Investigation of the polarized reflective properties of whitecap-covered regions based on vector radiative transfer model

The polarization of whitecap-covered regions significantly influences the accuracy of ocean polarization remote sensing and the parameter retrieval based on polarization information. In this study, a vector radiative transfer model based on the geometric structure of whitecap is proposed to calculate the reflectance and the degree of linear polarization (DoLP) of whitecap-covered regions. The whitecap-covered region is treated as a dual-layer system consisting of a surface foam layer and a seawater layer that contains bubbles. The radiative properties of the foam and bubble layers in whitecaps are obtained by the geometric optics approximation and Mie scattering method under the framework of independent scattering theory, while those of seawater are calculated using a bio-optical model. The Vector Monte Carlo method is employed to solve the four-component vector radiative transfer equation, and the computation program is validated through a classic test case in the atmosphere-ocean system. Based on this model, a systematic investigation was conducted to analyze the influence of whitecap types, incident radiation direction, and wavelength on both spectral reflectance and the DoLP. The results indicate that changes in the type of whitecaps and the angle of incident radiation affect the spatial distribution of reflectance and DoLP, while the variations in wavelength only alter their numerical values. The influence of underwater bubbles on the DoLP of foam-covered regions is less pronounced than on pure seawater. It should be noted that the foam-type whitecap region exhibits a zero point in DoLP near an exit zenith angle of 10° only in the event of an incident zenith angle of 15°. This phenomenon provides a new perspective for in-depth research into the polarization characteristics of whitecaps.