[H-DS09] Human environment and disaster risk

[HDS09-P01] Using synthetic aperture radar data for disaster prevention

*Takako Nakamura¹, Jun Matsushima¹, Shuichi Rokugawa² (1.The University of Tokyo, 2.National Research Institute for Earth Science and Disaster Resilience)

Keywords:Sentinel-1A/1B, ALOS-2/PALSAR-2, disaster prevention, sediment disaster

This study investigated the possibility of disaster prevention and mitigation before and after sediment-related disasters, such as debris flows, by using synthetic aperture radar (SAR) data. We will introduce test analysis results obtained using Sentinel-1A/1B VH cross-polarized images and ALOS-2/PALSAR-2 images. Several disaster-affected regions were considered, and the analysis areas were selected because of the occurrence of sediment disasters in recent years.The satellite image data used for the analysis were obtained before and after the disasters.The analysis areas selected for the test are the area around the Aizome River in Izusan District of Atami City, Shizuoka Prefecture, where a debris flow occurred on July 3, 2021, and the area of Atsuma Town, Hokkaido, which was damaged by the 2018 Hokkaido Eastern Iburi Earthquake and related effects. In addition to the above sites, the study region covers a wide area, including Miyagi, the northern Kanto region, Nagano, the southwestern part of Hiroshima, southern Okayama, and the Ehime and Saga Prefectures. These areas were affected by typhoon no. 19. Additionally, in recent years, these areas have been affected by floods caused by heavy rain triggered by typhoons and sediment disasters caused by earthquakes and heavy rainfall.We will introduce various analysis examples that focus on and classify the causes and types of these sediment disasters.ALOS-2/PALSAR-2 (level 1.1, polarization: HH, incident angle: 34.3°) and Sentinel-1A/1B (VV: horizontal polarization and VH: cross-polarization) data were used in the analyses.During these analyses, strong displacements were observed not only at the collapsed points but also uncollapsed locations, and these likely correspond to the predicted points of collapse.In addition, the flood damage distribution area was extracted fairly accurately from the VH cross-polarized Sentinel-1A/1B image.It matches the hazard maps well. Thus, the method seems to be very effective for extracting the outflow area of sediment containing abundant water. The resulting image is an intensity image generated at the initial stage of image analysis. It does not require complicated analysis, and it can be created from a single original image. Therefore, if an image acquired at a good timing can be obtained, it is likely to be useful for quickly assessing the current situation of the target area.To implement monitoring using SAR analysis, it is important to consider the geology and topography of the target area, geological phenomena that could occur, the characteristics of the meteorological phenomena, and any basic information on the target area that is accumulated and maintained during normal periods.It is also important to determine the analytical parameters that are appropriate for such regional characteristics.