利用矢量辐射传输的蒙特卡罗法,研究了球形和平面平行大气模式下冰云大气反射率的差异,并计算了三种波长(0.65, 0.85,1.55 μm)在大天顶角(85°)入射时,冰云大气的偏振辐射传输特性随不同冰晶粒子模型、光学厚度、有效半径、冰水含量、相对方位角和地表反照率的变化关系。结果表明:冰云大气反射率在两种大气模式下的误差随天顶角的增加而增大,误差可达55%。在球形大气模式下,对于不同波长、冰晶粒子模型和相对方位角,冰云大气反射率的差异较大,且冰云大气偏振度的变化更加复杂。冰云大气反射率和偏振度对冰云光学特性和地表反照率的变化也较敏感,随光学厚度、冰水质量浓度和地表反照率的增加,冰云大气反射率增加,偏振度减小,而随着有效半径的增加,冰云大气反射率减小,偏振度增加。

Herein, the Monte Carlo method of vector radiative transfer is used for comparing the difference between the reflectances of spherical and plane-parallel ice cloud atmospheres. The variations of polarized radiative transfer characteristics of the ice cloud atmospheres with the optical thickness, effective radius, ice water content, relative azimuth angle, surface albedo, and ice crystal model are calculated. These characteristics are obtained at three wavelengths (0.65, 0.85, and 1.55 μm) and a large zenith angle (85°). The results denote that the difference between the ice cloud atmospheric reflectances of two atmospheric modes increases with the increasing zenith angle. This difference can reach a maximum of 55%. For a range of wavelengths, ice crystal models, and relative azimuth angles, the atmospheric reflectance of ice clouds is observed to considerably vary in the spherical atmosphere mode, and the variation in the atmospheric polarization of ice clouds is complex. Further, the atmospheric reflectance and ice cloud polarization are sensitive to the changes in the ice cloud optical properties and surface albedos. The ice cloud atmospheric reflectance increases with the increasing optical thickness, mass concentration of ice water, and surface albedo, whereas the polarization degree decreases. Furthermore, with increasing effective radius, the ice cloud atmospheric reflectance decreases, whereas the polarization degree increases.