Subsea engineering ROV and seafloor observatory construction

Marine science starts shifting from the age of the exploration in the age of the observation. For the abyss research, submarine cabled seafloor observation is one of the expected engineering approaches to be realized real-time and long term observation of natural phenomenon. The DONET (Dense Ocean-floor Network system for Earthquakes and Tsunamis) is a submarine cabled seafloor observatory network design for earthquakes and tsunamis monitoring at the western part of the Pacific Rim. Twenty set of high performance observatories are installed to the seafloor in this project. One of the most difficult engineering in the project is to establish construction method of complex sensor observatory on seafloor. The use of ROV is necessary in the subsea construction. This paper describes the construction method of seafloor seismic observatory, tools design for construction, and experience result in an actual field.