Corridor Mapping of Sandy Coastal Foredunes with UAS Photogrammetry and Mobile Laser Scanning

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.coverage [11]. Indeed, spatial coverage of airborne LiDAR is unmatched [4]. Nonetheless, it involves technological, operational and logistic costs that prevent fast acquisition of pre-and post-storm data for instance. On the other hand, UAS photogrammetric surveys [10,12] are easier to perform, and incorporating post-processed or real-time differential GNSS processing techniques (PPK/RTK) and low-cost, low-to-medium tactical grade Inertial Measurement Units (IMU) implies a reduction in the use of surveyed Ground Control Points (GCPs) [13,14]. However, 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].Over the last decade, Mobile Laser Scanning (MLS) has emerged as a credible alternative for surveying coastal beaches and foredunes [18][19][20][21]. MLS mainly consist of one or several terrestrial laser scanners mounted on a moving vehicle together with a medium-to-high grade GNSS or IMU/GNSS system. Along the vehicle path, scanners collect 3D point clouds with an accuracy comparable to airborne LiDAR standards at reduced technological and logistic costs. Typical achieved point cloud densities are over 100 points per m 2 , therefore offering a valuable opportunity to study foredune growth with high resolution [20]. Yet, from a coverage standpoint, steep dune slopes create shadow areas and leave large portions of the dune top unscanned. This limitation gives rise to one of the core value proposit...

Evaluation of Long-Range Mobile Mapping System (MMS) and Close-Range Photogrammetry for Deformation Monitoring. A Case Study of Cortes de Pallás in Valencia (Spain)

“…A test was realized in Cap Ferret, France, where researchers combined MLS with aerial photogrammetry to deliver accurate 3D reconstruction of the dunes. They confirmed the good results of using mobile mapping devices for their high level of detail and greater spatial coverage [16]. The best results were also achieved in monitoring the lagoon area of Padre Island National Seashore, located in Texas, where mobile scanning devices may be preferred for the detailed and comprehensive final DEMs useful to detect 3D terrain features and so to monitor geomorphic changes [17].…”

A Review on Drone-Based Data Solutions for Cereal Crops

“…Applications of drone for aerial survey and mapping [49][50][51][52][53][54], forest [55][56][57][58], wildlife conservation [59][60][61], agriculture [22,[27][28][29][30][31], disaster management [90][91][92][93][94], documentation of cultural heritage [95][96][97][98][99][100][101][102], among many others, have been observed over the years. Examples of research cases in each of these domains are summarized in Table 2.…”

Evaluation of UAV LiDAR for Mapping Coastal Environments

“…For instance, Mateos et al [28] combined aerial imagery, UAV imagery, and Persistent Scatterer Interferometric Synthetic Aperture Radar (PSInSAR) for monitoring coastal landslide. Nahon et al [29] operated a UAV and a terrestrial mobile laser scanning vehicle simultaneously, and used UAV images to observe an optical target, which serves as a kinematic ground control point on the vehicle. By doing this, the number of GCPs can be reduced and it is possible to carry out a single pass survey.…”