Research On Transient Vector Radiative Transfer In Inhomogeneous Semi-transparent Media

Light wave is a kind of transverse wave, and polarization is the basic property of light. Polarized light has been used widely in many fields, such as remote sensing, biological tissue imaging, and camouflage recognition of military target. Propagation of polarized light in scattering media is described by vector(polarized) radiative transfer equation. Vector radiative transfer equation(VRTE) is more complex compared to scalar radiative transfer equation(SRTE), and solving VRTE is more difficult. So far, the research on vector radiative transfer is focusing on steady vector radiative transfer in one-dimenstional homogeneous media, while there are still less works on transient vector transfer in inhomogeneous media.In this paper, research on vector radiative transfer in inhomogeneous media is investigated systematically. A Monte Carlo model for vector radiative transfer in three-dimenontional space is built. The model can discribe exactly the physical processes of scattering, absorbing, reflection, refraction, and the change in Stokes vector carried by light. Vector radiative transfer in a arbitrary multilayer system is investigated by using this model. The influnce of different kinds of surfaces(Fresnel surface, Lambert surface) on intensity and polarzaiton is analysed.A model by multilayer approximation is used to simulate vector radiatvie transfer in a gradient index medium. In this model, a gradient index medium is divided into a series of sub-layers, and the refractive index of each sub-layer is assumed to be a constant. When the sub-layer number is big enough, the results will tend to converge, and the problem of vector radiative transfer in a gradient index medium can be approximatly solved with high precision.The apparent polarization characteristics of thermal emission in media with inhomogeneous temperature fields are investigated. The effects of different temperature distributions, wall emissivity, refractive index, and optical thickness on apparent polarization characteristics are investigated.The MC model of transient vector radiative transfer in three-dimentional system is developed. Transient and polarized behaviors of a laser pulse propagating in a 3D multilayer semitransparent media is examined. The model is validated by compaing to experimental data.A direct collocation meshless method(DCM) is developed for solving VRTE. The theory of DCM for VRTE is systematically expounded. For the solution to polarized radiative transfer in a multilayer system with Fresnel interfaces, a scheme by combining Monte Carlo method(MCM) and DCM is presented. The scheme has the advantages of both MCM with easy implementation and high accuracy and DCM with low calculation cost. Distribution law of Stokes vector for transmitted light and reflected light is investigated, and it is observed that the incident light with polarzaiton will lead an asymmetric rotation of Stokes-vector distribution in hemisphere space.An active imaging technology is developed based on the Monte Carlo model for vector radiative transfer. Steady imaging technology and transient imaging technology are explored, repectively. The polarization imaging can enrich the optical information of the target to be detected, and thus help distinguish the object from the background. Under the environment of low visibility, transient imgaing technology can eliminate the interference of barrier. For transient imaging, it is very important to open the detector at a appropriate time.