Liang S, Strahler A H
Appl Opt. 1994 Aug 20;33(24):5745-53. doi: 10.1364/AO.33.005745.
An analytical model characterizing the atmospheric radiance field over a non-Lambertian surface divides the radiation field into three components: unscattered radiance, single-scattering radiance, and multiple-scattering radiance. The first two components are calculated exactly. A δ-four-stream approximation is extended to calculate the azimuth-independent multiple-scattering radiance over a non-Lambertian surface, which is modeled by a statistical bidirectional reflectance distribution function (BRDF). Accuracy is assessed with respect to the exact results computed from a Gauss-Seidel iterative algorithm. Experiments comparing the results obtained with Lambertian and non-Lambertian surfaces show that incorporating the BRDF into the four-stream approximation significantly improves the accuracy in calculating radiance as well as radiative flux.
非散射辐射、单次散射辐射和多次散射辐射。前两个分量可精确计算。扩展了δ-四流近似法来计算非朗伯表面上与方位角无关的多次散射辐射，该非朗伯表面由统计双向反射分布函数（BRDF）建模。通过与高斯-赛德尔迭代算法计算出的精确结果对比来评估精度。比较朗伯表面和非朗伯表面所得结果的实验表明，将BRDF纳入四流近似法可显著提高辐射亮度以及辐射通量计算的准确性。
