Optical sensing of volcanic gas and aerosol emissions
Volcanic gas and aerosol surveillance yield important insights into magmatic, hydrothermal, and atmospheric processes. A range of optical sensing and sampling techniques has been applied to measurements of the composition and fluxes of volcanic emissions. In particular, the 30-year worldwide volcanological service record of the Correlation Spectrometer (COSPEC) illustrates the point that robust, reliable, straightforward optical techniques are of tremendous interest to the volcano observatory and research community. This chapter reviews the field, in particular the newer and more versatile instruments capable of augmenting or superseding COSPEC, with the aim of stimulating their rapid adoption by the volcanological community. It focuses on sensors that can be operated from the ground, since they generally offer the most flexibility and sensitivity. The success of COSPEC underlines the point, however, that such devices should be comparatively cheap, and easy to use and maintain, if they are to be widely used.