Objectives of the Committee
This committee was established to perform technical feasibility study
on the "Globe monitoring submarine cable network of the next generation",
and to summarize a proposal. The aim of the "Globe monitoring submarine
cable network of the next generation" is to perform various observations
continuously and in the long run by installing many sensors two-dimensionally
on the seabed using the cable network. It will provide us with a platform
that can be used in many fields, such as oceanography, geophysics, seismology,
and marine biology. It will bring us various knowledge that can not be
obtained with conventional method, and will create new science.
The result of the feasibility study is reported as a paper or a white
paper. The following is the outline of the report.
The "globe monitoring submarine cable network" is named ARENA
(Advanced Real-time Earth monitoring Network in the Area). Figure 1 shows its image.
It is known that the ocean that occupies 70% of the earth's surface
has big influence on earth environment, such as global warming. Moreover,
the ocean provides us with rich fishery resources and mineral resources.
It is important to understand the nature of the ocean deeply in order
to maintain earth environment and to continue maintainable development.
For that purpose, it is necessary to install many sensors in the ocean,
and to perform measurement continuously over a long period of time.
Moreover, it is known on the plate boundary under the seabed around
the Japanese Islands that a great earthquake will occur periodically.
In order to promote the research on such an earthquake and to mitigate damage,
it is important to deploy many sensors, such as seismometers, to the seabed
of the earthquake zone, and to perform continuous observation over a long
period of time.
Eight cabled observation systems have already been built around Japan
until now as shown in Figure 2. Most of these
cabled observation systems are for earthquake observation. It is confirmed
by the previous studies that using the cabled seismometers, the estimation
accuracy of earthquake center and the sensitivity of measurements were
improved, and more information concerning earthquakes under the seabed
that can not be obtained otherwise were obtained.
A cabled observation system can perform continuous observation in
real-time over a long period by providing electric power and signal transmission
line to the sensors through the submarine cable. It can observe earthquakes
but also marine organism, marine environment, heat flow, substance movement,
etc. Off-Hatsushima system and Off-Muroto system that Japan Marine Science
and Technology Center (JAMSTEC) developed, for example, are performing
multi-purpose observation using the comprehensive observation station
equipped with many sensors including television cameras and acoustic
current meters.
Cabled observation systems draw attention overseas as well. In the
U.S. and Canada, the new cabled observation system NEPTUNE over the
full length of 3,000km in the northwestern Pacific Ocean is proposed
and advancing. In Europe, the ESONET cable that stretches from Norway
to the Mediterranean is proposed.
On the other hand, related technology has also progressed rapidly
recently. The underwater telecommunication cable technology experienced
major breakthroughs of optical amplification technology and wavelength
division multiplex technology science it was put into practical use in
1987. Its transmission capacity becomes more than 10,000 times of the early
system. These advances enable the construction of more flexible cabled observation
systems. Technology, such as a computer and the Internet, is also remarkably
progressed. The observation technology in the seabed has also developed
by leaps and bounds in several of these years.
Due to the advances of the related technologies, the basic technology
for the cabled observation system of next generation with new feature
becomes matured. Then, IEEE OES Japan Chapter organized the "Technical
Committee on Globe Monitoring Cable Network" in February 2002, and conducted
the technical feasibility study.
Seismology and Geodynamics
Most of the seimogenic zone around Japan lies beneath the ocean.
ARENA network will provide a long-term and realtime seismic monitoring
network with 50 km intervals in which broadband seismometers(1000sec -
10Hz) will be connected. Arrays of short-period seismometers (1-30Hz)
will also be deployed for dense seismic monitoring in the particular interesting
area.
S wave is especially sensitive to the existence of the fluid which
often causes the slide of the plate boundary. The realtime monitoring
of time-series variation of S wave will contribute to the long and short-term
prediction of the earthquake occurrence. Horizontal hydrophone arrays
on the seafloor and vertical arrays in the water column will also improve
interpretation of observations. ARENA systems will include broadband
seismometers which are placed in IODP boreholes to isolate them from the
noise of ocean waves.
ARENA system will also provide geodetic monitoring. As pre-slips
observed before some big inter-plate earthquakes are quite small, the
monitoring close to the seismogenic zone with high sensitivity is required.
Strain meters (10-9 strain) and tilt meters (10 nano-radian) will deployed
in boreholes in order to directly measure deformation of rocks.
A combination of sea surface kinematic GPS positioning and underwater
acoustic positioning will provide long-term plate-scale horizontal geodetic
measurements of the distribution of strain across plate. A horizontal
seafloor acoustic ranging system with resolution of 1 cm is also feasible
for monitoring the movement across a big fault.
