The Inter-comparison of GOSAT, GOSAT-2 and OCO-2/3 XCO2 Measurements over East Asia and Validated with TCCON Observations

Satellite remote sensing provides an essential tool for monitoring atmospheric carbon dioxide (CO2) mole fraction. Currently, there are several satellite missions providing global column-averaged dry-air mole fraction of CO2 (XCO2) observations. Assessing the spatial coverage, temporal trends, accuracy and precision of these satellite products is critical for carbon cycle studies and informing climate policy. In this study, we conduct a comprehensive evaluation of the differences in XCO2 products among GOSAT, GOSAT-2, OCO-2, and OCO-3 over East Asia between August 2019 and November 2023. In addition, the satellite data are also validated with the ground-based TCCON measurements. It is found that GOSAT-2, whose the XCO2 is not bias-corrected, has the largest systematic biases of 3.27-5.81 ppm, with random uncertainties of 3.45-6.04 ppm at six TCCON sites. OCO-2 and OCO-3 show a good agreement, and their co-located differences are generally within ~1.5 ppm. The annual growth rates of XCO2 derived from the four satellite products are 1.23±0.31–2.75±0.34 ppm/year, while TCCON-derived values are 2.21±0.03–2.54±0.03 ppm/year. The amplitudes and phases of the XCO2 seasonal variation derived from the four satellite products also differ from those of TCCON, mainly due to the less frequent sampling of satellite XCO2 products.