Development and Field Application of Composite Type Submarine Cables for Coastal Wave Observation
Toshihiko NAGAI, Hiromi KADO, Masakatsu NAKAYAMA, Hiroyasu NAKASHIMA, Mitsuru INOUE, Yasuo SHIMIZU and Tohru NAKAGAWA
Abstract:
Acoustic and pressure type seabed installed wave sensors have advantage in observing long period infra-gravity wave and tsunami, while buoy type wave sensors which measure acceleration of the moored buoy motion are not able to detect long period waves. That's why most of the Japanese coastal wave observation sensors are seabed installed typed ones. Seabed coastal wave sensors are gradually clarifying tsunami profiles and infra-gravity wave characteristics. Seabed installed wave observation systems can be divided into two kinds in the data transmission method from the seabed sensor to the on-land station, one for relatively short-term, simple and cheap system without setting seabed connecting cable, the other is for permanent system with seabed cable. Real time wave monitoring was supposed to be difficult in the former one. Wireless data communication between a surface buoy and on-land station is easy. Nevertheless data transmission from seabed to surface buoy was not practically possible. Due to co-existence of data communication cable and relatively stronger mooring cable, data communication cable is sure to be damaged due to interaction with the mooring cable in high wave condition. For the latter permanent system, Japanese Nationwide Ocean Wave information network for Ports and HArbourS (NOWPHAS) has 54 seabed coastal wave sensors of 20-50m depth with 2-10km off the shore line. From a view point of the NOWPHAS management budget, seabed cable installation and repair takes a great part of the total cost. Almost every year in some NOWPHAS station, seabed cable suffers an accidental damage due to ship anchoring or fishery activities. Such accidents cause long term miss of precious wave information. That is why expensive seabed dredging is supposed to be necessary in order to keep the cable below the seabed. Nevertheless seabed dredging cable installation may damage the fishery resources. In addition even after expensive dredging, the cable may be exposed to the surface of bed due to scouring or liquefaction by high wave action. A new type of submarine cable named as "Composite Cable" has been developed and put into practical use in order to solve above mentioned problems of mooring and seabed cables. "Composite Cable" unified the signal transmission part and surrounding protection part consisted of many bands of steel wires, which proves the strength against the tension out force without loosing flexibility. This paper describes results of field experiments of the Composite Mooring Cable and of real time coastal wave monitoring system using the cable. The new real-time system with Composite Mooring Cable was proved to observe very high waves in the breaking zone with significant wave height of 6.3m, by using a modified connection part with the seabed wave sensor. It also describes prototype Composite Seabed Cable design and installation at one of the NOWPHAS stations facing to the south western Japan Sea. The original cable was damaged and cut due to some human oriented accident. The newly developed Seabed Composite Cable has been designed to keep high density more than 3.0 in order to promote self depression into the liquefied seabed sand, avoiding the cable exposure on the seabed, and to have stronger tension resistance than existing types of seabed cables. Use of the mooring and seabed Composite type submarine cables will reduce the trouble and increase reliability of coastal wave observation data.
Development, Testing and Track Record of Fiber-Optic Wet-Mate Connectors
Gary Brown
Abstract:
Underwater optical wet-mate connectors enable subsea system designers to build modular subsea components and systems utilizing optical communication systems. These modular systems can be assembled on the seafloor. The optical connectors enable connections and disconnections of optical systems underwater, providing connectivity for installation and maintenance purposes or for future system expansion, particularly as part of installed underwater optical communication hubs. In anticipation of future applications requiring the large bandwidth, high speed and long step-out distances achievable from using optical communication systems, optical wet-mate connectors have been qualified for use to 23,000 feet (7,000m) and so far been used to over 9,900 feet (3,017m). This paper presents an overview of the development and testing, plus a summary of the track record, of a full range of wet-mate optical fiber connectors suitable for the underwater industries.
