To understand the Earth's geophysical phenomena, it is important to obtain multicomponent, continuous, long-range, and real-time marine data in global scale. To carry out observations in the sea, the most reasonable way at present is to use submarine cables for communication and power supply. There are cable projects using decommissioned submarine cables in Japan. GeO-TOC and VENUS projects. The H2O project is a US version of the VENUS project. Outlines of the two systems are presented with some new results.
Some other projects using new fiber optic cables have been continued in Japan, but most of these projects are oriented toward seismic observations. The NEPTUNE and J-NEPTUNE projects are the most attractive projects in the near future to build multi-disciplinary observatories as Internet networks in the sea.