End of the chain? Rugosity and fine-scale bathymetry from existing underwater digital imagery using structure-from-motion (SfM) technology
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The rugosity or complexity of the seafloor has been shown to be an important ecological parameter for fish, algae, and corals. Historically, rugosity has been measured either using simple and subjective manual methods such as ‘chain-and-tape’ or complicated and expensive geophysical methods. Here, we demonstrate the application of structure-from-motion (SfM) photogrammetry to generate high-resolution, three-dimensional bathymetric models of a fringing reef from existing underwater video collected to characterize the seafloor. SfM techniques are capable of achieving spatial resolution that can be orders of magnitude greater than large-scale lidar and sonar mapping of coral reef ecosystems. The resulting data provide finer-scale measurements of bathymetry and rugosity that are more applicable to ecological studies of coral reefs than provided by the more expensive and time-consuming geophysical methods. Utilizing SfM techniques for characterizing the benthic habitat proved to be more effective and quantitatively powerful than conventional methods and thus might portend the end of the ‘chain-and-tape’ method for measuring benthic complexity.
KeywordsRugosity Bathymetry Imagery Structure-from-motion (SfM)
This is a contribution of the US Geological Survey’s (USGS) Pacific Coral Reef Project and was supported by the USGS Coastal and Marine Geology Program. This work is dedicated to Paul Jokiel (UH-HIMB), who taught so much about coral reefs and their monitoring to so many. We would like to thank Dave Zawada (USGS) and three anonymous reviewers who contributed numerous excellent suggestions. Use of trademark names does not suggest USGS endorsement of products.
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