Integrated Acoustics Systems for Ocean Observatories (IASOO)
Bruce M. Howe, James H. Miller, and the IASOO Committee
Abstract:
The concept of integrated acoustics systems to provide navigation and communications and to conduct acoustic measurements, all in support of science applications within the ocean's volume, is developed. The navigation function is analogous to the now-ubiquitous satellite based Global Positioning System (GPS), but because the ocean is opaque to electromagnetic waves and transparent to sound, acoustics systems are necessary. In the ocean, a series of nested systems are envisioned, from small-scales to regional to basin-scales as required. A small number of acoustic sources sending coded, low power signals can service unlimited numbers of inexpensive receivers. These sources can serve double duty by transmitting control data from users to remote instruments; if enabled as receivers, two-way acoustic communications links in large-scale networks can be established. Acoustic based instrumentation that shares the acoustic bandwidth with, and depends upon, the navigation and communications capabilities completes the concept of integrated acoustic systems.
This navigation and communications infrastructure is a prerequisite to the sustained presence of mankind in the ocean. Many applications require or are enabled by this infrastructure. Autonomous undersea vehicles (powered and gliding) can navigate themselves over the ocean bottom and through the water column without coming to the surface. They can obtain navigation fixes and communicate their data and status to users via acoustic modems to cabled or surface satellite telemetry systems without breaking away from their underwater missions. Profiling and drifting floats can more accurately measure the ocean's velocity structure, tagged fish and marine animals can be tracked with high precision, moorings can track their motion in ocean currents, and bottom-fixed instruments can measure seafloor motion.
The sources and receivers can serve multiple functions: sources as navigation and communications components as well as multi-static active transmitters, and receivers as communications components and as passive listening devices. With signal standards and protocols for managing the acoustic spectrum, the system will be an extensive multipurpose acoustics infrastructure, capable of supporting applications even beyond our present vision. Drawing a further analogy with GPS and its use for tomography of the atmosphere and ionosphere, the various acoustic sources and multitude of receivers can function similarly in the ocean. This has significant implications for observing the ocean's interior in real time, and measuring long-term climate variability. Receivers on globally distributed floats can also listen to ambient sound: wind and rainfall, seismic T-phases, marine mammals, and ships. Some of these natural sources of sound can in-turn be used as sources of opportunity for other purposes.
The provision of such a transformational infrastructure to the ocean community is expected to be one of the enabling technologies fueling a revolution in ocean observatories. This report examines the concept by addressing technical questions and implementation issues. The IASOO Committee is a newly formed specialty committee of the Acoustical Society of America. Broad community participation is encouraged.
Managing Sensor Network Configuration and Metadata in Ocean Observatories Using Sensor Pucks
Thomas C. O'Reilly, Michael Risi, Kent L. Headley
Abstract:
Cabled observatories such as MARS or NEPTUNE will consist of many deployed instruments which communicate with human operators and shore-side data repositories. In addition, these deployed devices may actually communicate with other, facilitating capabilities such as autonomous event response. These potentially complex interactions between multiple entities - human and machine - require that knowledge of the system configuration be available to participants. Users of instrument data require information - "metadata" - about the sensor that generated the data. Software which coordinates and controls instruments requires access to the software interfaces of those devices. "Manual configuration" has been used on small-scale systems, but in a network consisting of hundreds or thousands of instruments, the configuration challenge becomes critical. We propose to address the problem through automation of the configuration process, which will be achieved at several levels. Automated configuration will simplify the system operator's task of building and maintaining the observatory network. We describe a small, low-powered information storage device which we call a "sensor puck". When plugged into a suitable computer (lab workstation, deployed observing node), information can be written to or read from the puck. While an instrument is being prepared for initial integration into the observatory, a technician "loads" a puck with information necessary to configure the instrument within the observatory, and then physically attaches the puck to its instrument. Thereafter the attached puck always travels with its instrument, no matter where it is being installed in the observing network. The information loaded into the puck encompasses whatever is necessary to enable automatic configuration and system integration of the instrument when it is plugged into the observatory network, and any other information required by observatory policies. This information may include structured descriptions of the instrument's sensor and data characteristics (metadata). The information can also include actual software code that is retrieved from the puck and executed by an observatory node when the device is plugged in; this code could implement distributed instrument control and data retrieval interfaces, allowing network-wide access to the instrument functionality. We believe the puck concept to be a powerful one; a given instrument puck is configured just once, enabling automatic configuration of its instrument no matter where it is installed on the network thereafter. We also describe mechanisms by which an instrument and its puck can be "discovered" by the observatory network when the devices are plugged in. Several approaches are explored, with varying degrees of automation. We evaluate these approaches with special consideration to electrical and safety aspects of the undersea environment. Information and results from our prototyping efforts will also be presented.
