Impact of cloud inhomogeneity on bi-directional reflectance |
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Authors: | Wang Yue Lü DaRen Huo Juan |
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Institution: | Laboratory for Middle Atmosphere and Global Environment Observation, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China |
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Abstract: | This paper uses SHDOM (Spherical Harmonics Discrete Ordinate Method) to calculate the nadir bidirectional reflectance distribution
function (BRDF) of the cumulus and stratocumulus fields at the wavelengths of 0.67 μm and 2.13 μm, and discusses the impact
of cloud inhomogeneity on BRDF. The cloud fields are adopted from I3RC Phase II, which are used to compare 3D radiative transfer
models. The simulation results show that the cu field has 6% abnormal BRDF values (BRDF>1) with the increase of solar zenith
angle. Further analyses show that grid cells whose BRDF is greater than one gather together at the local trough of the top
of cloud. These regions can receive not only the direct incident solar beam, but also the beam scattered by the higher cloud
of its neighborhood. Hence, the BRDF of those regions is enhanced. The abnormal BRDF phenomenon shows that the cloud inhomogeneity
can result in inconsistency between satellite observation and plane parallel theory, implying that the reflectance observed
by high resolution satellite is maybe enhanced by the cloud 3D effects. Thus one should take this fact into account when using
the product retrieved by these data. The dominant solar zenith angles are quite large in the mid-high altitude area, and the
impact of cloud inhomogeneity on these areas may be more significant.
Supported by the National Natural Science Foundation of China (Grant Nos. 40333034 and 40505006) |
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Keywords: | cloud inhomogeneity bidirectional reflectance satellite retrieval |
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