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 groundbased 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.
[1] This report is the second in a series of companion papers describing the effects of atmospheric light scattering in observations of atmospheric carbon dioxide (CO 2 ) by the Greenhouse gases Observing SATellite (GOSAT), in orbit since 23 January 2009. Here we summarize the retrievals from six previously published algorithms; retrieving columnaveraged dry air mole fractions of CO 2 (X CO2 ) during 22 months of operation of GOSAT from June 2009. First, we compare data products from each algorithm with ground-based remote sensing observations by Total Carbon Column Observing Network (TCCON). Our GOSAT-TCCON coincidence criteria select satellite observations within a 5 radius of 11 TCCON sites. We have compared the GOSAT-TCCON X CO2 regression slope, standard deviation, correlation and determination coefficients, and global and station-to-station biases. The best agreements with TCCON measurements were detected for NIES 02.xx and RemoTeC. Next, the impact of atmospheric light scattering on X CO2 retrievals was estimated for each data product using scan by scan retrievals of light path modification with the photon path length probability density function (PPDF) method. After a cloud prefiltering test, approximately 25% of GOSAT soundings processed by NIES 02.xx, ACOS B2.9, and UoL-FP: 3G and 35% processed by RemoTeC were found to be contaminated by atmospheric light scattering. This study suggests that NIES 02.xx and ACOS B2.9 algorithms tend to overestimate aerosol amounts over bright surfaces, resulting in an underestimation of X CO2 for GOSAT observations. Cross-comparison between algorithms shows that ACOS B2.9 agrees best with NIES 02.xx and UoL-FP: 3G while RemoTeC X CO2 retrievals are in a best agreement with NIES PPDF-D.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.