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首页> 外文期刊>Journal of Geophysical Research. Biogeosciences >Impact of cumulus cloud spacing on Landsat atmospheric correction and aerosol retrieval
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Impact of cumulus cloud spacing on Landsat atmospheric correction and aerosol retrieval

机译：积云间距对Landsat大气校正和气溶胶反演的影响

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A Landsat 7 Enhanced Thematic Mapper Plus (ETM+) image acquired over the Southern Great Plains site of Department of Energy's Atmospheric Radiation Measurement Program during the Atmospheric Radiation Measurement Enhanced Shortwave Experiment II is used to study the effect of clouds on reflected radiation in clear gaps in a cumulus cloud field. A technique using the spectral information of background and clouds is applied to identify clouds. The path radiance technique is used to extract the apparent path radiance in a clear region of the cumulus cloud field. The result shows that the apparent path radiance is enhanced by nearby clouds in both band 1 (blue) and band 3 (red) of ETM+. More importantly, the magnitude of the enhancement depends on the mean cloud-free distance in the clear patches. For cloud-free distances <0.5 km the enhancement of apparent path radiance is more than 0.025 and 0.015 (reflectance units) in band 1 and band 3, respectively, which corresponds to an enhancement of apparent aerosol optical thickness of similar to0.25 and similar to0.15. Neglecting of the three-dimensional cloud effect would lead to underestimates of surface reflectance of similar to0.025 and similar to0.015 in the blue and red band, respectively, if the true aerosol optical thickness is 0.2 and the surface reflectance is 0.05, The enhancement decreases exponentially with mean cloud-free distance, reaching asymptotic values of 0.09 for band 1 and 0.027 for band 3 at a mean cloud-free distance about 2 km. The asymptotic values are slightly larger than the mean path radiances retrieved from a completely clear region: 0.086 and 0.024 for the blue and red bands, respectively. [References: 19]
机译：在大气辐射测量增强短波实验II期间，在能源部大气辐射测量计划的南部大平原站点上获得的Landsat 7增强型专题制图仪增强版（ETM +）图像用于研究云层中清晰间隙中云对反射辐射的影响。积云领域。应用了利用背景和云的光谱信息的技术来识别云。路径辐射度技术用于提取积云场的晴朗区域中的视在路径辐射度。结果表明，ETM +的波段1（蓝色）和波段3（红色）附近的云增强了视在路径辐射。更重要的是，增强程度取决于透明补丁中的平均无云距离。对于小于0.5 km的无云距离，波段1和波段3的视在路径辐射度的增强分别大于0.025和0.015（反射单位），这对应于视在气溶胶光学厚度的增强，类似于0.25和类似至0.15。如果真正的气溶胶光学厚度为0.2且表面反射率为0.05，则忽略三维云效应会分别低估蓝色和红色波段中的表面反射率分别接近0.025和0.015。增强随平均无云距离呈指数下降，在平均无云距离约为2 km时，频段1的渐近值达到0.03，频段3的渐近值达到0.027。渐近值略大于从完全清晰的区域获取的平均路径辐射度：蓝色和红色波段分别为0.086和0.024。 [参考：19]

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