Ocean bottom pressure monitoring is important for seafloor geodesy
(3), physical oceanography, and tsunami warning system.
Ocean Circulation Research
The ocean current transports water mass with heat, salinity, plankton,
various dissolved materials, and influences the climate and environment.
The dynamics of this ocean circulation and the roles in water mass formation
and climate change are important research items.
In the North Pacific the variations in velocity and current path
of the Kuroshio greatly influence the global climate and our economy.
The Japan Sea is a semi-enclosed deep marginal sea surrounded by Japan,
Korea, and Russia, influences climate, fishery, and marine pollution in these
countries. Although the Japan Sea is connected with open sea (the North
Pacific, the East China Sea, and the Sea of Okhotsk) through three shallow
straits, the Japan Sea is mostly isolated from the open sea. The Japan Sea
Proper Water is formed and extended by the intermediate and deep circulations.
ARENA network will provide a real-time, long-term monitoring system using
subsurface moorings which measure current, water temperature, salinity,
turbidity, oxygen, according to need.
Deep water carries vast heat and materials, and concerns a control
of climate changes and a global warming. The long-term real-time direct
current measurements using mooring current meters at several key sites
will clarify the routes of deep currents in the North Pacific.
Data from ARENA combined with data from Argos floats, satellites
will contribute to develop a high-resolution ocean models, estimate fields
of ocean temperature, salinity, velocity, nutrients, and plankton production.
Methan Hydrates Monitoring
Methane hydrates have been expected as a potential source of hydrocarbons.
Japan is keen on commercializing methane hydrates because Japan has depended
mostly on imports of fossil fuels. The Nankai Trough is one of sea area
where methane hydrates were found. The reserves are estimated at 77 trillion
cubic meters.
However, methane as greenhouse gases would cause environmental disruptions
if they are incorrectly handled. Detailed scientific studies are indispensable
to the commercialization of methane hydrates. There are a number of problems
that must be overcome before commercialization of methane hydrates.
Studies on methane hydrates are an important objective of the Integrated
Ocean Drilling Program (IODP). The IODP will scientifically study how
methane hydrates are formed, their properties, their reserves, and their
impacts on environmental changes. Achievements to be made by the IODP will
greatly contribute to commercialization of methane hydrate reserves.
Methane hydrates exist in the form of ice beneath the methane hydrate
layer. The proposed digging method is to inject steam or seawater into
the methane hydrate layer, to melt the methane hydrates, and to extract
methane. The collapse of layers above a methane hydrate layer is anticipated,
if methane hydrates are artificially melted. A new instrument connected with
ARENA network will play a role for monitoring of longer-term shifts of the
hydrate deposit boundaries.
Hydrothermal Flux Research
ARENA will enable studies of hydrothermal flow to understand the
energy, mineral, and hydrogen potential of hydrothermal fluids.
Chemical/physical/acoustic sensors will monitor vent flow, and moored
vertical sensor chains will monitor the plume above the target field. Video
camera will show the changes in organism behavior. Interactive experiments
connected ARENA will sample the organism and analyze it. ARENA includes
autonomous underwater vehicles (AUVs) that will be guided on wider surveys
over the vent field.
On the other hand, AUVs can expand the survey coverage of the vent
field. AUVs will park in the docking system of ARENA observation node
until the next mission for a long-term and will periodically survey the
area. AUVs will get electric power to recharge their batteries from the
cable network, and exchange data and command through the cable network.
Biology and Fishery Research
ARENA will provide long-term realtime measurements of subsurface
water properties, water chemistry, and plankton populations with acoustic,
optical, and chemical sensors. This time series data of plankton abundance,
nutrient and oxygen will be used for future fisheries management.
Marine Mammals Research
The ocean ecosystem is threatened by a large-scale change in a climate,
the diffusion of the pollutant, and so on. The whales that are the top
predator of oceanic food chain can be used as an indicator of the sustainable
ecosystem of the ocean. However, it was only possible for a short period
of time that it monitor the migratory patterns of the whales and other large
marine mammals. The hydrophone arrays of ARENA will allow detailed real-time
monitoring of its migratory patterns and feeding behavior.
Deep Sea Microbiology Research
The knowledge about ecosystems of the microorganisms inhabiting in
extreme environments such as deep-sea and deep-subsurface will reveal
the horizon of world of life. Microorganisms can also be used as an indicator
of characteristics of environments. Functional genes are useful biomarker
for the environmental property.
