论文标题
在极化中观察到的地球的云弓
The cloudbow of planet Earth observed in polarisation
论文作者
论文摘要
行星大气中的散射过程会引起特征特征，在极化中可以特别观察到。对于地球，小颗粒的分子和散射在其相曲线中的特定特定标志。液态水的大气层的明确预测是彩虹特征的存在，其散射角度约为138-144DEG。 Earthshine使我们能够观察线性极化中的主要彩虹。我们在非常大的望远镜处使用fors2观察到地球的极化光谱，从33DEG到65DEG（太阳 - 月球 - 月球角）。光谱用于得出B，V，R和I通过的极化程度，并从33DEG到136DEG。新的观察结果扩展到可以从地面观察到的最小阶段。地球的极化程度正在增加，以降低45度的相位角度。从与地球型气氛模型观察到的相曲线的比较中，我们能够确定水的折射率，并将平均水滴大小约束至6-7 MUM。此外，我们可以将液态水云的平均云部分检索到0.3，以及水云的平均光学深度至10到20之间。我们的观察结果使我们能够辨别出地球大气的两个根本不同的散射机制：分子和粒子散射。可以通过适当的相位曲线反转以高忠诚来检索物理和化学特性。对太阳系以外的行星的偏振相曲线的观察对于彻底表征其大气应该非常有价值。
Scattering processes in the atmospheres of planets cause characteristic features that can be particularly well observed in polarisation. For planet Earth, both molecular and scattering by small particles imprint specific signatures in its phase curve. An unequivocal prediction of a liquid-water-loaded atmosphere is the existence of a rainbow feature at a scattering angle of around 138-144deg. Earthshine allows us to observe the primary rainbow in linear polarisation. We observed polarisation spectra of Earthshine using FORS2 at the Very Large Telescope for phase angles from 33deg to 65deg (Sun--Earth--Moon angle). The spectra were used to derive the degree of polarisation in the B, V, R, and I passbands and the phase curve from 33deg to 136deg . The new observations extend to the smallest phases that can be observed from the ground. The degree of polarisation of planet Earth is increasing for decreasing phase angles downwards of 45deg. From comparison of the phase curve observed with models of an Earth-type atmosphere we are able to determine the refractive index of water and to constrain the mean water droplet sizes to 6-7 mum. Furthermore, we can retrieve the mean cloud fraction of liquid water clouds to 0.3, and the mean optical depth of the water clouds to values between 10 and 20. Our observations allow us to discern two fundamentally different scattering mechanisms of the atmosphere of planet Earth: molecular and particle scattering. The physical and chemical properties can be retrieved with high fidelity through suitable inversion of the phase curve. Observations of polarimetric phase curves of planets beyond the Solar System shall be extremely valuable for a thorough characterisation of their atmospheres.
