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04 Apr 2023
Solar-charged $5000 kit offers continuous monitoring of sulfur dioxide emissions indicating changes in activity.
A multinational team of scientists has designed a new lower-cost ultraviolet camera capable of monitoring volcanic emissions of sulfur dioxide (SO2) gas continuously - potentially offering more reliable forecasts of impending eruptions.
Led by researchers at the UK’s University of Sheffield, the team has completed initial tests of the system on two active volcanoes in Chile and Hawaii, using differential optical absorption spectroscopy (DOAS).
Thomas Wilkes, lead author of a new journal paper detailing the development, reported that the imager has the potential to aid the transition to more continuous geochemical monitoring of hazardous volcanoes around the world.
Instrument design
According to the open-access paper, published in Frontiers in Earth Science, the new hardware makes use of sensors from Raspberry Pi cameras, which have been modified to enhance UV sensitivity by removal of their Bayer filter.
The team wrote that the approach provides a significant cost reduction relative to the use of scientific-grade commercial UV cameras - reducing the cost from thousands of dollars to hundreds of dollars.
In addition to that modification, they designed a UV-transmissive optical system for a triplet lens setup using Zemax ray tracing software, to reduce the degree of spherical aberrations at the edges of images seen in previous efforts.
UV bandpass filters were mounted behind the triplet optics, to mitigate the effects of changing wavelength transmission that occurs with changing light incidence angle on the filter.
The system also features a “Flame” spectrometer from Ocean Insight that does not require thermoelectric cooling, helping to further reduce instrument cost and complexity, and restricting power consumption to less than 4 W.
“Overall, the cost of parts for a one-off instrument is [around] $5000, which is primarily controlled by the cost of the UV spectrometer and associated optics [of~$3500],” reported the team, adding that bulk purchasing for multiple instruments would further reduce part costs.
Field results
Using the equipment, Wilkes and his team have so far generated two preliminary data sets from Lascar, a volcano in Chile, and Kilauea, on Hawaii’s Big Island, where their camera is in continuous operation.
“Before now, only three volcanoes have had permanent SO2 cameras installed on them,” Wilkes added. “Discrete field campaigns have been carried out, and whilst they can be invaluable for a range of research questions, it is important to be able to measure volcanic activity continuously, since it can vary substantially from minutes to decades to centuries and beyond.”
There are also some significant limitations to bear in mind, with Wilkes pointing out that the cameras are dependent on meteorological conditions, working best under clear blue skies when a volcanic gas plume moves perpendicular to the viewing direction of the camera.
Results from Lascar with the new camera setup were said to show good agreement with earlier measurements on SO2 plumes, although the paper authors note a series of complicating factors that make direct comparisons with other techniques difficult.
“On many volcanoes it can be difficult to find a suitable viewing geometry to ensure that, given any wind direction and degassing strength, the camera will always be able to capture complete and robust emission rates,” they point out.
Overall though, they believe that widespread deployment of the lower-cost systems could provide useful surveillance on a continuous basis.
“Although we note that longer-term testing of instrument performance is still required, such instruments have the potential to provide valuable datasets for comparison with alternative ground-based remote sensing instruments, as well as ground-truthing satellite retrievals,” the team concludes.
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