OPTODAS

THE LEADING TECHNOLOGY FOR DISTRIBUTED ACOUSTIC SENSING

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Distributed acoustic sensing
OptoDas
OptoDAS Interrogator

OptoDAS provides unique characteristics for measurements in the submarine environment:

  • Long range (>150 km) and very low noise
  • High sensitivity with no noise degradation over the first 80 km
  • Spatial resolution equal to the configurable gauge length (down to 2 m whatever the fiber length)
  • Multi-channel capability for simultaneous recording of multiple fibers (2-4)
  • L-band version for co-existence with data traffic
  • Server class recording computer enabling remote operation and extensive RAID storage
  • Software suite providing excellent functionality for instrument control, data management, processing and display

OPTODAS​ TECHNOLOGY

The OptoDAS interrogator is using a unique interrogation technique providing low-noise and long-range quantitative phase measurements in single mode optical fibers.

03 interrogation graph

OptoDAS interrogation technique

The conventional technique for measuring the reflected DAS signal from the fiber is pulsed interrogation where  short pulses are launched into the fiber (grey graph). The OptoDAS technique is frequency swept interrogation where much longer pulses of frequency swept signals are launched into the fiber (green graph).

The consequence is that the fundamental noise limit of OptoDAS is shifted towards fiber lengths above 80 km- resulting in longer range (150 km) and lower noise (< 10 picostrain/rtHz for fiber lengths up to 100 km).

How OptoDAS works

OptoDAS in coexistence with telecom traffic

OptoDAS works well with standard telecom fibers. Normally a dark fiber (no data traffic) is required for DAS recordings. The L-band version of OptoDAS is designed to operate in coexistence with live telecom traffic with no impact to the transmission line capacity and Q factor and with the same specified performance characteristics as the standard C-band version.

The L-band version operates at a wavelength outside the C-band used for telecom traffic and can be multiplexed into the telecom transmission line by use of a C/L filter.

04 connection diagram
05 dual quad

OptoDAS with simultaneous interrogation of multiple fibers

OptoDAS enables simultaneous interrogation of 2, 3 or 4 sensing fibers by use of  an external mux unit. The dual and quad fiber mux option support simultaneous interrogation of multiple fibers without any degradation in the specified performance characteristics of OptoDAS .

Maximum total fiber length of the multiple fibers to be interrogated is limited to 250 km, and the sampling frequency is limited by the total fiber length. No change in instrument noise is introduced.

OptoDAS is accompanied by a recording computer

OptoDAS utilizes a server class computer running the OpenSUSE Linux operating system and is fully configured for operation with the OptoDAS interrogator. The computer is equipped with large RAID disks for data storage (> 60TB capacity, extendable).

The interrogator and computer can be permanently installed in a 19” rack or be assembled in a field rack suitable for shipment and field operation.

The computer features a powerful compute platform with a fast, multicore CPU and large memory. This enables real-time processing and edge-computing workflows with the toolbox of versatile built-in processing modules. The system also allows user access to the compute platform, to run custom software and data endpoint processes. Access to both raw and processed data is enabled from streaming protocols or via file storage in HDF5 format.

06 recording computer
07 software

OptoDAS software suite

The software includes basic features for instrument control, data display and data processing. The control software allows monitoring and control of the interrogator through a graphical user interface. The display software can process and plot real-time data from the interrogator and as well historic data from file. Multiple plots can run in parallel to visualize data from multiple fibre positions. All displays allow for zooming. The processing software includes a toolbox of fully user customizable, real-time processing modules such as temporal and spatial filters, noise suppression, event detection, spectral analysis and data decimation.

.Data acquisition features:

  • External optical switch integration
  • Reoccurring measurement sequences automation
  • Regions of interest (ROI) with customized spatial sampling in different regions.
  • Cyclic storage buffer (configurable) in RAID configuration
  • Configurable storage of raw data and processed data
  • Real-time data processing and display
  • Real-time streaming with ZeroMQ or Kafka-Avro protocols
  • Python library for reading, processing and saving HDF5 files
08 fishing vessel

OptoDAS Submarine Applications

OptoDAS has performance characteristics well suited for applications based on DAS recordings in submarine cables. An application software for cable threat monitoring is available.

Scientific measurements are focusing on tsunami and earthquake early warning systems. Another attractive application is monitoring of marine mammals.   Several scientific organisations worldwide perform research activities with use of OptoDAS.

Both active seismic acquisition and passive micro-seismic monitoring is feasible with OptoDAS.

