Topography impacts the fraction of radiation that reaches a target surface from the sun, sky, and surrounding terrains, which leads to distortions in the radiance levels that are observed by sensors. Although several mountain radiative transfer (RT) models have been developed, the surrounding topographic effects are rarely considered, which can cause non-negligible uncertainty in forward radiance modeling. In this study, we first extended the canopy reflectance model to be suitable for both continuous and discontinuous canopies over sloping terrain (BOST) to rugged terrain, and used it to investigate the impact of the surrounding topography on the reflected radiance and evaluate the contributions of diffuse irradiance from the sky and adjacent terrains. Discrete anisotropic RT (DART) simulations and remote sensing (RS) observations in a real mountain environment were used to evaluate the physical mechanism and model performance. The results suggested that the extended BOST model can capture terrain-induced variations in direct and diffuse radiation, which can be successfully used to simulate the reflected radiance in a real mountainous region. The model shows significant improvement compared with that before extension (i.e., root-mean-square error (RMSE) decreases ( $R^{2}$ increases) of 1.252 (0.025) and 2.035 (0.054) in the red and near-infrared (NIR) bands, respectively). In addition, we discovered that the surrounding topographic effects on the diffuse sky and terrain irradiance are significantly influenced by the wavelength, solar direction, and visible area of the sky and terrains. The extended BOST model serves as an effective tool for improving simulations of the observed radiance and facilitates the development of RT models for rugged terrains.

中文翻译：

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通过扩展 BOST 模型研究周围地形对目标反射辐射的影响


地形会影响从太阳、天空和周围地形到达目标表面的辐射比例，从而导致传感器观测到的辐射水平失真。尽管已经开发了几种山区辐射传输（RT）模型，但很少考虑周围的地形影响，这可能会导致前向辐射建模中不可忽略的不确定性。在本研究中，我们首先将冠层反射率模型扩展到适用于倾斜地形（BOST）的连续和不连续冠层到崎岖地形，并用它来研究周围地形对反射辐射的影响，并评估来自天空和邻近地形的漫射辐照度。使用真实山区环境中的离散各向异性 RT (DART) 模拟和遥感 (RS) 观测来评估物理机制和模型性能。结果表明，扩展的 BOST 模型可以捕获地形引起的直接辐射和漫射辐射的变化，可以成功地用于模拟真实山区的反射辐射。与扩展前相比，该模型显示出显着的改进（即红色和近红外区域的均方根误差 (RMSE) 降低（$R^{2}$ 增加）1.252 (0.025) 和 2.035 (0.054)） （NIR）波段，分别）。此外，我们发现周围地形对漫射天空和地形辐照度的影响受到波长、太阳方向以及天空和地形的可见面积的显着影响。扩展的 BOST 模型可作为改进观测辐射率模拟的有效工具，并促进针对崎岖地形的 RT 模型的开发。