[Expedition NT10-04: DONET observatory construction phase 1]
The subsea construction of the world first precise seafloor earthquake and tsunami observatory was started from the March 2010. R/V Natsushima and ROV Hyper-dolphin scheduled eight ROV dives for the DONET observatory construction in the expedition NT10-04.
March 6th, in the Hyper Dolphin dive#1083, the ROV placed science node on the DONET observation area “A” (see cable information page) and connected it to the termination unit (TU) “A” that was laid on the seafloor by the cable laying ship KDDI pacific link (KPL) in January 2010. Immediately after the connected operation, the physical condition of installed science node was tested from the node control interface in landing station at Owase,
March 11th, in the dive#1085, a DONET observatory (consist of a ground motion sensing system and a pressure sensing system) was setup in the observation site “A3”. The ground motion sensing component of the observatory was fixed in a burial casing that has been driving into the seafloor sediment in advance this expedition. The pressure sensing component of the observatory was put on the seafloor sediment about 10m away from of the burial hole.
The day next the observatory setup, in the dive#1086, the Hyper Dolphin connected the observatory “A3” to the science node “A” using the 10km length of extension cable system. This operation took approximately 10 hours to lay the cable on the 9,450m horizontal distance of seafloor. Right after the connection, the observatory was successfully boot up from landing station and start to acquire a data set of initial condition 3 over nights. The qualities of the initial data were contents that satisfied the researchers sufficiently. Because of the schedule of landing station construction, the whole system was shut down after correcting the initial data until the construction is completed in April.
Only three ROV dives were able to be conducted in the expedition NT10-04 because of the spring storm in Kumano-nada. The expedition became to an end by the dive#1086 March 12th. The construction of other science nodes and observatories are scheduled in the ship time of JAMSTEC research fleet in coming fiscal year.