[S-VC32] Active Volcanism

[SVC32-18] Development of UAV-mounted vertical sensor array system to estimate emission flux of hydrogen sulfide from fumarolic fields

*Yutaka Miyagi¹, Urumu Tsunogai¹, Masaaki Morita², Ryunosuke KAZAHAYA³, Fumiko Nakagawa¹ (1.Graduate school of Environmental Studies, Nagoya University, 2.Earthquake Research Institute, The University of Tokyo, 3.The National Institute of Advanced Industrial Science and Technology)

Keywords:UAV, Volcanic gas, Hydrogen sulfide, Gas sensor

The emission flux of volatiles from each volcano can be useful to evaluate the current states of magmatic activity and predict its future trends as the emission flux is sensitive to the condition of magma. Consequently, the emission flux of SO₂ has been quantified in many subaerial volcanoes in the world using remote sensing techniques, such as differential optical absorption spectroscopy (DOAS). However, the emission flux of SO₂ can be quantified only in active volcanoes wherein SO₂ occupies the major portion of total sulfur emissions. On the other hand, SO₂ is often depleted in the volatiles emitted from volcanoes in which a hydrothermal circulation system has developed. As a result, the emission flux of volatiles depleted in SO₂ have been quantified through direct determination on the distributions of the volatiles other than SO₂ in each fumarolic field, such as CO₂ or H₂S (Aiuppa et al., 2013; Tamburello et al., 2019; Miyagi et al., 2024). Especially in our previous report, we developed a vertical sensor array system (VSAS) in which H₂S sensors were distributed on a rod to monitor spatial or temporal variation on the vertical distribution of H₂S (Miyagi et al., 2024). By using this system, we determined the total amount of H₂S in a cross section of a volcanic plume together with the wind speed in the fumarolic field during the observation to estimate the emission flux of H₂S from the fumarolic field. However, the topography of fumarolic fields is often bumpy so that the volcanoes in which the VSAS can be applicable is limited.
In this study, we developed a Unmanned Aerial Vehicle (UAV)-mounted VSAS to overcome the limitation of the traditional VSAS. The inlets of 3 tubes of this system were distributed at 5 m intervals on a 20 m wire hanging down from a UAV. All the inlets were connected with a same H₂S sensor via pumps installed prior to the H₂S sensor. The H₂S concentration at an altitude of each inlet can be determined by switching ON/OFF of the pumps every 20 seconds. Then, the UAV was moved perpendicular to the direction of plume transport to determine the cross section of the distribution of H₂S. Thus, the emission flux of H₂S can be estimated from the total amount of H₂S in a plane perpendicular to the direction of plume transport and wind speed determined simultaneously in the fumarolic field.
A total of 4 test flights were done in Kirishima Iwo-yama volcano on Dec. 11, 2024. Each flight time was 10-15 minutes. The maximum flight altitudes during each flight were ranged from 24.1-74.8 m. The maximum H₂S concentrations during each flight were from 15.7 to 35.3 ppm. In this talk, we would like to report H₂S flux determined from the data obtained during the flights, together with the method of calculation.
This study was supported by the Earthquake and Coordinating Committee of Earthquake and Volcanic Eruption Prediction Researches (Phase 3, 2024) and Integrated Program for Next Generation Volcano Research and Human Resource Development (Theme B, Sub-theme No. 3).