A Low-Cost Smartphone Sensor-Based UV Camera for Volcanic SO2 Emission Measurements

Jon Willmott,Giancarlo Tamburello,Thomas Wilkes,Andrew McGonigle,Tom Pering

doi:10.3390/rs9010027

Abstract

Recently, we reported on the development of low-cost ultraviolet (UV) cameras, based on the modification of sensors designed for the smartphone market. These units are built around modified Raspberry Pi cameras (PiCams; ≈USD 25), and usable system sensitivity was demonstrated in the UVA and UVB spectral regions, of relevance to a number of application areas. Here, we report on the first deployment of PiCam devices in one such field: UV remote sensing of sulphur dioxide emissions from volcanoes; such data provide important insights into magmatic processes and are applied in hazard assessments. In particular, we report on field trials on Mt. Etna, where the utility of these devices in quantifying volcanic sulphur dioxide (SO2) emissions was validated. We furthermore performed side-by-side trials of these units against scientific grade cameras, which are currently used in this application, finding that the two systems gave virtually identical flux time series outputs, and that signal-to-noise characteristics of the PiCam units appeared to be more than adequate for volcanological applications. Given the low cost of these sensors, allowing two-filter SO2 camera systems to be assembled for ≈USD 500, they could be suitable for widespread dissemination in volcanic SO2 monitoring internationally.

Highlights

Since its first application to volcanology a decade ago, ultraviolet (UV) camera technology has become an important tool in constraining emission rates of sulphur dioxide (SO2 ) from volcanoes [1,2].This goes beyond the capacity provided previously from scanning or traverse-based differential optical absorption spectroscopy (DOAS) measurements of volcanic gas fluxes [3,4], firstly by imaging the plumes and providing detailed spatial information, and secondly by acquiring gas fluxes with at least two orders of magnitude higher temporal resolution than most DOAS techniques
Two of the aforementioned Pi cameras (PiCams) were deployed as a co-aligned pair, with a bandpass filter mounted before each lens, one centred on 310 nm and the other on 330 nm (Edmund Optics Ltd.), both with a 10 nm full width at half maximum bandwidth
The relative difference between the PiCam system error and the JAI system error is especially minor (≈1%), having a negligible impact on the total RMS error. This shows that a broadly similar performance from these systems is achievable in terms of overall uncertainty in determined emission rates, which is impressive considering the low cost of the PiCam system

Summary

Introduction

Since its first application to volcanology a decade ago, ultraviolet (UV) camera technology has become an important tool in constraining emission rates of sulphur dioxide (SO2 ) from volcanoes [1,2] This goes beyond the capacity provided previously from scanning or traverse-based differential optical absorption spectroscopy (DOAS) measurements of volcanic gas fluxes [3,4], firstly by imaging the plumes and providing detailed spatial information, and secondly by acquiring gas fluxes with at least two orders of magnitude higher temporal resolution than most DOAS techniques. We detail side-by-side comparisons against one such currently applied scientific grade UV camera system to gain a sense of the relative performance of these units, following, to a large extent, the inter-comparative approach detailed in [33]

The Camera Systems

Gas Flux Measurements

Images ofJAI

Characterising

Findings

Concluding Remarks