Remote sensing of cloud droplet radius profiles using solar reflectance from cloud sides – Part 1: Retrieval development and characterization
Remote sensing of cloud droplet radius profiles using solar reflectance from cloud sides – Part 1: Retrieval development and characterization
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DOI：
10.5194/amt-12-1183-2019
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发表时间：
2019-02
影响因子：
3.8
通讯作者：
Florian Ewald;T. Zinner;T. Kölling;B. Mayer
中科院分区：
文献类型：
--
作者：
Florian Ewald;T. Zinner;T. Kölling;B. Mayer
抽象。对流云对地球气候和区域天气事件起着至关重要的作用，因为它们对辐射收支和水循环有很大的影响。特别是，云的膨胀和降水的形成受到云中气溶胶粒子的影响。为了更好地了解从气溶胶活化到云滴增长到云辐射特性变化的过程，遥感技术变得越来越重要。虽然用于空间观测的被动检索在从云顶推断云的光学厚度和液滴大小方面已变得十分复杂和普遍，但液滴大小的剖面在很大程度上仍然是被动遥感的未知领域。原则上，它们可以从云面的观测中获得，但面对云面的小尺度异质性，“经典”被动遥感技术是不合适的。本文论证了利用云面反射的太阳辐射来研究云滴有效半径垂直变化的可行性。这项工作的核心方面，其路径上的工作云侧检索是未知的云表面几何形状的影响的分析，有效半径检索。本研究探讨了反射太阳辐射的敏感性，云液滴大小，使用广泛的3-D辐射传输计算的基础上，现实的液滴大小解决云模拟。此外，它还探索了一种进一步的技术，通过考虑每个像素的周围环境来解决由照明和云几何形状引起的模糊性。基于这些发现，统计方法被用来提供一个有效的半径检索。这种统计有效半径检索集中在对流水云的液体部分，例如，积云、浓积云和信风积云，它们的云面非常发达。最后，使用已知和未知的云侧场景进行测试，以分析其性能。
Abstract. Convective clouds play an essential role for Earth's climate as well as for regional weather events since they have a large influence on the radiation budget and the water cycle. In particular, cloud albedo and the formation of precipitation are influenced by aerosol particles within clouds. In order to improve the understanding of processes from aerosol activation, from cloud droplet growth to changes in cloud radiative properties, remote sensing techniques become more and more important. While passive retrievals for spaceborne observations have become sophisticated and commonplace for inferring cloud optical thickness and droplet size from cloud tops, profiles of droplet size have remained largely uncharted territory for passive remote sensing. In principle they could be derived from observations of cloud sides, but faced with the small-scale heterogeneity of cloud sides, “classical” passive remote sensing techniques are rendered inappropriate. In this work the feasibility is demonstrated to gain new insights into the vertical evolution of cloud droplet effective radius by using reflected solar radiation from cloud sides. Central aspect of this work on its path to a working cloud side retrieval is the analysis of the impact unknown cloud surface geometry has on effective radius retrievals. This study examines the sensitivity of reflected solar radiation to cloud droplet size, using extensive 3-D radiative transfer calculations on the basis of realistic droplet size resolving cloud simulations. Furthermore, it explores a further technique to resolve ambiguities caused by illumination and cloud geometry by considering the surroundings of each pixel. Based on these findings, a statistical approach is used to provide an effective radius retrieval. This statistical effective radius retrieval is focused on the liquid part of convective water clouds, e.g., cumulus mediocris, cumulus congestus, and trade-wind cumulus, which exhibit well-developed cloud sides. Finally, the developed retrieval is tested using known and unknown cloud side scenes to analyze its performance.