Listening to the Deep: How Fiber Optic Cables are Revolutionizing Underwater Surveillance
A vast, pre-existing infrastructure - over 2 million kilometers of fiber optic cables laid along the ocean floor – is being repurposed for a groundbreaking application in anti-submarine warfare: Distributed Acoustic Detection (DAS). originally designed for high-speed data transmission, these cables are now functioning as enormous, passive sonar arrays, capable of detecting, classifying, and tracking submarines, surface ships, and othre underwater activity along crucial sea lanes.
What began as a theoretical concept is rapidly transitioning into a practical defense capability. DAS leverages standard fiber optic cables as extended chains of acoustic sensors. A pulsed laser is sent through the cable, and minute variations in the backscattered light reveal vibrations or stress caused by nearby sound waves.These signals essentially “bounce off” underwater objects, indicating their presence, direction, and even approximate size.
Complex algorithms analyze these patterns to pinpoint underwater sounds – from the distinctive hum of submarine engines and the cavitation of ship propellers to even seismic events. This effectively transforms existing telecommunications cables into a continuous, real-time monitoring system, capable of “listening” to the ocean across thousands of kilometers at a significantly lower cost than customary sonar or hydrophone networks.
Recent research has validated DAS’s effectiveness in both deep and shallow water environments, demonstrating its ability to accurately track vessels. This is further enhanced by integrating acoustic readings with ships’ GPS or Automatic Identification System (AIS) data using artificial intelligence.
Consequently, nations including the United States, the United Kingdom, Australia, and several European countries have initiated programs to incorporate DAS into their broader maritime surveillance frameworks. Interest isn’t limited to these nations; China and Russia are also actively exploring the potential of DAS technology. China, with its exceptionally dense network of undersea cables, is highly likely evaluating DAS for both surveillance and counter-sabotage operations.
The core of DAS technology lies in the use of an ”interrogator” – a sensor that sends pulses of laser light through the fiber optic cable. Microscopic imperfections within the fiber cause the light to scatter back towards the interrogator. When acoustic energy from a passing submarine exerts pressure on the cable, it subtly alters the intensity of this backscattered light. The interrogator then receives and analyzes these changes, using algorithms and AI to interpret the patterns and locate the sound source.
This approach is especially beneficial as it utilizes an existing network, providing a constant stream of real-time data that can detect even the faintest underwater activity. Beyond military applications, DAS is also proving valuable in detecting cable tampering and monitoring natural phenomena like earthquakes.
Though,the sheer volume of data generated by the system necessitates advanced AI processing to filter out noise and identify meaningful signals. Perhaps the most notable challenge lies in control and access. The vast majority – 99% – of these undersea cables are owned by large telecommunications companies like Google and Microsoft, with the remaining portion having governmental investments. Determining who utilizes the sensors and on which cables presents a complex logistical and political hurdle, potentially more challenging than the technological growth itself.
