Study on ocean observatories by re-use of retired optical submarine cable

First and second-generation optical submarine cable systems have been retired. The first generation systems (OS-280M) operate at a rate of 295.6 Mbps per fiber pair and second generation systems (OS-560M) operate at a rate of 5912 Mbps per fiber pair. These cables run along geophysical important places such as the Japan Trench, the Nankai Trough, and along a seismic subduction zone off Aleutian Islands. Although an observatory sites are restrained on the vicinity of existing cable route, if we can re-use such cable systems, real-time geophysical observatories on a deep-sea floor could be realized with high reliability and at a reasonable cost as compared with laying a new monitoring cable system. The scientific re-use cable will consist of a backbone cable (existing cable) and observatory nodes. Many kinds of scientific instruments are connected to the node using standard IP interface. We have studied on the many technical and economic issues of scientific re-use of four cable systems. In conclusion there are no fundamental engineering limitations for effective re-use of retired cables. Re-used cable systems can provide power and data telemetry adequate for existing and near-term ocean observing system. This paper describes the technical issues of scientific re-use of retired optical submarine cable systems.