Although molecular biological technique based on gene analysis is
one of the major research methods for environmental microbiology, the technique
is time consuming and non-real time in principle. For more detailed and
accurate study on ocean environmental microbiology, in situ miniature genetic
analysis system which is automated or remotely controlled analyzer required.
The in situ genetic analysis system connected with ARENA network
will provide realtime and long-term data on physical and chemical properties
of the circumference seawater.
Outline
and Features of ARENA
The committee summarized the basic design for the
"Globe monitoring submarine cable network of the next generation" having
the following features as a result of the technical feasibility study.
The details are shown in the white paper.
Mesh-like Cable Architecture
The conventional cabled observation system consists of one submarine
cable to which sensors are connected. However in order to cover the
vast observation area and to increase the accuracy of measurement, it
is required to deploy many kind of sensors two-dimensionally. Then,
in ARENA, the cable network with mesh-like architecture as shown in Figure 3 was proposed. Two trunk cables are placed
on the both side of the Japan Trench. Observation nodes are arranged at
intervals of 50km in the trunk cables. Various sensors will be connected
to observation nodes. It becomes possible to place various kind of sensors
two-dimensionally in the vast research area by adopting mesh-like cable
architecture.
Although such a mesh-like cable network design is proposed also by
NEPTUNE, it is a completely new design that is not in the conventional
telecommunication cable system or in the submarine cable system for
observation.
In the committee, feasibility studies on power feeding system, a
data transmission system, underwater system and the construction / maintenance
method, were performed supposing the network of Figure
3. In order to simplify the study, a simplified engineering
model (Figure 4) was used for analysis.
Configuration of the Observation
Node
Each sensor is connected to the trunk cable through UHU (Underwater
Hub Unit) and NBU (Node Branching Unit), as shown in Figure
5.
Although UHU is also directly connectable with NBU, it is also connectable
with NBU through other UHU(s). The UHU can be placed dozens of km away
by connecting it with another UHU or NBU using a long extension cable.
Many sensors are connected in the shape of a tree within each observation
node. It is the same structure as connection of Ethernet. Since UHU
is separated from the trunk cable, it does not need to cut or recover
trunk cables when repairing or maintaining UHUs.
Each sensor is connected to UHU with underwater mateable connector.
Therefore, when these sensors break down, or when maintenance is required,
these sensors can be separated to be recovered and it can be re-installed
after maintenance. At this time, influence of the breakdown and repair
works hardly reach to other sensors. Moreover, it also becomes possible
to make additional connection of sensors developed newly.
Since NBU is inserted in the trunk cable, it has big influence on
power feeding and communication of the trunk cable, when performing repair
works. Therefore, NBUs are required to be simple and to have high reliability.
High Resistance against Fault
In order to repair the sensor installed on the seabed, it is necessary
to secure a work ship for several days. Therefore, considerable expense
and prior preparation are needed for repair. Although it is also important
to raise the reliability of the apparatus installed on the seabed. However,
considerable time and expense is needed to realize the high reliability
that is equal to the reliability of an artificial satellite or the underwater
telecommunication cable system. Then, it is not realistic to make all
the system extremely reliable.
In ARENA, even if a fault occurs to submarine apparatus, it is being
considered that the range influenced by the fault is limited as much
as possible. Moreover, for the trunk cable only those technologies that
are practically used of the underwater telecommunication system, and
their reliability is established will be used.
The mesh-like cable network has high resistance against faults. That
is, when a fault occurs in a submarine cable and the data transmission
and electric power feeding between an observation node and a landing station
on land disrupted, power feeding and data transmission can be performed
from other landing stations by changing a connection route. Moreover,
if a fault should occur, it is also important that the position of the
fault can be correctly measured from the landing station. The fault location
method is also studied and proposed in ARENA.
As described above, each sensor is connected to UHU with the underwater
mateable connector. Therefore, using a remotely operated vehicle, the
broken sensor can be separated from other systems, and can be recovered.
This has also heightened the resistance against fault as the whole system.
ARENA aims at securing reliability as the whole system, without raising
the cost more than necessary.
Constant Current Power Feeding
System
The underwater telecommunication cable has the concentric structure
as shown in Figure 6, in order to protect an
optical fiber from water pressure and tension. Thus, in an underwater
telecommunication cable, since there is only one electric supply line,
the return current flows in the seawater. This has big influence on the
power feeding system. This constant current power feeding system provides
a constant current to the underwater cable from a landing station. Usually,
the current with reverse polarity and the same value is provided simultaneously
from the landing station at the other end of the cable.
