Emergency Inundation Analysis of the August 2021 Japan Floods Using SAR Intensity Images

A heavy rainfall hit Western Japan from August 11 to 21, 2021, resulting in extensive damages caused by inundations in 68 rivers. This study utilizes two sets of pre- and post-event SAR satellite imagery to extract the inundations around Rokkaku River, a national class-A river located in Saga Prefecture, Kyushu Region, Japan. Inundation maps for August 14 at 13:13 and August 15 at 18:21, 2021 were generated using the respective satellite pairs by the different methods. These maps were validated by comparing them with aerial photos taken on August 15 and the estimated inundation data provide by the Geospatial Information Authority of Japan.