Evaluation and intercomparison of the atmospheric CO2 retrievals from measurements of AIRS, IASI, SCIAMACHY and GOSAT

Quantifications of the differences among currently available CO₂ products are very necessary for deeply understanding each product and their joint use. A spatio-temporal matching strategy has been proposed in this work to allow the CO₂ products from AIRS, IASI, GOSAT and SCIAMACHY to be physically comparable by accounting for the a priori CO₂ profiles employed in retrieval stage, averaging kernel functions and atmospheric pressure profiles etc. Based on this, these CO₂ products are intercompared in terms of magnitudes of CO₂ concentrations and their spatio-temporal distributions. The results show that relative large discrepancies are detected among these products, both in specific values of CO₂ concentrations and the spatio-temporal distributions, implying more efforts should be made to fully understand the differences of such measurements and to better constrain the uncertainties in CO₂ retrievals from space in the future.