毫米波/亚毫米波冰云探测辐射计模型仿真

Radiative Transfer Simulations for Millimeter/Submillimeter-wave Ice Cloud Imager

冰云对全球气候的显著影响,使得利用毫米波/亚毫米波辐射计探测冰云分布持续受到关注。为从辐射计亮温测量值中反演出冰云粒子参数,完善的辐射传输正演模型起到非常关键的作用。针对即将发射的冰云成像仪毫米波/亚毫米波星载辐射计,建立起了包含粒子散射在内的完整的辐射传输模型。传输模型读取大气廓线及云层粒子微观参数,仿真计算得到辐射计各通道的辐射亮温。给出了辐射传输模型的详细配置,并分析了不同通道对云层粒子的敏感性。结果表明:冰云成像仪各通道对冰云粒子、雪粒子均有很强的敏感性,但只有低频率通道能探测到水云粒子、雨粒子的变化。辐射计通道中,不同的中心频率对冰晶粒子敏感度不同,从而可使辐射计探测不同高度、不同特性的粒子。对于同一中心频率,不同频偏对应不同的大气透明度,使得辐射计可进一步探测到不同高度的云层信息。仿真工作将会为后续的毫米波/亚毫米波辐射计设计、反演算法研究等打下良好的基础。

Ice clouds remote sensing is in an ongoing focus as ice clouds play an important role in atmospheric energy budgets due to their reflection of sunlight and their entrapment of infrared radiation. Submillimeter-wave radiometry is an important technique in detecting ice clouds because of its distinctive advantage over other remote sensors. Developing a complete radiative transfer model that links the ice cloud parameters and the brightness temperature observations is of critical importance. The paper builds up a forward model that rigorously handles the ice particle scattering based on the Atmospheric Radiative Transfer Simulator(ARTS),and we conduct the simulations on a cloud cross section for the upcoming Ice Cloud Imager(ICI). The results indicate that the ICI channels possess high sensitivity to the ice cloud microphysics,and only the low-frequency channels are sensitive to the liquid clouds. For the double sidebands with the same center frequency,the large frequency-offset channels show higher brightness temperature values in clear sky conditions,and they have larger BT depressions when encountering thick ice cloud layers. The forward model allows us to develop retrieval algorithms upon it in the future.