Toward accurate CO2and CH4observations from GOSAT

The column-average dry air mole fractions of atmospheric carbon dioxide and methane (X_ (CO₂) and X_ (CH₄) ) are inferred from observations of backscattered sunlight conducted by the Greenhouse gases Observing SATellite (GOSAT). Comparing the first year of GOSAT retrievals over land with colocated ground-based observations of the Total Carbon Column Observing Network (TCCON), we find an average difference (bias) of −0. 05% and −0. 30% for X_ (CO₂) and X_ (CH₄) with a station-to-station variability (standard deviation of the bias) of 0. 37% and 0. 26% among the 6 considered TCCON sites. The root-mean square deviation of the bias-corrected satellite retrievals from colocated TCCON observations amounts to 2. 8 ppm for X_ (CO₂) and 0. 015 ppm for X_ (CH₄). Without any data averaging, the GOSAT records reproduce general source/sink patterns such as the seasonal cycle of X_ (CO₂) suggesting the use of the satellite retrievals for constraining surface fluxes.