Validation of Remotely Sensed XCO2 Products With TCCON Observations in East Asia

As an important greenhouse gas (GHG) in the atmosphere, carbon dioxide (CO
₂
) has a great impact on global climate change. Accurate knowledge of the spatiotemporal variations of CO
₂
is of great significance for understanding the carbon cycle and evaluating the effectiveness of carbon emission reduction. In recent years, several satellites with CO
₂
sensors have been launched and a series of atmospheric CO
₂
concentration products have been developed using different retrieval algorithms. This study validated nine satellite XCO
₂
products derived from Greenhouse gases Observing SATellite (GOSAT), GOSAT-2, Orbiting Carbon Observatory-2 (OCO-2), and OCO-3: including ACOS-GOSAT, NIES-GOSAT, BESD-GOSAT, OCFP-GOSAT, SRFP-GOSAT, EMMA, GOSAT-2, OCO-2, and OCO-3 XCO
₂
. The remotely sensed XCO
₂
products were compared with the XCO
₂
observations from six Total Carbon Column Observing Network (TCCON) stations in East Asia for validation. The results showed that the OCO-2 XCO
₂
product outperformed other products, with the highest R
²
of 0.94 and the lowest MAE of 1.24 ppm. The ACOS-GOSAT and EMMA-GOSAT XCO
₂
products also showed favorable accuracies, both achieving R
²
of 0.93 and corresponding MAE values of 1.29 and 1.31 ppm, respectively. The GOSAT-2 XCO
₂
product showed the poorest accuracy, with an R
²
of 0.77 and a mean absolute error of 3.28 ppm. There was a significant overestimation of the bias-uncorrected GOSAT-2 XCO
₂
product in East Asia, and it indicated that bias correction must be performed for this XCO
₂
product. The accuracy of TCCON XCO
₂
was not consistent with remotely sensed XCO
₂
at different stations. The RJ, JS, AN, and TK TCCON stations generally showed better agreements between satellite estimates and TCCON observations, except for the GOSAT-2 XCO
₂
product.