Wang M, Gordon H R
Appl Opt. 1994 Jun 20;33(18):4042-57. doi: 10.1364/AO.33.004042.
The multiangle imaging spectroradiometer (MISR) scheduled to be flown on the first platform of the Earth Observing System in 1998 provides an opportunity to enhance considerably the accuracy with which aerosol properties over the ocean can be retrieved through passive sensing from Earth orbit. As opposed to most radiometers in space that scan the earth in a plane normal to the subsatellite path, the MISR will scan the earth simultaneously in nine planes and thus provide the radiance exiting the atmosphere over a given pixel in nine different directions and at four wavelengths. We examine the problem of extracting the aerosol optical thickness (τ(a)) over the oceans from MISR data, and we produce two algorithms, a single-band algorithm and a spectral or two-band algorithm, for deriving τ(a). The algorithms are based on the use of realistic aerosol models as candidates on which to base an estimation of the aerosol optical properties. They take into account all orders of multiple scattering. Simulations suggest that for nonabsorbing or mildly absorbing aerosol (single-scattering albedo ω(a) > 0.90) the error in the recovered τ(a) is ≲ 10%, as long as the candidate models adequately cover the size refractive index distribution range of the expected aerosols. In the special case of a strongly absorbing aerosol (ω(a) ≍ 0.75), the error in τ(a) becomes large; however, the combination ω(a)τ(a) (the scattering optical thickness) can still be recovered with an error of ≲ 20%, although it is always underestimated. The reason for this decrease in accuracy is that multiple-scattering effects are a strong function of ω(a). A simple extension of the two-band algorithm permits the retrieval of the aerosol scattering phase function with surprising accuracy.
计划于1998年搭载在地球观测系统首个平台上的多角度成像光谱辐射仪（MISR），为大幅提高通过从地球轨道进行被动遥感获取海洋上空气溶胶特性的精度提供了契机。与大多数在垂直于卫星下传轨道平面内扫描地球的太空辐射计不同，MISR将在九个平面同时扫描地球，从而在九个不同方向和四个波长下提供给定像素处离开大气层的辐射亮度。我们研究了从MISR数据中提取海洋上空气溶胶光学厚度（τ(a)）的问题，并生成了两种算法，即单波段算法和光谱或双波段算法，用于推导τ(a)。这些算法基于使用现实的气溶胶模型作为估计气溶胶光学特性的候选模型。它们考虑了所有阶次的多次散射。模拟结果表明，对于非吸收性或轻度吸收性气溶胶（单次散射反照率ω(a) > 0.90），只要候选模型充分覆盖预期气溶胶的粒径折射率分布范围，恢复的τ(a)误差≲ 10%。在强吸收性气溶胶（ω(a) ≍ 0.75）的特殊情况下，τ(a)的误差会变大；然而，ω(a)τ(a)（散射光学厚度）仍可恢复，误差≲ 20%，尽管总是被低估。精度下降的原因是多次散射效应强烈依赖于ω(a)。双波段算法的一个简单扩展允许以惊人的精度反演气溶胶散射相函数。