This constant current power feeding system has some important features.
The first feature is that it has strong resistance against the shunt
fault of the underwater cable. As shown in Figure
7, even if a shunt fault occurs in an underwater cable, the constant
current is can be supplied continuously from landing stations at the
both end of the cable. Only the electric potential along the underwater
cable is changed. Therefore, if the optical fiber in a cable is not cut,
it can transmit optical data continuously.
The 2nd feature is that the power supply circuit in the underwater
repeaters inserted into the underwater cable is made very simply. Usually,
zener diodes are inserted in an electric supply line in series, and electric
power is supplied to an electronic circuit using the voltage difference
produced by the zener diodes.
The 3rd feature is that it does not need a sea water ground for the
electric power circuit in a submarine repeater. Therefore, insulation
against seawater is easily secured by covering the whole electronic circuit
with insulators, such as polyethylene. As the potential in an underwater
cable is very high (about 10kV maximum), it becomes a big merit when mounting
an electronic circuit.
Since the whole power supply circuit is insulated from seawater,
the 4th feature is that it can measure the distance to a shunt fault
point by measuring the resistance from the both end of the underwater
cable.
The 5th feature is that it can be applied to the underwater cable
that has only one electric supply line.
Except for some exceptions, since faults actually occurred in an
underwater cable are shunt faults, the above-mentioned feature has
a very important meaning.
Flexible Optical Data Transmission System
As mentioned above, the underwater telecommunication system has experienced
the rapid development recently through the breakthrough of optical
amplification technology that amplify the optical signal directly,
and wavelength division multiplex technology that enables plural wavelength
transmit through one optical fiber simultaneously. As the architecture
of the optical amplifier is simple and the number of devices is few,
highly reliable system with modest cost is commercially available. Moreover
as it is free from bit rate and formula of encode, it provides larger freedom
to the design. In addition, a network with complicated architecture can
easily realized using wavelength division multiplex technology.
Figure 8 shows the fundamental structure
of the proposed optical data transmission system. The both ends of the
underwater cable are connected to landing stations. It can secure high
reliability as commercialized parts for the underwater optical telecommunication
cable system, such as an optical amplifier and a wavelength division multiplexer
can be used in the backbone system.
Individual wavelength is assigned to each observation node.
The Ethernet switch in each observation node is connected directly
to the landing station. Therefore, even if the Ethernet switch in an
observation node should fail, it does not affect the communication
of other observation nodes. Since Internet Protocol is adopted as a
transmission protocol, it is easily connectable with IP network on land.
That is, it becomes possible to access directly sensors installed on the
seabed from the personal computer in a laboratory. Since increasing the
number of wavelength can increase the quantity of an observation node,
extension of a system can also be made flexible.
Figure 9 shows an example of assignment
of wavelength. By using two optical fibers, each observation node can
be accessed from two landing stations that heighten the resistance against
cable faults. Other dedicated wavelength is assigned to HDTV (High-Definition
Television) signal transmission that needs a high bit-rate. The other wavelengths
are assigned to time synchronizing signal with one microsecond precision,
to the backbone transmission line that connects between landing stations,
to surveillance of the data transmission system and to spare line.
Future vision of ARENA
In the feasibility study, though OFF-Sanriku area is supposed,
the area ARENA covers extends to throughout Japan (Figure
10). ARENA is the system that has rich extendibility. Furthermore,
it might extend to along the Aleutian Islands in the future, and it
will unites with NEPTUNE or a possibly will extend from the East China
Sea to the Philippine Sea.
Constitution of the Committee
45 engineers participated in the committee from universities, the
research organization, and the private enterprise. Three working groups
were organized that were for power feeding system, data transmission system
and underwater system including construction and maintenance technology.
The committee proposed the new scientific submarine cable network ARENA
in January 2003.
