Global Concentrations of CO2 and CH4 Retrieved from GOSAT: First Preliminary Results

TLDR

GOSAT was launched in 2009 to monitor global CO₂ and CH₄ levels from space, and the authors emphasize the need for calibration and validation to improve retrieval quality. GOSAT began operations after a system check, and the authors performed initial retrievals of CO₂ and CH₄ concentrations over cloud‑free land scenes. Preliminary GOSAT data reveal clear CO₂ and CH₄ spectral signatures, with higher column‑averaged dry‑air mole fractions in the northern hemisphere than the south, matching ground‑based and other satellite observations but indicating an overall underestimation of absolute concentrations.

Abstract

The Greenhouse Gases Observing Satellite (GOSAT) was launched on January 23, 2009, to monitor global atmospheric levels of CO2 and CH4 from space. GOSAT started initial operation of its instruments after an initial satellite system check. Although the radiant data obtained by the GOSAT instruments are currently in the preliminary stages of calibration and validation, the spectral absorption features of CO2 and CH4 are clearly identifiable. An initial retrieval of these gaseous concentrations was performed for measurement scenes of cloud-free conditions over land. These results showed that column-averaged dry air mole fractions of both CO2 and CH4 in the northern hemisphere were higher than those in the southern hemisphere. These latitudinal differences agree with data obtained from ground-based sources and other satellite observations; however, the absolute values of the gaseous concentrations from GOSAT data seem to have been underestimated. Calibrations as well as validation should be conducted to improve the quality of GOSAT retrievals.