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

The atmospheric infrared ultraspectral 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 CH
$_{4}$
mole fraction profiles from infrared absorption spectra. The retrieval algorithm is applied to the AIUS and successfully obtains CH
$_{4}$
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.