A Hybrid Interlayer Reflective Boundary Approximation for Hyperspectral Cloud Radiance Simulation Under Optically Thick Liquid Cloud Conditions

Accurate simulation of hyperspectral cloud radiance remains challenging under optically thick cloud conditions, where conventional layered radiative transfer (RT) models tend to underestimate cloud-induced backscattering and return radiance in the visible to shortwave infrared (VIS–SWIR) range. In this study, we propose an extinction-dependent interlayer reflective augmentation within a Curtis–Godson (CG)–based layered RT framework. Instead of introducing explicit cloud-top or cloud-bottom boundaries, the method adds a reflective coupling term at all discretized sublayer interfaces, scaled by local extinction properties, to compensate for the underrepresented backward radiative contribution in standard solvers. The proposed approach is designed for optically thick, plane-parallel cloud conditions and aims at improving forward radiance simulation rather than detailed microphysical retrieval. The formulation is constructed so that the reflective augmentation vanishes as the local extinction decreases, although the present experiments focus on optically thick cloud cases. Validation using Gaofen-5A (GF-5A) hyperspectral observations further confirms improved spectral fidelity of simulated cloud radiance in real scenes. Compared with conventional layered RT, the proposed method provides a favorable balance between computational efficiency and accuracy, making it suitable as a fast forward module for hyperspectral cloud radiance simulation of optically thick cloud scenes.