Optical Hydraulic Pressure Sensor using Frequency Shifted-feedback Laser for Ocean-Bottom-Tsunami Sensing
Takefumi Hara, Fumihiko Imamura, and Hiromasa Ito
Abstract:
We propose and demonstrate a hydraulic pressure measurement using an optical frequency domain reflectmetry technique in combination with a fiber-optic sensor for all optically real-time geophysical observatory system on deep seafloor. The hydraulic pressure causes a change in the optical strain of the fiber sensor. The sensor was constructed as Michelson interferometer with dispersion-shifted fiber with 2615-m in round-trip optical length, an optical coupler and two faraday rotator mirrors. It was rolled on a hollow mandrel with an aluminum-alloy material to obtain a linear response as elastic characteristic under the high pressure of 4,000-m depth. The sensitivities of this sensor were -0.0234-ppb/Pa and 28.5-ppm/degree-C, respectively, in hydraulic pressure and water temperature. To detect this slightness strain, we use a frequency-shifted feedback laser as an optical source. This laser cavity is closed via the first-order diffracted light of an intracavity acousto-optic modulator, and its output generates chirped frequency comb. The measuring accuracy of optical strain by using self-delayed heterodyne detection of this laser comes close to frequency accuracy of drive frequency of acousto-optic modulator.
In experimental setup, we obtained 9.6-ppb in standard deviation of optical strain measurement with two seconds period each, it corresponds 41-mm in pressure measurement with above-mentioned sensor and a thermistor temperature sensor for temperature compensation. Further improvement of the measurement accuracy is possible based on this first preliminary experiment.
Reliability Engineering the NEPTUNE Observatory
Paul Bowerman, Harold Kirkham, Gene Massion, George Fox, Philip Lancaster, Steve Lentz, Bruce Howe and Rich Kemski
Abstract:
This paper reviews Reliability Engineering aspects of the proposed NEPTUNE observatory. NEPTUNE has an equipment life requirement of around 30 years, and (because of the local weather) presents limited opportunity for repair. Therefore, it is advisable to model and understand the reliability and maintainability of the system, so as to give some confidence that these factors will be good enough when the system is built. Subsea telecommunications systems and deep space exploration system have some similar considerations in terms of reliability engineering, but they are not identical. Further, the requirements on coastal observatories are likely to be very different from those on deep water ones. Because of these differences, there are likely to be some differences in the way reliability engineering is done. Nevertheless, in all these examples, it is a lot less expensive to revise designs at the early stages of the development process than it would be later. Experience in ocean engineering and in space shows that it is necessary to go beyond what might be termed "reliability arithmetic." It is necessary to use methods and parts that assure the system is built sufficiently reliable and maintainable. Among the factors that influence construction are appropriate parts selection criteria, quality assurance inspections, thorough testing of qualification hardware, understanding and accommodating the shock environment of deployment and maintenance cycles, assuring that there will not be material compatibility issues, minimizing the risk that software will result in system failure, analyzing the hardware designs to assure that they should still work correctly after 30 years and that failures do not propagate, and tracking all anomalies to make sure they are appropriately resolved. Aspects of NEPTUNE's power and communication subsystems are examined in this light, and simulation results presented.
