2D and 3D Mapping of a Littoral Zone with UAS and Structure from Motion Photogrammetry

Abstract

Advancements in the miniaturization of sensors and their integration in light‐weight, smallscale unmanned aerial systems (UAS) have resulted in an explosion of uses for inexpensive and easily obtained remotely sensed data. This study examines the capabilities of a small‐scale UAS equipped with a consumer grade RGB camera for 2D and 3D mapping of a sandy bay shoreline using Structure from Motion (SfM) photogrammetry. Several key components are analyzed in order to assess the utility of UAS‐based SfM photogrammetry for beach and boundary surveying of the littoral zone. First, the accuracy of the 3D point cloud produced by the SfM densification process over the beach is compared to high accuracy RTK GPS transects. Results show a mean agreement of approximately 7.9 cm over the sub‐aerial beach with increased error in shallow water. Minimal effects of beach slope on vertical accuracy were observed. Secondly, bathymetric measurements extracted from the UAS/SfM point cloud are examined, and an optical inversion approach is implemented where the SfM method fails. Results show that a hybrid elevation model of the beach and littoral zone consisting of automatic SfM products, post‐processed SfM products, and optical inversion provide the most accurate results when mapping over turbid water. Finally, SfM‐derived shoreline elevation contour (boundary) is compared to a shoreline elevation contour derived using the currently accepted RTK GPS method for conducting legal littoral boundary surveys in the state of Texas. Results show mean planimetric offsets < 25 cm demonstrating the potential of UAS‐based SfM photogrammetry for conducting littoral boundary surveys along non‐occluded, sandy shorelines.