Carbon dioxide and methane RemoTeC retrievals from GOSAT (2009-2019) and GOSAT-2 (2019)

The Japanese Greenhouse gases Observing SATellite (GOSAT), in orbit since January 2009, and its successor GOSAT-2, in orbit since October 2018, are dedicated to enhancing our knowledge of the carbon cycle. We use our RemoTeC full-physics algorithm to infer atmospheric concentrations and auxiliary parameters from the measured solar SWIR radiances backscattered at the earth´s atmosphere and surface. Accuracy requirements are a major challenge for these space-based measurements of column-averaged dry-air mole fractions of carbon dioxide and methane (XCO₂ and XCH₄).

Here we present 1) a consolidated ten years GOSAT XCO₂ and XCH₄ dataset and 2) first results for GOSAT-2 XCO₂ and XCH₄ retrievals. For GOSAT, 4.8 % of all measurements pass our cloud filter, based on the O₂ A-band signal and several quality filters. For validation and bias-correction, we use collocated measurements from ground-based stations of the Total Carbon Column Observing Network (TCCON). The dataset shows a scatter of well below 1 %. For GOSAT-2, we are able to reliably process measurements in land nadir and ocean glint geometry. In addition to the retrieval windows implemented for GOSAT, we use the spectral ranges at 4290 - 4328 cm^-1 and 4354 - 4441 cm^-1 to retrieve carbon monoxide and nitrous oxide concentrations. We evaluate instrument performance and precision by comparing XCO₂ and XCH₄ retrievals to both collocated GOSAT and ground-based TCCON measurements.