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[Twenty-eight observatories of DONET2 are working now; just three observatories remain to be installed]


Eight observatories of DONET2 have newly been activated during Expedition KY15-16 conducted from Oct. 16 to Dec. 3, 2015. Consequently, twenty-eight observatories of DONET2 are currently in operation and just three observatories remain to the completion of DONET2 installation (Figure 5).

Strong wind and mighty wave couldn’t stop us from continuing the DONET2 construction. Two big events were accomplished in this expedition. One is to reinstall the Node 2D that was recovered before to avoid a risk when recovering the troubled terminal unit 2D and installing a new one. The other is to activate the observatories that are too far from the nodes (the distance is 15-17 km) to be connected by a single cable-laying operation; two cable-laying operations are needed because the total length of the cable wound on the cable bobbin is 10.5 km. There are three remote observatories in DONET2 and two observatories have been activated in this expedition.

To summarize, the following operations were carried out in Expedition KY15-16: three sets of observational equipment have been installed; the inside of five caissons was cleaned for housing the seismometer package; ten cable-laying operations have been conducted; and a pressure sensor system has been calibrated at the borehole observatory C0002. The remaining three observatories will be deployed and activated in the coming expedition in Jan. 27-Mar. 1, 2016.

Figure 1: The Hyper-Dolphin ROV with the sunrise.

Figure 2: Node 2D reinstalled.

Figure 3: Just before the launch of the cable-laying operation for connecting a remote observatory. The connection module for two cable-laying operations is attached at the front of the Hyper-Dolphin ROV.

Figure 4: The connection module placed on the seafloor.

Figure 5: The construction situation of DONET2 after Expedition KY15-16.