Comparison of discrete ordinate and Monte Carlo simulations of polarized radiative transfer in two coupled slabs with different refractive indices

BRDF characteristics of different textured fabrics in visible and near-infrared band

The directional reflection characteristics of fabrics with various texture structures is an important and challenging topic in computer graphics and visual simulation. In the present study, the Bidirectional Reflectance Distribution Function (BRDF) of four different textured fabrics is measured via a self-designed Scatterometry to analyze the effect of surface textures and illuminated wavelengths. Furthermore, a fast and simple BRDF model is provided, and optimal model parameters for fabric BRDF calculation were obtained via a genetic algorithm. The results indicate that the reflected distribution of fabrics is dominated by diffuse reflection and is modulated by surface textures and irradiated wavelengths.

Time-dependent polarized radiative transfer in an atmosphere-ocean system exposed to external illumination

Time-dependent polarized radiative transfer in an atmosphere-ocean system exposed to external illumination is numerically investigated. The specular reflection and transmission effects based on the relative refractive index between the atmosphere and water are considered. A modified Monte Carlo (MMC) algorithm combined with time shift and superposition principle, which significantly improves the computational efficiency of the traditional Monte Carlo (TMC) method, is developed to simulate the time-dependent polarized radiative transfer process. The accuracy and computational superiority of the MMC for polarized radiative transfer in the atmosphere-ocean system are validated, and the time-resolved polarized radiative signals are discussed.

Progress in Forward-Inverse Modeling Based on Radiative Transfer Tools for Coupled Atmosphere-Snow/Ice-Ocean Systems: A Review and Description of the AccuRT Model

A tutorial review is provided of forward and inverse radiative transfer in coupled atmosphere-snow/ice-water systems. The coupled system is assumed to consist of two adjacent horizontal slabs separated by an interface across which the refractive index changes abruptly from its value in air to that in ice/water. A comprehensive review is provided of the inherent optical properties of air and water (including snow and ice). The radiative transfer equation for unpolarized as well as polarized radiation is described and solutions are outlined. Several examples of how to formulate and solve inverse problems encountered in environmental optics involving coupled atmosphere-water systems are discussed in some detail to illustrate how the solutions to the radiative transfer equation can be used as a forward model to solve practical inverse problems.

New treatment of strongly anisotropic scattering phase functions: The Delta-M+ method

The treatment of strongly anisotropic scattering phase functions is still a challenge for accurate radiance computations. The new Delta-M+ method resolves this problem by introducing a reliable, fast, accurate, and easy-to-use Legendre expansion of the scattering phase function with modified moments. Delta-M+ is an upgrade of the widely-used Delta-M method that truncates the forward scattering peak with a Dirac delta function, where the '+' symbol indicates that it essentially matches moments beyond the first M terms. Compared with the original Delta-M method, Delta-M+ has the same computational efficiency, but for radiance computations the accuracy and stability have been increased dramatically.

Transient polarized radiative transfer analysis in a scattering medium by a discontinuous finite element method

Transient (time-dependent) polarized radiative transfer in a scattering medium exposed to an external collimated beam illumination is conducted based on the time-dependent polarized radiative transfer theory. The transient term, which persists the nanosecond order time and cannot be ignored for the time-dependent radiative transfer problems induced by a short-pulsed beam, is considered as well as the polarization effect of the radiation. A discontinuous finite element method (DFEM) is developed for the transient vector radiative transfer problem and the derivation of the discrete form of the governing equation is presented. The correctness of the developed DFEM is first verified by comparing the DFEM solutions with the results from the literature. The DFEM is then applied to study the transient polarized radiative transfer induced by a pulsed beam. The time-dependent Stokes vector components are calculated, plotted and analyzed as functions of the axis coordinate and discrete direction. Effects of the diffuse/specular boundary and the incident beam polarization state with respect to the Stokes vector components are further analyzed for cases of different boundary reflection modes and incident beam illuminations.

Investigation of the spectral reflectance and bidirectional reflectance distribution function of sea foam layer by the Monte Carlo method

Spectral properties of sea foam greatly affect ocean color remote sensing and aerosol optical thickness retrieval from satellite observation. This paper presents a combined Mie theory and Monte Carlo method to investigate visible and near-infrared spectral reflectance and bidirectional reflectance distribution function (BRDF) of sea foam layers. A three-layer model of the sea foam is developed in which each layer is composed of large air bubbles coated with pure water. A pseudo-continuous model and Mie theory for coated spheres is used to determine the effective radiative properties of sea foam. The one-dimensional Cox-Munk surface roughness model is used to calculate the slope density functions of the wind-blown ocean surface. A Monte Carlo method is used to solve the radiative transfer equation. Effects of foam layer thickness, bubble size, wind speed, solar zenith angle, and wavelength on the spectral reflectance and BRDF are investigated. Comparisons between previous theoretical results and experimental data demonstrate the feasibility of our proposed method. Sea foam can significantly increase the spectral reflectance and BRDF of the sea surface. The absorption coefficient of seawater near the surface is not the only parameter that influences the spectral reflectance. Meanwhile, the effects of bubble size, foam layer thickness, and solar zenith angle also cannot be obviously neglected.