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March 2015 Issue

Reaching Farther With Cabled Ocean Observatories
Robert Thomas
Cabled ocean observatories, such as Ocean Networks Canada, the National Science Foundation’s Ocean Observatories Initiative, and CSnet International’s OCB system, which delivers data to shore via the Poseidon subsea cable network, provide environmental monitoring, tsunami detection, and real-time undersea video. Key benefits of their fiber-optic undersea cables include tremendous data transmission bandwidth and the ability to power systems from shore. As systems like these expand and proliferate, their sensors will provide essential real-time scientific and operational data worldwide. Installing ocean observatories farther offshore and in deeper waters enables scientists to collect data continuously, in remote areas previously accessible only by shipboard observatories or ship-serviced facilities. With a permanent monitoring presence in these locations, we can better understand the geological, physical, chemical and biological processes taking place in the oceans.

Many existing observatories depend on nonrepeatered fiber-optic shore connections, limiting their reach and, thus, the location of data collection. Since the mid-2000s, undersea repeatered (optically amplified) fiber-optic technology developed for international telecom applications has been combined with subsea hardware and connection techniques to provide offshore oil and gas facilities with high-bandwidth, low-latency communication paths. Applying this same technology to cabled ocean observatories extends the reach of both the observatories and their instrument packages.

A cabled ocean observatory includes one or more scientific nodes connected to shore using a powered fiber-optic cable backbone, which may be repeatered depending on distance, enabling the observatory to be electrically powered from shore facilities and exploiting the high bandwidth and low latency of fiber optics.

The primary aspect of extending the reach of observatories is significantly increasing the backbone length via undersea repeaters, enabling the observatory location to stretch to thousands of kilometers from shore in remote deepwater environments.

Repeatered systems rely on electrically powered optical amplifiers spaced regularly (50 to 150 kilometers) along undersea cable. Despite the significant difference between typical telecom capacities (terabits per fiber pair) and the more modest needs of scientific observatories (gigabits per fiber pair), the same fundamental elements of the amplifier product can be used. Today’s erbium-doped fiber amplifier (EDFA) provides a clear channel that can be tailored to support applications with a wide variety of data rates and modulation formats. Economical datacom transceivers, already in use subsea, offer sufficient bandwidth for cabled ocean observatory applications.

The undersea telecom industry has developed specific products for scientific applications that complement repeatered architectures, offering connection flexibility and powering options. A high-current repeater has internal power-conditioning circuits that provide power to the amplifiers and divert excess current, enabling a scientific user to equip a single custom power source that can power in-line repeaters and provide observatory auxiliary operational power.

Dual-conductor undersea cable (DCC) provides two independent electrical paths in one common cable structure. The second conductor provides a fully independent electrical powering path to power branches and undersea devices from diverse power sources.

The secondary aspect of extending the reach of observatories is to improve the quality, reliability and survivability of the extension cables that connect observatory nodes with their instrument packages. Improved platforms, tools and processes are available for secure installation of these cables. Cable connections between nodes and sensors have typically been limited to short distances, approximately 5 to 10 kilometers, for subsea installations using an ROV approach. However, cable-laying vessels are capable of loading and laying more than 10,000 kilometers, easily supporting long extensions. Modern cable-laying vessels are equipped with dynamic positioning class-two technology for precise route placement of cables and use proven cable installation equipment. Most importantly, the ship, all equipment, and crew training are designed for cable laying as the primary mission.

Facilities are available for electronic storage, power testing and splicing of all elements of an undersea system. This makes extension cables in the 10-to-100-kilometer range, or longer, practical beyond the capability of ROV installation.

Deployment pallets have been developed for terminating subsea cable to a multiport, wet-mate connector housing. The independent flying lead design and connection approach has been in use with single-conductor telecom cables in oil and gas applications for nearly a decade and is also suitable for use with DCC.

An alternative approach is to use a single, integrated wet-mate connector and flying lead. This direct-connect architecture is currently in-service with DCC.

Time-proven technologies combined with newer ones will place observatories in unexplored regions. Clear-channel EDFA repeaters, high-current repeaters, dual-conductor cable, and cable-ship installation can position observatories thousands of kilometers from a shore station, changing the very nature of the science that can be conducted. With the objective of extending the reach of ocean science, observatory planners can employ a variety of tools that are currently serving observatories worldwide.

Robert Thomas is a system engineer at TE SubCom (Eatontown, New Jersey) responsible for telecom projects in the scientific and offshore oil and gas areas. For over 30 years he has worked with undersea cable systems in commercial and government applications. The material here summarizes “Extending the Reach of Cabled Ocean Observatories,” originally presented at OCEANS’14 MTS/IEEE St. John’s, Canada.

2015:  JAN | FEB | MARCH | APRIL

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