Ground-based and space-borne sensing of volcanic gas fluxes or gas amounts.

Although working at a much lower frequency than dual UV-cameras, DOAS (Differential Optical Absorption Spectroscopy) can be usefully operated to determine time-averaged SO2 plume fluxes and their change over hourly or daily time scales. Space-borne sensors provide the bulk quantities of volcanic SO2 discharged into the atmosphere in sizeable eruptive clouds with at most daily time-averaged figures for the source variables. However, techniques relying on ground-based UV-DOAS spectroscopy are limited when the volcanic plume becomes opaque to ultraviolet radiations, which happens during ash-rich eruptions or when the plume is highly concentrated in liquid water droplets, sulfur-rich aerosols or ice crystals. In these conditions, space-borne spectroscopic sensors, which provide the bulk quantities of volcanic gases of any remote volcano every 12 or 24 hours (for instruments on a low Earth orbit) or down to a few tens minutes (for instruments on a geostationary orbit), can be used. In addition, exploitation of satellite gas imagery through an inverse modeling scheme, which involves the use of a chemistry-transport model (WP3), can provide hourly-resolved time series of both the emission flux and altitude of injection of gas emissions. Building a single database gathering complementary ground- and satellite-derived gas fluxes would be valuable to provide reliable volcanic emission inventories necessary as input for modelling the atmospheric impact (WP3).