Volcanic degassing drives eruptions and influences Earth’s atmospheric composition and climate over geological timescales. Measuring the emission rates of the key magmatic gases emitted through passive degassing and eruptions is crucial for volcano monitoring, and remote sensing techniques plays an absolutely central role in this task. This chapter reviews the principles, techniques, and applications of remote sensing for volcanic gas monitoring, focusing on four key methods: 1. Differential Optical Absorption Spectroscopy (DOAS)—Measures SO2 and some halogen oxides (BrO, OClO) via Ultraviolet spectroscopy, enabling flux calculations either through mobile measurements or fixed scanning instruments, as implemented the NOVAC network. I present the formulas used to calculate SO2 flux for each measurement set-up, and discuss their respective merits and limitations, concluding that mobile measurements provide a better accuracy while scanning measurements offer a higher time resolution and automation. 2. SO2 Cameras—Provide high-temporal-resolution flux measurements and 2D images of SO2 in the plume. The lack of highly-resolved spectral information and viewing geometry inherent to this methods results in the need of corrections for light dilution and aerosol interference. Several satisfying options exist for the former, much less for the latter. 3. Open-Path Fourier Transform Infrared (OP-FTIR) Spectroscopy—Measures multiple gases (SO2, HCl, HF, H2O, CO2, SiF4) in infrared atmospheric windows. The three most common instrumental set-up are reviewed and discussed: solar occultation, short-path, and thermal emission each one being suited to different volcanic settings, wavelength ranges and gas species. 4. Satellite Remote Sensing—Tracks global SO2 emissions using UV (e.g., TROPOMI) and IR sensors (e.g., IASI), though retrievals depend on plume altitude and atmospheric conditions. Satellite remote sensing still lacks the sensitivity of ground-based methods but usually gives more accurate results for very large emissions. Recent advances in sensors and algorithms has allowed measuring other more volcanic gases than just SO2.  Then, I briefly discuss the processes that control the gas composition (geodynamic context, magma source depth, degree of previous degassing and hydrothermal interactions) and SO2 flux (change in magma supply, bubble migrations, outgassing, conduit sealing and hydrothermal scrubbing).  Finally I review recent advancements in the field, such as hyperspectral gas imaging, Fabry-Perot based UV cameras, and geostationary satellites (e.g., TEMPO) for real-time monitoring, and expose its current challenges, such as retrievals of gas in ash-laden plumes and correcting for radiative transfer complexities.

Remote Monitoring of Volcanic Gases

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发表日期：

2025年

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Robin Campion

摘要

Volcanic degassing drives eruptions and influences Earth’s atmospheric composition and climate over geological timescales. Measuring the emission rates of the key magmatic gases emitted through passive degassing and eruptions is crucial for volcano monitoring, and remote sensing techniques plays an absolutely central role in this task. This chapter reviews the principles, techniques, and applications of remote sensing for volcanic gas monitoring, focusing on four key methods: 1. Differential Optical Absorption Spectroscopy (DOAS)—Measures SO2 and some halogen oxides (BrO, OClO) via Ultraviolet spectroscopy, enabling flux calculations either through mobile measurements or fixed scanning instruments, as implemented the NOVAC network. I present the formulas used to calculate SO2 flux for each measurement set-up, and discuss their respective merits and limitations, concluding that mobile measurements provide a better accuracy while scanning measurements offer a higher time resolution and automation. 2. SO2 Cameras—Provide high-temporal-resolution flux measurements and 2D images of SO2 in the plume. The lack of highly-resolved spectral information and viewing geometry inherent to this methods results in the need of corrections for light dilution and aerosol interference. Several satisfying options exist for the former, much less for the latter. 3. Open-Path Fourier Transform Infrared (OP-FTIR) Spectroscopy—Measures multiple gases (SO2, HCl, HF, H2O, CO2, SiF4) in infrared atmospheric windows. The three most common instrumental set-up are reviewed and discussed: solar occultation, short-path, and thermal emission each one being suited to different volcanic settings, wavelength ranges and gas species. 4. Satellite Remote Sensing—Tracks global SO2 emissions using UV (e.g., TROPOMI) and IR sensors (e.g., IASI), though retrievals depend on plume altitude and atmospheric conditions. Satellite remote sensing still lacks the sensitivity of ground-based methods but usually gives more accurate results for very large emissions. Recent advances in sensors and algorithms has allowed measuring other more volcanic gases than just SO2. Then, I briefly discuss the processes that control the gas composition (geodynamic context, magma source depth, degree of previous degassing and hydrothermal interactions) and SO2 flux (change in magma supply, bubble migrations, outgassing, conduit sealing and hydrothermal scrubbing). Finally I review recent advancements in the field, such as hyperspectral gas imaging, Fabry-Perot based UV cameras, and geostationary satellites (e.g., TEMPO) for real-time monitoring, and expose its current challenges, such as retrievals of gas in ash-laden plumes and correcting for radiative transfer complexities.