Landform variation during the Typhoon Morakot deduced from the amplitude of ALOS

The most serious flood in Taiwan caused by Typhoon Morakot for more than half a century was also known as the "eight or eight floods". The scale of its losses exceeded the "eighty-seven floods" in 1959 and was the deadliest typhoon in recorded history. Typhoon Morakot dropped the strong precipitation (the maximum cumulative rainfall is 2777 mm) and caused catastrophic losses in Taiwan, including 675 deaths, 24 missing, and approximately $3.3 billion in losses. During the typhoon period, the hazardous mudflows, landslides and flooding triggered by the extreme rainfall caused the serious damages. For example, a catastrophic landslide (and subsequent flood) destroyed the entire town of Xiaolin, killing more than 400 people. In a past decade, seismic methods, which rapidly provide the parameters (e.g., location, sliding direction and collapsed mass), have been applied to study the landslide events occurred during Typhoon Morakot. In order to understand movement behavior of above landslide events in details, we further investigate the distribution of topographic changes by using the amplitude of Advanced Land Observing Satellite (ALOS). In a case of the Chashan landslide area, the vertical change can reach tens of meters during Typhoon Morakot. In the additional application, the water area variation of the Zengwun Reservoir could also be detected. With an available deformation velocity calculated from the resulting of Permanent Scatterers Differential Interferometric Synthetic Aperture Radar (PS-DInSAR), we cannot observe the obvious movement in the Chashan area in the recent year. Our study demonstrated that a combination of amplitude-tracking technologies and the real-time monitoring systems (i.e., RLMS; http://collab.cv.nctu.edu.tw/main.html) can provide more comprehensive information for the disaster prevention system in hazard mitigation and assessment.