Structure-from-Motion-Derived Digital Surface Models from Historical Aerial Photographs: A New 3D Application for Coastal Dune Monitoring

Abstract

Recent advances in structure-from-motion (SfM) techniques have proliferated the use of unmanned aerial vehicles (UAVs) in the monitoring of coastal landform changes, particularly when applied in the reconstruction of 3D surface models from historical aerial photographs. Here, we explore a number of depth map filtering and point cloud cleaning methods using the commercial software Agisoft Metashape Pro to determine the optimal methodology to build reliable digital surface models (DSMs). Twelve different aerial photography-derived DSMs are validated and compared against light detection and ranging (LiDAR)- and UAV-derived DSMs of a vegetated coastal dune system that has undergone several decades of coastline retreat. The different studied methods showed an average vertical error (root mean square error, RMSE) of approximately 1 m, with the best method resulting in an error value of 0.93 m. In our case, the best method resulted from the removal of confidence values in the range of 0–3 from the dense point cloud (DPC), with no filter applied to the depth maps. Differences among the methods examined were associated with the reconstruction of the dune slipface. The application of the modern SfM methodology to the analysis of historical aerial (vertical) photography is a novel (and reliable) new approach that can be used to better quantify coastal dune volume changes. DSMs derived from suitable historical aerial photographs, therefore, represent dependable sources of 3D data that can be used to better analyse long-term geomorphic changes in coastal dune areas that have undergone retreat.

Seasonal morphodynamics of multiple intertidal bars (MITBs) on a meso‐ to macrotidal beach

“…It faces southeast into the Irish Sea and is well exposed to storm waves. It is bounded by rocky headlands in the southwest and northeast, and comprises a wide sandy beach backed by a high‐tide cobble beach and extensive Holocene dunefield (Grottoli et al, 2021; Orford et al, 2003). A relatively deep (up to 4 m) inlet channel with an extensive ebb‐tidal delta divides Dundrum Bay's shoreline into the Murlough and Ballykinler beach systems (Navas et al, 2001; Pye & Blott, 2017).…”

Review of Advanced Image Processing Techniques: Digital Elevation Model

“…Each of these methods have a different approach to achieving the final Digital Image. A special mention of Agisoft (2,11,12) which has become a boom in recent years which has enabled people to create their own versions of the algorithm.…”

Identifying Geomorphological Changes of Coastal Cliffs through Point Cloud Registration from UAV Images

“…However, if a georeferenced point cloud of a cliff exists in the past, one can align a newly collected non-georeferenced point cloud from our method to the existing georeferenced one through the registration method established in this study. In terms of geomorphological changes, our method assumes that only a small portion of the cliff experiences erosion while the remainder of the cliff remains unchanged during inspections, which could be commonly found in coastal surveying [46]. Investigating dramatic geomorphological changes of a cliff due to severe erosions is out of the scope of this study.…”