从反射太阳光谱反演大气气溶胶体积谱分布的理论研究

由大气顶射出太阳辐射的形式解出发,结合球形粒子的米散射理论,由反射太阳光谱推导获得了反演整层大气气溶胶粒子体积谱分布的权重函数。在权重函数特征分析的基础上,根据一个简单的线性反演算法,利用大气辐射传输计算模拟的大气顶反射太阳光谱,反演获得了不同气溶胶浓度和复折射率条件下的气溶胶粒子体积谱。结果表明,初步建立了一套自洽的大气气溶胶体积谱分布的反演方法。通过米散射计算获得的反演参数考虑了波长对粒子半径的权重特征,使气溶胶体积谱的反演具有了明确的物理依据;同目前常用的查算表方法相比,简化了反演方案中参数化的复杂程度。

THE THEORETIC STUDY ON THE RETRIEVAL OF AEROSOLS' VOLUME DISTRIBUTION FROM SOLAR SPECTRAL REFLECTANCE

The outgoing solar radiation at the top of the atmosphere can be solved by the basic radiation theory. At the same time, the spheric particles' scattering can be solved by Mie theory. With these two solutions, the kernel function to retrieve atmospheric aerosols' volume distribution (integrated over the vertical column of atmosphere) was derived from the solar spectral reflectance in this paper. The kernel function here was affected by two factors: scattering angle and wavelength. And its weighting properties decide whether the particle size can be retrieved successfully from solar spectral reflectance. After analyzing the characteristics of kernel function, a quite simple linear inversion scheme was designed. With it, two sets of trials were performed to retrieve the aerosols' volume distribution. In the trials, the solar spectral reflectance at the top of the atmosphere was simulated by a pre ?built radiation transfer model. One trial is designed to test the effect of different aerosol loading on retrieval scheme and the other is to test the effect of different aerosol complex refractive index. Both of trials show that the retrieved volume distributions keep good coincidence with the given one. These results prove that aerosols' volume distribution can be inferred from the solar spectral reflectance. By introducing the concept of kernel function, the aerosol size inversion can be explained with explicit physical basis. In addition, the inversion processing here just depends on a few parameters calculated from Mie theory. Compared with the look- up table method, which is used frequently and widely in the present, the database to retrieve aerosols' size distribution was simplified greatly.