2017 Fiscal Year Annual Research Report
AUV exploration of the mesophotic reef zone in the South Ryukyu Islands
| Project/Area Number |
16K17819
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| Research Institution | Nagoya University |
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Principal Investigator |
HUMBLET Marc 名古屋大学, 環境学研究科, 特任准教授 (40623616)
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| Project Period (FY) |
2016-04-01 – 2018-03-31
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| Keywords | Coral reefs / Mesophotic habitats / Benthic communities / Seafloor topography / AUV / ROV |
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| Outline of Annual Research Achievements |
The autonomous underwater vehicle (AUV) HATTORI (Highly Agile Terrain Tracker for Ocean Research and Investigation, Prof. Toshihiro Maki’s lab, the University of Tokyo) was deployed at 4 sites in and around the Sekisei Lagoon, South Ryukyus, Japan, in May 2017. This lightweight AUV is equipped with two GoPro cameras, one looking forward and one downward, to acquire video images of the seafloor along a predefined path. The sequential images can be combined into a photomosaic of the surveyed area to quantify the live benthic cover and obtain information on the nature of the substrate (e.g., sediment size and sorting, bedforms). The images can also be processed to obtain a 3D picture of the seafloor, and therefore enable to match biotic distribution with local topography. The first two sites surveyed by the AUV HATTORI were located inside the lagoon at shallow depth (20 m or less). Several dives were conducted at these sites to fine-tune navigation parameters, such as speed and elevation. After these trials, the AUV was deployed at mesophotic depths, first along the southern margin of the Sekisei Lagoon (Kataguwa site, 11 dives), then north of Taketomi island (Taketomi north site, 2 dives), at water depths of 40-45 m, along transects up to 40 m in length. Additional video images were acquired using the remotely operated vehicle (ROV) Kukanchi (Ambient Intelligence Technologies Lab., Co.Ltd.) a small ROV (QI, Co.Ltd.). The AUV was equipped with sensors to obtain temperature, salinity, and light intensity profiles down to 45 m at Kataguwa and Taketomi north sites.
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