  • Protection of submarine cables (telecom and power cables) and infrastructure including detection of (i) external threats like fishing activities, anchor drops and unidentified threats and (ii) natural threats like underwater landslides, seismic activity and sea currents.
  • Scientific measurement including monitoring of (i) seismological and geological effects, (ii) marine life and (iii) oceanographic conditions.
  • Seismic monitoring within offshore (i) oil and gas production and (ii) carbon storage – by monitoring in-well cables or seabed cables.
Screenshot

Cable Threat Monitoring

Most submarine cable faults are caused by fishing gear and anchors that snag the cable, causing cable cuts or shunt faults.

Learn more
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Monitoring of Marine Mammals

Baleen whale species are indicators of the health of our oceans and their conservation requires global and reliable monitoring efforts.

 

Learn more
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Seismic Monitoring with OptoDAS

The OptoDAS technology provides cost-effective solutions for  geophysical monitoring of offshore CO2 storage sites.

Learn more

OptoDAS Terrestrial Applications

OptoDAS is also well suited for different terrestrial applications where low noise, long range and simultaneous monitoring of multiple fibers are beneficial characteristics.

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Geological hazards

Monitoring of rock falls, landslides and avalanches

13-Smart-cities

Smart cities/traffic

Detecting position of moving objects, traffic patterns/flows, disruptive events and supporting  autonomous vehicles.

14-railways

Railway

Detecting moving trains (position, speed, anomalies ), third party activity and falling rocks and landslide events (track conditions).

15-border-control

Border control

Intrusion – Detecting moving objects

16-energy-network

Energy distribution network

Health monitoring of aerial power line networks

17 ASN network
Download ASN Cable Map
18 fiber optics

Industry Leader

ASN has continuously led the development of new technologies enabling submarine telecommunication network capacity to meet the growing broadband traffic loads efficiently as well as to connect all territories and islands to the worldwide internet backbone. More than 800,000 km of optical submarine systems are deployed worldwide, enough to circumnavigate the globe 19 times. To the right, the ASN Cable Map – explore the unseen arteries of global connectivity.

The ASN innovative design approach is also found in the development of sensing systems.

Design and Manufaturing

The ASN team located in Trondheim in  Norway has 40 years of experience in designing and manufacturing optical fiber sensing solutions for operation in harsh environment. The unique OptoDAS technology has been designed by this world leading team which has also created the Optowave PRM system  where optical cable networks on the seabed with  several tens of thousands individual optical sensors are interrogated simultaneously by a highly advanced instrumentation system. Some of this technology is utilized to realize the frequency swept interrogation technology of OptoDAS.

The ASN experience from being a manufacturer of  more than 800.000 km submarine cables deployed around the world) is reflected in the OptoDAS manufacturing process established in Trondheim.

Technical Support

ASN has an experienced engineering group in Trondheim providing immediate technical support to OptoDAS customers. A service and maintenance agreement is offered to be included in the two-years standard warranty period. This agreement will provide for an annual performance test conducted remotely by ASN, support on operational issues, spares available from stock and software updates.

19 publications

OptoDAS Publications

A list of key publications and associated abstracts with search function can be found here.

Publications

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How does distributed acoustic sensing (DAS) work?

DAS is a technique for dynamic monitoring of strain distribution along an optical fiber. If a section of the optical fiber is subjected to strain, the propagating light will experience an optical phase delay. By analyzing the back-reflected signal one can extract the optical phase modulations induced along the optical fiber.  Any measurand impacting the cable strain condition can, in principle, be recorded.

Real-time cable threat monitoring software for marine asset protection

Most submarine cable faults are caused by fishing gear and anchors that snag the cable, causing cable cuts or shunt faults. OptoDAS can measure acoustic seabed waves generated by objects moving on the seabed several kilometers away from the cable and track the movement in real time for damage prevention and risk analysis.

The processed detections are co-visualized in a GIS environment with AIS data for vessel identification and situation awareness.

Key Features
  • Enable proactive cable protection by detecting threats in real time
  • Statistical analysis of cable interference for targeted cable protection
  • Real-time data processing for detection, localization, and tracking of seabed objects like fishing gear and anchors
  • Integration with AIS vessel information and standard nautical navigation maps
  • Alerts based on customizable proximity thresholds, and for physical contact with the cable
  • Interactive data analysis in GIS platform with cable routes and metadata inspection
Interfaces
  • Web application interface for end-user interpretation in real-time and historical data visualization
  • Data streams from several OptoDAS instruments can be integrated for monitoring multiple cables
  • Data access from custom dashboards and operating center systems using standard protocols

Wildlife Monitoring with OptoDAS

Baleen whale species are indicators of the health of our oceans and their conservation requires global and reliable monitoring efforts. Using whale sounds to study habitat use, map migration patterns and assess stock is a well-established practice.

