| Abstrakt: |
The glory, a striking optical phenomenon seen from space in unpolarized satellite images can be mapped onto the cloud's droplet sizes with a characteristic scale of 10μm $\mu m$. Such a mapping allows us to infer the mean and variance of the cloud droplets' radius, an important property that has remained elusive and inaccessible to passive unpolarized satellite sensing. Here, we propose a simple and robust polarization‐like differential approach to map the glory's spectral properties to the desired moments of the droplet size distribution. By taking the differences between two spectrally close channels, we reduce multiple scattering contributions and amplify the single‐scattering signal, thus allowing for a simple and rapidly converging map from glory to droplet size distribution. Moreover, the droplet information reflects the upper part of the cloud, adding another sample to the traditional multiple scattering‐based retrievals that reflect droplet properties deeper in the cloud. Plain Language Summary: Glories appear as colored rings around the perfect backscatter angle. The pattern can often be seen in mountains where the sun is behind the observer, projecting the observer's shadow onto a cloud. Faint glories can be found in non‐polarized satellite images, forming over marine Stratocumulus clouds. We can translate the optical properties of the glories that were collected by satellites for more than 20 years to the cloud's droplet size‐distribution (DSD) mean and variance. So far, the cloud's DSD variance, which is an important climate property, was not retrieved from non‐polarized satellite data. To do so in a simple and robust way, we propose a differential approach that enhances the glory's signal relative to the background reflectance. The DSD information that is retrieved from the glory reflects the uppermost part of the cloud. An area that reflects the interactions between the cloud and the cloud‐free atmosphere above it. Moreover, for thick clouds, it provides information from a higher point along the cloud profile in addition to the information that is retrieved by the multi‐scattering approaches that represent deeper areas within the cloud. Key Points: A simple and robust method is proposed to map the glory's properties to the droplets' mean and varianceThe method uses unpolarized reflectance images in a few spectral bands, enabling the analysis of 20 years of moderate resolution imaging spectroradiometer (MODIS) dataDifferences between two spectral images enhance the glory's single scattering signal relative to the background [ABSTRACT FROM AUTHOR] |
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