Several submarine cables for communication network with suspension of business has been laid on the global seabed. Recycling them, the scientific observations of global ocean scale are expected to come true. The general conception of utility is recognized to apply successive long term scientific observations fixed to a submarine cable by installing a number of sensors (hereafter fixed type of observation system). However, it is not enough from the viewpoints of including comprehensive undersea space and observing the phenomena of unforeseen incidents (earthquake, eruption of submarine volcanoes and seasonal abnormal weather etc. with the duration of a few weeks or a few months). Because most of the incidents are not predicted or forecasted both of when and where it happens, moreover the best matched installations are unable to extend in advance. So that an appropriate system for extraordinary observations is requested to meet the demands on easily moving and extending it by vessels or shipping shifts adding to the fixed type of observation system. The submarine cables are of course used as a transmission route to send the data obtained by the extraordinary system.
From these points of view, the extraordinary observation system is brought up by using an acoustic transmission and the submarine cable for communication network [TCP-2] as a transmission route. One of the distinctive features is that it uses ultrasonic waves traveling through sea water as data transmission medium. It is composed of a 'basic part' mechanically and electrically branched out of the submarine cable [TCP-2] and a 'mobile part' connected to a sort of observation sensors to meet an incident and an acoustic transmission device. This R & D aims to realize the extraordinary observation system. 1)