Seafloor Geomagnetic Observatories
Pascal Tarits, Mioara Mandea, Michel Calzas, Christine Drezen and Alain Dubreule
Abstract:
The accurate determination of the main geomagnetic field and its secular variation at the global scale remains limited by the number of observatories and their poor distribution over the Earth's surface, particularly over the ocean areas. This biases significantly the determination of the source field geometry even at very long wavelength. In France, a collaborative action is undertaken to build a semi-permanent seafloor observatory that matches the INTERMAGNET measurement requirements. This observatory comprises a triaxial variometer and an Overhauser magnetometer measuring absolute total field intensity. The main difficulty remains the measurement of the geomagnetic declination, which needs a known geographical reference within a few tens of arc-seconds. We show that the declination may be obtained using a precise mechanical gyro. A full working absolute observatory has been built and tested. The observatory is going to be deployed in the North Pacific ocean at the site H2O in September 2003 along with a US observatory for intercomparison and qualification of the absolute measurement. The whole project has become a reality because of the US initiative to equip a telephone cable between Hawaii and the West coast of the US so that scientific instruments may be powered and data recovered in quasi-realtime. The US and Japan are leading the international effort to re-use abandonned cables for scientific purposes. Soon, new cables are going to be equiped such as in the Philippine Sea. This paper wants to emphasize that through international cooperation, using the expertise (sensors, data qualification, cable handling, etc) available in different countries, the completion of large part of the global networks of geophysical observatories becomes possible with the use of available cables.
Development of Laser Tsunami-meter (P)
Shoji SAKATA, Mikhail A. GUBIN, Akito ARAYA, and Daiske TSUBOI
Abstract:
Observation of tsunami wave heights in off-shore areas by tsunami-meters installed on the seafloor would be very important for mitigation of tsunami disasters, the off-shore observations could be used to precisely predict the arrival times and accurate tsunami heights at the sea shore. The goal of this project is to develop an innovative tsunami-meter that uses precision measurements by laser interferometry, which was adopted in development of borehole laser strain meter of the Sakata-Gubin type. The laser tsunami-meter has advantages over conventional quartz oscillator type instruments, namely, low cost of production and installation, low maintenance cost, higher precision, and long-term reliability. The tsunami-meter discussed here consists of three parts; the under-water part, the land part, and the optical fiber cable. The cylinder wall of the under-water vessel has two thicknesses, and two resonators are arranged to coincident with two perpendicular diameters. The difference of two diameter changes under an external pressure change is proportional to that pressure change. Two lasers in the land part are connected to the two resonators by the optical fiber cable, and servo circuits lock the lasers to the resonators. The beat frequency change between the two resonatorsis proportional to the external pressure change. Changes of the inner diameters due to thermal expansion are expected to be the same when the temperature distribution in the cylinder becomes stationary, this characteristic provides a self-compensation function for temperature changes. Tests under varying water pressures in the factory showed sensitivity of 12MHz (beat frequency)/1cm (water head). This corresponds to 2.6nm (diameter difference)/1cm (water head). The instrument was installed on the sea floor of depth 20m, and we found that the laser often deviated from a locked state. This is due to pressure fluctuations caused by surface waves. We plan to add a cover around the cylinder to greatly reduce the high frequency pressure changes. In deeper ocean areas no cover is necessary since the wave effects diminish to zero on the sea floor. The under-water resonators need only four optical fibers, which are contained in a slender 2mm diameter pipe. This means low cost of production and installation of the cable, in which the maximum length is expected to be of 100km order. The cylindrical vessel contains neither moving parts nor electric circuits and will guarantee a long-time reliability. What is crucially important is reliability of lasers under long-term continuous operation.
