The development of deep sea research systems-manned and unmanned submersibles-made it possible to carry out visual surveys of the deep seafloor at any depth on the earth. These surveys have revealed a great number of phenomena that occur on the seafloor, such as hydrothermal vents and chemosynthetic biological communities at mid-oceanic ridges.
Unmanned submersibles include ROV (Remotely Operated Vehicle), UROV (Untethered Remotely Operated Vehicle), which have thrusters and are operated by mother ship through a tether cable or a thin optical fiber respectively, AUV (Autonomous Underwater Vehicle) which moves under pre-programmed commands and does not have a cable, and deep-tow system which is also operated by mother ship through. a cable but does not have a thruster.
In order to see objects under very low illumination in deep seas, a Super-HARP (High-gain Avalanche Rushing Amorphous Photoconductor) video camera which is far more sensitive than CCD cameras, was developed. Recently, the Super HARP Hi-vision video camera, which provides high-resolution video images, has been developed.
The location of the submersible in water is obtained by three acoustic positioning systems. These are called LBL (Long Base Line), SBL (Short Base Line), and SSBL (Super Short Base Line) positioning systems.
In order to achieve effective dive surveys by manned submersibles or ROVs, it is necessary to select dive points by considering the results of pre-surveys carried out over a wide area, including bathymetric mapping using multi-narrow beam echo sounder, side-scan sonar survey, and deep-towed camera surveys.
Submersibles enable not only visual observation, but also sampling and geophysical measurement at aimed points on the deep seafloor. In order to construct multi-disciplinary real-time and long-term deep seafloor observatories, such as off Hatsushima Island Observatory and VENUS off Okinawa Island Observatory, or to carry out borehole measurements, submersibles have been playing important roles in installing instruments, extending cables, and connecting connectors of instruments to underwater telemetry systems, or in recovering data. Submersibles are also necessary when searching for the causes of events observed by the observatory.
The ROV and the Super HARP Hi-vision video camera made it possible for many scientists on board to see high-resolution video images of the seafloor simultaneously as if they were viewing it with the unaided eye. The AUV will enable surveys over wide areas in the near future. However, observations by submersibles are limited by survey time. On the other hand, long-term observatories enable observations only at fixed points. Complimentary observations using both long-term observatories and submersibles are expected in order to extend survey area in terms of both temporality and spatiality to provide an understanding of phenomena that occur on the seafloor.