Abstract
UV cameras have been used for over a decade in order to remotely sense SO2 emission rates from active volcanoes, and to thereby enhance our understanding of processes related to active and passive degassing. Whilst SO2 column density retrievals can be more accurate/sophisticated using alternative techniques (e.g., Differential Optical Absorption Spectrometer (DOAS), Correlation Spectrometer (COSPEC)), due to their higher spectral resolutions, UV cameras provide the advantage of high time-resolution emission rates, a much greater spatial resolution, and the ability to simultaneously retrieve plume speeds. Nevertheless, the relatively high costs have limited their uptake to a limited number of research groups and volcanic observatories across the planet. One recent intervention in this regard has been the introduction of the PiCam UV camera, which has considerably lowered instrumental cost. Here we present the first data obtained with the PiCam system from seven persistently degassing volcanoes in northern Chile, demonstrating robust field operation in challenging conditions and over an extended period of time, hence adding credence to the potential of these units for more widespread dissemination to the international volcanic gas measurement community. Small and weak plumes, as well as strongly degassing plumes were measured at distances ranging 0.6–10.8 km from the sources, resulting in a wide range of SO2 emission rates, varying from 3.8 ± 1.8 to 361 ± 31.6 td−1. Our acquired data are discussed with reference to previously reported emission rates from other ground-based remotely sensed techniques at the same volcanoes, in particular considering: resolution of single plume emissions in multi-plume volcanoes, light dilution, plume geometry, seasonal effects, and the applied plume speed measurement methodology. The main internal/external factors that influence positive/negative PiCam measurements include camera shake, light dilution, and the performance of the OpenCV and control points post processing methods. A simple reprocessing method is presented in order to correct the camera shake. Finally, volcanoes were separated into two distinct groups: low and moderate SO2 emission rates systems. These groups correlate positively with their volcanological characteristics, especially with the fluid compositions from fumaroles.
Highlights
Sulfur dioxide (SO2) is a toxic gas arising from various anthropogenic sources, which is emitted from persistently degassing and eruptive volcanoes, leading to significant potential impacts upon the environment and local economies [1]
The PiCam UV camera has been successfully deployed on seven persistently degassing volcanoes from northern Chile, demonstrating the capacity to measure small and weak plumes (e.g., Olca and Putana volcanoes), as well as strongly degassing sources (e.g., Isluga volcano), resulting in resolution of SO2 output rates ranging 3.8 ± 1.8–361 ± 31.6 td−1, with measurements performed at a variety of distances from the gas sources (0.6–10.8 km)
Given the low cost of the PiCam modules, with respect to traditionally applied scientific grade UV cameras, and the fact that these have delivered fail free service in these challenging field environments, over a protracted period of time, this affirms the suitability of these units for widespread dissemination to the end user community, worldwide
Summary
Sulfur dioxide (SO2) is a toxic gas arising from various anthropogenic sources, which is emitted from persistently degassing and eruptive volcanoes, leading to significant potential impacts upon the environment and local economies [1]. The UV camera is capable of capturing high time-resolution flux data, which when combined with other techniques can be used to: understand flow dynamics in volcanic conduits (e.g., [24,25]); determine mass flow rates models (e.g., [26]); evaluate eruptive periods of a single volcano (e.g., [27]); determine the gas fluxes arising along volcanic zones/arcs (e.g., [10]); correlate degassing and seismological data The introduction of the low-cost smartphone sensor-based PiCam UV camera [30,31] can be considered as the starting point of a new stage in the applications of UV cameras in volcanology, based on the characteristics of these units, namely: their small size and light weight, which enables easy transportation; user friendly acquisition and post processing software; but, most importantly, their low cost, facilitating the potential for uptake by almost all volcanic gas research groups and volcanic observatories, worldwide
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