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    A relationship between blue and near‐IR global spectral reflectance and the response of global average reflectance to change in cloud cover observed from EPIC

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    Date Issued
    2019-08
    Publisher Version
    10.1029/2019ea000664
    Author(s)
    Wen, Guoyong
    Marshak, Alexander
    Song, Wanjuan
    Knyazikhin, Yuri
    Mõttus, Matti
    Wu, Dong
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    Permanent Link
    https://hdl.handle.net/2144/40773
    Version
    Accepted manuscript
    Citation (published version)
    Guoyong Wen, Alexander Marshak, Wanjuan Song, Yuri Knyazikhin, Matti Mõttus, Dong Wu. 2019. "A Relationship Between Blue and Near‐IR Global Spectral Reflectance and the Response of Global Average Reflectance to Change in Cloud Cover Observed From EPIC." Earth and Space Science, Volume 6, Issue 8, pp. 1416 - 1429. https://doi.org/10.1029/2019ea000664
    Abstract
    We performed a detailed analysis of Earth Polychromatic Imaging Camera (EPIC) spectral data. We found that the vector composed of blue and near‐infrared (NIR) reflectance follows a counterclockwise closed‐loop trajectory from 0 to 24 UTC as Earth rotates. This nonlinear relationship was not observed by any other satellites due to limited spatial or temporal coverage of either low Earth orbit or geostationary satellites. We found that clouds play an important role in determining the nonlinear relationship in addition to the well‐known cloud‐free land‐ocean reflectance contrast in the two bands. The nonlinear relationship is the result of three factors: (1) a much larger cloud‐free land‐ocean contrast in the NIR band compared to the blue band, (2) significantly larger difference between cloudy land and cloudy ocean reflectance in the NIR band compared to the blue band, and (3) the periodic variation of fractions of clear land, clear ocean, cloudy land, and cloudy ocean in the sunlit hemisphere as Earth rotates. We found that the green vegetation contributes significantly to the NIR global average reflectance when the South and North Americas appear and disappear in the EPIC's field of view. The blue and NIR relationship can be useful for exoplanet research. Clouds impose a strong impact on global spectral reflectance, and the reflectance response to a change in cloud cover depends on whether the change is over land or over the ocean. On average, an increase of 0.1 in cloud coverage will lead to a 7% increase in spectrally integrated global average reflectance.
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    • CAS: Earth & Environment: Scholarly Papers [141]
    • BU Open Access Articles [4833]


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