Study On Sensitivity And Signal-to-noise Ratio Of FY-4A Satellite Infrared Hyper-spectral Atmospheric Sounder GIIRS

Infrared hyper-spectral atmospheric sounder has the characteristics of high spectral resolution,high sensitivity and high precision of spectral radiation calibration etc.Its significant advantages are widely used in atmospheric profile inversion,climate change research,numerical weather prediction assimilation and atmospheric trace gases detection.The previous satellite infrared hyper-spectral data are all from polar-orbiting satellites with low temporal resolution.The latest generation of China's geostationary meteorological satellite FY-4A is equipped with Geosynchronous Interferometric Infrared Sounder(GIIRS)for the first time in the world,which realizes the observation of the atmosphere with high temporal resolution and hyperspectral resolution.It is of great importance to analyze the sensitivity and signal-to-noise ratio(SNR)of satellite infrared hyper-spectral atmospheric sounder signals to different atmospheric parameters for effective utilization of detection data.Sensitivity and SNR are important radiation performance indexes of remote sensors.In this paper,the concepts of sensitivity and SNR of infrared hyper-spectral sounding are extended for the in-orbit application of sounder from the sounder noise sensitivity to the atmospheric parameter sensitivity and the surface temperature error sensitivity,sounder SNR to atmospheric target SNR and atmospheric sounding comprehensive SNR.The corresponding calculation models and their relations are introduced.These models are applied to the sensitivity and SNR evaluation of FY-4A GIIRS.And the physical mechanisms of these characteristics are analyzed.The main conclusions of this study are as follows:(1)The conversion relationship between different expression modes of sounder noise sensitivity is given.According to the infrared atmospheric radiation transfer equation,the atmospheric sensitivity and the surface temperature error sensitivity are defined,the corresponding calculation models are established,and the relationship between the atmospheric single parameter sensitivity,multi-parameter comprehensive sensitivity and the total atmospheric parameter sensitivity is established.(2)The above definition and calculation model are applied to the detection sensitivity evaluation of FY-4A satellite infrared hyperspectral atmospheric sounder GIIRS.The results show that sounder noise sensitivity varies from 0.03521K to0.5448K within the detection spectrum of FY-4A GIIRS.The sensitivity of atmospheric water vapor and ozone is generally at the level of several K.The sensitive channel range of ozone is limited to several very narrow absorption zones such as 9.6?m,while water vapor is very wide.The sensitivity of CO₂and N₂O is lower than 0.1K,and the sensitivity of CH₄is even lower.Atmospheric temperature has a wide range of sensitive channels,and its sensitivity is generally higher than that of water vapor and ozone.The variation characteristics of surface temperature error sensitivity with channel are opposite to that of atmospheric temperature,which is generally at the level of a few tenths of K.The comprehensive sensitivity of atmospheric parameters is the comprehensive embodiment of the sensitivity of various parameters,and the magnitude and the variation with channels tend to be the atmospheric parameters with the largest sensitivity.(3)The evaluation results of the atmospheric parameters sensitivity and the surface temperature error sensitivity are analyzed by physical mechanism.The analysis shows that the atmospheric absorption gas sensitivity is positively correlated with the strength of its own absorption and negatively correlated with the strength of other absorption gases.The atmospheric temperature sensitivity is positively correlated with the absorption intensity of each absorbed gas,and the surface temperature error sensitivity is negatively correlated with the absorption intensity of each absorption gas.The sensitivity of CO₂,N₂O and CH₄is much lower than that of other atmospheric parameters because their concentrations are stable in the atmosphere.(4)The sounder SNR,the atmospheric target SNR and the atmospheric sounding comprehensive SNR of in-orbit application are defined,and their calculation models and relationships are established.(5)The definition and calculation models of SNR are applied to the SNR evaluation of FY-4A GIIRS sounding.The results show that the sounder SNR decreases with the increase of wave-number in the whole range of GIIRS channels.In the atmospheric target SNR,the atmospheric temperature channels are selected the most.The priority band range of the selected sounding channels is 700?800cm^-1,1650?1800 cm^-1and 2000?2200 cm^-1in sequence.However,due to atmospheric target SNR of water vapor and ozone is not high as a whole,it is not suitable to be used as detection parameters alone,and it is necessary to combine atmospheric temperature as detection target parameters together,that is,temperature and water vapor can be used as detection target parameters,or temperature,water vapor and ozone can be used as detection target parameters respectively.The dominant channels are in 1650?2000cm^-1,followed by 700?800cm^-1and 2000?2200 cm^-1.From the point of view of the atmospheric sounding comprehensive SNR,due to the superposition of the sounder noise sensitivity,it is less than the atmospheric target SNR,but the variation trend of the two is basically the same.The results of the selected channels for different SNR ranges are similar to the atmospheric target SNR.The study is of great value for the evaluation of the in-orbit application performance of satellite infrared hyper-spectral atmospheric sounder,which can provide support for the application channel optimization of the infrared hyper-spectral atmospheric sounder,as well as a reference for the evaluation of the in-orbit application performance of other atmospheric sounders.