Yuichi Shirasaki

Approaching whales by autonomous Underwater vehicle

There are few studies on the ecology of whales in underwater except for small whales (Baird, R., 1996, Otani, S., 1998). It is hoped that through the use of Autonomous Underwater Vehicles (AUVs) new knowledge about whales can be gained. The whale makes sounds, and especially the humpback whale (Megaptera novaeangliae) makes a specific sound called a song. We started our project to develop the technology for AUVs to follow and observe humpback whales by analyzing their songs and locating them underwater. A small size passive SONAR was designed, fabricated, and fitted on the AUV AQUA EXPLORER 2000. An observation experiment was conducted in March 2001 off the Kerama Islands, Okinawa. Prior to our studies, there were no examples of AUV observations on whales anywhere in the world. This experimental observation was conducted as a joint project of the Underwater Technology Research Center at the Institute of Industrial Science in the University of Tokyo, KDDI Co. Research Institute, and the Okinawa EXPO Aquarium. The AUV succeeded in detecting a humpback whale underwater and approaching it within 50m in this experiment.

Proposal of next-generation real-time seafloor globe monitoring cable-network

A feasibility study on a new scientific submarine cable network of next generation around Japanese Islands is presented. The proposed cable network has a mesh-like topology covering a vast area and has many observation nodes with 50-km intervals. In observation nodes, various sensors can be installed, that are exchangeable for maintenance and replacement. The cable network supplies electric power to sensors and provides continuous and long-term data to researchers and agencies. It will be used in a vast research field in such as seismology, geodynamics, marine environmentology, ecology and biology. In this paper, topology of the cable network, structure of the observation node, optical data transmission system and power feeding system are described.

ARENA: a versatile and multidisciplinary scientific submarine cable network of next generation

Seafloor observation system using the underwater cable is one of the most reliable ways to provide high-speed data transmission and continuous power feeding to underwater devices. Recent evolution in the optical submarine cable and Internet technology make it possible to develop a versatile scientific submarine cable network. IEEE OES (Institutes of Electrical and Electronics Engineers, Oceanic Engineering Society) Japan chapter has conducted the feasibility study on the new scientific study on the new scientific submarine cable network. The proposed scientific cable network named ARENA has the following feature: (1) mesh-like cable network configuration covering vast research area with 3,600 km of total cable length; (2) over 66 observation nodes with 50 km intervals; (3) robustness against failures; (4) wideband optical transmission system capable of transmitting plural HDTV (high definition television) signal and synchronizing time signal with accuracy of one microsecond; (5) system extensibility; and (6) exchangeability of sensors. This paper will describe the outline of ARENA.

Control performance of autonomous underwater vehicle "AQUA EXPLORER 1000" for inspection of underwater cables

The paper deals with analysis of control performance of an autonomous underwater vehicle named AQUA EXPLORER 1000 (AE1000) for inspection of underwater telecommunication cables up to 1000 m depth, reviewing results of sea trials in autonomous tracking. The control performance of the cable tracking at 40 m water depth, consisting of descent from the surface, cable searching, cable tracking and ascent to the surface, is discussed based on the measured data. Next, the performance of spiral motion control in a limited area from the mother ship, which is an important operation for the AE1000 not to be lost during descent and ascent, is discussed by showing test results. Finally, the performance of the fuzzy controller for cable tracking control in tidal currents is discussed by use of numerical simulation.<<ETX>>

Scientific application of ARENA networks

A new scientific submarine cable network named ARENA (advanced real-time earth monitoring network in the area) will be planed to encircle Japanese island and cross several tectonic plates in Japan. ARENA network will provide researchers a long-term, real-time, wide-bandwidth infrastructure for multidisciplinary seafloor observation in the deep sea to explore problems unapproachable with existing methods. This observatory network consists of many observation nodes with 50 km intervals, and each node is connected with many kinds of sensor for studies within a wide spectrum of scientific field and for the disaster-related measures to earthquake, tsunami and volcano. This paper will describe new observation ideas using ARENA has been discussed at the committee organized by the Research Institute for Ocean Economics (RIOE) and JAMSTEC.

