High-frequency monitoring of SO₂ plumes from moderate-scale volcanic eruptions using a synergy of GEO and LEO satellites: A case study of the 2024 Kanlaon eruption

Abstract. Satellite remote sensing is crucial for monitoring volcanic sulfur dioxide (SO₂) globally. However, the rapid evolution of volcanic plumes necessitates high-frequency observations, which typical twice-daily overpasses of Low Earth Orbit (LEO) sensors fail to capture. To address this limitation, this study presents a synergistic Geostationary Earth Orbit (GEO) and LEO observation framework. Specifically, we show the first quantitative SO₂ retrieval from a GEO hyperspectral infrared sounder (FY-4B/GIIRS), using an optimal-estimation-based retrieval algorithm. Because current and upcoming GEO infrared sounders lack the strong ν3 absorption band, our algorithm uniquely leverages the weaker ν1 absorption band. Simulation experiments indicate that the detection limit (retrieval error > 100 %) is 3 DU for plumes at 10 km altitude. During the June 2024 Kanlaon eruption, GIIRS captured early, high-concentration plume dynamics, though tracking diluted plumes remained challenging. Crucially, it provided the earliest satellite detection by continuously monitoring the initial nighttime burst (posterior error of 53.7 ± 24.1 %), filling critical temporal gaps left by ultraviolet sensors. Combined with LEO (HIRAS, IASI, CrIS, TROPOMI and MLS) and GEO sensor (GEMS), the synergistic framework achieved high frequency quantification of SO₂ mass loading and transport pathways. We estimated a peak SO₂ mass loading of ∼40 kt and an e-folding time of 5.2 ± 0.5 days. Furthermore, multi-platform observations identified significant discrepancies in the CAMS global model regarding the plume's evolution and magnitude. This geostationary-driven synergistic framework delivers high-fidelity observational records, establishing a robust basis for monitoring moderate-scale volcanic events and evaluating atmospheric chemical transport models.