# Video Monitoring of Shoreline Positions in Hujeong Beach, Korea
## 2 Video Monitoring System  
The video monitoring system was constructed in the middle of Hujeong Beach, which is on the east coast of South Korea (Figure 1a). In the northern end of the beach, an intake breakwater is located to protect the intake system of the Hanul nuclear power plant (NPP), as shown in Figure 1b [11]. This breakwater does, however, block the sediments that are discharged from Bugu River to be transported south to Hujeong Beach. Therefore, the beach is vulnerable to erosion because the input amount of sediments has decreased due to the breakwater whereas they are still lost to the southeast of the beach through Jukbyeon Port. To monitor this process, the East Sea Research Institute (ESRI) of the Korea Institute of Ocean Science and Technology (KIOST) has operated the video monitoring system since December 2016. In total, eight video cameras were installed on top of a 30 m-high metal tower. The height of the tower was determined to obtain secure angles for the cameras because berms have occasionally formed along the beach shore causing blind spots. The coverage of the monitoring system is ~2.4 km, with ~1.2 km at either side of the tower. The cameras capture images every second. Figure 2a shows a picture of the video monitoring tower constructed at S1, and a magnified view of the top of the tower where the video cameras were installed is shown in Figure 2b. In Figure 2c-i, snapshots taken by each of the cameras are shown as an example of the image data. To extract the shoreline data more precisely, 600 snapshot images are averaged over 10 min to remove the noise produced by wave breaking [12]. Every hour, only the first 10 min of data were averaged to produce one representative image of the hour. As the images were not visible during the night, only 12-15 image data were available per day to be processed for the estimation of shoreline positions. The image data were transferred to the processing center using an internet network system [13]. Once the 600 snapshot images were averaged, the shoreline area appeared as a white narrow band due to the swash zone. The shorelines were manually extracted from these averaged images by taking a line in the middle of each band. Because errors in this extraction process might increase when the waves were actively breaking, the extracted shoreline data were accepted only when the band widths were narrow under mild wave conditions (wave heights \(<\) 0.5m). Figure 1: (**a**) Location of Hujeong Beach; (**b**) map of Hujeong Beach with location of the video monitoring system (L1). This figure is taken from [11]. Figure 2: (**a**,**b**) Photographs of the video monitoring tower installed in Hujeong Beach, December 2016. (**c**-**i**) Examples of shoreline image data measured by the video cameras. These images are taken from [12]. The shoreline positions that are obtained by averaging the snapshot images may contain errors when removing the noise by wave breaking, which requires validation of the data. Figure 3 shows a comparison of the shoreline position data estimated by the video monitoring system with beach topography data outside the water. The land topography data were measured by a mobile LiDAR that was mounted on a boat on 12 March 2017. The mobile LiDAR was equipped with a real time kinematic (RTK), global navigation satellite system (GNSS), and inertia measurement unit (IMU). Ship-mounted mobile LiDARs have advantages over the land-based mobile LiDARs as they can survey a larger area relatively fast by exploring along the coastline. The mobile LiDAR has a measurement range of 1 km and a scanning range up to 80\({}^{\circ}\) in the vertical and up to 360\({}^{\circ}\) in the horizontal, with accuracy of 2 cm. As shown in Figure 3, the shoreline positions estimated by the video monitoring system accurately match the positions measured by the mobile LiDAR. Discrepancies can be found specifically near the areas where the horizontal gradient of the shoreline is relatively large.