Abstract
Recurrent monitoring of sandy beaches and of the dunes behind them is needed to improve the scientific knowledge on their dynamics as well as to develop sustainable management practices of those valuable landforms. Unmanned Aircraft Systems (UAS) are sought as a means to fulfill this need, especially leveraged by photogrammetric and LiDAR-based mapping methods and technology. The present study compares different strategies to carry UAS photogrammetric corridor mapping over linear extensions of sandy shores. In particular, we present results on the coupling of a UAS with a mobile laser scanning system, operating simultaneously in Cap Ferret, SW France. This aerial-terrestrial tandem enables terrain reconstruction with kinematic ground control points, thus largely avoiding the deployment of surveyed ground control points on the non-stable sandy ground. Results show how these three techniques—mobile laser scanning, photogrammetry based on ground control points, and photogrammetry based on kinematic ground control points—deliver accurate (i.e., root mean square errors < 15 cm) 3D reconstruction of beach-to-dune transition areas, the latter being performed at lower survey and logistic costs, and with enhanced spatial coverage capabilities. This study opens the gate for exploring longer (hundreds of kilometers) shoreline dynamics with ground-control-point-free air and ground mapping techniques.
Highlights
The demand for accurate and recurrent monitoring of sandy beaches is pressing as much as it has ever been [1]
On 21 September 2018, a mapKITE tandem consisting of an Mobile Laser Scanning (MLS) and a Unmanned Aircraft System (UAS) was deployed at the distal extremity of the Cap Ferret sandspit, on the Atlantic coast of France (Figure 1)
The experiment was designed to investigate how the cost-accuracy ratio of UAS photogrammetry could be improved for topographic applications along beach corridors; it was motivated by the interest that a flexible and efficient corridor mapping solution would represent for monitoring long coastal stretches before and after storms
Summary
The demand for accurate and recurrent monitoring of sandy beaches is pressing as much as it has ever been [1]. Data collected with Total Station Theodolites (TST) and Global Navigation Satellite Systems (GNSS) receivers continue to fuel knowledge on coastal processes [8]. As they can be quickly deployed to acquire accurate positioning, they remain largely used as ground truth, with a low coverage-to-time ratio. Concerning linear coastal landforms, GCPs remain largely necessary to mitigate accuracy degradation along the corridor, i.e., “bowl effects” [15,16] This constraint hampers the use of UAS over hundreds of kilometers of shore, as for instance, to survey long sandy beaches after storms [17]
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