Research On Millimeter Wave Scattering Characteristics And Retrieval Of Hydrometeor In Clouds

The cloud plays an important role in the atmospheric space environment,and it has an important influence on the transmission of millimeter wave in the atmosphere.In order to ensure the transmission effect of millimeter wave in the atmosphere,it is necessary to study the characteristics of the scattering,attenuation of the millimeter wave and the type of hydrometeor in the cloud.The irregularity of ice crystal particles in the roll clouds increases the difficulty of cloud research.The main research results of this thesis are as follows:(1)Using the discrete dipole approximation algorithm to calculate and analyze the millimeter wave scattering characteristics of the ice crystal particles in the cloud under different conditions,and the calculated results are compared with the Mie theoretical results under the same conditions.The comparison results show that the discrete dipole approximation algorithm can accurately calculate the millimeter wave scattering characteristics of ice particles.When the ice crystal particles thaws,the scattering characteristics of the millimeter wave are also changed.In this thesis,the scattering characteristics of the thawed ice crystals under different conditions are calculated by using the concentric bilayer ball and the concentric double decker ellipsoid model.The single scattering characteristics of the cirrus layer in millimeter wave band are analyzed.The results show that the size of ice crystal particles has a great influence on the scattering characteristics of cirrus clouds.(2)The millimeter wave scattering characteristics of cloud droplets under different conditions are calculated and compared by the Rayleigh approximation,Mie theory and DDA method.According to the classical formula and the empirical formula of engineering calculation,the attenuation of cloud is calculated and the relative error of the empirical formula is analyzed,and its attenuation characteristics are calculated according to the actual conditions of different types of clouds(high clouds,middle clouds,low clouds,cumulus clouds,rain clouds and rain stratus clouds).(3)The fuzzy logic algorithm is combined with the cloud parameters obtained by the polarization radar detection to retrieve the type of hydrometeor in the cloud.The results show that the fuzzy logic algorithm is basically accurate in judging the type of hydrometeor.But in some special cases,for a group of radar input parameters,the intensity of different types of water condensate may be the same,so an improved algorithm combining neural network algorithm with fuzzy logic algorithm is introduced: neural fuzzy algorithm.By automatically adjusting the parameters of the membership function,the neural fuzzy algorithm makes up for the inadequacy of the type of the hydrometeor in the cloud,and improves the accuracy of the retrieval of the water in the cloud.The thesis considers the different precipitation types,the content of water in the non precipitation cloud and precipitation cloud is retrieved,and the results of the retrieval are compared with those of the previous ones,which have not considered the precipitation type.The results of comparison show that the correctness of the retrieval results of the water content in clouds enriches the method of retrieval of water content in clouds.