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

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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