Satellite-Based Monitoring of Crescentic Nearshore Sandbar Migration at Hujeong Beach, South Korea

Field-based monitoring of coastal morphology requires high costs and is often constrained to calm wave conditions, which limits operational frequency. As a result, despite high spatial resolution, conventional surveys typically suffer from low temporal resolution. To improve temporal resolution between discrete surveys, we developed a satellite-based framework to estimate intermediate morphological changes by tracking crescentic nearshore sandbar (CNSB) migration.

The study area, Hujeong Beach, is a wave-dominated sandy shoreline located along the East Sea of South Korea. Between 2017 and 2022, twelve high-resolution topographic and bathymetric surveys were conducted using RTK drone, LiDAR, and single-beam echosounder measurements. These surveys covered coastal morphology from the beach face to approximately 50 m water depth and were strategically conducted before and after typhoons or high-energy winter wave events when significant morphological changes were expected. To supplement these discrete surveys, a total of 175 cloud-free Sentinel-2 Level-1C images from the same period were processed without atmospheric correction to preserve visible-band contrast for submerged features. CNSBs were identified using the VIS-G2R index, which enhances the spectral distinction of shallow submerged sandbars. The peak detection algorithm was applied to shore-normal brightness profiles to extract sandbar crest locations across the 0–15 m depth zone.

These satellite-derived sandbar positions used to track migration patterns and estimate morphological changes between field surveys. Analysis of the satellite-derived sandbar positions revealed consistent patterns of nearshore morphological change between field survey intervals. This study demonstrates that satellite-derived CNSB positions offer a reliable indicator of coastal morphological change, bridging the temporal gaps between field surveys and enabling cost-effective, high-frequency monitoring in wave-dominated, microtidal environments.