Derivation of tropospheric carbon dioxide and methane concentrations in the boreal zone from satellite-based hyper-spectral infrared sounders data

Introduction The development of space-borne hyper-spectral IR sounders (AIRS/EOS-Aqua, IASI/MetOp) opens new opportunities for detecting the variations of atmospheric carbon dioxide (CO2) and methane (CH4) concentrations. The capabilities to retrieve atmospheric column-average CO2 mixing ratio and similar column-average CH4 mixing ratio (or CH4 columns) from satellite measurements is of significant importance in the context of global carbon cycle research, climate change studies and due to sparse network of ground-based CO2&CH4 observations. Bearing in mind these issues the main objectives of our research were as follows: Improvement of the technique for column-average CO2 mixing ratio (QCO2) retrieval in the upper troposphere from AIRS/EOS-Aqua data over Western Siberia; Validation of QCO2 retrievals against aircraft flask CO2 observations (over boreal zone); Development and testing of the novel technique for tropospheric CH4 column (CACH4) retrieval from IASI and AIRS data. This paper presents at first an updated status of QCO2 retrieval scheme based on clear-sky or cloudcleared AIRS inversion algorithm. The validation effort carried out with real AIRS data for two areas in the boreal zone of Western Siberia (Novosibirsk and Surgut regions) and for 10 months of year 2003 demonstrates the successful performance of proposed technique. With respect to the CH4 column retrieval from AIRS and IASI data the approach has been developed based upon the application of iterative physical inversion algorithm to clear-sky AIRS or IASI data in the subsets of CH4 – dedicated superchannels (linear combinations of measurements in temperatureand CH4dedicated channels). Using the data in super-channels reduces the effect of inaccurate temperature profile T(p) knowledge on accuracy of CACH4 retrievals in sounding points. The performance of the retrieval algorithm is evaluated in the case study experiment involving datasets of IASI and AIRS data covering Kiruna (Sweden) region and complemented with quasi-synchronous and collocated ground based and radiosonde observations as well as with AIRS-based L2 retrievals.