Extraction of damaged area caused by debris flows in Hiroshima using COSMO-SkyMed images

Abstract

The heavy rain occurred in Hiroshima city on 20 August 2014. Then, debris flows and shallow slides were induced by the heavy rain. Rapid damage assessment after natural disasters is crucial for initiating effective emergency response actions. Synthetic Aperture Radar (SAR) has a great potential due primarily to its all-weather day-and- night imaging capabilities. In this study, we examined an extraction of damaged area caused by debris flows using three COSMO-SkyMed images. The extraction methods are interferometric coherence, intensity correlation and normalized difference sigma nought index (NDSI) calculated from COSMO-SkyMed image pair. In this study, we investigated the applicability of the methods for extraction of damaged area caused by debris flows. The single look complex data of COSMO-SkyMed were co-registered each other for calculating interferometric coherence. The interferometric coherence images were ortho-rectified using 10 m gridded Digital Elevation Model (DEM) generated by the Geospatial Information Authority of Japan (GSI). The intensity correlation and NDSI were calculated from ortho-rectified images. For damaged area extraction, we investigated the mean and standard deviation of interferometric coherence, intensity correlation and NDSI using pre- and co-disaster image pairs. The mean values derived from the three methods in damaged area almost increased between pre- and co-disaster images. As a result, NDSI in damaged area indicated good separation between pre- and co-disaster images. In conclusion, NDSI showed good capability for extraction of damaged area caused by the debris flows at a rapid disaster response phase.