Minutely monitoring of swash zone processes using a lidar-camera fusion system

The advancement of effective remote sensing technologies is critical for understanding the dynamics of coastal systems, enabling efficient and sustainable management strategies. Video cameras have been widely used for this purpose, significantly advancing our knowledge of coastal dynamics. However, traditional optical devices cannot directly provide three-dimensional (3D) information, such as beach profiles or runup heights. Recently, lidar scanners have gained attention within the coastal research community for their ability to directly capture high-resolution data on hydro-sediment interactions near shorelines across various scales, providing valuable insights into coastal dynamics. This study presents a fusion system that combines a 3D lidar with a video camera, capable of simultaneously capturing 3D coordinates and surface colors of beaches and nearshore waves. The fusion system was tested at two coastal sites in Japan, demonstrating its high potential for coastal monitoring. At the Hasaki coast, characterized by fine sand, it captured alongshore variations in topographic changes, linked to runup heights and seepage processes over one day. At the Namiita coast, characterized by a mixed sand-gravel beach, the fusion system observed the development of cusp structures over 3 h. The data suggest sand accumulation around gravel and gravel retrieval from the beach surface following an increase in tide level. Although this fusion system was tested at only two coastal sites in Japan, it demonstrates high flexibility and potential for studying swash zone processes across diverse spatiotemporal scales and beaches, including mixed sand-gravel beaches.