Journal cover Journal topic
Natural Hazards and Earth System Sciences An interactive open-access journal of the European Geosciences Union
https://doi.org/10.5194/nhess-2018-59
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
Review article
26 Mar 2018
Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Natural Hazards and Earth System Sciences (NHESS).
Detection of inundation areas due to the 2015 Kanto and Tohoku torrential rain in Japan based on multi-temporal ALOS-2 imagery
Wen Liu and Fumio Yamazaki Department of Urban Environment Systems, Chiba University, Chiba, 263-8522, Japan
Abstract. Torrential rain triggered by two typhoons hit the Kanto and Tohoku regions of Japan from September 9 to 11, 2015. Due to the record-breaking amount of rainfall, several river banks were overflowed and destroyed, causing floods over wide areas. The PALSAR-2 sensor onboard the ALOS-2 satellite engaged in emergency observations of the affected areas during and after the heavy rain. Two pre-event and three co-event PALSAR-2 images were employed in this study to extract flooded areas in Joso city, Ibaraki prefecture. The backscattering coefficient of the river water was investigated first using the PALSAR-2 intensity images and a land-cover map with a 10-m resolution. The inundation areas were then extracted by setting threshold values for backscattering from water surfaces in the three temporal Synthetic Aperture Radar (SAR) images. The extracted results were modified by considering the land-cover and a digital elevation model (DEM). Next, the inundated built-up urban areas were extracted from the changes in SAR backscattering. The results were finally compared with those from visual inspections of airborne imagery by the Geospatial Information Authority of Japan (GSI), and they showed a good level of agreement.
Citation: Liu, W. and Yamazaki, F.: Detection of inundation areas due to the 2015 Kanto and Tohoku torrential rain in Japan based on multi-temporal ALOS-2 imagery, Nat. Hazards Earth Syst. Sci. Discuss., https://doi.org/10.5194/nhess-2018-59, in review, 2018.
Wen Liu and Fumio Yamazaki
Wen Liu and Fumio Yamazaki
Wen Liu and Fumio Yamazaki

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Short summary
Five Synthetic Aperture Radar images are employed to monitor the changes in the inundation areas caused by a torrential rain from September 9 to 11, 2015, in Joso city, Ibaraki prefecture, Japan. The inundation areas were then extracted by setting threshold values for backscattering intensity. The results were modified by considering the land-cover and a digital elevation model. Comparing with the results from visual inspections, 85 % of the inundation area could be extracted successfully.
Five Synthetic Aperture Radar images are employed to monitor the changes in the inundation areas...
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