Estimation of clearsky longwave downward radiatio

Authors: ShanShan Yu XiaoZhou Xin QinHuo Liu

Publish Date: 2012/11/21

Volume: 56, Issue: 5, Pages: 829-842

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Abstract

To satisfy the requirement of surface energy budget research on the meso and microscale a parameterization is developed to calculate high spatial resolution clearsky downward longwave radiation DLR from HJ1B thermal data The DLR algorithm is established based on extensive radiative transfer simulation and statistical analysis To address the problem that HJ1B has a single thermal channel and lacks atmospheric information the brightness temperature of HJ1B and water vapor content are used in the algorithm An accuracy evaluation and error analysis for the algorithm is conducted using a simulated radiation dataset The result shows that the algorithm performs well in most circumstances but there is obvious underestimation when water vapor content is greater than 4 g/cm2 Error analysis indicates the accuracy of estimated DLRs is affected by uncertainties in input parameters including water vapor content and topofatmosphere radiance It is also affected by the difference between ground and nearsurface air temperature The algorithm is applied to actual HJ1B data and validated by ground data from six stations in the Heihe River and Haihe River basins The estimated DLRs have good consistency with measured data except at Huazhaizi and root mean square errors at most sites are around 20 W/m2 which is slightly better than the result of MODIS There is significant overestimation of DLR at Huazhaizi during summer which is mainly produced by the large groundair temperature difference A correction process based on temperature difference is proposed and applied at Huazhaizi The result shows that the positive bias is largely diminished after correction

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