By Jay Landers

The rise of the internet has changed the world in profound ways, some highly visible and others less so. Among the latter is the proliferation of telecommunications cables located on seafloors around the world. More than 1 million km of these commercial submarine cable systems exist today, linking communication networks on multiple continents.

Looking to take advantage of such systems, a wide-ranging team of researchers at multiple institutions aims to deploy environmental sensors as part of telecommunications cables that are to be installed in the future.

Key goals of the project include using the sensors to measure such phenomena as ocean bottom temperature, pressure, and seismic acceleration.

Ultimately, the resulting data could be used to improve observations related to climate and ocean characteristics. More critically, widespread deployment of such sensors along the seafloor could facilitate early detection and warnings of submarine earthquakes, tsunamis, and volcanic activity, potentially reducing disaster risks associated with these events.

SMART cables

In 2012, three United Nations agencies — the International Telecommunication Union, the World Meteorological Organization, and the Intergovernmental Oceanographic Commission of UNESCO — established the Joint Task Force, Science Monitoring and Reliable Telecommunications, or SMART, Subsea Cables.

This joint task force is charged with investigating the use of submarine telecommunications cables for ocean and climate monitoring and disaster warning.

The task force is chaired by Bruce Howe, Ph.D., a research professor in the Department of Ocean and Resources Engineering within the School of Ocean and Earth Science and Technology at the University of Hawaii at Manoa. Howe was the lead author of “SMART Subsea Cables for Observing the Earth and Ocean, Mitigating Environmental Hazards, and Supporting the Blue Economy,” an article published Feb. 7 in the journal Frontiers in Earth Science.

Although complicated in nature, the issues to be addressed as part of the design of the SMART subsea cables present “no insurmountable engineering challenges,” Howe says. Rather, the various factors pose a “complex optimization problem” that must account for such additional concerns as cost and the possibility of adding other sensors to the systems in the future, he says.

Multiple benefits

Widespread deployment of SMART subsea cables could greatly boost scientific understanding of conditions related to climate change, ocean circulation, sea level monitoring, and the structure of the Earth itself. At the same time, significant use of the technology could vastly improve current knowledge regarding earthquakes occurring in the Earth beneath the oceans.

“The inclusion of high-sensitivity accelerometers and pressure sensors on SMART cables holds great potential for significant advances for the field of seismology by improving our capacity to detect and locate small earthquakes below the ocean floor, improving our ability to determine the rupture type and dynamics for larger offshore earthquakes, and enhancing our ability to image the interior of the Earth, both locally and globally, from earthquakes occurring all around the globe,” says the journal article.

As of 2021, the global submarine telecommunications network comprises more than 1 million km of cable, which typically is refreshed and expanded every 10 to 25 years. Cable color indicates the approximate time frame when each cable was or will be ready for service. Potential SMART repeaters are indicated as dots, nominally shown here at every 300 km, though actual spacing would typically range from 50 to 120 km. The inset shows a typical repeater. (Cable data provided by TeleGeography’s Telecom Resources and licensed under Creative Commons’ ShareAlike; inset image courtesy of Alcatel ASN; map courtesy of JTF SMART Cables)

With their potentially broad geographic reach, SMART cables have the potential to improve upon the capabilities of existing ocean-based tsunami detection systems. “As a tsunami warning system, SMART cables can provide broader coverage and greater reliability than the existing network of moored/buoy-based detection systems,” the journal article states. More accurate data regarding tsunami activity can save lives as well as minimize the likelihood of unnecessary warnings and evacuations.

Tsunamis typically result from large earthquakes below or near the ocean floor. Approximately twice a year, tsunamis occur that result in damage or deaths near their source, according to the website for the U.S. Tsunami Warning System, which is run by the National Weather Service within the U.S. National Oceanic and Atmospheric Administration. Tsunamis that cause damage or deaths on distant shores, defined as more than 1,000 km away, occur twice a decade, according to the website.

Integrating the sensors

The SMART subsea cable systems comprise multiple components. “Necessary functional elements include the sensors, digital signal processing, optical transceivers, and associated power supply circuits,” according to the journal article. “Data may be transmitted to shore over fibers added for that purpose or as an out-of-band channel on the main fibers.”

To succeed, efforts to deploy SMART subsea systems must find a way to integrate the technology seamlessly with commercial submarine fiber-optic cables. Such cables already include devices known as repeaters at regular intervals. The repeaters amplify the light wave passing through the cables, offsetting the signal loss that occurs over the long distances covered by the cables.

The sensors at the heart of the SMART subsea systems have to be incorporated into the repeaters, presenting certain obstacles to be overcome. “Adding these elements requires substantial modifications to the repeater leading to several engineering challenges that must be addressed,” according to the journal article.

Although accelerometers can be mounted inside the repeater housing, the temperature and pressure sensors cannot because they must be placed in contact with the environment that they are measuring and then connected through the housing to the cable’s internal circuitry, according to the journal article. In addition, “the sensors must be isolated from high voltages present within the repeater.”

The long-term goal is to develop SMART subsea systems having operating and engineering lives of 25 years, the same as for telecommunications cables and repeaters. Even so, “given the large numbers of sensors, it is probable a few will fail,” Howe says. “This will be mitigated with redundant sensors in a repeater and/or in adjacent repeaters.”

As the article notes, preliminary simulations indicate that long life of the sensors “will require some level of redundancy, particularly in the optical transceiver functions.”

Projects in development

The cost to deploy the SMART subsea systems is expected to total approximately 10% of the expense associated with installing a telecommunications cable. Typical submarine cable system costs range between $20,000 and $40,000 per kilometer, according to the journal article.

In November 2021, the nonprofit Gordon and Betty Moore Foundation awarded a $7.2 million grant to the University of Hawaii to support the development of the overall SMART initiative as well as the integration of SMART sensors into a subsea telecommunications cable in the Vanuatu-New Caledonia region of the South Pacific Ocean. This project is in the planning phase.

Other projects in various stages of development include a demonstration effort involving a 19 km long cable to be deployed in the western Ionian Sea by two Italian research institutes. In French Polynesia, the government is considering the inclusion of SMART subsea technology as part of a planned 820 km extension of an existing undersea cable system. Meanwhile, in Portugal, an existing 3,700 km undersea cable system linking the mainland with the Azores and Madeira archipelagoes is scheduled to be replaced in the next several years. The government is requiring that the replacement include environmental and seismic monitoring capabilities.

SMART systems are under consideration in other parts of the world, including the Mediterranean Sea; Indonesia; mainland New Zealand to the Chatham Islands; New Zealand to McMurdo Bay in Antarctica; Chile to King George Island, off the coast of Antarctica; Chile to Sydney, Australia; and Norway to Japan via the Northwest Passage along the northern coast of North America.

The Joint Task Force, SMART Subsea Cables is endorsed as a project of the United Nations’ Decade of Ocean Science for Sustainable Development, which extends from 2021 through 2030. In this context it is affiliated with the Intergovernmental Oceanographic Commission’s Tsunami Program and the Ocean Observing Co-Design Program, part of the Global Ocean Observing System.