| Cirrus clouds play an important role in the atmospheric environment,which is mainly composed of ice crystal particles.Studying the microcosmic physical characteristics of cirrus clouds is of great significance to optical communication technology,cloud radar,satellite remote sensing and so on.The wavelength of terahertz wave is the same as the size of cirrus ice crystal particles,so it has unique advantages in cirrus cloud detection.In this paper,the scattering and absorption characteristics of ice crystal particles and water droplets are studied.The main work is as follows:1.Aiming at the three frequency bands of 94 GHz,220GHz and 340 GHz,Mie scattering method and discrete dipole approximation(DDA)are used to calculate the scattering and absorption characteristics of a single spherical ice crystal particle,and their relative errors are calculated.The DDA method is verified to be correct by analysis and comparison.2.DDA method is used to calculate the influence of different frequencies and different complex refractive indexes on the scattering and absorption characteristics of spherical ice crystal particles,and the reasons for choosing 94 GHz,220GHz and 340 GHz are explained.The scattering and absorption characteristics of spherical ice crystal particles and spherical water droplets varying with the equivalent radius in these three frequency bands are calculated.3.DDA method is used to calculate the effects of different complex refractive indexes,different frequencies,shapes,aspect ratios and spatial orientations on the scattering and absorption characteristics of non-spherical ice crystal particles at 340 GHz.Furthermore,the influence of ? angle interval in spatial orientation on scattering and absorption characteristics of hexagonal ice crystal particles with different aspect ratios is deeply studied.4.The modified satellite data simulator unit(M-SDSU)model is put forward,and the simulation results of SDSU and M-SDSU are compared for spherical ice crystal particles,so as to verify the correctness of M-SDSU.The forward simulation of non-spherical ice crystal particles is realized by using M-SDSU.The results show that DDA method and Mie scattering show almost the same results for spherical ice crystal particles,which shows that DDA method has better calculation accuracy.The scattering characteristics of particles in terahertz band are richer,and ice crystal particles are easier to detect.Different frequencies,different shapes,different aspect ratios and different spatial orientations have certain influences on the scattering and absorption characteristics of ice crystal particles.It is unreasonable to assume that the shape of ice crystal particles is spherical or ellipsoidal.Spatial orientation has different effects on hexagonal ice crystal particles with different aspect ratios.Compared with the traditional SDSU simulator,the proposed M-SDSU model is accurate and can realize the forward simulation of non-spherical ice crystal particles.The research results provide an important theoretical basis for the detection of cirrus clouds in THz band and the design of THz cloud radar. |
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