Mid- and Short-Term Monitoring of Sea Cliff Erosion based on Structure-from-Motion (SfM) Photogrammetry: Application of Two Differing Camera Systems for 3D Point Cloud Construction

Abstract

Yu, J.J.; Kim, D.W.; Lee, E.J., and Son, S.W., 2022. Mid- and short-term monitoring of sea cliff erosion based on structure-from-motion (SfM) photogrammetry: Application of two differing camera systems for 3D point cloud construction. Journal of Coastal Research, 38(5), 1021–1036. Coconut Creek (Florida), ISSN 0749-0208. Sea-level rise due to climate change is influencing coastal areas globally, which represent an important food and recreational resource for humanity. Accordingly, coastal monitoring is of vital importance. Recently, coastal erosion monitoring has been performed using various methods related to structure-from-motion (SfM) photogrammetry. In coastal topography, sea cliffs can have high elevations and uneven surfaces, making them challenging to model using SfM photogrammetry when capturing images using a single device from one direction owing to occluded areas during the construction of a three-dimensional point cloud (3D PCD). Therefore, in this study, two types of cameras were used to construct an appropriate 3D PCD of sea cliffs. Sea cliffs were photographed by an unmanned aerial vehicle (UAV) and by terrestrial cameras, and the resulting 3D PCD was constructed using fusion and integration methods during image processing. Sea cliff monitoring was performed separately for mid- (9 mo) and short-term (pre- and posttyphoon) periods, during which geomorphological changes could be monitored using the multiscale model-to-model cloud comparison (M3C2) technique. The proposed method effectively reduced the occluded area while sufficiently detecting geomorphological changes in the sea cliffs.