Atmospheric Aerosol Detection And Experimental Research Based On Multiwavelength Lidar And In-situ Instruments

Great attentions have been paid to the effects on global climate,environment and human health arisen from atmospheric aerosols.As a climate forcing factor,atmospheric aerosol plays an important role in radiation and energy budget of the Earth.High aerosol concentration may decrease air visibility and quality,and may cause epidemic diseases,especially for children and teenagers.Study on aerosol vertical distributions and their optical and microphysical properties in high accuracy have already been great intuitive appeal.A multiwavelength lidar has the characteristics with high temporal and spatial resolutions,wide detectable range of particle size,obtained many optical and microphysical parameters,such as particle number concentration,particle size distribution,complex refractive index,etc,which has become one of the most powerful tools in atmospheric active remote sensing.In-situ measurement instruments,particle size spectrometers for example,and other passive remote sensing devices,e.g.sunphotometer,have also been used widely,as they can directly measure the particle size distribution,particle number concentration,surface area concentration,volume concentration and so on.In this work,we mainly combine a multiwavelength lidar and particle size spectrometer,sun photometer instruments to perform the studies on atmospheric aerosol optical and microphysical properties at day and night time,including1.We develop a multiwavelength Mie scattering lidar operating at 355nm,532nm,1064nm based on the designed spectral spectroscopy system using narrow band filters and broadband reflective mirrors,in which solar background light can be strongly suppressed.The signal to noise ratio at daytime measurement is effectively improved.Both theoretical analysis and experimental studies show that the detectable ability of the developed lidar is at heights of 8 km and 11 km at daytime and nighttime respectively.2.Aiming to the detection blind zone of the multiwavelength lidar in the near range,a new correction method based on the Mie scattering theory and the particle size distribution at the ground level were developed.This algorithm first calculates the aerosol extinction coefficients at the surface,following the exponential decline rule of aerosol number density in lower troposphere,and then obtains the fitting aerosol extinctions within the blind zone.The proposed method can be used to correct directly the multiwavelength lidar blind zone.3.In order to resolve effectively and accurately the technical difficulty of inversing lidar ratios,we proposed a method for correcting multi-wavelength lidar ratios by iterative algorithm using the optical depth data obtained by sun photometer.The correcting function was given in the thesis and the experimental results show that this method is able to improve the precision of the vertical inversion of aerosol optical coefficients,providing an effective algorithm for the fine aerosol distribution study.4.The correlation between particle size distributions obtained by aerodynamic particle size spectrometer and multiwavelength lidar ratios calculated by Mie scattering theory has also been analyzed.As a result,we found that the volume ratios of coarse particle to fine one,the particle effective radius,and the multiwavelength lidar ratios follow the linear relation by each other.This will provide a feasible way for studying the correlation of multiwavelength lidar ratio and aerosol size distribution.In addition,particle size distribution was retrieved from multiwavelength optical parameters of aerosols through the algorithm of Generalised Cross Validation(GCV)regularization.Obtained results were found to be agreed with the particle size distribution monitored by aerodynamic particle size spectrometer.Finally,the vertical distribution rules of particle size distribution were firstly investigated based on obtained color ratios and Angstrom indexes of multiwavelength.As conclusions,combined multiwavelength lidar and particle size spectrometer,sun photometer instruments,can provide supplementary and sufficient data for the studies on atmospheric aerosol optical and microphysical properties.