Monitoring the carbon dioxide mixing ratio in the troposphere and the methane total column over Siberia according to the data of the AIRS and IASI IR sounders

Abstract

The development of the AIRS (EOS/Aqua) and IASI (MetOp) satellite hyperspectral IR sounders opens new opportunities for determining the average tropospheric carbon dioxide concentration ($X_{CO_2 }$) and total methane content ($Q_{CH_4 }$) in the atmosphere from large distances, which is important in climatic studies and since the ground network for CO₂ and CH₄ observations is scarce. The improved scheme for $X_{CO_2 }$ retrieval from the AIRS data, which was used to construct the $X_{CO_2 }$ spatial distribution based on the AIRS data for July 2003 and 2010 covering Siberia, is presented. A similar methodology was also used to retrieve instantaneous $X_{CO_2 }$ values from the cloud-cleared IASI data for July 7, 2008 and the YAK-AEROSIB experimental region. A comparison of the satellite data with quasi-synchronous aircraft observations gives an error of about 2.2 million⁻¹. The iterative physical algorithm was developed in order to retrieve $Q_{CH_4 }$. The efficiency of the proposed algorithm was estimated during the experiments with actual IASI data covering the Siberian region during several days in July 2008. The $Q_{CH_4 }$ estimates were validated by comparing them with the spatially superimposed and quasi-synchronous $Q_{CH_4 }$, estimates based on the AIRS data. The standard deviations of both types of estimates are not more than 3%.