講演情報
[U05-P02]Estimation and characterization of surface displacement using interferometric SAR analysis in sub-circular depressions of natural hydrogen seepage areas
*宮原 康輔1、石塚 師也1、清水 貴斗1、林 為人1 (1.京都大学大学院)
キーワード：
地表変動、天然水素、干渉SAR解析
Hydrogen is attracting significant attention as a zero-emission energy for realizing a decarbonized society, as it emits no greenhouse gases during combustion. While most hydrogen is currently produced from fossil fuels, natural hydrogen is anticipated to be a promising clean energy source because it can be produced without artificial processes. In several regions where natural hydrogen seepage has been reported, sub-circular depressions (SCD) exist. SCDs are depressed geographical features suggested to have formed due to hydrogen seepage and abnormal vegetation patterns are frequently observed within these depressions. This study evaluated the potential of surface displacement as a new clue for SCD exploration and assessed the effectiveness of interferometric synthetic aperture radar (InSAR) analysis as an exploration method.
InSAR analysis was conducted on the area around the Ségou Region in Mali where a SCD was reported. InSAR analysis enables the estimation of surface displacement over a wide area with high resolution. We employed LiCSBAS (Morishita et al., 2020), an InSAR time-series analysis package, to mitigate multiple errors distributed in time and space, thereby achieving more accurate surface displacement estimation. However, due to the lack of comparative ground truth data for surface displacement in the target area of Mali, we first validated the accuracy of the LiCSBAS analysis by applying it to areas in the Kanto Plain, Japan, where land subsidence has been reported, demonstrating the validity of the methods. Subsequently, InSAR analysis was performed on 44 scenes of Sentinel-1 SAR data acquired between December 6, 2022, and October 3, 2025, followed by time-series displacement estimation using LiCSBAS.
The estimated time-series surface displacement at the center of an SCD in Mali (around 13.19°N, 6.24°W) indicated clear surface subsidence at the center of the SCD, which is like the subsidence reported in a previous study applying InSAR analysis to SCDs in Brazil (Békési et al., 2025). However, the negative displacement velocity in Mali was higher than in Brazil, despite the lower hydrogen seepage flux. Given that the lateritic soil distributed in Mali is rich in iron oxides, volume reduction caused by mineral dissolution due to reduction reactions in the subsurface of SCD where natural hydrogen exists may be accelerating the subsidence. Although surface displacement estimation alone cannot identify whether hydrogen is gushing from depression, this study demonstrated that surface displacement can serve as a powerful approach for characterizing potential SCDs in the early stages of natural hydrogen exploration.
Acknowledgement: PALSAR-2 level 1.0 data are shared among PIXEL (PALSAR Interferometry Consortium to Study our Evolving Land surface) and provided by JAXA under a cooperative research contract with ERI, Univ, Tokyo. The ownership of PALSAR-2 data belongs to METI (Ministry of Economy, Trade and Industry) and JAXA.
InSAR analysis was conducted on the area around the Ségou Region in Mali where a SCD was reported. InSAR analysis enables the estimation of surface displacement over a wide area with high resolution. We employed LiCSBAS (Morishita et al., 2020), an InSAR time-series analysis package, to mitigate multiple errors distributed in time and space, thereby achieving more accurate surface displacement estimation. However, due to the lack of comparative ground truth data for surface displacement in the target area of Mali, we first validated the accuracy of the LiCSBAS analysis by applying it to areas in the Kanto Plain, Japan, where land subsidence has been reported, demonstrating the validity of the methods. Subsequently, InSAR analysis was performed on 44 scenes of Sentinel-1 SAR data acquired between December 6, 2022, and October 3, 2025, followed by time-series displacement estimation using LiCSBAS.
The estimated time-series surface displacement at the center of an SCD in Mali (around 13.19°N, 6.24°W) indicated clear surface subsidence at the center of the SCD, which is like the subsidence reported in a previous study applying InSAR analysis to SCDs in Brazil (Békési et al., 2025). However, the negative displacement velocity in Mali was higher than in Brazil, despite the lower hydrogen seepage flux. Given that the lateritic soil distributed in Mali is rich in iron oxides, volume reduction caused by mineral dissolution due to reduction reactions in the subsurface of SCD where natural hydrogen exists may be accelerating the subsidence. Although surface displacement estimation alone cannot identify whether hydrogen is gushing from depression, this study demonstrated that surface displacement can serve as a powerful approach for characterizing potential SCDs in the early stages of natural hydrogen exploration.
Acknowledgement: PALSAR-2 level 1.0 data are shared among PIXEL (PALSAR Interferometry Consortium to Study our Evolving Land surface) and provided by JAXA under a cooperative research contract with ERI, Univ, Tokyo. The ownership of PALSAR-2 data belongs to METI (Ministry of Economy, Trade and Industry) and JAXA.