Uncertainty of cloud parameters on satellite estimation of radiation budget in climate change study

我们的研究成果如下：[回顾和重新检查云的光学特征，以高精度地估计辐射收支和云辐射强迫]到目前为止，我们继续使用GMS-5估计每小时的云量、云光学厚度、表面亮温和表面向下太阳辐射。从1996年开始。这些产品应使用在地面观察到的数据进行验证。我们的团队一直在东亚运营SKYNET观测网络，研究气候变化中的云、气溶胶和辐射问题。比较给出了两个明显的趋势;对于晴天，比较显示出相当好的一致性，但对于阴天，在某些情况下，差异大于50 W/m2。这将给辐射收支的估算带来严重影响。为此，我们明确了原因，并改进了估计算法， ...更多信息 错误是;（1）传感器响应的灵敏度变化，（2）数字化噪声，（3）云的不均匀性，对于第（1）项，我们已经分析了GMS-5的这种退化趋势，并得到了每年几次的灵敏度下降。在这项研究中，我们定量估计的效果与MODIS数据相比。由于GMS可见光通道具有低分辨率（6 bit，64步）和对输入辐射的二阶多项式响应，因此它对较低的反射辐射（换句话说，相对薄的云）高度敏感，而对高反射辐射（例如厚云）不敏感。通过与MODIS数据的比较，给出了两者在数量上的差异。另外，MODIS和GMS同时拍摄相同的云图像，但卫星天顶角不同，这意味着如果云不是平面平行的，则从云接收到的辐射的可能性会产生误差。对云的三维结构的影响作了估计。这些分析结果反映了我们估算云参数和辐射收支的算法。少

We have the research results as follows,[Review and re-examination of optical characteristics of clouds for estimating the radiation budget and cloud radiative forcing with high accuracy]Up to now, we have continued to estimate the hourly data of cloudiness, cloud optical thickness, surface brightness temperature and downward solar radiation at the surface using the GMS-5 from 1996. These products should be validated with the data observed at the surface. Our team has been operating the SKYNET observation network in the East Asia for the research of cloud, aerosol and radiation issues in the climate change. The comparison gave two distinguished trends ; for clear days, the comparison shows the quite good agreement, but for cloudy days it has large discrepancies with more than 50W/m2 in some cases. This would bring serious effects on the estimation of radiation budget. So we have made the reason clear and improved the algorithm for estimation.The most important parameters for giving the … More se errors are ;(1)sensitivity change of sensor response, (2)digitization noise, and (3)inhomogeneity of cloud.Regarding the item (1), we have already analyzed this trend of degradation of GMS-5 and got the decrease of sensitivity with several percents per year. In this research, we have quantitatively estimated the effect compared with MODIS data. Since the GMS visible channel has a low resolution (6bit, 64 steps), and a second-order polynomial response for the input radiance, it is highly sensitive for the lower reflected radiance, in other words, a relatively thin cloud, and the poor sensitive for the high reflected radiance, such as thick clouds. The comparison with MODIS data gave the quantitative difference between them. Also the MODIS and the GMS take the same images of cloud simultaneously, but the satellite zenith angles are different which means the possibility of the radiance received from the cloud can give the error if the cloud is not plane parallel. The effect of 3-dimensional structure of cloud has been estimated. These analytical results in the project reflect our algorithms to estimate the cloud parameters and radiation budget. Less