Underwater Three-Dimensional Measurements
The main objective of this study is to demonstrate the possibility of underwater three-dimensional measurement (underwater SfM) in a coral reef area by structure from motion (SfM). The possibility of underwater SfM using a small submarine (small remotely operated vehicle, sROV) was also investigated. After we conducted underwater SfM and conventional measurements simultaneously for dendritic coral, massive coral, and seaweed Enhalus acoroides in a coral reef area in Amitori Bay of Iriomote Island, we compared and examined the results. Underwater SfM allowed us to measure the heights, major and minor axes, and branch thicknesses of dendritic coral with the accuracy of a maximum and minimum error of 4.5 cm and 0.1 cm, respectively. Consequently, it was verified to be useful for monitoring coral preservation. However, three-dimensional measurements of Enhalus acoroides by SfM were not satisfactory because of swaying of leaves by waves or currents during the taking of sequential photographs. Investigation by sROV provided a clear three-dimensional model, but some technological problems were also revealed.
KeywordsAmitori Bay Coral reef Remotely operated vehicle (ROV) Structure from motion Underwater photography
Field observations at Iriomote Island were conducted with the cooperation of Ken Sakihara of the Okinawa Regional Research Center and of Mayumi Suzuki and Seina Miyauchi, who were then students of the School of Marine Science and Technology, Tokai University. The survey conducted in Suganuma and Aio Bay was assisted by Takashi Komuro. This study was conducted as a research project of National Research Institute for Earth Science and Disaster Resilience, joint research by Tokai University and National Research Institute for Earth Science and Disaster Resilience, and JSPS Grants-in-Aid for Scientific Research Nos. 26281055 and 17K18534. The authors extend their deepest gratitude for this kind support from so many sources.
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