| Cloud is one of the important factors that affects the weather change.If we can effectively detect the macroscopic and microscopic physical characteristics of the cloud,it will help to eliminate or weaken some extreme weather phenomena as much as possible by artificially influencing weather technology.The effective detection of the distribution of supercooled clouds is the key technology to affect the weather operation.Combined with the existing visible ban d polarization lidar retrieval technology for aerosol particle sphericity,a scheme of near-infrared band polarization lidar to retrieve cloud particle characteristics is proposed,which can effectively detect the real-time distribution of supercooled clouds.The light scattering characteristics of cloud particles are analyzed by using the theoretical model of light scattering of non-spherical particles based on the discrete dipole approximation and geometric optics approximation.It is solved that it is difficult to effectively analyze the light scattering characteristics of non-spherical cloud particles based on Mie scattering theory.In this paper,the Mie scattering theory,geometrical optics approximation theory and discrete dipole approximation theory used to analyze the lig'ht scattering characteristics of cloud particles are studied.The study based on Mie scattering theory shows that 1550nm near-infrared band is suitable for detecting the scattering characteristics of cloud particles with a radius of 3?m.At the same time,a near-infrared polarization lidar system for inversion of cloud particle characteristics is proposed,the system structure and main parameters are designed in det'ail.Based on the above three light scattering theories,a model for calculating the light scattering characteristics of cloud particles is established.The geometrical optical approximate model mainly calculates the light scattering characteristics of cloud particles by matrix operation among Stokes vector matrix,Fresnel matrix and coordinate transformation matrix,whereas the discrete dipole approximate model mainly calculates the light scattering characteristics of cloud particles by matrix operation amo ng fml matrix,scattering amplitude matrix and Muller matrix.The related programs are written based on Matlab platform.The discrete dipole approximation theory and the geometrical optics approximation theory are compared with the Mie scattering theory,the reliability of two light scattering theory for non-spherical p articles is verified.In order to satisfy th e characteristic that cloud particles are arbitrary orientations distribution in space,the number of 104 orientations can meet the convergence requirements for the geometrical optics approxim ation theory while the size parameter of particle is more than 20.Whereas approximate 800 orientations can satisfy the convergence requirements for th e discrete dipole approximation th eory while the size parameter is less than 20.Two kinds of non-spherical particle light scattering theories are compared with the equal volume Mie scattering method,and it can be seen that a large number of errors will be introduced by the equal volume Mie scatterin g method while the asphericity of the particle is high.In order to make the detection performance analysis results of polarization lidar closer to the real situation,the cylinder particle whose length-radius ratio is 6:1 is taken,the detection performance of polarization lidar is simulated by using discrete dipole approximate theory.Compared with the Mie scattering method,the power of echo signal is reduced by about on e-tenth,and thus the detectio n distance is reduced from 140m to 60m.The depolarization ratio of a single cylindrical particle on the whole cloud particle spectrum is accumulated and averaged,and the depolarization ratio of the whole cloud particle spectrum is about 0.65,which has a few reference value for determining the shape of cloud particles according to the depolarizatio n ratio m easured in practical application. |
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