Satellite-based inversion of global methane fluxes: Capabilities and implications of GOSAT-2 measurements

Abstract. Methane (CH₄) is a key greenhouse gas with a strong climate impact and a relatively short atmospheric lifetime, making accurate monitoring essential for mitigation strategies. Satellite observations provide global coverage and independent constraints on CH₄ emission estimates, and GOSAT-2, launched in 2018 as the successor to GOSAT, was designed to improve retrieval accuracy and enhance flux estimation. This study presents an evaluation of the GOSAT-2 Level 4 (G2L4) CH₄ flux product, supported by analysis of the underlying Level 2 (L2) XCH₄ retrievals, and summarizes key findings on global and regional CH₄ budgets. Using an atmospheric inversion framework, we generated G2L4 posterior CH₄ fluxes and assessed their consistency by comparing them with inversions constrained by alternative observational datasets, including GOSAT L2 retrievals and ground-based and aircraft measurements. GOSAT-2 achieved substantial improvements in observational coverage and data density compared to its predecessor, particularly in tropical and high-latitude regions. Posterior flux estimates derived from G2L4 are broadly consistent with global CH₄ budgets reported in synthesis studies, while prior-to-posterior differences reveal positive corrections in tropical regions and negative adjustments in several mid-latitude industrial areas. A preliminary sector-focused assessment further demonstrates the potential of GOSAT-2 to inform anthropogenic CH₄ emission evaluations in regions where such sources dominate. These findings highlight the capability of GOSAT-2 to refine regional and global CH₄ emission estimates and underscore priorities for future improvements in retrieval algorithms, observation strategies, and integration with complementary datasets.