Study On Wave Propagation And Scattering Characteristics Of Atmospheric Discrete Random Media

According to the atmospheric radiative transfer theory, wave propagation and scattering characteristics of discrete random media are studied. The main works and results are as follows:1. Based on the Lorentz-Mie theory, the single scattering characteristics of multi-dispersed spherical and multi-layered spherical particles are studied. The extinction coefficients, scattering coefficients, single albedos, single scattering phase functions and asymmetry factors of different clouds are presented. Numerical results for single scattering of spherical and non-spherical particles are obtained in the approximation of geometrical optics. The single scattering phase matrixes of non-spherical aerosols are calculated by using the T matrix method.2. The scattering and reflection of light by clouds are studied by scalar radiative transfer theory. The plane albedos and bidirectional reflectance of clouds are given. The influences of clouds types, clouds thickness and liquid water content on the light scattering characteristics of clouds are discussed. The multiple scattering errors caused by substituting Henyey-Greenstein phase function for Mie phase function and substituting equivalent spheres for ice clouds particles are studied in detail. Light scattering characteristics of ice-water mixed clouds are studied by using of the two-layered spherical particle models, and the clouds absorption anomaly is studied.3. The intensity and polarization of sunlight reflected by clouds are computed with the adding method based on the vector radiative transfer theory. The influences of clouds optical thickness and effective radius on polarized light scattering are discussed. Multiple scattering of polarized light by ice-water mixed clouds are studied. The results of computations indicate that the polarization is more sensitive than the intensity to cloud microstructure, such as the particle size, shape and phase. Hence polarization measurements, particularly in the near infrared, are the potentially a valuable tool for cloud identification and for studies of the microphysics of clouds.4. A more practical three-layered sphere model of melting ice particle has been given. Based on this model, the radar reflectivity, together with the specific phase shift and the specific attenuation of a melting layer of precipitation, were computed by using the Mie theory. These results are in agreement with the conclusion given in literatures. It demonstrates that the three-layered snow sphere model is appropriate and practicable. The melting layer is composed of melting snow particles which is a mixture of ice water and air. The melting process starts with the snow particle falling, so the microphysical characteristics of melting layer are continuous. Base on the radiative transfer theory, the Monte Carlo method is used to compute the reflectivity of the whole melting layer.5. A method for computing various functions and constants that appears in asymptotic equation is imposed. The bidirectional reflection function of optically semi-infinite particulate layers is found by a simple iterative solution of the Ambartsumian's nonlinear integral equation. Escape function, diffusion pattern and diffusion exponent are computed in terms of the reflection function of optically semi-infinite layers. Since this method bypasses the computation of the internal radiation field, it is a fast and. effective approach. We also illustrate the accuracy of the approximations for an atmosphere containing water clouds by comparing them with the exact results.6. A method is presented for determining the optical thickness and effective particle radius of clouds from reflected solar radiation measurements, and a detailed study is presented for its feasibility. We use numerically accurate solutions of the vector radiative transfer equation to simulate aerosol retrievals utilizing radiance measurements alone, polarization measurements alone, and radiance and polarization measurement combined. We have restricted all simulations to a visible wavelength of 0.75 pan and a near-infrared wavelength of 3.3μm. Our analysis demonstrates that radiance-only or polarization can pose a severe uniqueness problem with a single wavelength, but measurement of polarization as well as radiance can resolve such uniqueness problems...