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辐射度模型(RGM)用于计算植被二向性反射(BRDF)。但是目前基于辐射度方法的计算机模拟模型的应用被局限在较小的、比较单一的场景范围之内。把RGM模型扩展为大场景辐射度模型(LRGM),关键在于如何把大场景分为子场景,既保证模拟精度,又可以显著缩短计算时间。通过不同地形条件下模拟结果的对比,分析讨论了子场景划分方法的敏感性,分析表明:①地形对BRDF是有影响的,主要表现在后向观测方向的增强作用和前向观测方向的减弱作用;②子场景个数对模拟结果影响不大,最大偏差不超过0.007。然后,选取黑河流域大野口山区水源涵养林带为观测试验区,利用大场景辐射度模型进行真实结构模拟,将模拟结果与ASTER数据进行对比,结果表明,二者最大绝对误差不超过0.0382,证明LRGM模型模拟遥感像元尺度的BRDF是可行的。
The radiometric model (RGM) is used to calculate the vegetation bifurcation reflex (BRDF). However, the current application of the computer simulation model based on the radiometric method is limited to a small and relatively single scene. The key to extend the RGM model to LRGM is to divide the large scenes into sub-scenes, which not only guarantees the accuracy of simulation but also shortens the computation time significantly. Through the comparison of simulation results under different topographic conditions, the sensitivity of sub-scene classification method is analyzed and discussed. The analysis shows that: 1) Topography has an impact on BRDF, which is mainly manifested in enhancement of backward observation direction and weakening of forward observation direction The number of sub-scenes has little effect on the simulation results and the maximum deviation does not exceed 0.007. Then, the water source conservation belt in Dayekou Mountain area of Heihe River Basin was selected as the experimental area for observation, and the real structure simulation was conducted by using the radiation model of large scene. The simulation results were compared with ASTER data. The results showed that the maximum absolute error of the two was less than 0.0382. It is feasible that the model simulates the remote sensing cell scale BRDF.