Cloud thermodynamic phase (CTP) classification is a vital piece of information for determining how clouds affect climate and electromagnetic wave propagation. We describe a passive shortwave infrared (SWIR) three-channel polarimeter for CTP remote sensing. This instrument adds polarimetric sensitivity to the traditional radiance ratio method that capitalizes on the difference in spectral absorption between liquid water and ice. The ground-based polarimeter was used to measure the first three Stokes parameters in three SWIR spectral bands alongside a dual-polarization lidar system for validation. Additionally, we operated the polarimeter in division-of-time and division-of-aperture modes to explore the severity of polarization artifacts that arose from fast-moving clouds. Although temporal smearing of polarization signatures was identified, the impacts were found to be minimal. Using a surface fitting technique, the radiance ratio method was directly compared with a method that combined radiance ratios with the S1 Stokes parameter. We found that the addition of polarimetry improved cloud phase classification ability from ∼73 % to 95%.

中文翻译：

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云热力学相位的被动短波红外偏振传感

云热力学相位 (CTP) 分类是确定云如何影响气候和电磁波传播的重要信息。我们描述了一种用于 CTP 遥感的被动短波红外 (SWIR) 三通道旋光仪。该仪器利用液态水和冰之间光谱吸收的差异，为传统的辐射比方法增加了偏振灵敏度。地基旋光仪用于测量三个 SWIR 光谱带中的前三个斯托克斯参数，同时使用双偏振激光雷达系统进行验证。此外，我们在时间分割和孔径分割模式下操作偏振计，以探索由快速移动的云产生的偏振伪影的严重程度。尽管确定了极化特征的时间拖尾，发现影响很小。使用表面拟合技术，将辐射率方法与结合辐射率与 S1 斯托克斯参数的方法进行了直接比较。我们发现添加偏振法将云相分类能力从~73% 提高到 95%。