Reference Radiative Transfer Model Including the Polarization Effect in a Coupled Atmosphere-ocean System

Solar radiation is unpolarized at the top of the atmosphere, but the state of polarization and the radiant intensity change through the multiple-scattering process by cloud/aerosols in the atmosphere. Moreover, the ocean surface has significant polarization properties, and its interaction with scattered solar radiation is one of important processes of radiative transfer in the Earth. In this study, a vector radiative transfer (RT) model has been developed in order to simulate the radiation field of the coupled atmosphere-ocean system that includes polarization effect. The basic RT scheme is based on a hybrid method comprised of discrete-ordinate and matrix-operator method. For the cases of Rayleigh, aerosol, and cloud scattering layers, computational accuracy of the RT scheme has been confirmed by inter-comparison of several vector RT models. Furthermore, the RT scheme is flexible for a vertically inhomogeneous system including the oceanic layers as well as the rough ocean surface. Results of sun glint simulations have shown reasonable characteristics such as the strongly peaked but slightly smoothed radiation by the rough ocean surface and depolarization effect through multiple scattering by the aerosol-loading atmosphere. The RT model developed in this study is available as reference model for simulating radiation field of a coupled atmosphere-ocean system, and is widely applicable to many RT problems including the polarization effect such as satellite- and ground-based remote sensing.