Insulation Measurement of Undersea Equipments and Failure Analysis of the Underwater Connector on VENUS System
Junichi Kojima (P)
Abstract:
This paper reports the development of the insulation measuring instrument using ROV developed for the failure analysis of the VENUS system and its measurement result, and also reports the corrosion of the underwater connector which was the cause of failure of the VENUS system. An ocean bottom broadband seismometer (OBBS) was installed at 2,170m-deep on the slope of the Ryukyu Trench with other sensors through the VENUS project in 1999. About three months after the installation of the equipments, this system stopped with the failure of the power supply system of the data transmission repeater. Then, visual investigation was conducted by ROV for cause investigation. Some corrosion was found out around the titanium pressure vessel of the data transmission repeater. Therefore, degradation of insulation occurred in some observation devices and the data transmission repeater which are connected with the underwater pluggable connectors. Therefore, it was presumed corrosion occurred due to the fact that electric current flowed between the equipments. Then, the authors developed the insulation measuring device for observation devices and the data transmission repeater which are installed on the seabed. A ROV is equipped with this equipment. An underwater pluggable connector of the observatory is connected to the connector of this device using the manipulator of the ROV. Measurement is remotely and automatically performed by the onboard equipment. Actual measurement was performed to all nine underwater connectors connected to the data transmission repeater using ROV "KAIKO". After the mesurement, bad insulation was observed by some observation equipment and the data transmission repeater. When expanding the cable in the seabed and installing the observation device on it, there is a possibility the cable being damaged. In addition there is a possibility observation device has some damage by the impact while installing. In order to discover such failure in advance, this insulation measuring instrument is useful. The data transmission repeater was recovered in January 2001, and investigation of the cause of failure was conducted. As a result, insulation deterioration was found in the oil filled underwater connector which connects with the power source section and the data transmission section of the data transmission repeater. It became clear that the pins which supply the power source short-circuit.
Corrosion of the pins advanced due to the fact that very small electric current flows between the pins where high voltage is impressed because the minute moisture was included inside the connector. Finally, it was presumed that the pins short-circuited to the fact that the gold-plating of the pin exfoliates. In order to verify this, the examination was performed as follows.
Several drops of water was put into the plug of a connector, and this plug and receptacle were connected each other. When 100 volts DC were impressed between a pin and body of the connector, the current of dozens of micro ampere flowed. After several weeks, the pin which was impressed DC voltage suddenly short-circuited. This is proving that assumption was right.
Development of Fiber-Optical Microsensors for Geophysical Use
Hiroshi Asanuma, Satoshi Hashimoto, Shin-ichi Tano, Shoichi Takashima, Hiroaki Niitsuma and Yugo Shindo
Abstract:
Technologies related to the Micro ElectroMechanical Systems (MEMS) has been remarkably progressed in this decade, and various kinds of microsensors have been developed using the MEMS technologies. Microsensors have a potential to drastically improve the geophysical instrumentation, because they have advantages in size, weight, sensitivity, mobility, and cost to the conventional sensors. Researchers in Graduate School of Environmental Studies, Tohoku University, Sendai, Japan, have been developing microsensors for geophysical use under the Subsurface Microsensing Project since 1993. The microsensors can be employed in wide area including geophysical exploration, logging, seismic observation, prevention of disaster, and evaluation of structural integrity etc.
In this poster presentation, the authors show principles behind a miniaturized fiber-optic hydrophone and an optical accelerometer. A Fabri-Perot interferometer, which consists of a half mirror at the edge of optical fiber and a full mirror on diaphragm, is fabricated using the MEMS technologies for the detection of dynamic pressure in water and acceleration in both sensors. The design concept, fabrication process, performance and future development plan will be shown.
Pioneering Subsea Fiber Optic and Electric Solutions - Communication interconnect advances and solutions for cabled observatory installation, operation and maintenance (P)
Steven Thumbeck, John Toth, Stewart Barlow
Abstract:
Since the mid 1990's, the growth in subsea exploration and expansion of scientific cabled observatories have resulted with the increased usage and desire for reliable subsea cabling and connections (focusing on wet-mate capabilities.) Installation locations and deployment requirements provide unique challenges that need to be addressed and resolved so long term successful science experiments may be realized. Initial design review, reliability analysis and considerations for component selection will have a significant impact on determining the level of success for a subsea cabled experiment. Following is a discussion and overview with considerations that should be made when specifying and selecting interconnected cabling systems for subsea applications. Attention is given to the selection of materials, functions of operating depth/pressure, and a review of general electrical/optical operating considerations. Specific attention is given to the advances in deepwater, high voltage, and high fiber count interconnection technologies. Considering these new advances will allow for future discussions involving the approaches that may be taken when configuring and installing science projects that may enable new developments within the oceanographic community.