At present, we can dive to a depth of up to 6,500m in a small manned submersible, which is only half of the maximum depth of the ocean. The vast area of sea floor and huge volume of underwater world still remain unknown even though the ocean significantly influences the global environmental change, which is one of our concerns in regard to our daily life in 21st century.
For underwater survey and exploration, we can use manned submersibles, remotely operated vehicles, and autonomous underwater vehicles as mobile platforms. If we want to tele-operate the underwater unmanned vehicle, it should be connected with an umbilical cable to the support ship for communication because of non-availability of radio communication link in salty water and low data rate of acoustic communication link. Handling of a long umbilical cable is very troublesome on deck and the cable is sometimes broken resulting in loss of the vehicle.
The Autonomous Underwater Vehicle (AUV), being free from physical restriction can operate with a high degree of freedom of movement, is the anticipated robot which dives on behalf of us and shows us spectacles that are happening under water. Since the AUV works in an isolated environment, it can behave independently and concentrate on its mission without interference by human beings. Consequently the AUV can be the artifact which competes with us.
AUV technology is about to be on the stage of practical use for understanding the underwater world. Our laboratory has constructed more than 10 AUVs since 1984 and operated them in the open sea. The "R-One Robot" undertook a successful fully autonomous expedition to Teisi Knoll in 2000, got into the crater and obtained many acoustic images of the sea floor from various directions. The "r2D4", the newest AUV observed one fault-line off Sado Island in 2003 and will be used for research in advanced underwater robotics and survey areas of deep-sea hydro-thermal vents. The "Tri-Dog 1" can observe underwater structures such as piles and caissons by turning around them and takes pictures of their surface which are integrated after diving by mosaicking technology. A new project of marine mammal observation, such as humpback whale, sperm whale and river dolphin, using AUVs was initiated in 1999. The "Aqua Explorer 2000" followed a humpback whale for two hours in March 2000. In order to identify individuals, we are now analyzing clicks of sperm whales which are presumably used for detection of giant squids for food. The passive SONAR system we developed for AUV will be implemented on the "Aqua Explorer 2000" or "r2D4" in the summer of 2004. Then, the AUV will dive up to 2,000m following a specified sperm whale and hopefully take its pictures.
There are certainly many underwater missions which are suitable for AUVs as described. We would like to find more to develop AUV's potential and demonstrate their various fascinating performances