Advances in ultraviolet remote sensing of volcanic gas plumes

As magma ascends towards the surface and the surrounding pressure from the rock drops, diluted gases (mainly C02, H20 and S02) are released and reach the surface prior to the magma itself. Accurate measurements of volcanic gases are thus essential in order to acquire an overview of the magmatic processes of a volcano in collaboration with geophysical data with the end goal of forecasting eruptions and managing volcanic crises. The standard approach for volcanic S02 flux measurements has been to traverse, by car, beneath the plume, with a UV spectrometer measuring overhead S02 concentrations. Recently, a number of compact and inexpensive commercially available UV spectrometers have become standard in the application. The first part of this thesis details the first intercomparison between these different devices, defining which attributes and models are optimal. Error sources e.g., from thermal effects and stray light, and proposed mitigative actions, are described. The second part of the thesis details the development of a freely downloadable stand-alone application (UVolc), which is compatible with the best identified spectrometers. This user friendly code, with meticulously written instructions, enables volcanologists, the vast majority of whom have little expertise in optics, to perform their own S02 flux measurements. Given that the associated hardware is inexpensive (;:::: €5k), this is particularly significant in the many developing countries where monitoring budgets are low, but risks high. This software incorporates routines designed to characterise and correct the errors identified during the intercoparison of the spectrometers, for improved accuracy. Finally, a novel upgrade to these spectrometers, based on UV camera technology, is described. These units image the plume, providing gas concentration profile maps, and so fluxes once per second, cf. 2-3 data per week, from the manual traverses. A rigorous study into optimum operational protocols, including validation, via intercomparison with conventional UV spectrometer observations, has been conducted on Mt. Etna and Stromboli in Italy. This approach is set to revolutionise volcanology, reflecting a step change in our capacity to understand volcanic processes, particularly transient explosions, and the first possibility of non-aliased corroboration with the other sources of volcanic data, from geophysics, which are acquired at 1 Hz. The latter has long been an aim of observational volcanology, allowing the prospect of far more holistic insights than available from the individual series in isolation.EThOS - Electronic Theses Online ServiceGBUnited Kingdo