Simulation Of The Depolarization Characteristics Of Dust Aerosol Particles With Multi-wavelength

Dust aerosol is a typical non-spherical particle,which is an important part of atmospheric aerosol.By changing the energy balance of solar radiation and thermal radiation,the life time and the formation of clouds,it has an impact on the radiation budget of the earth-atmosphere,and then has a significant impact on the earth climate system.It is very important to study the light scattering characteristics of dust aerosol for understanding their influence on radiative transfer.Depolarization ratio is often used to characterize the morphology of non-sphericity of non-spherical aerosol particles quantitatively.To study the depolarization characteristics of dust aerosol particles is helpful to improve the understanding of their optical and microphysical properties.The simulation of light scattering characteristics of dust aerosol particles is mainly affected by the shape model.In this thesis,the super-ellipsoid particle model is established firstly to numerically model the shape of the non-spherical particle taking the advantage of the high degree of freedom in dimensions.The light scattering characteristics of single dust aerosol particle are simulated by using the discrete dipole approximation method by changing the shape model,scale parameters,wavelength and complex refractive index.The simulation results show the feasibility and practicability very well of our methodology.In addition,the depolarization ratio of backscattered light of single dust aerosol particles with different models is also calculated.Combined with the size distribution information of dust aerosol particles provided by the OPAC(Optical Properties of Aerosols and Clouds)package,the light scattering characteristics of group dust aerosol particles are simulated to study their wavelength dependency.Three wavelengths such as 1064nm,532nm and 355nm are used for calculating the depolarization ratios of different super-ellipsoid particles and the simulation results show 0.317,0.397 and 0.446 for each wavelength respectively.Comparing with the lidar measurements,the depolarization ratio at 1064nm wavelength shows the highest consistence,and then at the 532nm wavelength.The depolarization ratio at 355nm wavelength has larger bias with the lidar measured value which may be caused by the same numbers of the dipole used for all wavelengths and needs to be investigated in the future.The methodology and non-spherical models used in this study will greatly lead our understandings on the wavelength dependence of the depolarization properties of the dust aerosol and guide the development of the multi-wavelength polarization lidar.And also,it could provide a unique technique to research the mixing state and the evolution of the pollution aerosols.