Assessment of UAV Photogrammetric Mapping Accuracy in the Beach Environment

Abstract

This study evaluated the accuracy of UAV photogrammetry for subaerial beach morphology. Beach is characterized by complicated morphology due to the influence of coastal processes and is mainly composed of monochromatic sandy sediments. Therefore, it is required to validate the applicability of UAV photogrammetry that finds matching points from geographical features within images to create the 3D topographic data. For the accuracy test, a beach site which consisted of both typical sandy beach characteristics at the beach face and tidal flat features at the intertidal zone, was selected. The vertical accuracy of both the fixed-wing and the rotary-wing UAVs were tested using various flight altitudes, image overlap percentages, and GCPs configurations. The accuracy of the photogrammetric surveying results were examined by comparing them to reference data measured by LiDAR. The flight altitude should be set in such a way that the captured images include more geographical features in the beach environment, especially in the tidal flat. When the UAV photogrammetry is performed at a flight altitude of less than 150 m and with over 70% overlap using GCPs of 50 m grid spacing in the beach, topography with a RMSE accuracy of less than 4.9 cm can be obtained. And, it is required to place at least 5 GCPs homogeneously within the area of 300 x 100 m for accurate beach mapping by UAV photogrammetric survey.