ALOS-2 Coherence-based Urban Flood Detection: Methodological Evaluation Using a Flood Experimental Field

Abstract

Increasing human and economic losses due to urban floods demand rapid flood monitoring using synthetic aperture radar (SAR). In a global first, this study conducted simultaneous experiments using a flood experimental field that can reproduce the conditions of submerged buildings and satellite monitoring using the L-band SAR aboard the Advanced Land Observing Satellite-2 (ALOS-2). Through these experiments, we investigated the relationships among the threshold of interferometric coherence, the accuracy of urban flood detection, the multi-look number in interferometric processing, and floodwater depth. To achieve a better understanding of our experimental results, we also performed theoretical coherence simulations. Our results revealed that the coherence and flood detection accuracy statistically depends on the multi-look number and that 3×3 looks are needed to obtain reasonable accuracy. We also found that coherence-based change detection can detect urban floods with a depth of as little as 6 cm. There was no clear correlation between coherence and water depth. We also performed urban flood detection using ALOS-2 data from observed flood events; the results proved the validity of our theory and its applicability to actual disaster activities. Our findings enable robust urban flood monitoring and contribute to disaster prevention and mitigation.

SAR, PALSAR-2, disaster monitoring, flooding, interferometry