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Coral Reefs (2017) 36:269275
DOI 10.1007/s00338-016-1522-0
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Mapping coral reefs using consumer-grade drones and structure from motion photogrammetry techniques
Elisa Casella1 Antoine Collin2 Daniel Harris1,3 Sebastian Ferse1
Sonia Bejarano1 Valeriano Parravicini6,7 James L. Hench4 Alessio Rovere1,3,5
Received: 26 June 2016 / Accepted: 17 November 2016 / Published online: 28 November 2016 Springer-Verlag Berlin Heidelberg 2016
Abstract We propose a novel technique to measure the small-scale three-dimensional features of a shallow-water coral reef using a small drone equipped with a consumer-grade camera, a handheld GPS and structure from motion (SfM) algorithms. We used a GoPro HERO4 with a modied lens mounted on a DJI Phantom 2 drone (maximum total take-off weight\2 kg) to perform a 10 min ight and collect 306 aerial images with an overlap equal or greater than 90%. We mapped an area of 8380 m2, obtaining as output an orthorectied aerial photomosaic and a bathymetric digital elevation model (DEM) with a resolution of 0.78 and 1.56 cm
pixel-1, respectively. Through comparison with airborne LiDAR data for the same area, we veried that the location of the ortho-rectied aerial photomosaic is accurate within *1.4 m. The bathymetric difference between our DEM and the LiDAR dataset is -0.016 0.45 m (1r). Our results show that it is possible, in conditions of calm waters, low winds and minimal sun glint, to deploy consumer-grade drones as a relatively low-cost and rapid survey technique to produce multispectral and bathymetric data on shallow-water coral reefs. We discuss the utility of such data to monitor temporal changes in topographic complexity of reefs and associated biological processes.
Keywords Drone mapping Coral reefs Bathymetry
from drones Structure from motion underwater
Bathymetry from photogrammetry
Introduction
Monitoring the characteristics of coral reefs is essential to understand their trajectories under scenarios of climatic or anthropogenic stress or their recovery from these impacts (Hedley et al. 2016). Large-scale studies on shallow-water coral reefs are usually carried out analysing either satellite (Mumby et al. 1997) or other airborne imagery such as aerial photographs, which are currently extensively used to monitor the trajectory of bleaching events (Normile 2016; Witze 2016). Bathymetric information on coral reefs is most often collected using echosounders or multibeam techniques (Bejarano et al. 2011), shallow-water LiDAR...