Degassing at Sabancaya volcano measured by UV cameras and the NOVAC network

Abstract

We used low-cost Raspberry Pi ultraviolet (UV) cameras to measure sulphur dioxide (SO 2 ) fluxes from Sabancaya volcano, Peru, during eruptive activity on 27 April 2018. Light dilution corrections were made by operating instruments at two distances simultaneously. Estimated SO 2 fluxes of 27.1 kg s −1 are higher than previously reported, likely due to the current eruptive episode (ongoing since November 2016). Each eruptive event included frequent (2-3 per minute), ash-rich emissions, forming gas pulses with masses of 3.0-8.2 tonnes SO 2 . Sustained degassing and lack of overpressure suggest open-vent activity. Mean fluxes are consistent with those measured by a permanent NOVAC station (25.9 kg s −1 ) located under the plume, with remaining differences likely due to windspeed estimates and sampling rate. Our work highlights the importance of accurate light dilution and windspeed modelling in SO 2 retrievals and suggests that co-location of UV cameras with permanent scanning spectrometers may be valuable in providing accurate windspeeds. ResumenUtilizamos cámaras ultravioletas (UV) Raspberry Pi para medir los flujos de dióxido de azufre (SO 2 ) en el volcán Sabancaya, Perú, durante la actividad del 27 abril 2018. La corrección por dilución de luz se realizó midiendo simultáneamente en dos sitios a diferentes distancias. Los flujos promedio (27.1 kg s −1 ) son superiores a los reportados previamente, probablemente debido al actual episodio explosivo. Cada evento tuvo frecuentes emanaciones ricas en ceniza y gas, emitiendo 3.0-8.2 toneladas de SO 2 . La desgasificación sostenida, sin sobrepresión, indica una chimenea abierta. Estos flujos son similares a los medidos en una estación permanente de NOVAC (25.9 kg s −1 ) debajo de la pluma. La diferencia restante es por velocidad del viento estimada y la frecuencia de la muestreo. Nuestro trabajo muestra la importancia de modelar con precisión la dilución de luz y velocidad del viento, y que co-instalar cámaras UV y espectrómetros permanentes podrían dar velocidades del viento más exactos.

Ultraviolet Camera Measurements of Passive and Explosive (Strombolian) Sulphur Dioxide Emissions at Yasur Volcano, Vanuatu

“…Light dilution has a larger effect during hazier conditions, which were not present during our successful measurement days. Ilanko et al [84] calculated that at~10.3 km distance from the plume (during clear conditions at Sabancaya volcano, Peru), SO 2 fluxes could be underestimated by 2.5 times, while at 4.25 km SO 2 fluxes could be underestimated by 1.5 times (which would correspond to~1.18 times (18%) at our maximum distance of 2300 m at Yasur). It is important to note that light dilution estimates are very specific to the measurement location and conditions.…”

“…One of the most significant and yet frequently overlooked errors in UV camera image analysis is that associated with plume velocity determination, for which three main methods are commonly used: cross-correlation [78,79], optical-flow [71,73,[80][81][82][83], and manual tracking [84]. The optimal method will largely be determined by the plume conditions, as no single method is ideally suited to all situations.…”

Ultraviolet camera measurements of passive and explosive sulphur dioxide emissions at Yasur volcano, Vanuatu

“…Light dilution has a larger effect during hazier conditions, which were not present during our successful measurement days. Ilanko et al, (2019), calculated that at ~10.3 km distance from the plume (during clear conditions at Sabancaya volcano, Peru) SO2 fluxes could be underestimated by 2.5 times, and at 4.25 km by 1.5 times (which would correspond to ~1.18 times [18%] at our maximum distance of 2300 m at Yasur). It is important to note that light dilution estimates are very specific to each measurement location and conditions, and given our range of distances to the plume and clear measurement conditions we suggest therefore that error relating to light dilution is <+20%.…”

“…One of the most significant, and yet frequently overlooked, errors in UV camera image analysis is that associated with plume velocity determination, for which three main methods are commonly used: cross-correlation (McGonigle et al, 2005;Williams-Jones et al, 2006), optical-flow (Delle Donne et al, 2019Gliß et al, 2017;Kern et al, 2015;Peters et al, 2015;Peters and Oppenheimer, 2018), and manual tracking (Ilanko et al, 2019). The optimal method will largely be determined by the plume conditions, as no single method is ideally suited to all situations.…”

Quantifying Light Dilution in Ultraviolet Spectroscopic Measurements of Volcanic SO2 Using Dual-Band Modeling

“…While a high aerosol loading of the air between the plume and the detector increases the effect, even a clear atmosphere can cause significant underestimation of the observed SO 2 SCD (Moffat and Millan, 1971;Mori et al, 2006). First-order correction of the dilution relies on its distance-dependence, using simultaneous measurements of the plume from multiple locations (e.g., Bluth et al, 2007;Vogel et al, 2011;Ilanko et al, 2019). Other studies shift their measurements to a higher wavelength range, where both the SO 2 absorption and scattering efficiency are lower, reducing, but not eliminating, the impact (e.g., Bobrowski et al, 2010;Gliß et al, 2015;Fickel and Granados, 2017).…”