An analytic BRDF model of canopy radiative transfer and its inversion
An analytic BRDF model of canopy radiative transfer and its inversion
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DOI：
10.1109/36.263779
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发表时间：
1993-09
期刊：
影响因子：
--
通讯作者：
S. Liang;A. Strahler
中科院分区：
文献类型：
--
作者：
S. Liang;A. Strahler
叶片冠层双向反射分布函数（BRDF）的辐射传输建模是将多角度遥感数据与叶片冠层生物物理参数联系起来并从多角度影像中提取这些参数的有力工具。然而，在现有模型的反演中使用的多次散射近似方法非常有限，并且天空辐射经常被简单地视为各向同性。本文提出了一种基于严格的冠层辐射传递方程的解析模型，该模型采用渐近理论逼近多重散射分量，并简化了单散射计算，因为单散射计算需要数值积分来适当地适应热点效应。由于该模型对天空辐射的角度变化很敏感，作者提供了一种新的定向辐射公式，其中精确计算了未散射太阳辐射和单散射辐射，并用著名的delta双流方法近似了多次散射。一系列对精确计算的验证表明，这两种模型都非常准确，特别是当视角小于55度时。基于冠层和天空辐射分布模型，利用Powell算法从多角度观测数据中检索生物物理参数。>
Radiative transfer modeling of the bidirectional reflectance distribution function (BRDF) of leaf canopies is a powerful tool to relate multiangle remotely sensed data to biophysical parameters of the leaf canopy and to retrieve such parameters from multiangle imagery. However, the approximate approaches for multiple scattering that are used in the inversion of existing models are quite limited, and the sky radiance frequently is simply treated as isotropic. This paper presents an analytical model based on a rigorous canopy radiative transfer equation in which the multiple-scattering component is approximated by asymptotic theory and the single-scattering calculation, which requires numerical integration to properly accommodate the hotspot effect, is also simplified. Because the model is sensitive to angular variation in sky radiance, the authors provide an accompanying new formulation for directional radiance in which the unscattered solar radiance and single-scattering radiance are calculated exactly, and multiple-scattering is approximated by the well-known delta two-stream approach. A series of validations against exact calculations indicates that both models are quite accurate, especially when the viewing angle is smaller than 55 degrees . The Powell algorithm is then used to retrieve biophysical parameters from multiangle observations based on both the canopy and the sky radiance distribution models. >