Development of Image-based field observation system for behavior of infragravity waves along the surf zone

沿海风暴波灾害往往局部集中，这一特征可能部分是由于次重力波的存在，这种波周期较长，而不是风致风暴波。由于现场观测的困难，特别是在风浪作用下的冲浪区附近，几乎没有得到定量的数据来进一步研究风浪作用下冲浪区周围的长波行为。本研究成功地开发了基于图像的监测系统来捕捉这样的海浪水动力。将该系统应用于Seisho海岸，发现在暴风浪条件下，长波在近岸方向形成了部分驻波，这一特征合理地解释了2007年台风袭击Seisho海岸时所观察到的淹没高度。

Coastal disasters due to stormy waves often locally concentrate and this feature may be partially due to existence of infragravity waves, which have longer wave period rather than wind-induced stormy waves. Due to difficulty of field observation especially around the surf zone under the stormy waves, there are nearly no quantitative data obtained for further investigation of the behaviors of such long waves around the surf zone under the stormy waves. This study successfully developed image-based monitoring system to capture such surf one hydrodynamics. The system was applied to Seisho coast and found that long waves dominantly formed partial standing waves in the alongshore directions under the stormy wave conditions and this feature reasonably explains the inundation heights observed just after the disaster when the typhoon hit the Seisho coast in 2007.