Retrieval of Global Carbon Dioxide From TanSat Satellite and Comprehensive Validation With TCCON Measurements and Satellite Observations

To cope with global climate change and monitor global CO₂ concentration distribution, the first Chinese carbon dioxide satellite (TanSat) has been successfully launched in December 2016. In this study, we implemented a CO₂ retrieval scheme by calibrating the TanSat sun-glint (GL) mode spectra and adapting the Iterative Maximum <inline-formula> <tex-math notation="LaTeX">$A$ </tex-math></inline-formula> <italic>Posteriori</italic> Differential Optical Absorption Spectroscopy (IMAP-DOAS) algorithm for CO₂ spectral retrieval. The global terrestrial CO₂ total vertical column density (VCD) and column-averaged dry-air mole fractions of CO₂ (<inline-formula> <tex-math notation="LaTeX">$\text{X}_{\text {CO2}}$ </tex-math></inline-formula>) were simultaneously retrieved from TanSat GL spectral observations. Then, a comprehensive verification was performed between TanSat CO₂ retrieval and other measurements including Total Carbon Column Observing Network (TCCON), the Japanese Greenhouse gases Observing SATellite (GOSAT), and the US Orbiting Carbon Observatory-2 (OCO-2). Further comparisons between our TanSat CO₂ retrieval and ground-based FTIR measurements from TCCON indicated a good correlation with the mean bias of −0.78 ppm, the standard deviation at 1.75 ppm, and the Pearson correlation coefficient of 0.81. In addition, cross-satellite CO₂ validations of TanSat with GOSAT and OCO-2 showed consistently spatiotemporal trends for both CO₂ VCD and <inline-formula> <tex-math notation="LaTeX">$\text{X}_{\text {CO2}}$ </tex-math></inline-formula>. In summary, we can conclude that the presented CO₂ retrieval scheme has achieved global CO₂ retrieval from TanSat GL mode spectra with high precision and accuracy, as suggested by the results of independent ground-based and satellite validations.