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

风暴波引起的海岸灾害往往局部集中，部分原因可能是由于亚重力波的存在，其波周期比风暴波长。由于野外观测的困难，特别是在风暴波作用下的冲浪带周围，几乎没有定量的数据来进一步研究风暴波作用下冲浪带周围的长波行为。本研究成功地开发了基于图像的监测系统，以捕捉海浪的水动力。将该系统应用于Seisho海岸，发现在暴风雨条件下，长波主要在沿岸方向形成局部驻波，这一特征合理地解释了2007年台风袭击Seisho海岸时灾后观测到的淹没高度。

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.