11:00 AM - 1:00 PM
[SVC31-P02] Estimation of sulfur dioxide flux from Mt. Tokachi by ground-based and satellite observation
Keywords:volcanic gas, Mt.Tokachi, satellite observation
Quantifying the flux of volcanic gas that includes information about magma under the volcano is essential to understanding the mechanisms of volcanic activity. The quantification of the sulfur dioxide (SO2) flux has been conducted since the 1970s. Recently, ground-based observations and satellite observations have been carried out at many volcanoes. There are many examples of satellite observations of large volcanic plumes such as eruption plumes. However, in the case of low volcanic gas flux during non-eruptive periods, there are few examples of observations and comparisons with ground-based observations and verifications have not been sufficiently made.
Mt. Tokachi, located in the center of Hokkaido, is an active volcano that made a magmatic eruption in 1988. In recent years, various volcanic activity has been observed, such as ground deformation suggesting inflation just below the crater, change in the total magnetic field suggesting heat accumulation, and an increase in surface activity. Quantification of volcanic gas flux at Mt Tokachi is essential for clarifying the mechanisms of ongoing non-eruptive activity by comparing it with inflation and heat accumulation.
In previous studies, Mt. Tokachi has been shown to have a high sulfur dioxide flux of 400-500 t/day in 2014-2015 and is the second most continuously plummeting volcano in Japan after Asama. The gas emitted from Mt. Tokachi is rich in SO2, making it a suitable field to verify the measurement of volcanic gas flux during non-eruption periods by satellite observation. The purpose of this study is to validate satellite observations of the SO2 flux during the non-eruption period by comparing ground-based and satellite observations of Mt.Tokachi.
A car traverse method was used as a ground observation. First, a car equipped with a compact UV spectrometer traversed under the fumaroles emitted from Mt. Tokachi. The vertical column density (VCD) of the vertical section of the fumes was measured. The SO2 flux was estimated by multiplying the sum of VCDs by the wind speed. We used the data observed by TROPOMI (Tropospheric Monitoring Instrument) as the satellite observation data, a sensor onboard the S5P (Sentinel-5 Precursor) satellite. TROPOMI has been providing data since 2017 and observes the areal VCD once a day with a high spatial resolution (3.5 × 7.0 km2 at nadir).. The travel distance of the fumes was estimated from the wind speed, and the emission rate was estimated by integrating the VCDs in a 1-hour time window. The wind speed was reconstructed from the analysis of the Grid Point Value of the Meso Scale Model by the Japan Meteorological Agency (JMA), which is provided by the Research Institute for Sustainable Humanosphere, Kyoto University.
As a result, the SO2 flux was estimated to be 80-1250 t/day for ground-based observations from June to December 2021 and 50-3635 t/day for satellite observations from August 2019 to January 2022. The satellite observations showed higher SO2 flux in winter than in summer. In comparison with ground-based observations, there was good agreement with satellite observations in summer, but satellite observations were overestimated in winter. This may be due to the overestimation of VCD caused by the change in the ground surface reflectance by snow accumulation.
Only five ground-based observations were conducted in this study, which is too few to be compared with satellite observations. In the future, it is necessary to increase the number of ground observations during the winter season. In addition, wind direction is not considered in the analysis of satellite observation data, which may be an error factor in the estimation. In order to improve this, the analysis method of satellite data needs to be upgraded.
Mt. Tokachi, located in the center of Hokkaido, is an active volcano that made a magmatic eruption in 1988. In recent years, various volcanic activity has been observed, such as ground deformation suggesting inflation just below the crater, change in the total magnetic field suggesting heat accumulation, and an increase in surface activity. Quantification of volcanic gas flux at Mt Tokachi is essential for clarifying the mechanisms of ongoing non-eruptive activity by comparing it with inflation and heat accumulation.
In previous studies, Mt. Tokachi has been shown to have a high sulfur dioxide flux of 400-500 t/day in 2014-2015 and is the second most continuously plummeting volcano in Japan after Asama. The gas emitted from Mt. Tokachi is rich in SO2, making it a suitable field to verify the measurement of volcanic gas flux during non-eruption periods by satellite observation. The purpose of this study is to validate satellite observations of the SO2 flux during the non-eruption period by comparing ground-based and satellite observations of Mt.Tokachi.
A car traverse method was used as a ground observation. First, a car equipped with a compact UV spectrometer traversed under the fumaroles emitted from Mt. Tokachi. The vertical column density (VCD) of the vertical section of the fumes was measured. The SO2 flux was estimated by multiplying the sum of VCDs by the wind speed. We used the data observed by TROPOMI (Tropospheric Monitoring Instrument) as the satellite observation data, a sensor onboard the S5P (Sentinel-5 Precursor) satellite. TROPOMI has been providing data since 2017 and observes the areal VCD once a day with a high spatial resolution (3.5 × 7.0 km2 at nadir).. The travel distance of the fumes was estimated from the wind speed, and the emission rate was estimated by integrating the VCDs in a 1-hour time window. The wind speed was reconstructed from the analysis of the Grid Point Value of the Meso Scale Model by the Japan Meteorological Agency (JMA), which is provided by the Research Institute for Sustainable Humanosphere, Kyoto University.
As a result, the SO2 flux was estimated to be 80-1250 t/day for ground-based observations from June to December 2021 and 50-3635 t/day for satellite observations from August 2019 to January 2022. The satellite observations showed higher SO2 flux in winter than in summer. In comparison with ground-based observations, there was good agreement with satellite observations in summer, but satellite observations were overestimated in winter. This may be due to the overestimation of VCD caused by the change in the ground surface reflectance by snow accumulation.
Only five ground-based observations were conducted in this study, which is too few to be compared with satellite observations. In the future, it is necessary to increase the number of ground observations during the winter season. In addition, wind direction is not considered in the analysis of satellite observation data, which may be an error factor in the estimation. In order to improve this, the analysis method of satellite data needs to be upgraded.