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Remote Sens. 2017, 9(7), 740; doi:10.3390/rs9070740

How Reliable Is Structure from Motion (SfM) over Time and between Observers? A Case Study Using Coral Reef Bommies

1
Department of Biological Sciences, Macquarie University, Sydney 2109, Australia
2
School of Environmental and Life Sciences, University of Newcastle, Ourimbah 2258, Australia
*
Author to whom correspondence should be addressed.
Academic Editors: Raphael M. Kudela and Xiaofeng Li
Received: 19 June 2017 / Revised: 30 June 2017 / Accepted: 12 July 2017 / Published: 18 July 2017
(This article belongs to the Section Ocean Remote Sensing)
View Full-Text   |   Download PDF [1398 KB, uploaded 19 July 2017]   |  

Abstract

Recent efforts to monitor the health of coral reefs have highlighted the benefits of using structure from motion-based assessments, and despite increasing use of this technique in ecology and geomorphology, no study has attempted to quantify the precision of this technique over time and across different observers. This study determined whether 3D models of an ecologically relevant reef structure, the coral bommie, could be constructed using structure from motion and be reliably used to measure bommie volume and surface area between different observers and over time. We also determined whether the number of images used to construct a model had an impact on the final measurements. Three dimensional models were constructed of over twenty coral bommies from Heron Island, a coral cay at the southern end of the Great Barrier Reef. This study did not detect any significant observer effect, and there were no significant differences in measurements over four sampling days. The mean measurement error across all bommies and between observers was 15 ± 2% for volume measurements and 12 ± 1% for surface area measurements. There was no relationship between the number of pictures taken for a reconstruction and the measurements from that model, however, more photographs were necessary to be able to reconstruct complete coral bommies larger than 1 m3. These results suggest that structure from motion is a viable tool for ongoing monitoring of ecologically-significant coral reefs, especially to establish effects of disturbances, provided the measurement error is considered. View Full-Text
Keywords: volume; surface area; management; photogrammetry; accuracy; precision; 3D; bleaching; drones; aerial survey volume; surface area; management; photogrammetry; accuracy; precision; 3D; bleaching; drones; aerial survey
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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Raoult, V.; Reid-Anderson, S.; Ferri, A.; Williamson, J.E. How Reliable Is Structure from Motion (SfM) over Time and between Observers? A Case Study Using Coral Reef Bommies. Remote Sens. 2017, 9, 740.

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