Submarine fiber optic cables form the backbone of global telecommunications, carrying over 99% of intercontinental internet traffic. As of 01/2026, more than 550 active submarine cable systems span approximately 1.4 million kilometers across the world's ocean floors, connecting continents and enabling the digital economy. However, these cables represent far more than mere data highways. They traverse some of the most scientifically significant yet poorly monitored regions of our planet, the deep ocean basins that cover over 70% of Earth's surface.

The deep ocean remains one of the least understood environments on Earth. While we have detailed maps of Mars and the Moon, more than 80% of the ocean floor remains unmapped and unexplored. This knowledge gap has serious consequences for climate science, disaster preparedness, and our understanding of Earth systems. Ocean temperature changes drive weather patterns and climate trends, seismic activity on the seafloor can trigger devastating tsunamis, and ocean dynamics influence everything from sea level rise to marine ecosystems.

Recognizing this opportunity, the International Telecommunication Union (ITU) approved two groundbreaking recommendations in August 2024: ITU-T G.9730.1 (Dedicated scientific sensing submarine cable system) and ITU-T G.9730.2 (Scientific monitoring and reliable telecommunication submarine cable systems). These standards establish the technical framework for transforming submarine telecommunications infrastructure into a global distributed sensor network, capable of monitoring ocean conditions, detecting seismic events, and providing early warning of natural disasters.

This approach offers a unique solution to a long-standing problem. Traditional oceanographic monitoring relies on research vessels, autonomous buoys, and satellite measurements, all of which are expensive to deploy and maintain, particularly in remote ocean regions. A single oceanographic buoy can cost hundreds of thousands of dollars and requires regular servicing. By leveraging existing submarine cable infrastructure and incorporating sensors into new cable deployments, we can create a persistent, high-resolution monitoring network at a fraction of the cost of dedicated systems.

The scope of these new ITU-T recommendations extends beyond simple sensing capabilities. They address the complete system architecture, from sensor specifications and power requirements to data communication protocols and integration with existing telecommunications systems. G.9730.1 covers dedicated scientific sensing cables where monitoring is the primary function, while G.9730.2 addresses SMART (Scientific Monitoring And Reliable Telecommunication) cables that combine both telecommunications and sensing capabilities without compromising either function.

This article provides an in-depth examination of both recommendations, exploring their technical requirements, system architectures, implementation challenges, and the potential impact on climate science and disaster preparedness. We will analyze the sensor technologies, power feeding strategies, data communication methods, and reliability requirements that make these systems viable. For engineers designing the next generation of submarine cable systems, policymakers considering infrastructure investments, and scientists seeking to expand ocean monitoring capabilities, understanding these standards is essential for realizing the vision of a globally connected ocean observing network.

1.1 From Pure Telecommunications to Dual-Purpose Infrastructure

The concept of using submarine cables for scientific monitoring is not entirely new, but it has evolved significantly over the past two decades. Early experiments in the 1990s and early 2000s demonstrated that telecommunication fibers could detect seismic activity through changes in signal propagation. Researchers discovered that earthquakes and ocean bottom pressure variations caused measurable strain in the fibers, which could be detected using sensitive interferometric techniques.

In 2010, a seminal paper by You in the journal Nature proposed harnessing telecommunications cables for science, arguing that the global submarine cable network represented an untapped resource for ocean and Earth observation. This sparked interest from the scientific community, leading to several pilot projects. The HFAST (Hawaii Scientific and Forensic ATlas) experiment in 2008 successfully used a 6,400 km submarine cable to detect earthquakes on the other side of the Pacific Ocean, demonstrating the potential of fiber-optic sensing for seismology.

The 2011 Tohoku earthquake and tsunami in Japan served as a catalyst for more serious consideration of submarine cables for disaster warning. The tsunami caused over 18,000 deaths and demonstrated critical gaps in ocean-based early warning systems. While coastal tide gauges and the Deep-ocean Assessment and Reporting of Tsunamis (DART) buoy network provided some warning capability, vast stretches of the Pacific Ocean remained unmonitored. The disaster highlighted the need for dense, persistent monitoring infrastructure that submarine cables could provide.

In 2012, the SMART Cables initiative was launched as a joint task force among the ITU, World Meteorological Organization (WMO), and the Intergovernmental Oceanographic Commission (IOC) of UNESCO. This collaborative effort brought together telecommunications experts, oceanographers, seismologists, and climate scientists to develop practical approaches for integrating scientific sensors into commercial submarine cable systems. The task force worked on technical specifications, business models, and policy frameworks to make SMART cables a reality.

Several demonstration projects paved the way for the 2024 ITU-T recommendations. The CAM (Continent Azores Madeira Islands) cable ring, deployed in 2020, incorporated scientific sensors for earthquake and tsunami monitoring in the Atlantic Ocean. The project demonstrated the feasibility of including temperature, pressure, and acceleration sensors in repeater housings without compromising telecommunications performance. Data from the CAM system has been successfully used to detect seismic events and monitor ocean conditions, validating the SMART cable concept.

