m.The CCD saves the scattered signal as an image in the software console,and matlab is used for noise filtering and signal extraction.The grayscale information of the image is converted into the intensity of the scattering signal,which is substituted into the algorithm to obtain the scattering phase function and extinction coefficient of the aerosols.The Adam algorithm is also introduced to obtain the vertical profile of the scattering phase function,which reduces the uncertainty.In addition,the reliability of the constructed DCLS was also verified using a polarized Mie scattering Lidar.The regions where both have high signal-to-noise ratio are selected,and their extinction coefficient profiles are compared.The results show that the correlation coefficients are above 0.95 and the relative errors are below 5%.（2）The geometric overlap factor（GOF）is introduced to correct the incomplete scattered signal in the transition zone of a conventional Mie Lidar.The errors introduced by GOF are difficult to eliminate due to the limitations of hardware parameters and inhomogeneous atmospheric distribution.To specifically evaluate the errors introduced by the GOF in correcting the transition zone signal,several joint detection experiments were conducted using the DCLS and the Mie scattering Lidar.By comparing the aerosol extinction coefficient profiles in the transition zone of the two system and analyzing the linear fitting results,it was found that the DCLS showed a finer vertical structure of the atmosphere.The degree of linear fitting varied greatly at different times,which might be due to the non-uniformity of aerosol variation with time and space causing the GOF to have different performance in correcting the transition zone signal.The experimental results show that the average relative error of the Mie Lidar in its transition region with the DCLS is around 20%.Finally,a method to correct the GOF of the Mie Lidar using the DCLS is proposed,and the obtained GOF curves are more reliable compared with the traditional slope method.The DCLS has a very high resolution in the lower atmosphere,which can completely cover the blind zone and transition zone of the backscatter Lidar.The DCLS can be applied to the data correction of the backscatter Lidar in the transition zone,which provide a finer vertical distribution of aerosols and a useful reference for air pollution control and traceability issues.