Chair ： Yuichi Shirasaki （Institute of Industrial Science,
University of Tokyo)
Secretary： Kenichi Asakawa (JAMSTEC)
Katsuyoshi Kawaguchi (JAMSTEC)
Working group leaders
(1) Power Feeding System: Yuichi Shirasaki
(2) Data Transmission System (Data Transmission, Time Syncronization,
Protocol, Data Management): Minoru Yoshida (Hakusan Corporation)
(3) Underwater System (Underwater System, Construction, Maintenance,
Reliability): Takato Nishida (OCC Corporation)
Ist Meeting February 14, 2002 14:00～17:40、 29 persons
2nd Meeting January 21
Power Feeding System WG
1st April 4, 2002 14:00-16:00, ５ persons
2nd May 15, 2002 13:00～15:00, 7 persons
3rd June 27, 2002 13:00～14:30, 7 persons
Data Transmission System WG
1st April 9, 2002 10:00～12:00, 10 persons
2nd May 14, 2002 10:00～12:00, 11 persons
3rd June 18, 2002 10:00～12:00, 11 persons
4th November 27, 2002 13:00～15:00, 10 persons
Underwater System WG
1st March 26, 2002 10:00～12:00, 14 persons
2nd May 15, 2002 10:00～12:00, 15 persons
3rd June 26, 2002 10:00～11:30, 18 persons
Content
Chapter 1: Preface
Chapter 2: Outline of the Network
Chapter 3: Power Feeding System
Chapter 4: Data Transmission System
Chapter 5: Underwater System
Outline
(1) Y. Shirasaki, T. Nishida,
M. Yoshida, Y. Horiuchi, J. Muramatsu, M. Tamaya, K. Kawaguchi and
K. Asakawa, "Proposal of Next-Generation Real-time Seafloor Globe Monitoring
Cable-network", Proc. Of OCEANS 2002, pp.1688-1694, 2002
(2) J. Muramatsu, K. Asakawa, K. Kawaguchi and
Y. Shirasaki, "Outline of Earth Observation Submarine Cable System -
ARENA (Advanced Real-time Earth Monitoring Network in the Area) -",
Proc. Of Techno-Ocean 02, SI-4
(3) K. Asakawa, Y. Shirasaki,
M. Yoshida and T. Nishida, "Feasibility Study on Long-term Continuous
Monitoring from Seafloor with Underwater Cable Network", Proc. of
4th International Workshop on Very Large Floating Structures, pp.350-357,
2003,
(4) Y. Shirasaki, M. Yoshida, T. Nishida, K. Kawaguchi,
H. Mikada and K. Asakawa, "ARENA : A Versatile and Multidisciplinary
Scientific Cable Network for Next Generation", Proc. of Scientific
Submarine Cable 03, pp.226-231, 2003
(5) Kenichi Asakawa, Yuichi
Shirasaki, Takato Nishida, Minoru Yoshida, Katsuyoshi Kawaguchi and
Hitoshi Mikada, "Feasibility Study on Scientific Submarine Cable Network
ARENA", Proc. of the 17th Ocean Engineering Symposium, pp.483-490, 2003
(in Japanese)
Application
(1) J. Kasahara, Y. Shirasaki,
K. Asakawa and K. Kawaguchi, "Scientific Application of ARENA Networks",
Proc. of Scientific Submarine Cable 03, pp.272-275, 2003
Powser Feeding
(1) K. Asakawa, J. Muramatsu,
M. Aoyagi, K. Sakaki and K. Kawaguchi, "Feasibility Study on Real-time
Seafloor Globe Monitoring Cable-network -Power System - ", Proc.
of the 2002 Inter. Symp. on Underwater Technology, pp.116-122, 2002
(2) K. Asakawa, J.
Muramatsu, J. Kojima and Y. Shirasaki, "Feasibility Study on Power
Feeding System for Scientific Cable Netwrok ARENA", Proc. of Scientific
Submarine Cable 03, pp.307-314, 2003
(3) Kenichi Asakawa, Junichi Kojima, Jun
Muramatsu and Tatsuo Takada, "Novel Current to Current Converter for Mesh-like
Scientific Underwater Cable Network - Concept and Preliminary Test
Result -", Proc. of OCEANS2003, pp1868-1873, 2003
Data Transmission
(1) M.
Yoshida and Y. Hirayama, "The Data Transmission System for the Real-time
Seafloor Monitoring Cable Netwrok", Proc. of Scientific Submarine
Cable 03, pp.197-200, 2003
Related Meetings and Workshops
(1) SSC03 : International
Workshop on Scientific Saubmarine Cables
Organizers： IEEE OES、Earthquake Research Institute, University
of Tokyo, Institute of Industrial Science University of Tokyo,
Ocean Research Institute University of
Tokyo, Japan Marine Science and Technology Center
June 25-27, 2003, ＠Komaba Campus, University of Tokyo
(2) IUGG:
June 30 - July 11, 2003, @Sapporo
http://www.epsu.jp/jmoo2003/advertising/IUGG_030106.html
Inter-Association Symposium：
"Long-term in-situ Ocean Observatories and
Observations"
