Development of Japanese Scientific Cable Technology

Japanese ocean science community has installed eight cabled observatories in Japanese water in the past. Japan started installing cabled observatories in the middle of 1970's for disaster mitigation as countermeasure to possible megathrust earthquake in the Tokai region, about 100 km away from Tokyo. Their first system composed of metal wires used frequency modulated signal transmission for carrying data acquired on the seafloor to land. The first Japanese cabled observatory was installed in 1978, i.e., five years after the initiation of engineering development Since 1990, all newly installed cabled observatories have used fiber optic communication lines following the technological development in the telecom industry. Obviously, the development of scientific cabled observations adjusted their stride with that in the industry. Since the major telecom cables have been installed in a point-to-point configuration, scientific cabled observatories have been developed in the same way. In general, they have a land station and a line of cable along which observational instruments or junction boxes are connected in-line in the place of repeaters. Recently, scientists started trying to expand their observations in a way to enhance observational capabilities using multi-disciplinary sensors as the growth of their understanding to invisible processes in the sea. Cabled observatory projects are now underway to enable next-step data acquisition on the seafloor with much wider spatial coverage and dense observational instruments. Technological development from a point-to-point configuration to a network, whose topology could be either ring or star shape, has become necessary. Power supply and communication mechanisms to all of sensors attached to observatory need to be revisited as well.