China's First Infrared Occultation Spectrometer (GaoFen-5/AIUS) Monitoring Atmosphere Above Antarctic: Evaluation of Methane Profiles

The Atmospheric Infrared Ultra-Spectral Sounder (AIUS) is China's first infrared occultation spectrometer onboard the GaoFen-5 satellite. This instrument provides measurements in the near- infrared and mid- infrared spectral regions with a spectral resolution of 0.02 cm $^{-1}$ , monitoring key greenhouse gases like methane (CH $_{4}$ ). In this study, we have developed a physics-based retrieval algorithm for accurately deriving methane mole fraction profiles from infrared absorption spectra. The retrieval algorithm is applied to AIUS and successfully obtains methane mole fraction profiles from January to December 2019 over Antarctic. The validation results show that the retrieval algorithm has a satisfactory performance using AIUS measurements, with average relative standard deviation of the differences less than 7.2 % throughout the altitude range of 10-70 km.