The polarized emissivity of a wind-roughened sea surface: A Monte Carlo model

We use a Monte Carlo ray-tracing model to compute the thermal-infrared emissivity of a wind-roughened sea surface. The model includes the effects of both shadowing and the reflected component of surface emission. By using Stokes vectors to quantify the radiation along a given ray path, we compute the effects of polarization as well. We separate the direct emission from surface reflections to show how each affects the nature of the emitted field. The reflected component is an important part of the radiative transfer and affects nearly 10% of the ray paths at emission angles between 60° and 80° at wind speeds ≳5 m/s, increasing the effective emissivity by as much as 0.03. The modeled emissivities agree nicely with recent sea surface emissivity measurements. We also compare the Monte Carlo results to a recently published analytic model and show that the two vary somewhat due to differences in the amount of the reflected component included in the calculations. Surface roughness has a large effect on the polarization between 60° and 90° but less so at smaller angles. Including the reflected component has a small but noticeable effect which actually enhances the degree of polarization at intermediate angles.