等效球模型模拟冰晶云反射的误差分析

用射线光学理论计算了具有一定尺度分布的六角冰晶粒子在可见和近红外光谱区一系列波长上(0.2～5μm)的单次散射特性.利用米氏(Mie)理论,计算了与六角冰晶具有相同截面积的球形粒子的单次散射特性.根据辐射传输理论,应用累加法,分别计算了由冰晶粒子和等效球形粒子构成的卷层云的多次散射特性,计算结果表明当入射波长λ≈3.0 μm时,等效球Mie理论可以很好地用于计算卷层云的反射特性,但是当λ＜2.8μm时,尤其在可见光区,将引起显著的误差.最后提出了计算冰云光学特性的两种方案.

Error Analysis of Equivalent Spheres Model for Computing the Reflection Properties of Ice Clouds

The single scattering properties of the hexagonal ice crystals with a gamma particle size distribution were calculated by using the ray-optical theory at some wavelengths located in the visible and infrared spectral region (0.2～5 μm). The single scattering properties of the sphere particles having equal surface area with hexagonal ice crystals are calculated with Mie theory. Based on radiative transfer theory, the reflection properties of cirrostratus consisting of hexagonal ice crystals or equivalent spheres are computed by using the adding-doubling method,respectively. The results show that the Mie scattering calculations at the region of λ≈3.0 μm give good agreement with the hexagonal ice crystals. However, there are large errors at the region of λ＜2.8 μm, especially, at the visible region. Finally, the schemes for calculations of the optical properties of ice clouds are proposed.