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Volume 18, issue 7 | Copyright
Nat. Hazards Earth Syst. Sci., 18, 1905-1918, 2018
https://doi.org/10.5194/nhess-18-1905-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Review article 10 Jul 2018

Review article | 10 Jul 2018

Review article: 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 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 9 to 11 September 2015. Due to the record-breaking amount of rainfall, several riverbanks were overflowed and destroyed, causing floods over wide areas. The PALSAR-2 sensor on board 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 the city of Joso, 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 10m 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 more than 85% of the maximum inundation areas were extracted successfully.

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Five synthetic aperture radar images are employed to monitor the changes in the inundation areas caused by torrential rain from 9 to 11 September 2015, in the city of Joso, 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. Compared 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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