| Beach topography is a fundamental observation element of the coastal zone, with great significance for coastal development, protection, and research. In recent years, advances in observation technologies such as LiDAR (light detection and ranging) and photogrammetry have enabled large-scale, high-precision monitoring of beach topography. However, the accuracy of different measurement systems for beach morphology still requires further investigation. This study employs conventional validation and Triple Collocation (TC) methods to assess and analyze the monitoring accuracy and errors of three observation systems: ground-based real time kinematic (RTK), unmanned aerial vehicle (UAV) photogrammetry, and airborne LiDAR. The study further examines the influence of beach surface coverage types and rainfall conditions on monitoring performance. High-accuracy topographic data were acquired from Rainbow Beach, Tong'an District, Xiamen, Fujian Province, supporting a detailed analysis of geomorphological processes and contributing factors. The results show that ground-based surveys achieve the highest accuracy, with an error variance of 0.001 2 m2, while aerial methods slightly overestimate the elevation, with UAV photogrammetry and airborne LiDAR producing error variances of 0.020 4 m2 and 0.048 0 m2, respectively. Under normal weather conditions, both airborne techniques yield results close to those of ground RTK, with UAV photogrammetry achieving better accuracy (with an RMSE of 0.082 m) than airborne LiDAR (with an RMSE of 0.114 m). Under rainy conditions, UAV photogrammetry provides accuracy comparable to ground observations in terms of error variance (0.002 7 m2), outperforming ground RTK (-0.003 0 m2), whereas airborne LiDAR substantially overestimates the elevation with an error variance of 0.143 9 m2. Regarding surface coverage, UAV photogrammetry significantly overestimates elevations in shrub and shallow water areas, while airborne LiDAR performs better in these environments. This study provides an important reference for the selection of coastal dynamic geomorphological observation methods at medium and small scales. |
