Development of an ultra-violet digital camera for volcanic SO 2 imaging

Abstract

In an effort to improve monitoring of passive volcano degassing, we have constructed and tested a digital camera for quantifying the sulfur dioxide (SO 2) content of volcanic plumes. The camera utilizes a bandpass filter to collect photons in the ultra-violet (UV) region where SO 2 selectively absorbs UV light. SO 2 is quantified by imaging calibration cells of known SO 2 concentrations. Images of volcanic SO 2 plumes were collected at four active volcanoes with persistent passive degassing: Villarrica, located in Chile, and Santiaguito, Fuego, and Pacaya, located in Guatemala. Images were collected from distances ranging between 4 and 28 km away, with acceptable detection up to approximately 16 km. Camera set-up time in the field ranges from 5–10 min and temporal resolution of up to 6 images per minute is possible, which combined with the camera's field of view makes a continuous SO 2 dataset attainable. Variable in-plume concentrations can be observed and accurate plume speeds (or rise rates) can readily be determined by tracing individual portions of the plume within sequential images. Initial fluxes computed from camera images require a correction for the effects of environmental light scattered into the field of view. At Fuego volcano, simultaneous measurements of corrected SO 2 fluxes with the camera and a Correlation Spectrometer (COSPEC) agreed within 25%. Experiments at the other sites were equally encouraging, and demonstrated the camera's ability to detect SO 2 under variable background meteorological and environmental conditions. This early work has shown great success in imaging SO 2 plumes and offers promise for volcano monitoring due to its rapid deployment and data processing capabilities, relatively low cost, and improved interpretation afforded by synoptic coverage from a range of distances.