Protocols for UV camera volcanic SO2 measurements

Ultraviolet camera technology offers considerable promise for enabling 1 Hz timescale acquisitions of volcanic degassing phenomena, providing two orders of magnitude improvements on sampling frequencies from conventionally applied scanning spectrometer systems. This could, for instance enable unprecedented insights into rapid processes, such as strombolian explosions, and non-aliased corroboration with volcano geophysical data. The uptake of this technology has involved disparate methodological approaches, hitherto. As a means of expediting the further proliferation of such systems, we here study these diverse protocols, with the aim of suggesting those we consider optimal. In particular we cover: choice and set up of hardware, calibration for vignetting and for absolute concentrations using quartz SO2 cells, the retrieval algorithm and whether one or two filters, or indeed cameras, are necessary. This work also involves direct intercomparisons with narrowband observations obtained with a scanning spectrometer system, employing a differential optical absorption spectroscopic evaluation routine, as a means of methodological validation.