Improved Snow-Covered Forest Bidirectional Reflectance Model Incorporating Canopy-Intercepted Snow and Atmospheric Effects

Snow-covered forests are widely distributed in middle- and high-latitude regions of the Northern Hemisphere and have significant impacts on global climate change and albedo feedback. However, knowledge of the radiative transfer mechanism in snow-canopy-atmosphere systems is insufficient. Existing bidirectional reflectance models often oversimplify, assuming that snow only persists on the floor, and neglect the interactions between the atmosphere and snow-covered forests. In our previous snow-covered forest bidirectional reflectance (SFBR) model, we considered ground snow, the concentration of soot pollution, needle leaf characteristics, and discontinuous canopy distributions. Furthermore, this study proposed an improved snow-covered forest bidirectional reflectance (SFBR2) model by considering canopy-intercepted snow (CIS) and atmospheric effects. Specifically, the SFBR2 model was constructed by a series of analytical models for CIS, ground snow (asymptotic radiative transfer (ART) snow model), soil [brightness shape moisture (BSM)], needle leaf [leaf incorporating biochemistry exhibiting reflectance and transmittance yields (LIBERTY)], canopy [two-layer version of four-stream scattering by arbitrarily inclined leaves (4SAIL2)], and atmosphere [simplified method for atmospheric correction (SMAC)], in which the CIS is parameterized by snow optical properties and two-stream theory, and the interaction between the atmosphere and snow-covered forests is optimized by a four-stream theory. It makes the model able to simulate the reflectance at the top of the canopy/atmosphere (TOC/TOA). Validations against 3-D large-scale remote sensing data and image simulation framework over heterogeneous 3-D scenes (LESS) model, unmanned aerial vehicle (UAV) observations, and MODIS data indicated a good consistency with SFBR2 model in the reflectance simulation. The established model has the ability to simulate the bidirectional reflectance of different snow-covered forest scenes whether CIS exists or not. Potential applications include satellite signal simulation, radiation mechanism analysis, and parameter inversion in snow-covered forests.