Evaluating the Extraction Approaches of Flood Extended Area by Using ALOS-2/PALSAR-2 Images as a Rapid Response to Flood Disaster

Abstract

Flash floods are recurrent events around the Japan region almost every year. Torrential rain occurred around Kanto and Tohoku area due to typhoon No. 18 in September 2015. Overflowing of the Kinugawa River led to river bank collapse. Thus, the flood extended into Joso City, Ibaraki Prefecture, Japan. ALOS-2/PALSAR-2 was the fastest satellite to record this flood disaster area. A quick method to extract the flood inundation area by utilizing the ALOS-2/ PALSAR-2 image as a rapid response to the flood disaster is required. This study evaluated three methods to extract the flood immediately after the flood occurring. This study compared the extraction approaches of flooded area by unsupervised classification, supervised classification and binary/threshold of backscattering value of flood. The results show that unsupervised classification and supervised classification are overestimated. This study recommends the binarization of the backscattering value to extract the extended flood area. This method is a straight forward approach and generates a similar distribution with the field survey by using the aerial photo with high accuracy (94% of kappa coefficient). We utilized slope map which derived from DEM data to eliminate the overestimated area due to shadowing effect in SAR images.

A Decadal Historical Satellite Data and Rainfall Trend Analysis (2001–2016) for Flood Hazard Mapping in Sri Lanka

“…The fusion of multi-sensor images is critical for flood monitoring applications to address the need for data acquisition in all weather conditions and daily coverage [32]. The high resolution SAR images from numerous platforms such as ALOS PALSAR, Radarsat-2, Risat-1, TerraSAR-X and Sentinel-1, enabled to rapidly process and deliver the inundation maps in near real time for relief activities and other emergency operations [33]. The Sentinel Asia (SA) initiative further increased the accessibility of satellite data for national disaster management agencies, within the shortest turnaround time [34].…”

Review article: Detection of inundation areas due to the 2015 Kanto and Tohoku torrential rain in Japan based on multi-temporal ALOS-2 imagery

“…The images were all acquired with HH polarization and in the ultra-fine mode (JAXA, 2017a). The images for path A were the same data used in the study of Rimba and Miura (2017). The five datasets were provided as ranges and single-look azimuths compressed at a processing level of 1.1, which is represented by the complex I and Q channels to preserve the amplitude and phase information (JAXA, 2017a).…”

“…The 2015 Kanto and Tohoku torrential rain was the first flood event that occurred on a large scale in Japan after the ALOS-2 was launched. PALSAR-2 performed emergency observations of the impacted areas during and after the heavy rain (Natsuaki et al, 2016;Kwak et al, 2017;Rimba and Miura, 2017).…”

Response to comments

“…It is now possible to monitor affected areas shortly after a disaster strikes (JAXA, 2017a). PALSAR-2 images have been used to detect damage following the 2015 earthquake in Gorkha, Nepal (Watanabe et al, 2016), and to detect pyroclastic ash coverage on Kuchinoerabu Island, Japan (Hara et al, 2017;Natsuaki et al, 2017). The 2015 Kanto and Tohoku torrential rain was the first flood event that occurred on a large scale in Japan after the ALOS-2 was launched.…”

“…The 2015 Kanto and Tohoku torrential rain was the first flood event that occurred on a large scale in Japan after the ALOS-2 was launched. PALSAR-2 performed emergency observations of the impacted areas during and after the heavy rain (Natsuaki et al, 2016;Kwak et al, 2017;Rimba and Miura, 2017).…”