The VENUS project-instrumentation and underwater work system

The VENUS project is a five-year plan between 1995 and 1999 to utilize the retired trans-Pacific telephone cable from Okinawa to Guam Islands for multidisciplinary geo-scientific studies. The first seafloor observatory off Okinawa Island was deployed in March 1998 in the landward slope of Nanseishoto Trench at a depth of 2,200 m. Among several ideas to transmit the data from sophisticated sensors into the cable, such as inductive data coupling system, direct data coupling system was adopted in the VENUS phase I in order to get sufficient power from the cable for the instruments. Integrated seafloor observatory is comprised of broadband and velocity-type seismometers, tsunami pressure gauge, magnetometer, hydrophone array, sub-bottom temperature probe, geo-potential probes, precision transponders for baseline measurement, digital camera, CTD, current meter, etc. These sensors were deployed precisely by JAMSTEC/deep tow and connected with the main cable by manned submersible Shinkai 6500 and ROV Kaiko. In order to carry out underwater works in situ, ROV matable coaxial, electrical and optical connectors were developed. Also, cable cutter and grip were developed for underwater operations by Shinkai 6500. The VENUS project will contribute greatly to expand global seismic network, and to reuse economically retired submarine coaxial and optical telephone cables over the world ocean floor. Also, a revolutional progress is expected in the deep sea technology and deep sea research.