Rapid Response to a Typhoon-Induced Flood with an SAR-Derived Map of Inundated Areas: Case Study and Validation

Abstract

Abstract:We report the successful case of a rapid response to a flash flood in I-Lan County of Taiwan with a map of inundated areas derived from COSMO-SkyMed 1 radar satellite imagery within 24 hours. The flood was caused by the intensive precipitation brought by Typhoon Soulik in July 2013. Based on the ensemble forecasts of trajectory, an urgent request of spaceborne SAR imagery was made 24 hours before Typhoon Soulik made landfall. Two COSMO-SkyMed images were successfully acquired when the center of Typhoon Soulik had just crossed the northern part of Taiwan. The standard level-1b product (radiometric-corrected, geometric-calibrated and orthorectified image) was generated by using the off-the-shelf SARscape software. Following the same approach used with the Expert Landslide and Shadow Area Delineating System, the regional threshold of each tile image was determined to delineate still water surface and quasi-inundated areas in a fully-automatic manner. The results were overlaid on a digital elevation model, and the same tile was visually compared to an optical image taken by Formosat-2 before this event. With this ancillary information, the inundated areas were accurately and quickly identified. The SAR-derived map of inundated areas was OPEN ACCESSRemote Sens. 2015, 7 11955 published on a web-based platform powered by Google Earth within 24 hours, with the aim of supporting the decision-making process of disaster prevention and mitigation. A detailed validation was made afterwards by comparing the map with in situ data of the water levels at 17 stations. The results demonstrate the feasibility of rapidly responding to a typhoon-induced flood with a spaceborne SAR-derived map of inundated areas. A standard operating procedure was derived from this work and followed by the Water Hazard Mitigation Center of the Water Resources Agency, Taiwan, in subsequent typhoon seasons, such as Typhoon Trami (August, 2013) and Typhoon Soudelor (August, 2015).

Spatiotemporal Variation of Cold Eddies in the Upwelling Zone off Northeastern Taiwan Revealed by the Geostationary Satellite Imagery of Ocean Color and Sea Surface Temperature

“…It passed over the warm waters of the Kuroshio Current the following day and later made landfall on 12 July 2013 in northern Taiwan with torrential rains of 900 mm (35 in) in Bailan, destructive winds of 190 km/h (120 mph), and gusts as high as 220 km/h (140 mph). As a result, the low-lying areas of Ilan City were seriously flooded [61], and a significant amount of terrestrial materials were flushed from the watersheds of mountainous areas through the Lanyang River to the Lanyang River plume. Since this is one of the major agriculture areas of Taiwan, a lot of fertilizer with ingredients such as nitrogen and phosphorous was also exported to the coast off northeastern Taiwan.…”

Flood Prevention and Emergency Response System Powered by Google Earth Engine

“…However, the limitations of deploying a UAV under severe weather conditions to cover a large area were also highlighted by this mission. To remove those limitations, we were motivated to seek another type of imagery from SAR to derive an inundation map [4]. Chung et al reported a successful case of rapid response with a map of inundated areas derived from COSMO-SkyMed 1 radar satellite imagery during the July 2013 flood in I-Lan County in Taiwan, which was caused by Typhoon Soulik [4].…”

“…In the aftermath of Japan's earthquake and tsunami on March 11, 2011, we demonstrated that Formosat-2 imagery can be rapidly acquired, processed, and distributed through the Internet to global users by deploying the system through cloud servers [3]. Therefore, FPERS was developed with an intention to collect and display the huge amount of relevant geospatial imagery, including Formosat-2 pre-and post-flood imagery (2-m resolution) used to detect and monitor barrier lakes, the synthetic aperture radar (SAR) imagery used to derive an inundation map [4], and the high-spatial-resolution photos taken by unmanned aerial vehicles (UAV) to evaluate the damage to river channels and structures due to a debris flow [5]. In spite of these successes, these data were mainly used for disaster assessment at the post-flood stage.…”

Flood Extent Mapping Using Dual-Polarimetric Sentinel-1 Synthetic Aperture Radar Imagery

“…This will contribute to generating flood extent maps and estimating the flood depth. Moreover, the flood maps from the proposed method can be used for the cross-validation of those from the existing methods (Chung et al, 2015;Twele et al, 2016;Zhang et al, 2017).…”