利用静止卫星反演晴天和云天下行长波辐射的方法研究

To obtain contiounus downwelling longwave radiation (DLR) for surface energy research, this study aims to develop an approach for retrieving DLRs from geostationary satellite (Meteosat-9) under all skies. The DLR parameterizations for clear and cloud skies are developed based on extensive radiative transfer simulation, also different atmospheric condition and cloud properties are considered in the simulation. The recent parameterizations always overestimate clear-sky DLRs in daytime over arid regions, and cloudy-sky DLRs when low cloud exists. To overcame these problems, the proposed parameterizations considered the difference between ground and air temperature in clear sky, and longwave radiation above cloud weaken by cloud in cloud sky. Cloud top parameters, the primary factors of cloud, are retrieved with from geostationary satellite, combining look-up table technology and cloud vertical stastical models. Based on the developed DLR algorithm and retrieved cloud parameters, the DLRs under cloudy skies are retrieved with the integration of Meteosat-9 and atmospheric reanalysis data. The DLRs are validated by the field measurements from the sites of Baseline surface radiation network (BSRN) and Atmospheric Radiation Measurement (ARM), and also compared with some longwave radiation datasets.

为了获取时间连续的地表辐射数据，本项目以Meteosat静止卫星为数据源，开展下行长波辐射反演方法研究。利用大气辐射传输模型和典型大气数据库，构建具有较强适宜性的下行长波辐射反演模型。新的晴天模型通过引入地气温差来改进现有模型在干旱区白天产生的高估；云天模型考虑云的衰减、云底发射率等辐射项，从而改进低云时DLR高估的问题。为了获取云天长波辐射的关键参数，利用查找表技术，以及云垂直结构的统计信息，来提高云顶参数反演的效率和准确程度。最后在反演模型构建和云参数反演的基础上，结合静止卫星和大气再分析数据实现有云条件下的下行长波辐射估算。利用BSRN、ARM等站点的实测数据、以及现有的长波辐射产品对反演结果进行验证，并对验证结果进行深入探讨。

项目以获取时空连续的下行长波辐射为目标，开展了晴天和云天下行长波辐射参数化算法研究、下行长波辐射的关键输入大气廓线和云参数获取方法研究，提出了Meteosat-9反演全天候下行长波辐射的一整套方法并进行了产品生产和验证。本项目取得了如下成果：.（1）改进并完善了直接从热红外亮温和大气水汽含量反演晴空下行长波辐射的参数化算法。本算法中通过考虑地气温差来解决同类算法在干旱区高估的问题。该算法具有普适性，通过模型系数重建可应用于多颗卫星。.（2）通过多数据集对现有云天辐射算法进行对比，得到了现有算法在输入参数、输入参数质量较高、输入参数质量较差情况下的精度，分析了反演误差与输入参数间的关系，提供了不同情况下的最优算法，为实际应用中算法和数据选择提供了依据。.（3）提出了利用静止卫星反演下行长波辐射的一整套方法和流程，实现了全天候下行长波辐射的估算。利用Meteosat-9卫星数据生产了2012年7月的下行辐射产品，并利用全球观测数据和同类卫星辐射产品对反演结果进行了验证。验证得到产品精度为30W/m2，且不低于现有产品精度。