Simultaneous Mapping of Coastal Topography and Bathymetry From a Lightweight Multicamera UAS

Abstract

A low-cost multicamera Unmanned Aircraft System (UAS) is used to simultaneously estimate open-coast topography and bathymetry from a single longitudinal coastal flight. The UAS combines nadir and oblique imagery to create a wide field of view (FOV), which enables collection of mobile, long dwell timeseries of the littoral zone suitable for structure-frommotion (SfM), and wave speed inversion algorithms. Resultant digital surface models (DSMs) compare well with terrestrial topographic lidar and bathymetric survey data at Duck, NC, USA, with roor-mean-square error (RMSE)/bias of 0.26/-0.05 and 0.34/-0.05 m, respectively. Bathymetric data from another flight at Virginia Beach, VA, USA, demonstrates successful comparison (RMSE/bias of 0.17/0.06 m) in a secondary environment. UAS-derived engineering data products, total volume profiles and shoreline position, were congruent with those calculated from traditional topo-bathymetric surveys at Duck. Capturing both topography and bathymetry within a single flight, the presented multicamera system is more efficient than data acquisition with a single camera UAS; this advantage grows for longer stretches of coastline (10 km). Efficiency increases further with an on-board Global Navigation Satellite System-Inertial Navigation System (GNSS-INS) to eliminate ground control point (GCP) placement. The Appendix reprocesses the Virginia Beach flight with the GNSS-INS input and no GCPs. The resultant DSM products are comparable [root-mean-squared difference (RMSD)/bias of 0.62/−0.09 m, and processing time is significantly reduced.

Spatial Variability of Coastal Foredune Evolution, Part A: Timescales of Months to Years

“…While the recent increase in use of unmanned aircraft systems (UAS) coupled with structure-from-motion algorithms for measuring coastal beach topography (e.g., [78,91]) represents a marked step forward in our ability to characterize detailed three-dimensional coastal dune evolution [92], there remain challenges in obtaining high-accuracy, consistent data in many coastal settings. For example, it is sometimes unclear what elevation is returned on densely vegetated dune faces and differences between UAS and lidar point clouds can range from 0.5 to 1 m (see [93] for an example at the south dune site). Except in the presence of very dense vegetation, lidar-based systems can obtain bed points through the vegetation canopy, and therefore do not suffer from the same challenges as UAS technologies.…”

Application of Remote Sensing Methods in Research of Nearshore Sandbars, Curonian Spit, Lithuania

“…Also, a system for estimation of nearshore bathymetry based on celerity of the wave crests in time series UAS imagery has been developed (Holman et al, 2011;Matsuba and Sato, 2018). Brodie et al (2019) accurately estimated nearshore bathymetry using multicamera UAS with cBathy algorithm (Holman et al, 2013). Although great potential of UAS-based remote sensing to calculate nearshore bathymetry has been demonstrated, methodology for such estimations are still under development and is not yet being applied in investigatory studies of bar morphodynamics.…”

Lessons learned from coastal mapping efforts during the 2018 hurricane season using unmanned aerial systems (UAS) at Sandbridge, Virginia

“…The three flights shown in Figure 2B were conducted from three different take-off locations (dots in Figure 2B) to allow for sufficient overlap of the aerial imagery. While VLOS limitations with other UAS platforms have been addressed by chasing the UAS in a vehicle (e.g., Brodie et al 2019b), the FireFLY6 PRO RTK-GPS system operates over the same datalink as the controls; therefore, platform controls are tethered to the same location as the RTK-GPS base station receiver, and mobile flight control is not feasible. The RTK-GPS base had to be moved and re-established for each take-off location to allow for VLOS operations.…”