从FY-4A卫星遥感数据和GFS资料估算全天空状况下的地表长波辐射通量

Estimating Surface Longwave Radiation Flux Under All-Sky Condition from FY-4A and GFS Data

本文介绍一种利用FY-4A成像仪遥感数据和全球预报系统(GFS)资料估算全天空地表长波辐射通量的反演方法。该方法通过辐射传输模拟和统计回归计算建立云天地表下行长波辐射通量的反演模式,并基于GFS资料处理云覆盖地区的地表上、下行长波辐射通量。这种全天空状况下两种通量的反演结合了FY-4A晴空地表长波辐射业务产品和本文反演模式处理的云天地表上、下行长波辐射通量。2018年9月1日的处理结果与Aqua/CERES同类产品相对比,精度为:RMSE=20.52 W·m^-2,R=0.9481,Bias=3.3 W·m^-2(夜间地表下行辐射通量对比);RMSE=25.58 W·m^-2,R=0.9096,Bias=5.4 W·m^-2(白天地表下行辐射通量对比);RMSE=10.97 W·m^-2,R=0.9762,Bias=-3.3 W·m^-2(夜间地表上行辐射通量对比);RMSE=19.97 W·m^-2,R=0.9283,Bias=5.0 W·m^-2(白天地表上行辐射通量对比)。这些结果表明本文发展的方法能够反演出精度较好的云天上下行长波辐射通量资料,为今后利用FY-4后续星处理生成全天空状况下的地表长波辐射通量产品奠定了理论基础。

In this study,the specific methods of estimating surface longwave radiation fluxes under all-sky condition are elucidated.An inverse model for cloudy-sky surface downward longwave radiation(DLR)flux retrieval is developed based on infrared radiative transfer calculation,statistical regression analysis of simulated data,and atmospheric profiles.After that,we combine the inverse model and GFS data to calculate FY-4A clean-sky and cloudy-sky DLR values.Then,on the basis of the Aqua/CERES global DLR product,it validates the corresponding product of FY-4A during day or night time.The final results show that RMSE=20.52 W·m^-2,R=0.9481,BIAS=3.3 W·m^-2(nighttime);RMSE=25.58 W·m^-2,R=0.9096,BIAS=5.4 W·m^-2(daytime).Besides,we also successfully calculate the cloudy-sky upwelling longwave radiation(ULR)product at surface,which is combined with the operational FY-4A clear-sky ULR product to make a joint all-sky product.The validations of FY-4A all-sky ULR show that RMSE=10.97 W·m^-2,R=0.9762,BIAS=-3.3 W·m^-2(nighttime);RMSE=19.97 W·m^-2,R=0.9283,BIAS=5.0 W·m^-2(daytime).The validation results mentioned-above indicate the retrieval methods developed in this research are feasible and high-quality,which could be used for retrieving new operational DLR/ULR products for FY-4 series satellites in future.