FY-3C/VIRR热红外通道精细化再定标模型的构建和精度验证

Construction and validation of FY-3C/VIRR infrared window channel refinement re-calibration model

风云三号可见光红外扫描辐射计(FY-3/VIRR)自2008年FY-3A发射以来,在轨提供了十余年的对地观测数据。这些数据对于大气、地表和环境产品反演、天气和气候变化研究具有重要意义。本文分析了FY-3/VIRR热红外通道的偏差特征,针对定标偏差的昼夜差异和季节变化,结合业务定标模型初步确认误差的主要来源,并分别对星上定标模型和星上黑体辐射模型进行优化,构建热红外通道精细化再定标模型。FY-3/VIRR热红外通道再定标模型直接采用二次定标方程进行星上定标,并考虑了仪器环境辐射影响。以国内外公认的高精度红外大气探测仪器(IASI)为参考仪器,基于GSICS推荐的近同时星下点观测(SNO)匹配样本,实现了精细化再定标模型的参数确定。结果表明,该精细化再定标模型对VIRR热红外通道的系统性偏差,以及偏差的昼夜差异和季节性变化均有明显的修正效果,利用精细化再定标模型重定标后的月平均偏差均在±0.3 K以内;以2018年为例,冬季昼夜差异由业务定标的0.4 K左右减小至小于0.1 K。

FY-3 visible infrared scanning radiometer(FY-3/VIRR)has provided Earth-observation data in orbit for more than 10 years since the launch of FY-3A in 2008.These data are important for atmospheric,surface,and environmental product inversion,weather,and climate change research.In this study,the calibration bias characteristics of FY-3/VIRR thermal infrared channel were analyzed,and the main sources of error were preliminarily identified in combination with the operational calibration model in day-night difference and seasonal variation of the operational calibration bias.In addition,the on-board calibration model and the on-board blackbody radiation model were optimized to construct the fine re-calibration model of the thermal infrared channel.In the linear calibration model plus nonlinear correction adopted by the FY-3/VIRR infrared channel,the quadratic term is related to the calibrated blackbody radiation.When the satellite is in orbit,the temperature change of the blackbody causes change in the quadratic term coefficient.As a result,the shape of the quadratic response of the infrared channel is changed.When the blackbody temperature changes,the quadratic term coefficient is changed,thereby introducing calibration deviation.In addition,the blackbody radiation on the infrared channel is calculated using the equivalent brightness temperature coefficient of the blackbody obtained from the pre-launch test.In fact,the radiation in the blackbody observation path is reflected in a set of polynomial fitting coefficients.This fitting process is based on the pre-launch vacuum test,and the on-orbit application results in calibration deviation.The FY-3/VIRR re-calibration model of thermal infrared channel directly uses quadratic calibration equation for on-board calibration model and considers the influence of instrument environmental radiation.The blackbody radiation model on the planet is reconstructed by considering the blackbody temperature as the proxy ambient temperature given that traditional instruments lack temperature measurement points on the planet.Based on the matching samples of Simultaneous Nadir Observation(SNO)recommended by GSICS,The parameters of the refined re-calibration model were determined using the internationally recognized high-precision Infrared Atmospheric Sounding Interferometer(IASI)as the reference instrument.The results show that the refined re-calibration model has a significant correction effect on the systematic deviation,diurnal difference,and seasonal variation of the operational calibration model,and the monthly mean deviation is within±0.3K after re-calibration using the refined re-calibration model.In 2018,for example,the difference between day and night in winter decreased from approximately 0.4 K of the service calibration to less than 0.1 K.