| Aerosol is an important parameter in atmospheric physics,and it is of great significance in the study of global radiation transmission,climate change and environmental pollution.Lidar is an important instrument for remote sensing of atmospheric parameters,which has the advantages of high temporal and spatial resolutions,long detection range and high detection accuracy.The lidars,including the traditional Mie scattering lidar,the Raman lidar and the high-spectral-resolution lidar,has the liminations in the the detection of aerosols in lower atmosphere due to the existence of geometric overlapping factor.As a new type of laser remote sensing technology,the lateral scattering lidar has the capability to detect aerosol optical parameters from the ground to the heigh of concern,as the transmitter and receiver are bistatique and overcome the weakness of the backscattering lidar in the detection of lower tropospheric aerosols.The lateral scattering image lidar is builit to detect the aerosol optical properties in the lower troposphere,based on the investigation of the working principle of the lateral scattering lidar.The transmitter of the lateral scattering lidar selects the high power pulsed Nd:YAG laser,which is used as the transmitter in the elastic backscattering lidar in the lab and has the parameters of transmitting wavelength of 532 nm,pulse energy of 500 mJ,and the repetitation rate of 10 Hz.The image CMOS camera sensor of Canon EOS 80D is used to receive and record the lateral scattering light of the laser beam.The aerosol optical properties can be retrieved after the determination of relationship between the image pixel and the lateral scattering of laser beam,including the position of image pixel and the height of the laser beam,the brightness of image pixel and the intensities of laser beam and so on.The retrieval method of aerosol optical properties using the lateral scattering image lidar is deduced in detail.Considering the camera images are used to record the lateral scattering signals of the transmitted laser beam,the pre-processing of image is performed firstly.To reduce the background noise and enhance the extraction accuracy of laser lateral scattering signal from the recorded images,three image noise reduction methods are studied,including the method of background subtraction,the noise estimation by averaging multiple photos,and the denoising algorithm based on gradient value of pixel function.The process results show that the denoise algorithm based on gradient value of pixel function has more advantages.After optimizing the extraction algorithm of laser lateral scattering signal and overcoming the phenomenon of breakpoints in the image,the profiles of aerosol extinction coefficient using the lateral scattering image lidar is retrieved using the techniques of data normalization and comparision with the surface visibility,which is verified to overcome the difficulities of the geometric overlapping factor of the elastic backscattering lidar.Therefore,we propose a novel aerosol detection method,which uses both the elastic backscattering lidar and the lateral scattering lidar and realizes the aerosol detection from the ground to the height of corcern.The continuous observations of trospospereic aerosols in Xi’an using the lateral scattering image lidar are performed for three months from November 2020 to January 2021.The detection cases in three weather conditions are analyzed,including the sunny day,the haze day and cloud day during the observation time,aiming to understand the the similarities and differences of the lateral scattering image lidar in the applications of different weather conditions.The experimental results show that the lateral scattering image lidar can realize the aerosol detection from the ground to the heigh of concern,and overcome the influence of the geometric overlapping factor of the traditional backscattering lidar.The analyzed results of three months continuous detection of aerosol optical properties present the aerosol variation of the lower troposphere. |
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