Update on the GOSAT TANSO–FTS SWIR Level 2 retrieval algorithm

The National Institute for Environmental Stud-ies has provided the column-averaged dry-air mole fraction of carbon dioxide and methane (XCO2 and XCH4) prod-ucts (L2 products) obtained from the Greenhouse gases Ob-serving SATellite (GOSAT) for more than a decade. Re-cently, we updated the retrieval algorithm used to produce the new L2 product, V03.00. The main changes from the pre-vious version (V02) of the retrieval algorithm are the treat-ment of cirrus clouds, the degradation model of the Thermal And Near-infrared Spectrometer for carbon Observation- Fourier Transform Spectrometer (TANSO-FTS), solar irra-diance spectra, and gas absorption coefficient tables. The re-trieval results from the updated algorithm showed improve-ments in fitting accuracies in the O-2 A, weak CO2, and CH4 bands of TANSO-FTS, although the residuals increase in the strong CO2 band over the ocean. The direct comparison of the new product obtained from the updated (V03) algorithm with the previous version V02.90/91 and the validations using the Total Carbon Column Observing Network revealed that the V0(3) algorithm increases the amount of data with-out diminishing the data qualities of XCO2 and XCH(4 )over land. However, the negative bias of XCO2 is larger than that of the previous version over the ocean, and bias correction is still necessary. Additionally, the V0(3) algorithm resolves the underestimation of the XCO2 growth rate compared with the in situ measurements over the ocean recently found using V02.90/91 and V02.95/96.