Distributed Acoustic Sensing (DAS)
Fibre-optic sensing for underwater passive acoustic monitoring, sound detection and source localisation
Distributed Acoustic Sensing (DAS) with underwater fibre-optic cables enables large-scale passive acoustic monitoring by transforming existing telecom infrastructure into dense arrays of virtual acoustic sensors (Figure 1). DAS works by sending laser pulses through fibre-optic cables and detecting minute backscatter changes caused by acoustic vibrations. When deployed on subsea cables, this technique can capture sound waves from marine life, vessel traffic, and geophysical events without the need for dedicated sensors.
The main advantage is coverage and scalability. Traditional hydrophone arrays are costly and limited in spatial extent, whereas DAS leverages thousands of kilometres of existing fibre, providing continuous monitoring over vast areas. This approach supports real-time detection of biological sounds (e.g., whale calls — Figure 2), anthropogenic noise, and seismic activity, offering a powerful tool for marine research and conservation at a fraction of the cost of conventional systems.
Current research and development are focused on enhancing DAS systems for underwater passive acoustic monitoring by optimising data collection parameters and developing advanced signal processing techniques. Machine learning-based denoising, signal detection and extraction, and improved beamforming algorithms are key to detecting weak biological signals and reducing ocean noise interference. Accurate localisation and tracking of sound sources, along with real-time data handling and integration with existing observation networks, remain critical challenges.
These advancements aim to transform global fibre-optic infrastructure into scalable platforms for continuous marine monitoring, enabling applications such as marine mammal detection, vessel traffic assessment, and seismic event observation. This approach offers unprecedented coverage and cost efficiency compared to traditional hydrophone arrays.
Current research and development objectives are:
- Optimisation: Gauge length, sampling rates, spatial resolution for better SNR.
- Signal Processing: ML-based denoising, feature extraction, advanced beamforming.
- Localisation & Tracking: Improved algorithms, hybrid DAS + conventional sensors.
- Integration: Real-time data handling, interoperability with observation networks.
- Applications: Marine mammal monitoring, vessel traffic analysis, seismic event detection.
- Goal: Scalable, cost-effective monitoring using global fibre-optic infrastructure.