Multi-disciplinary VENUS observation at the Ryukyu Trench using Guam-Okinawa geophysical submarine cable

A multi-disciplinary VENUS (versatile eco-monitoring network by undersea-cable system) observatory, which equips seven geophysical instrument groups, was installed at the depth of 2,170 meters on the slope of the Rukyu Trench. Prior to the installation of the VENUS multi-disciplinary ocean bottom (MDOBO) observatory, an ocean-bottom telemetry system, which has functions to supply electrical power to the MDOBO, and the submarine coaxial cable were installed at ocean bottom. The installation of the multi-disciplinary ocean bottom observatory was done by use of deep-towing unit and ROV Kaiko-10K. During the period of August-September 1999, seven instrument groups of MDOBO were deployed at the target position, at 80-100 meter distances from the telemetry system, with several meters allowances using a deep-towing unit. To install the instrument at the exact location, the mother ship of deep-towing unit was precisely navigated. The extension cables were also dropped from the deep-towing unit. The ROV Kaiko-10K extended multi-conductor extension cables from instrument units towards the ocean-bottom telemetry system and connected them to undersea mateable connectors on the junction box. The MDOBO collected one and half month records. Some useful data were observed since the installation.

Metal Detector for Tracing Submarine Telecommunication Cables

The characteristics and the optimum design of a metal detector are studied theoretically and experimentally. This metal detector is expected to be mounted on an unmanned submersible and to be used for the location finding and tracing of the submarine telecommunication cables. The detector consists of one exciting coil and two receiving coils which are fixed perpendicularly to the excitation coil. The receiving coils detect the magnetic field induced by the eddy current flowing in the outer conductor of the submarine cable. Although the detection range is narrow, about 40 cm, this detector has some advantages that the other cable-locating sensors do not have. The detecting characteristics are calculated numerically under several assumptions and compared with experimental results.

Fiber-optic-tethered unmanned submersible for searching submarine cables

A newly developed, fiber-optictethered, unmanned submersible called MARCAS (Marine Cable Search System) has been operating successfully. The mission of MARCAS is to inspect submarine communication cables and the seabed up to 200m in depth. MARCAS has dc and ac magnetometers (proton magnetometers and fluxgate magnetometers) and a metal detector in order to find and trace the cable even if buried under the seabed. A wavelength division multiplex optical fiber transmission system has been developed for the data transmission between the submersible and the mother vessel. MARCAS can be equipped optionally with soil property testing instruments. These characters will be discussed.

Development of optical fiber/power line composite tether cable for remotely operated unmanned submersible

A new type of tether cable with high quality signal transmission characteristics was developed by adopting optical fibers. As the tether cable is subject to frequent and various mechanical and thermal loads under the severe operating conditions in the offshore environment, the greatest care should be paid to the design of its structure to preserve the optical fibers from those loads. This paper describes the design requirements and the characteristics of the optical fiber/power line composite tether cable under the loads such as tensile loading, bending, twisting, water pressure, and cable heating. The termination of the tether cable is also discussed. This tether cable has been in practical use for remotely operated submersible MARCAS whose mission is inspection and location of the submarine telecommunication cables.

Feasibility study on power feeding system for scientific cable network ARENA

Power feeding system is the most challenging technical issue to realize a mesh-like underwater cable network for scientific use. IEEE OES (Institute of Electrical and Electronics Engineers Oceanic Engineering Society) Japan Chapter organized a committee on the underwater cable-network for scientific seafloor monitoring, and conducted a technical feasibility study. In this paper, outline of the proposed power feeding system will be presented. In the feasibility study, three systems were proposed and compared, namely, (a) constant current (CC) power feeding system, (b) constant voltage (CV) power feeding system, and (c) hybrid system that consists of constant voltage feeding subsystem and constant current feeding subsystem. As a result of the feasibility study, the authors think the CC power feeding system is the most promising system for the proposed scientific cable network. The authors also proposed a new current-to-current converter that is the key devise for the CC power feeding system.