Uavs to Assess the Evolution of Embryo Dunes

Abstract

ABSTRACT:The balance of a coastal environment is particularly complex: the continuous formation of dunes, their destruction as a result of violent storms, the growth of vegetation and the consequent growth of the dunes themselves are phenomena that significantly affect this balance. This work presents an approach to the long-term monitoring of a complex dune system by means of Unmanned Aerial Vehicles (UAVs). Four different surveys were carried out between November 2015 and November 2016. Aerial photogrammetric data were acquired during flights by a DJI Phantom 2 and a DJI Phantom 3 with cameras in a nadiral arrangement. GNSS receivers in Network Real Time Kinematic (NRTK) mode were used to frame models in the European Terrestrial Reference System. Processing of the captured images consisted in reconstruction of a three-dimensional model using the principles of Structure from Motion (SfM). Particular care was necessary due to the vegetation: filtering of the dense cloud, mainly based on slope detection, was performed to minimize this issue. Final products of the SfM approach were represented by Digital Elevation Models (DEMs) of the sandy coastal environment. Each model was validated by comparison through specially surveyed points. Other analyses were also performed, such as cross sections and computing elevation variations over time. The use of digital photogrammetry by UAVs is particularly reliable: fast acquisition of the images, reconstruction of high-density point clouds, high resolution of final elevation models, as well as flexibility, low cost and accuracy comparable with other available techniques.

Effect of survey parameters on unmanned aerial vehicles-derived topography for coastal dune monitoring

“…Most of the studies on monitoring coastal dunes using UAVs were performed flying between 60 and 100 m 8,9,35 and obtained variable mean accuracies ranging between 0.03 and 0.05 m, demonstrating that there is not a simple relation between accuracy and flight altitude. The present work supports the results from Taddia et al 7 who found that high accuracies can be also obtained flying at low altitudes (around 30 m), depending on the flight settings. In this regard, the results suggest that a strategy to ensure data quality includes the overlap of two flight surveys using perpendicular flight orientations, which appear to improve significantly the accuracy of the topographic map.…”

“…5 However, unmanned aerial vehicles (UAVs) have been increasingly used to monitor morphological changes in dynamic environments such as beaches and dunes. [7][8][9] UAVs combined with the structure from motion (SfM) approach allow for the elaboration of high-resolution topographic maps, 10,11 being a cost-effective survey tool that can provide high-quality data. [6][7][8][9][11][12][13][14] Several authors proved the suitability of UAVs for coastal dune monitoring by obtaining similar results and errors when comparing the topographic maps generated with this technique to alternative ones, such as TLS or airborne LiDAR.…”

“…[7][8][9] UAVs combined with the structure from motion (SfM) approach allow for the elaboration of high-resolution topographic maps, 10,11 being a cost-effective survey tool that can provide high-quality data. [6][7][8][9][11][12][13][14] Several authors proved the suitability of UAVs for coastal dune monitoring by obtaining similar results and errors when comparing the topographic maps generated with this technique to alternative ones, such as TLS or airborne LiDAR. 11,[15][16][17][18] These authors also highlighted the limitation of UAV products where vegetation is dense due to the inability of photogrammetric methods to map the ground surface below the vegetation, making it extremely difficult to obtain highly accurate digital terrain models (DTMs) in areas with dense vegetation.…”

Crop Height Monitoring Using a Consumer-Grade Camera and UAV Technology

“…Digital surface models generated from UAV-borne sensor data capture are becoming useful tools in many applications such as rapid mapping for disasters (Batzdorfer et al 2017), heritage documentation (Chiabrando and Losè 2017), building inspection (Duarte et al 2017), power line corridors mapping (Maurer et al 2017), tree crown structure mapping (Hese and Behrendt 2017), wetland species mapping and coastal environmental mapping (Taddia et al 2017). For all these applications UAVs are used to collect data at very high spatial and/or temporal resolutions.…”

UAVs for Structure-From-Motion Coastal Monitoring: A Case Study to Assess the Evolution of Embryo Dunes over a Two-Year Time Frame in the Po River Delta, Italy

“…Gonçalves and Henriques [14] studied a similar sandy coastal environment, while more recent applications regarding the Adriatic littoral have been shown by Scarelli et al [15] in the Emilia-Romagna region. Taddia et al [16] illustrated a very first approach about embryo dunes surveying techniques, but without showing the results of a long-term assessment. In addition, other authors also tested the SfM approach by UAV assessing the vertical accuracy of the products compared to TLS technology [17] or investigated the accuracy of georeferenced point clouds produced via multi-view stereopsis from UAV imagery flying at an altitude very close to ours [18].…”