Estimation of downward shortwave radiation (DSR) is of great importance in global energy budget and climatic modeling. Although various algorithms have been proposed, effective validation methods are absent for rugged terrains due to the lack of rigorous methodology and reliable field measurements. We propose a two-step validation method for rugged terrains based on computer simulations. The first step is to perform point-to-point validation at local scale. Time-series measurements were applied to evaluate a three-dimensional (3-D) radiative transfer model. The second step is to validate the DSR at pixel-scale. A semiempirical model was built up to interpolate and upscale the DSR. Key terrain parameters were weighted by empirical coefficients retrieved from ground-based observations. The optimum number and locations of ground stations were designed by the 3-D radiative transfer model and Monte Carlo method. Four ground stations were selected to upscale the ground-based observations. Additional three ground stations were set up to validate the interpolated results. The upscaled DSR was finally applied to validate the satellite products provided by MODIS and Himawari-8. The results showed that the modeled and observed DSR exhibited good consistency at point scale with correlation coefficients exceeding 0.995. The average error was around 20 W/m² for the interpolated DSR and 10 W/m² for the upscaled DSR in theory. The accuracies of the satellite products were acceptable at most times, with correlation coefficients exceeding 0.94. From an operational point of view, our method has an advantage of using small amount of ground stations to upscale DSR with relatively high accuracy over rugged terrains.

中文翻译：

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一种验证崎岖地形下行短波辐射的操作方法

向下短波辐射 (DSR) 的估计在全球能量收支和气候建模中非常重要。尽管已经提出了各种算法，但由于缺乏严格的方法和可靠的现场测量，对于崎岖地形缺乏有效的验证方法。我们提出了一种基于计算机模拟的崎岖地形的两步验证方法。第一步是在本地范围内执行点对点验证。应用时间序列测量来评估三维 (3-D) 辐射传输模型。第二步是在像素级验证 DSR。建立了一个半经验模型来插入和放大 DSR。关键地形参数由从地面观测中检索到的经验系数加权。地面站的最佳数量和位置是通过3-D辐射传输模型和蒙特卡罗方法设计的。选择了四个地面站来放大地面观测。另外设立了三个地面站以验证插值结果。最终应用升级后的 DSR 来验证 MODIS 和 Himawari-8 提供的卫星产品。结果表明，建模和观察到的 DSR 在点尺度上表现出良好的一致性，相关系数超过 0.995。理论上，插值 DSR 的平均误差约为 20 W/m²，放大 DSR 的平均误差约为 10 W/m²。卫星产品的精度在大多数情况下是可以接受的，相关系数超过0.94。从操作的角度来看，