Title :

Close-range airborne Structure-from-Motion Photogrammetry for high-resolution beach morphometric surveys: Examples from an embayed rotating beach

Author(s) :

Fleury, Jules [Auteur]
Centre européen de recherche et d'enseignement des géosciences de l'environnement [CEREGE]
Brunier, Guillaume [Auteur]
Centre européen de recherche et d'enseignement des géosciences de l'environnement [CEREGE]
Anthony, Edward [Auteur]
Centre européen de recherche et d'enseignement des géosciences de l'environnement [CEREGE]
Gardel, Antoine [Auteur]
Laboratoire d’Océanologie et de Géosciences (LOG) - UMR 8187 [LOG]
Dussouillez, Philippe [Auteur]
Centre européen de recherche et d'enseignement des géosciences de l'environnement [CEREGE]

Journal title :

Geomorphology

Pages :

76 - 88

Publisher :

Elsevier

Publication date :

2016-05-15

ISSN :

0169-555X

English keyword(s) :

Low-cost photogrammetry
Structure-from-Motion photogrammetry
Digital surface model
Beach rotation
Beach morphometry

HAL domain(s) :

Sciences de l'environnement/Ingénierie de l'environnement
Sciences de l'environnement/Milieux et Changements globaux
Planète et Univers [physics]/Sciences de la Terre

English abstract : [en]

The field of photogrammetry has seen significant new developments essentially related to the emergence of new computer-based applications that have fostered the growth of the workflow technique called Structure-from-Motion ...
Show more >The field of photogrammetry has seen significant new developments essentially related to the emergence of new computer-based applications that have fostered the growth of the workflow technique called Structure-from-Motion (SfM). Low-cost, user-friendly SfM photogrammetry offers interesting new perspectives in coastal and other fields of geomorphology requiring high-resolution topographic data. The technique enables the construction of topographic products such as digital surface models (DSMs) and orthophotographs, and combines the advantages of the reproducibility of GPS surveys and the high density and accuracy of airborne LiDAR, but at very advantageous cost compared to the latter. Three SfM-based photogrammetric experiments were conducted on the embayed beach of Montjoly in Cayenne, French Guiana, between October 2013 and 2014, in order to map morphological changes and quantify sediment budgets. The beach is affected by a process of rotation induced by the alongshore migration of mud banks from the mouths of the Amazon River that generate spatial and temporal changes in wave refraction and incident wave angles, thus generating the reversals in longshore drift that characterise this process. Sub-vertical aerial photographs of the beach were acquired from a microlight aircraft that flew alongshore at low elevation (275 m). The flight plan included several parallel flight axes with an overlap of 85% between pictures in the lengthwise direction and 50% between paths. Targets of 40 × 40 cm, georeferenced by RTK-DGPS, were placed on the beach, spaced 100 m apart. These targets served in optimizing the model and in producing georeferenced 3D products. RTK-GPS measurements of random points and cross-shore profiles were used to validate the photogrammetry results and assess their accuracy. We produced dense point clouds with 150 to 200 points/m², from which we generated DSMs and orthophotos with respective resolutions of 10 cm and 5 cm. Compared to the GPS control points, we obtained a mean vertical accuracy less than ± 10 cm, with a maximum of 20 cm in marginal sectors with sparse vegetation and in the lower intertidal zone where water-saturated surfaces generated lower-resolution data as a result of a lack of coherence between photographs. The overall results show that SfM photogrammetry is a robust tool for beach morphological and sediment budget surveys. Our SfM workflow enabled the discrimination of beach surface features at a scale of a few tens of centimetres despite the low textural contrasts exhibited by the quartz beach sand and the relatively uniform upper beach topography, as well as the calculation of beach sediment budgets. 66,000 m³ of sand were removed from the northern sector of the beach, of which 22,000 m³ were transferred to the southern sector in the course of rotation. Finally, we briefly highlight: (1) the advantages of SfM photogrammetry compared to other high-resolution survey methods, (2) the advantages and disadvantages of, respectively, a microlight aircraft and an unmanned aerial vehicle (UAV) in undertaking SfM photogrammetry, and (3) areas of potential future improvement of the SfM workflow technique. These concern more extensive cross-shore deployment of ground control points to reduce possible tilt, and oblique cross-shore photography to improve parallax.Show less >

Language :

Anglais

Peer reviewed article :

Oui

Audience :

Internationale

Popular science :

Non

Collections :

• Laboratoire d'Océanologie et de Géosciences (LOG) - UMR 8187

Source :

Harvested from HAL