Scientists have used one OptoDAS unit to record data from whale vocalizations at the coast of Svalbard by converting the first 120 km length of a submarine telecommunication cable into a DAS array. The whale vocalizations were recorded with remarkable sensitivity (nearly 10 km away from the cable).

Reference: L. Bouffaut et al., “Eavesdropping at the speed of light: distributed acoustic sensing of baleen whales in the Arctic”, Journal of Frontiers in Marine Science (2022).

Seismic Monitoring with OptoDAS

The OptoDAS technology provides cost-effective solutions for geophysical monitoring of offshore CO2 storage sites – with different acquisition geometries by using cables installed in the wells and on the seabed to enhance seismic detection of the plume as well as the overburden.

A small shooting vessel can be used at the surface for time-lapse sensing and imaging. In addition, the cables can also be used for passive sensing of micro-seismic events, as well as monitoring shear wave resonance triggered by background noise or minor earthquakes.

Seismic imaging results for DAS (OptoDAS) and PRM (Optowave). Active seismic was simultaneous collected, with cable alongside the PRM 4C array cable. DAS exhibited higher spatial resolution and detailed seismic imaging compared to PRM in the overburden, despite being a single-component system using a weaker seismic source.

Reference: A. Pedersen et al, “A North Sea case study: Does DAS have potential for Permanent Reservoir Monitoring?”, EAGE Annual 2022.

Micro-seismic event recorded with OptoDAS connected to an in-well cable at an operational CO2 storage site. Raw OptoDAS data display with event of magnitude -0.679.

Reference: S. Wienecke et al.,”DAS interrogation in CO2 injection well for microseismic event detection- technology demonstration during ongoing operation”, SPE workshop In-Well Fiber-Optic Sensing (2023).

OptoDAS Publications

O. H. Waagaard et al, “Real-time low noise distributed acoustic sensing in 171 km low loss fiber”, OSA Continuum, pp 688-701, Issue 2, 2021.
https://doi.org/10.1364/OSAC.408761

Abstract

We demonstrate distributed acoustic sensing (DAS) by interrogation of Rayleigh backscattering from fibers with long linearly frequency modulated pulses and coherent detection. This system provides sustained real-time phase demodulation without inline amplification over a range of 148 km in standard single mode fiber and up to 171 km in low-loss OFS TeraWave SCUBA 125 fiber. This is the longest reported range for DAS measurements. The optical dynamic range of the recording is 57 dB. With a 10 km fiber, we obtain a record-low interrogation noise above 50 Hz (rms average over position) of 134 and 89 µrad/√Hz with gauge lengths (equal to spatial resolution) of 10 and 34 m, respectively. A total harmonic distortion of −42 dB (rms average over position) is demonstrated with a gauge length of 10 m.

©2021 Optical Society of America under the terms of the OSA Open Access Publishing  Agreement

J. K. Brenne et al, “DAS interrogation on standard single mode fibers in long tie-back subsea wells”, 2nd EAGE Workshop on Distributed fiber Optic Sensing, Online event, March 2021. https://www.earthdoc.org/content/papers/10.3997/2214-4609.202131025

Summary

A key challenge to implement DAS in subsea wells is the limited capability of existing DAS interrogators to operate over several kilometres of lead-in cable and wet-mate connector losses. We report here the results from an experiment performed with a new DAS interrogator in a simulated subsea well scenario. We demonstrate that DAS can be adopted to subsea well interrogation utilizing standard single mode optical fibers without any need for specialized or engineered fiber. Even with 10 dB additional loss (one-way) from lead-in fiber and wet-mate connectors, marginal impact on the instrument self-noise is observed.

©EAGE Publications BV

L. Bouffaut et al, “Eavesdropping at the speed of light: Distributed  Acoustic Sensing of Baleen Whales in the Arctic”, Journal of Frontiers in Marine Science, 2022.
https://doi.org/10.3389/fmars.2022.901348

Abstract

In a post-industrial whaling world, flagship and charismatic baleen whale species are indicators of the health of our oceans. However, traditional monitoring methods provide spatially and temporally undersampled data to evaluate and mitigate the impacts of increasing climatic and anthropogenic pressures for conservation. Here we present the first case of wildlife monitoring using distributed acoustic sensing (DAS). By repurposing the globally-available infrastructure of sub-sea telecommunication fiber optic (FO) cables, DAS can (1) record vocalizing baleen whales along a 120 km FO cable with a sensing point every 4 m, from a protected fjord area out to the open ocean; (2) estimate the 3D position of a vocalizing whale for animal density estimation; and (3) exploit whale non-stereotyped vocalizations to provide fully-passive conventional seismic records for subsurface exploration. This first example’s success in the Arctic suggests DAS’s potential for real-time and low-cost monitoring of whales worldwide with unprecedented coverage and spatial resolution.

