CARE Radiative Transfer Model: a tool for supporting polarization and hyperspectral radiative transfer simulation in the coupled atmosphere-ocean system

Radiative transfer modeling in coupled atmosphere-ocean systems provides a fundamental theoretical basis for retrieving atmospheric and oceanic optical parameters from remote sensing observations. The accurate retrieval of these parameters relies on forward radiative transfer calculations performed by flexible and high-precision radiative transfer models (RTMs). Despite substantial progress, RTMs that simultaneously achieve benchmark-level hyperspectral gas absorption with enhanced computational efficiency, incorporate irregular particle scattering, and account for polarized radiative transfer in coupled atmosphere–ocean systems remain limited. In this study, we develop CARE-RTM, a comprehensive radiative transfer model designed to support polarimetric and hyperspectral simulations across ultraviolet to infrared wavelengths in coupled atmosphere-ocean systems, through sophisticated modelling of absorption and scattering processes in both atmospheric and oceanic substances. Particularly, the CARE-RTM incorporates a GPU-accelerated line-by-line scheme with line-mixing refinement, a Voronoi ice crystal scattering model, and comprehensive bio-optical ocean modules, enabling the accurate treatment of hyperspectral gas absorption, irregularly shaped ice cloud scattering, and underwater light simulation, respectively. Validation against benchmark solutions confirms the high accuracy of CARE-RTM, with errors typically below 0.02% (relative values) for total radiance and 0.005% (absolute values) for the degree of linear polarization at the top of the atmosphere under various scenarios, including coupled atmosphere-ocean conditions. Additional intercomparisons with established models further verify the accuracy of in-water solar radiation and water-leaving radiance simulations. The model’s performance is further demonstrated through extensive comparisons with satellite observations, underscoring its capability in ocean color remote sensing applications.