MODIS数据的云顶高度反演

云的辐射特性和它的高度影响到辐射的收支可以导致地球的变暖或变冷,在地球大气能量收支平衡中．云具有特别显著的调节作用,是影响气候变化的一个重要因子。云顶性质包括云顶气压、云顶温度和有效云量或有效比辐射率。很多方法被用来从多光谱资料中估计云参数,而CO₂薄片算法(截断法)则是使用被动遥感资料反演云顶性质的重要方法之一。利用15μmCO₂吸收带的几个吸收不同的MODIS红外波段,对于大气不同高度层次的不同敏感度,通过从地球大气系统的几个CO₂波段同时测量向上红外辐射,以及大气的温度和透射率廓线的基础上,可以推断出云顶气压。这项技术应用于HIRS资料上已经有20年的历史,而EOS系列地球环境卫星的升空,使EOS上搭载的MODIS探测器成为第一个拥有CO₂薄片波段的高空间分辨率探测器。本文依据CO₂薄片算法(截断法)的理论模型结合实例讨论算法的特点及不足,同时分析其误差以利改进。

Retrieval of Cloudtop Properties from MODIS Data

Cloudtop properties constitute one of the important cloud properties. Cloudtop properties include cloudtop pressure, cloudtop temperature and cloud effective emissivity. One of the greatest current uncertainties in Global Climate Models is the role of clouds. The CO2 slicing algorithm is one of the important methods for retrieval of cloudtop properties. It is founded based on the difference in atmospheric absorptions due to CO2 between two spectrally neighboring channels in the wings of CO2 absorption band with a resolution of 1km. This technique has been applied to HIRS data for about 20 years. Since Earth Observing System (EOS) platform launched in December 1999, the Moderate Resolution Imaging Spectroradiometer(MODIS) has been the first sensor to have CO2 slicing bands at high spatial resolution. This paper mainly describes the theoretical model of CO2 slicing and it' s applications. An analysis of the characteristics of the method and the estimate of errors will also be discussed. Finally, research issues are recommended for future studies.