Parallel developments in fiber sensing technology also contributed to the evolution. Distributed Acoustic Sensing (DAS) and Distributed Temperature Sensing (DTS) technologies matured significantly between 2010 and 2025. These techniques allow the fiber itself to act as a continuous sensor along its entire length, detecting vibrations, temperature changes, and strain without requiring discrete sensor packages. While DAS and DTS are complementary to the point-sensor approach specified in G.9730.1 and G.9730.2, they demonstrate the versatility of fiber optic cables for environmental monitoring.

1.2 Key Drivers for Standardization

The development of ITU-T G.9730.1 and G.9730.2 was driven by several converging factors. First, the cable industry needed clear technical standards to ensure compatibility and interoperability. Without standardized interfaces and requirements, each SMART cable project would need custom engineering, increasing costs and complexity. The ITU-T recommendations provide a common framework that vendors can design to, enabling economies of scale.

Second, the scientific community required assurance that sensor data would meet quality standards for research and operational use. Climate scientists need precisely calibrated temperature measurements with known accuracy and drift characteristics. Seismologists need accelerometers with specific bandwidth and sensitivity requirements. Tsunami warning centers need pressure sensors with rapid sampling rates and low noise floors. The ITU-T standards specify these performance requirements, ensuring that SMART cables produce scientifically useful data.

Third, cable owners and operators needed confidence that adding sensors would not compromise the reliability or performance of the telecommunications system. Submarine cables are designed for 25-year lifetimes with extremely high availability requirements. Any modification that increases failure rates or degrades signal quality is unacceptable. The G.9730.2 recommendation specifically addresses this concern by requiring complete isolation between the "telecom part" and the "observer part" of the system, ensuring that sensor failures cannot affect communications.

Fourth, funding agencies and governments considering investments in SMART cables needed technical specifications to inform planning and procurement. The ITU-T recommendations provide a reference that can be cited in requests for proposals, funding applications, and international agreements. This facilitates the business and policy aspects of deploying SMART cables alongside the technical implementation.

2.1 Core Sensor Types and Performance Specifications

Both ITU-T G.9730.1 and G.9730.2 specify three essential sensor types that form the foundation of scientific monitoring capability: temperature sensors, pressure sensors, and three-axis accelerometers. These three sensor types were chosen based on their ability to address the primary scientific and safety applications: climate monitoring, tsunami detection, and seismic observation. While additional sensor types such as salinity sensors, hydrophones, and seismometers may be incorporated depending on specific application requirements, the three core sensors represent the minimum configuration for a system to be considered scientifically useful.

Temperature Sensors

Ocean temperature measurements are critical for climate science. The ocean absorbs over 90% of the excess heat from global warming, and changes in ocean temperature drive weather patterns, sea level rise, and marine ecosystem changes. However, deep ocean temperature measurements are sparse, with limited coverage in many regions. Submarine cable temperature sensors can provide continuous, long-term monitoring of ocean bottom temperatures in areas that would otherwise be unobserved.

The ITU-T recommendations specify several key parameters for temperature sensors. The measurement range must cover 0 to 40°C, encompassing the full range of ocean bottom temperatures from polar to tropical regions. Initial accuracy should be within 0.002°C, which is sufficient for detecting climate-relevant temperature changes. Long-term stability is particularly important for climate applications, sensor drift must be characterized and should remain within acceptable bounds over the 25-year design life of the cable system. Sampling rates of 0 to 0.5 Hz are specified, allowing for detection of both gradual climate trends and faster oceanographic phenomena.

Temperature sensors must be "wet," meaning they require direct contact with seawater to provide accurate measurements. This presents engineering challenges, as any seawater contact creates the potential for a fault that could propagate to the power feeding system. Careful isolation using DC-DC converters and optoisolators is required to ensure that a sensor fault cannot compromise the entire cable system. The sensor housing design must also ensure that temperature equilibrates rapidly with the surrounding water while maintaining the mechanical integrity needed to withstand the harsh submarine environment.

Pressure Sensors

Pressure sensors serve multiple critical functions in submarine cable monitoring systems. For tsunami detection, pressure sensors can detect the small changes in water column height (typically 1-2 cm) associated with tsunami waves passing overhead. These pressure variations propagate to the seafloor and can be measured with sufficient sensitivity. For seismology, pressure sensors complement accelerometers by detecting vertical ground motion associated with earthquakes. For oceanography, pressure sensors provide absolute water depth measurements that can be used to monitor tides, sea level changes, and oceanographic processes.

Sanjay Yadav

Optical Communications & Network Automation Expert | Author of 3 Books for Optical Engineers | Founder, MapYourTech

Optical networking engineer with nearly two decades of experience across DWDM, OTN, coherent optics, submarine systems, and cloud infrastructure. Founder of MapYourTech. Read full bio →

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