Optical efficiencies of large particles of arbitrary shape and orientation
Optical efficiencies of large particles of arbitrary shape and orientation
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DOI：
10.1016/0021-9797(69)90396-8
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发表时间：
1969-07
期刊：
影响因子：
--
通讯作者：
F. Bryant;P. Latimer
中科院分区：
文献类型：
--
作者：
F. Bryant;P. Latimer
范德胡斯特的“反常衍射”近似扩展到新的粒子及其取向。它预测了大于波长和折射率与介质相差不大的粒子的消光和吸收效率（kextandkab）。在重新定义颗粒参数的情况下，发现对于任意取向的相同颗粒，通常取向的薄圆盘和长薄圆柱的现有表达式同样适用。利用几何关系证明，如果适当地重新定义粒径参数，均匀球的van de Hulst表达式也可以描述任意轴比和方向的旋转椭球。给出了基本关系式叉叉的数值解，并进行了说明。它们适用于几乎任何形状、大体内部结构和方向的颗粒。为了支持这种“大粒子”近似的扩展，根据射线在粒子内传播所需的条件，重新检查了它的域。这些条件可以决定粒子的光学模型应该有多复杂。如果使用的粒子不是太大，他们也可以证明用球形模型来表示非球形粒子。采用新的表达式和方法来确定随机粒子方向对各种粒子有效值的影响。发现随机取向使许多非球形粒子在光学上的行为几乎像等体积的球形粒子。
The “anomalous diffraction” approximation of van de Hulst is extended to new particles and orientations thereof. It predicts the extinction and absorption efficiencies,KextandKabs, of particles larger than the wavelength and of refractive index not too different from that of the medium. Existing expressions for the normally oriented thin disc and long thin cylinder are found to be equally applicable to the same particles when arbitrarily oriented if the particle parameters are redefined. Geometrical relations are used to prove that van de Hulst's expressions for the homogeneous sphere also describe the ellipsoid of revolution of arbitrary axial ratio and orientation if the particle size parameter is suitably redefined. Numerical solutions of the basic relations forKextare outlined and illustrated. They are applicable to particles of almost any shape, gross internal structure, and orientation. To support the extension of this “large particle” approximation, its domain is re-examined in terms of the conditions needed for ray propagation within the particle. These conditions can define how sophisticated an optical model of the particle should be. If the particle used is not too large, they can also justify the representation of a nonspherical particle by a spherical model. New expressions and methods are used to determine the effects of random particle orientation on effectiveKvalues of various particles. Random orientation is found to cause many nonspherical particles to behave optically almost like spherical particles of equal volumes.