Determination of Cloud Radiative Properties from Satellite Observations

国际卫星云气候学项目(ISCCP)对卫星视场的处理只允许两个描述性类别：无云或被云污染。对于被云污染的情况，采用单层有效云模型来推导云的辐射特性，假定云在空间上是均匀的，具有固定的散射特性。区分破碎云或均匀云的能力对计算大气表面和顶部的辐射通量有着深远的影响。“空间相干方法”(Coakley and Bretherton，1982)就是为了解决这个问题而设计的，它利用像素之间的“结构”来提取云量百分比。使用4公里的AVHRR数据，科克利博士将对南纬50度至北纬50度的太平洋和大西洋盆地的云量和辐射特性进行经验估计。他将确定云的几何形状对其反射率的影响，并评估云在红外波长的不透明度，以及空间相干方法可能存在的偏差。科克利博士还将与ISCCP的科学家合作，比较两种不同方法的结果。

The treatment of satellite fields-of-view in the International Satellite Cloud Climatology Project (ISCCP) permits only two descriptive categories: either free of or contaminated by clouds. For the cloud-contaminated cases, a single-layer "effective" cloud model is then used to derive the radiative properties of the cloud, which is presumed to be spatially homogeneous plane-parallel with fixed scattering properties. An ability to distinguish either broken or uniform clouds has profound consequences for computing radiative fluxes at the surface and top of the atmosphere. The "spatial coherence method" (Coakley and Bretherton, 1982) is designed to address this problem by taking advantage of the "structure" amongst the pixels to retrieve percentage cloud cover. Using the 4 km AVHRR data, Dr. Coakley will derive empirical estimates of cloud cover and radiative properties for the Pacific and Atlantic Ocean basins from 50 degrees South to 50 degrees North. He will determine the effect of cloud geometry on its reflectivity, and assess the opacity of clouds at IR wavelengths and possible bias of the spatial coherence method. Dr. Coakley will also collaborate with ISCCP scientists to compare and contrast the results from two different approaches.