Detecting super‐thin clouds with polarized sunlight

Sun, Wenbo; Videen, Gorden; Mishchenko, Michael I.

doi:10.1002/2013gl058840

Cited by 29 publications

(38 citation statements)

References 26 publications

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“…Particularly, Fig. 10 shows that the AOLP from the ADRTM has a pattern in the neighborhood of the backward-reflecting angle that is very similar to those for clouds reported in Sun and Lukashin (2013) and Sun et al (2014Sun et al ( , 2015. This likely is because the refractive index for dust aerosols in our modeling is assumed to be 1.5 and the imaginary part is 0.…”

Section: Resultssupporting

confidence: 57%

Deriving polarization properties of desert-reflected solar spectra with PARASOL data

et al. 2015

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Abstract. One of the major objectives of the Climate Absolute Radiance and Refractivity Observatory (CLARREO) is to conduct highly accurate spectral observations to provide an on-orbit inter-calibration standard for relevant Earthobserving sensors with various channels. To calibrate an Earth-observing sensor's measurements with the highly accurate data from the CLARREO, errors in the measurements caused by the sensor's sensitivity to the polarization state of light must be corrected. For correction of the measurement errors due to the light's polarization, both the instrument's dependence on the incident polarization state and the onorbit knowledge of the polarization state of light as a function of observed scene type, viewing geometry, and solar wavelength are required. In this study, an algorithm for deriving the spectral polarization state of solar light from the desert is reported. The desert/bare land surface is assumed to be composed of two types of areas: fine sand grains with diffuse reflection (Lambertian non-polarizer) and quartz-rich sand particles with facets of various orientations (specular-reflection polarizer). The Adding-Doubling Radiative Transfer Model (ADRTM) is applied to integrate the atmospheric absorption and scattering in the system. Empirical models are adopted in obtaining the diffuse spectral reflectance of sands and the optical depth of the dust aerosols over the desert. The ratio of non-polarizer area to polarizer area and the angular distribution of the facet orientations are determined by fitting the modeled polarization states of light to the measurements at three polarized channels (490, 670, and 865 nm) by the Polarization and Anisotropy of Reflectances for Atmospheric Science instrument coupled with Observations from a Lidar (PARASOL). Based on this physical model of the surface, the desert-reflected solar light's polarization state at any wavelength in the whole solar spectra can be calculated with the ADRTM.

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Section: Resultssupporting

confidence: 57%

Deriving polarization properties of desert-reflected solar spectra with PARASOL data

et al. 2015

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“…As a complement to the work in Sun et al (2014), we further modeled the angle of linear polarization (AOLP) of reflected sunlight from clouds of different thermodynamic phases, particle shapes, and optical depth over oceans. In the modeling, the atmosphere, including the cloud and aerosol layers, is assumed to be plane-parallel.…”

Section: P -Polarization Feature Of Reflected Sunlight From Cloudsmentioning

confidence: 99%

“…In Sect. 2, modeling results supplementary to the work in Sun et al (2014) are reported for the polarization feature of reflected sunlight from clouds. The algorithm for retrieving the OD of super-thin clouds with polarized sunlight is introduced in Sect.…”

Section: Introductionmentioning

confidence: 98%

“…Super-thin clouds of optical depths smaller than ∼ 0.3 cover ∼ 50 % of the globe (McFarquhar et al, 2000;Sun et al, 2011bSun et al, , 2014 and play an important role in the radiation energy balance of the Earth (Dessler and Yang, 2003;Lee et al, 2009;Sun et al, 2011a, b), as well as in the remote sensing of aerosols (Sun et al, 2011b;Omar et al, 2013) and surface temperature (Sun et al, 2011a). Even a sky overhead that looks very clear and blue can still have "blue" clouds at over 34 000 ft. altitude (Packer and Lock, 1951).…”

Section: Introductionmentioning

confidence: 99%

“…In our previous work (Sun et al, 2014), we studied solar radiation backscattered from clouds with both the Polarization and Anisotropy of Reflectances for Atmospheric Science coupled with Observations from a Lidar (PARASOL) (Deschamps et al, 1994) data and an adding-doubling radiativetransfer model (ADRTM) (Sun and Lukashin, 2013). We found that the dominant backscattered electric field from the clear-sky Earth-atmosphere system is nearly parallel to the ocean surface.…”

Section: Introductionmentioning

confidence: 99%

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A method to retrieve super-thin cloud optical depth over ocean background with polarized sunlight

et al. 2015

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Abstract. In this work, an algorithm that uses the polarization angle of the backscattered solar radiation to detect clouds with optical depth (OD) < ∼ 0.3 is further developed. We find that at viewing angles within ± ∼ 8 • around the backscattering direction, the p-polarized intensity that is parallel to the meridian plane of reflected light from the surface is sensitive to, and nearly linearly related to, the optical depth of super-thin clouds. Moreover, our sensitivity study suggests that the p-polarized intensity at these viewing angles is not sensitive to the ocean surface conditions. Using this property of p-polarized intensity, super-thin clouds' optical depth can be retrieved.

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High‐resolution photography of clouds from the surface: Retrieval of optical depth of thin clouds down to centimeter scales

2017

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This paper describes the approach and presents initial results, for a period of several minutes in north central Oklahoma, of an examination of clouds by high‐resolution digital photography from the surface looking vertically upward. A commercially available camera having 35 mm equivalent focal length up to 1200 mm (nominal resolution as fine as 6 µrad, which corresponds to 9 mm for cloud height 1.5 km) is used to obtain a measure of zenith radiance of a 30 m × 30 m domain as a two‐dimensional image consisting of 3456 × 3456 pixels (12 million pixels). Downwelling zenith radiance varies substantially within single images and between successive images obtained at 4 s intervals. Variation in zenith radiance found on scales down to about 10 cm is attributed to variation in cloud optical depth (COD). Attention here is directed primarily to optically thin clouds; COD less than about 2. A radiation transfer model used to relate downwelling zenith radiance to COD and to relate the counts in the camera image to zenith radiance permits determination of COD on a pixel‐by‐pixel basis. COD for thin clouds determined in this way exhibits considerable variation, for example, an order of magnitude within 15 m, a factor of 2 within 4 m, and 25% (0.12 to 0.15) over 14 cm. This approach, which examines cloud structure on scales 3 to 5 orders of magnitude finer than satellite products, opens new avenues for examination of cloud structure and evolution.

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Detecting super‐thin clouds with polarized sunlight

Cited by 29 publications

References 26 publications

Deriving polarization properties of desert-reflected solar spectra with PARASOL data

Deriving polarization properties of desert-reflected solar spectra with PARASOL data

A method to retrieve super-thin cloud optical depth over ocean background with polarized sunlight

High‐resolution photography of clouds from the surface: Retrieval of optical depth of thin clouds down to centimeter scales

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