摘要
卫星3.7μm通道被广泛用于反演云粒子有效半径。为了解云的垂直非均一性对该通道反射率的影响,作者基于SBDART辐射传输模式,分别计算了有效粒子半径垂直连续变化分布下和垂直分层均一分布下的3.7μm反射率。结果表明对于有效粒子半径垂直连续变化分布的云,当云比较薄(光学厚度小于10)时,如果把有效粒子半径垂直非均一的云当作垂直均一的云进行反演,会出现一定的误差,该误差随着光学厚度的增大而减小。当云足够厚(光学厚度大于10)时,该误差小于10%,可以认为此处云粒子垂直结构的变化对3.7μm通道反射率没有影响。对于有效粒子半径垂直分层均一分布的云,当光学厚度比较大时,只有靠近云顶的"浅层"(即有效辐射层,其光学厚度约为3～10)的云参数变化才能对3.7μm反射率产生影响。有效辐射层的光学厚度与云上层有效粒子半径、太阳天顶角和卫星天顶角等因素呈反相关,与相对方位角无无明显的联系。
The satellite＇s 3.7 μm channel is widely used in the retrieval of cloud droplet effective radius. In order to know the effects of cloud droplets vertical inhomogeneity on the reflectance of this channel, based on the SBDART radiative transfer scheme, the 3.7 μm reflectance is calculated separately for two particle profiles, the droplet effective radius in the vertical stratified homogeneous distribution and the droplet effective radius in the vertical continuous changing distribution. For the first type, if it is the thin cloud （optical thickness less than 10）, there will exist obvious errors when the effective radius of vertical inhomogeneous cloud is retrieved as the vertical homogeneous cloud, and the error decreases with the in- crease of the optical thickness. If the cloud is thick enough （optical thickness greater than 10）, the error will be less than 10%. In this case, we can regard that the changes of cloud droplets＇ vertical structure do not influence the reflectance of 3.7μm channel. For the second type, the results show that when the opti- cal thickness is large, the 3.7 μm reflectance only can be affected by the cloud parameters near the cloud top＇s ＂shallow＂ part （effective radiation layer, whose optical thickness is about 3--10）. There existsnegative us near c tween th correlation between the loud top, the solar zen e optical thickness and optical thickness of effective radiation layer and the droplet effective radi- ith angle and satellite zenith angle, but there has no obvious relation be- relative azimuth angle.
出处
《气象》
CSCD
北大核心
2013年第1期80-87,共8页
Meteorological Monthly
基金
国家高新技术863课题(2012AA120902)资助
关键词
3
7μm通道反射率
粒子有效半径
辐射传输模式
有效辐射层
非均一性
reflectance of 3.7 μm channel, droplet effective radius, radiative transfer mode, effective radia- tion layer, inhomogeneity
