UAV survey of a coastal cliff face - Selection of the best imaging angle

Type Article
Date 2019-06
Language English
Author(s) Jaud MarionORCID1, Letortu Pauline2, Thery Claire2, Grandjean Philippe3, Costa Stephane4, Maquaire Olivier4, Davidson Robert4, Le Dantec Nicolas5, 6
Affiliation(s) 1 : Univ Bretagne Occidentale, IUEM, CNRS, UMS 3113,Technopole Brest Iroise, Rue Dumont dUrville, F-29280 Plouzane, France.
2 : Univ Bretagne Occidentale, IUEM, CNRS, UMR 6554,LETG,Technopole Brest Iroise, Rue Dumont dUrville, F-29280 Plouzane, France.
3 : Univ Lyon 1, CNRS, UMR 5276, Lab Geol Lyon, 2 Rue Raphael Dubois,Batiment GEODE, F-69622 Villeurbanne, France.
4 : Normandie Univ, UNICAEN, CNRS, UMR 6554,LETG, F-14000 Caen, France.
5 : Cerema, Direct Eau Mer & Fleuves, 134 Rue Beauvais, F-60280 Margny Les Compiegne, France.
6 : Univ Bretagne Occidentale, IUEM, CNRS, UMR 6538,Geosci Ocean,Technopole Brest Iroise, Rue Dumont dUrville, F-29280 Plouzane, France.
Source Measurement (0263-2241) (Elsevier Sci Ltd), 2019-06 , Vol. 139 , P. 10-20
DOI 10.1016/j.measurement.2019.02.024
WOS© Times Cited 19
Keyword(s) UAV, SfM photogrammetry, Tilted camera, Cliff face erosion, Coastal monitoring, Normandy
Abstract

UAVs are relevant for monitoring cliff faces. In this study, several flights are performed with various imaging angles (nadir, 20 degrees, 30 degrees and 40 degrees off-nadir) to assess the impact of the imaging angle on the 3D cliff face reconstruction. Occlusions issues arising with sub-vertical cliffs make nadir surveys nearly irrelevant. The results obtained with 20 degrees, 30 degrees and 40 degrees off-nadir imaging angles are satisfactory regarding texture restitution and accuracy with respectively 5.5 cm, 5.9 cm and 4.9 cm of error, higher tilting angles yielding better reconstructions on sub-vertical or overhanging parts of the cliff. This article also investigates other parameters affecting tiepoint detection on the cliff face, as the effective overlap, the UAV-cliff face distance and the cliff face illumination. Guidelines are provided for UAV survey parameterization, aiming at capturing the whole cliff face with a good trade-off between distance to the cliff, flight height and spatial resolution of the photographs.

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