Photon transport in vegetation canopies with anisotropic scattering Part IV. Discrete-ordinates/exact-kernel technique for two-angle photon transport in slab geometry
Photon transport in vegetation canopies with anisotropic scattering Part IV. Discrete-ordinates/exact-kernel technique for two-angle photon transport in slab geometry
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DOI：
10.1016/0168-1923(88)90071-8
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发表时间：
1988
影响因子：
6.2
通讯作者：
R. Myneni;V. Gutschick;G. Asrar;E. Kanemasu
中科院分区：
文献类型：
--
作者：
R. Myneni;V. Gutschick;G. Asrar;E. Kanemasu
讨论了一种考虑各向异性散射的植被冠层双角度光子输运计算方法。用精确核方法计算分布和第一次碰撞源项，消除了对勒让德多项式展开的需要，从而消除了固有的展开误差。相函数现在采用传递矩阵的形式，其元素是在离散正交角处计算的实际相函数。为了在输运计算中使用非展开散射截面，提出了一种稍作修改的离散坐标有限差分法。所采用的负通量固定程序是带有阶跃函数的修正菱形差关系。对代码进行了光子守恒测试，并与中子输运理论的结果进行了比较。该方法与两种不同植被冠层的定向反射率实测数据吻合良好。
A computational technique for two-angle photon transport in vegetation canopies involving anisotropic scattering is discussed. The exact-kernel method of evaluating the distributed and the first-collision source terms eliminates the need for Legendre polynomial expansion and thus the inherent expansion errors. The phase function now takes the form of a transfer matrix, whose elements are the actual phase function evaluated at discrete quadrature angles. To use the non-expanded scattering cross-sections in transport calculations, a slightly modified discrete-ordinates finite-difference method is formulated. The negative flux fixup procedure employed is a modified diamond difference relation with a step function. The code was tested for photon conservation and also by comparisons with results from neutron transport theory. The method showed good correspondence with measured directional reflectance data collected on two different vegetation canopies.