Mapping the inundated area caused by the July 2018 Western Japan torrential rain using multi-temporal ALOS-2 data

摘要

Successive heavy rainfall affected the western Japan from the late June to the early July 2018. Increased river water overflowed and destroyed river banks, which caused flooding in vast areas. In this study, two pre-event and one co-event ALOS-2 PALSAR-2 images were used to extract inundation areas in Kurashiki and Okayama Cities, Okayama Prefecture, Japan. First, the difference between the pre-event and co-event coherence values was calculated. The decreased coherence areas were extracted as possible inundation. Then the water regions were extracted by the threshold values from the three-temporal intensity images. The increased water regions in July 2018 were obtained as inundation. Finally, the extracted results from the coherence and intensity images were merged to create an inundation map. The results were verified by comparing with a web-based questionnaire survey report and visual interpretation of aerial photos.