The Theoretic Study On The Retrieval Of Atmospheric CO₂ Concentration From FY-3 IRAS Soundings

In recent years the ground monitoring sites of CO₂ concentration is becoming more and more, but its spatial resolution is still limited. The use of satellite remote sensing to detect atmospheric CO₂ concentrations can get its global distribution, therefore, it will be greatly helpful to improve the understanding of the carbon cycle and the climate change in the earth system.FY-3 meteorological satellite is the second generation of polar-orbit meteorological satellite in China, it will carry InfRared Atmospheric Sounder (IRAS),Microwave Atmospheric Sounder,Microwave Atmospheric Humidity Sounder for the first time. Based on the characteristics and spectral response function of the IRAS sounding channels and the latest version of atmospheric molecular spectroscopic database HITRAN 2004, a new atmospheric radiative transfer model of IRAS is developed in this paper. The measured radiance of the CO₂ channel, which is one of the channels of infrared spectrometer (IRAS) on the Fengyun-3 meteorological satellite, and its sensitivity to changes in atmospheric CO₂ concentration were calculated to explore the ability of the channel to remote sensing of atmospheric CO₂ concentration by an exact line-by-line (LBL) radiative transfer model, the uncertainties due to changes in other absorption gases concentration also included, the results showing that the channel is particularly well suited for remote sensing of atmospheric CO₂ concentration. The study of the effect of different heights of the atmosphere on the radiation that would reach the satellite shows that the change of CO₂ concentration in 4.5km is in the greatest influence on the outgoing radiation, and the contribution is almost exclusively from 0-20km, the height above 20km no longer have an impact. At the same time, changes in atmospheric CO₂ concentration is also first action in the troposphere, so the channel can be timely detect the changes of the concentration of CO₂ in the atmosphere, very beneficial to the earlier discovery of CO₂ sources and sinks changes. With the linearization of the infrared radiative transfer equation, a numerical simulation study was conducted by the simulated radiance. The 1980-2006 global annual average concentration of CO₂ inversion test results shows that the inversion value is very closed to the real value, and the inversion error is less than the annual growth rate of atmospheric CO₂ concentration. The initial value have a certain impact on the inversion results, the more close to the true value, the better results of the inversion. The study of the changes in O₃ and H₂O concentration shows that although the changes in the O₃ and H₂O concentration has some influence on the inversion results, but its impact is so small that the basic inversion error is also less than 2ppmv.Furthermore, the outgoing infrared emitting spectrum at the top of the atmosphere and its sensitivity to changes in atmospheric CO₂ concentrations were calculated by a line-by-line (LBL) radiative transfer mode to study the feasibility of inversion the CO₂ profile for a reference to the China's further development of high-resolution spectral satellite detectors inversion CO₂ profile. It is found that the outgoing infrared emitting spectrum in the 4.3 micron absorption band of CO₂ reduces significantly with the increases of CO₂ concentration, particularly in the bands of 2241-2249 cm^-1,2250-2258 cm^-1,2259-2267 cm^-1 and 2382-2390 cm^-1, and seldom affected by changes in other atmospheric components, and therefore particularly well suited for remote sensing of atmospheric CO₂ concentration changes. With the method of optimal nonlinear inversion, atmospheric CO₂ profile between 0 and 15km has been retrieved. The results show that atmospheric CO₂ concentrations retrieval is accurate in free troposphere by using the four channels.