Flood Area Detection Using ALOS-2 PALSAR-2 Data for the 2015 Heavy Rainfall Disaster in the Kanto and Tohoku Area, Japan

Rapid and all-weather detection of flood area is needed for monitoring and mitigating flood disasters. This paper addressed flood area detection by using ALOS-2 PALSAR-2 data acquired during the 2015 heavy rainfall disaster in Kanto and Tohoku area, Japan. We propose an approach to detect flood area by thresholding of amplitude image and interferometric coherence image for non-urban area and urban area, respectively. The PALSAR-2-derived flood areas are validated using the inundation map provided by the Geospatial Information Authority of Japan (GSI) and showed 75% accuracy and 0.51 kappa coefficient in flood/non-flood discrimination. Effectiveness of lower incidence angle (less than 40 degrees) and a high sensitive observation mode (6m resolution mode) for detecting non-urban flood are also demonstrated by a comparative study. Interferometric phase variation was revealed to be effective for detecting urban-area flood compared to conventional interferometric coherence. The results demonstrated the feasibility of PALSAR-2 for rapid flood monitoring and can be used as a reference for possible future flood disasters.