微波真实光谱响应对快速辐射模拟影响分析

Impact Analysis of Microwave Real Spectral Response on Rapid Radiance Simulation

为分析国产微波遥感器真实光谱响应在数值天气预报系统同化模块中对微波辐射快速模拟的影响,基于逐线吸收模型,采用TOVS辐射传输(RTTOV)预报因子和风云三号D星微波温度探测仪(FY-3D/MWTS-2)搭载的大气和陆地均有辐射贡献的第四通道真实光谱响应和理想光谱响应,通过最小二乘法,分别拟合生成真实光谱响应和理想光谱响应对应的快速微波辐射光学厚度拟合系数。将两种拟合系数应用于中国气象局全球预报系统(CMA-GFS)的四维变分同化系统,采用美国环境预报中心(NCEP)的分析资料(FNL)作为CMA-GFS的气象要素背景场,模拟不同光谱响应驱动下的微波辐射背景场,并与FY-3D/MWTS-2真实观测场进行对比统计分析,分别计算真实光谱响应和理想光谱响应驱动时,不同海陆类型下的观测背景差(OMB),分析真实光谱响应相比理想光谱响应,对不同海陆类型的微波辐射模拟的差异。分析结果表明,在微波辐射观测场值较低的情况下,真实光谱响应和理想光谱响应驱动模拟的微波辐射背景场值略高于观测场值,随着微波辐射场值增大,模拟的微波辐射背景场值与观测场值更为接近;除南半球靠近极区的少部分地区外,真实光谱响应驱动模拟的OMB均小于理想光谱响应驱动的模拟结果,真实光谱响应驱动的辐射背景场模拟更接近于观测场;相比采用理想光谱响应驱动,采用真实光谱响应驱动后,在陆地地区,微波辐射OMB的均方根误差(RMSE)减小约1.80%;在海洋地区,RMSE减小约2.6%;在海陆交界地区,RMSE减小约4.72%,全球总体RMSE减小2.17%;采用真实光谱响应驱动后,OMB总体的标准差(STDV)和平均绝对误差(MAE)分别减小为0.75%和4.6%。

To analyze the effects of the real spectral response of microwave remote sensors on microwave radiance simulation in the assimilation modules of numerical weather prediction systems,the real and ideal spectral responses of the fourth channel,which reflects the atmospheric and terrestrial radiance simultaneously,of FengYun-3D Microwave Temperature Sounders-2(FY-3D MWTS-2)were applied.Based on line-by-line atmospheric absorption models and predictors of Radiative Transfer for TOVS(RTTOV),different optical depth fitting parameters by real and ideal spectral responses of FY-3D MWTS-2 were generated by applying the least square method.Radiance background fields by real and ideal spectral responses can be simulated from four dimension variation assimilation module of the China Meteorological Administration-Global Forecast System(CMA-GFS)by using the Final(FNL)global operational analysis dataset from the National Center of Environmental Prediction(NCEP)as the meteorological background fields.Observation Minus Background(OMB)under different sea and land types could be calculated using the observations of FY-3D/MWTS-2 and simulated radiance backgrounds.The results show that microwave radiance backgrounds simulated by real spectral response were higher than ideal spectral response under low radiance observation situations.Simulated radiance backgrounds were closer to observations when the radiance observation increased.Radiance backgrounds by real spectral response were closer to radiance observations than by ideal spectral response under global region except for a small part of the Antarctic region.Compared with using ideal spectral response,when the real spectral response was applied,the Root Mean Square Error(RMSE)of OMB on land region decreased by 1.8%;the RMSE of OMB in sea region decreased by 2.6%;the RMSE of OMB in land sea border region decreased by 4.72%,the total RMSE of OMB decreased by 2.17%.Standard Deviation(STDV)and Mean Absolute Error(MAE)also decreased by 0.75%and 4.6%.