Remote sensing of gas speciation and distribution in the near-source volcanic plume.
Several existing and new remote sensing methods enable to spatially characterise a range of gases (as well as SO2) in the near-source emissions and plume. These include UV DOAS observations of BrO, OClO alongside SO2, enabling to trace the plume chemistry in the first kilometers of plume evolution, or to make time-averaged plume images by scanning-imaging DOAS. Spatial mapping of volcanic gases is also made possible by differential absorption Lidars for CO2 recently developed by European groups. Instrument-analysis developments that are ongoing include IR-hyperspectral cameras for SO2, CO2 and OCS, and IR imaging of H2O. These latter developments aim to expand the plume speciation that can be measured by current use of FTIR in occultation mode (provided plume and sun are aligned) for HCl and SO2, and IR imaging camera for SO2.
Many of these methods can be operated onboard of airborne platforms (aircraft, helicopter, or drone). This is especially useful in case of powerful explosive eruptions, allowing sampling/measurements as close as possible to the volcanic source. Ongoing advances in both small and large drone technology definitely offer new opportunities for near-source measurements of plume chemistry and fluxes. Sensors on balloons may also offer complementary information (with less experimental control and requiring relatively large emission-plume to ensure transect, but with fewer flight restrictions, perhaps easier today to make flights-on-command).