5:15 PM - 6:45 PM
[MZZ43-P02] Estimation of Cracks and Hydrothermal Inflows Using UAV in the Jigokunuma Area
Keywords:UAV, Remote sensing, Cracks, Geothermal exploration
Understanding the underground fracture system is important for geothermal power generation because high-temperature, high-pressure hot water, which is the heat source for geothermal power generation, exists within fractures in geothermal reservoirs. Investigations of these fracture systems have traditionally been conducted using literature surveys, topographic maps, aerial photographs, geophysical surveys, underground geological surveys, water quality surveys, etc. Among these, surveys using remote sensing can be carried out over a wide area, so they are useful in the early stages of geothermal exploration. In addition to exploration using satellite images, aerial geophysical exploration is also being carried out using helicopters equipped with measurement instruments for gravity anomaly surveys and electromagnetic and magnetic surveys. Although this method has enabled high-resolution estimation over a wide area, it has the problems of high cost for a single flight survey and difficulty in individual measurements. On the other hand, exploration using UAVs allows instant aerial photography of any location where it is possible to fly. However, the instruments that can be mounted on UAVs are still limited. Therefore, in this study, in order to verify the practicality of geothermal exploration using UAVs, we installed several measuring instruments on UAVs and examined the data.
The study area is located about 750 m southeast of Jigokunuma in the North Hakkouda Volcano Group in the central part of Aomori Prefecture. The North Hakkouda Volcanoes are located in the Towada-Hachimantai National Park and have high geothermal potential. Among them, Jigokunuma is an area with particularly active geothermal features, such as steam fumaroles. Since hydrothermal gushes at 27.0°C and 28.9°C were also observed in the study area, the surrounding area was selected as the target of the study (Watanabe et al., submitted).
In this study, a UAV was equipped with a camera capable of taking thermographic images and a laser measurement device in October 2022 to acquire temperature information and point cloud data in the study area. The temperature distribution maps were created from the thermographic images, and the locations of heat sources were estimated. A digital elevation model (DEM) was created from the point cloud data, and the shape of the ground surface in the study area was observed from the equally spaced cross sections drawn from the DEM. Furthermore, the relationship between the fractures and water inflow was estimated by superimposing the temperature distribution map and the DEM.
The thermal distribution maps were superimposed on the DEM using the characteristic areas such as National Route 103 as reference points, and a map was created that provides information on temperature and their location relationships. The created thermal distribution maps enabled us to confirm the flow of the rivers. Furthermore, the highest temperature (H1) in the study area was confirmed to be 27.7°C. This point was close to the hydrothermal discharge point reported by Watanabe et al. (submitted). In this study, we were able to confirm the areal distribution of the hotter than ambient spring water around the highest temperature point. The DEM was created by connecting the points with their location information using 3D modeling software, and then displaying the height of the ground surface excluding the height of buildings and trees. Compared with publicly available geological maps, more detailed and accurate maps can be obtained. The DEM and the cross-sectional maps show that the ground surface is uneven, and in particular, three consecutive ruptures can be confirmed. In addition, it was confirmed that the shape and elevation of the ground surface change with the rupture as a boundary. By superimposing the temperature distribution map and the DEM, we confirmed that the continuous fractures on the ground surface and the heat source H1 are in contact with each other.
As described above, it was possible to estimate the location of hydrothermal upwellings and cracks by remote sensing using UAV. Compared with the previous exploration, the low-cost, short-time, and safe exploration facilitated the creation of highly accurate maps, suggesting that the UAV survey is applicable to the initial geothermal exploration.
The study area is located about 750 m southeast of Jigokunuma in the North Hakkouda Volcano Group in the central part of Aomori Prefecture. The North Hakkouda Volcanoes are located in the Towada-Hachimantai National Park and have high geothermal potential. Among them, Jigokunuma is an area with particularly active geothermal features, such as steam fumaroles. Since hydrothermal gushes at 27.0°C and 28.9°C were also observed in the study area, the surrounding area was selected as the target of the study (Watanabe et al., submitted).
In this study, a UAV was equipped with a camera capable of taking thermographic images and a laser measurement device in October 2022 to acquire temperature information and point cloud data in the study area. The temperature distribution maps were created from the thermographic images, and the locations of heat sources were estimated. A digital elevation model (DEM) was created from the point cloud data, and the shape of the ground surface in the study area was observed from the equally spaced cross sections drawn from the DEM. Furthermore, the relationship between the fractures and water inflow was estimated by superimposing the temperature distribution map and the DEM.
The thermal distribution maps were superimposed on the DEM using the characteristic areas such as National Route 103 as reference points, and a map was created that provides information on temperature and their location relationships. The created thermal distribution maps enabled us to confirm the flow of the rivers. Furthermore, the highest temperature (H1) in the study area was confirmed to be 27.7°C. This point was close to the hydrothermal discharge point reported by Watanabe et al. (submitted). In this study, we were able to confirm the areal distribution of the hotter than ambient spring water around the highest temperature point. The DEM was created by connecting the points with their location information using 3D modeling software, and then displaying the height of the ground surface excluding the height of buildings and trees. Compared with publicly available geological maps, more detailed and accurate maps can be obtained. The DEM and the cross-sectional maps show that the ground surface is uneven, and in particular, three consecutive ruptures can be confirmed. In addition, it was confirmed that the shape and elevation of the ground surface change with the rupture as a boundary. By superimposing the temperature distribution map and the DEM, we confirmed that the continuous fractures on the ground surface and the heat source H1 are in contact with each other.
As described above, it was possible to estimate the location of hydrothermal upwellings and cracks by remote sensing using UAV. Compared with the previous exploration, the low-cost, short-time, and safe exploration facilitated the creation of highly accurate maps, suggesting that the UAV survey is applicable to the initial geothermal exploration.