# Monitoring of Recovery Process at Yeongildae Beach, South Korea, Using a Video System
## 2 Materials and Methods
### Video Monitoring System  
At Yeongildae Beach, two VMSs were constructed at S1 and S2, as shown in Figure 1c. The monitoring by the VMS was initiated in November 2018 and in February 2019 at S1 and S2, respectively. The VMSs were built at the top of buildings in both locations to save the cost of constructing new towers to mount the VMSs. At S1, four video cameras were mounted to cover the central and southern part of the beach, and two additional cameras were mounted at S2 to cover the resting northern end of the beach.  
Figure 3: (**a**) Map of the two locations of the wave measurements. Wave height and period were measured at M1 using a pressure transducer moored at water depth 8.5 m in the nearshore area of Yeongildae Beach. \(D_{p}\) was measured at M2 using an AWAC moored at water depth 21.6 m in the middle of Yeongil Bay, (**b**) a rose diagram for wave conditions measured at M2 for 2.5 years (from 21 May 2018 to 26 November 2020).  
The VMS consists of the cameras, camera controller, data processing, and data transfer systems that send processed data (averaged images) to the main server. Every 30 min from 7:00 a.m. to sunset, each camera took snapshot pictures for 3 min every half-second. In Figure 5a,b, examples of the snapshot images taken at S1 and S2 are shown. The 180 snapshot images collected for 3 min were then averaged to produce an 'averaged image'; in this way, the averaged images were provided twice per hour. The averaged images stored in the controller were transferred to the main server one time per day in the nighttime, when the internet network was not busy. The snapshot images were not saved in the system unless specified to do so, to save the cost of running the VMS. Once the averaged-image data were transferred to the main server, the locations of the images were corrected in the x-y coordinate system. Because the images were obliquely measured with angles that were different between the cameras, the data needed to be converted into orthogonal images to the ground. After this, the images from each camera were combined into one-image data that covered the whole beach. Figure 5c shows the data in which the orthogonal images are combined into one.  
The shoreline positions and beach width were estimated from the image data of the whole beach. For this process, a set of baselines needed to be established, as shown in Figure 5d. The baselines started from the inner line set, along the landward end of the backshore of the beach. Each baseline was set perpendicular to the inner line to be ended in the water so that the position of the shore could be determined manually by comparing the color of the pixels along the baseline. Once the shoreline positions were determined, the beach width could be calculated by connecting the shoreline positions of a baseline to that of the adjacent baselines. Similarly, the position where a baseline crossed the inner line could be connected to the adjacent positions to form a polygon, as marked with the blue solid lines in Figure 5. The beach width was then obtained by calculating the area inside the polygon. To measure the time variation of the beach width, the inner line and baselines were fixed once determined. In the case of Yeongildae Beach, a total of 34 baselines were established.  
Figure 4: Track of Typhoon TAPAH (T1917).