Å. Pedersen et al, “A North Sea case study: Does DAS have potential for Permanent Reservoir Monitoring?”, EAGE Annual 2022, June 2022.
https://doi.org/10.3997/2214-4609.202210170

Summary

In this presentation the potential for using Distributed Acoustic Sensing (DAS) in a PRM setting during active seismic acquisition is investigated. Data examples and results from a field trial where DAS-data recorded in a seafloor fiber cable at the Johan Sverdrup field in the North Sea are compared to reference data from the Johan Sverdrup PRM system. Our findings are that DAS provides high quality seismic data and could be a cost-effective alternative to conventional ocean bottom seismic acquisition.

©EAGE Publications BV

E. Rebel et al, “Are fiber optic cables part of the next generation toolbox for CO2 storage monitoring?”, EAGE Annual 2022, June 2022.
https://doi.org/10.3997/2214-4609.202210491

Summary

The work presented in this paper investigates the imaging capabilities of fiber optic cables deployed at seabed with the objective of using this acquisition technology to monitor future CO2 storages. A unique data set acquired with a Permanent Reservoir Monitoring system (both on conventional 4Component sensors and fiber optic cables as DAS) is analyzed. As results, the comparison between Pwave amplitudes recorded by both types of sensors is done and their variations as a function of angle of propagation relatively to the direction of the cable have been investigated. In addition, a classical PP processing sequence is applied independently to each type of sensors (PZ summation, radial accelerometer and DAS) and its relative quality is compared. The results obtained are very encouraging and are clearly placing fiber optic cables horizontally deployed at seabed as part of the next generation of CO2 storage monitoring toolbox.

©EAGE Publications BV

R. Rørstadbotnen et al, “Analysis of a Local Earthquake in the Arctic Using a 120 KM Long fiber-Optic Cable”, EAGE Annual 2022, Madrid, Spain June 2022.
https://doi.org/10.3997/2214-4609.202210404

Summary

For this extended abstract, a 120 km long fiber-optic cable has been used to enhance the Signal-to-Noise Ratio of recorded P- and S-wave signals from a local earthquake and to estimate the earthquake hypocenter location. The Distributed Acoustic Sensing (DAS) technique provides a unique possibility to increase the receiver density globally. It can, for example, improve the detection rate of small, induced earthquakes in CO2 storage sites or producing oil and gas fields. This work shows how DAS alone can be used to locate a small magnitude mid-Atlantic earthquake using arrival times, enhanced by various signal processing techniques, from the measurement on an Arctic fiber-optic cable. The earthquake location obtained using the DAS data was found to be within 17 km of the catalogue location reported by NORSAR and the Norwegian National Seismic Network. This shows how fiber-optic cables offer unique complementary methods to enhance received seismic signals and to traditional source localization for earthquakes and other seismic sources.

©EAGE Publications BV

O. H. Waagaard et al, “Experience from long-term monitoring of subsea cables using distributed acoustic sensing”, 27th International Conference on optical Fiber Sensors, Alexandria, USA, August 2022.
https://doi.org/10.1364/OFS.2022.Th2.4

Abstract

A 92 km section of a subsea telecom cable has been monitored using distributed acoustic sensing (DAS) throughout one year. Real-time processing detects cable threats from bottom-trawl fishing and ship anchoring, and we analyze seismic events including a magnitude 1.0 earthquake.

©2022 The Author(s)

M. Landrø, “Sensing whales, storms, ships and earthquakes using an Arctic fiber optic cable”, Sci Rep 12, 19226 (2022).
https://doi.org/10.1038/s41598-022-23606-x

Abstract

Our oceans are critical to the health of our planet and its inhabitants. Increasing pressures on our marine environment are triggering an urgent need for continuous and comprehensive monitoring of the oceans and stressors, including anthropogenic activity. Current ocean observational systems are expensive and have limited temporal and spatial coverage. However, there exists a dense network of fiber-optic (FO) telecommunication cables, covering both deep ocean and coastal areas around the globe. FO cables have an untapped potential for advanced acoustic sensing that, with recent technological break-throughs, can now fill many gaps in quantitative ocean monitoring. Here we show for the first time that an advanced distributed acoustic sensing (DAS) interrogator can be used to capture a broad range of acoustic phenomena with unprecedented signal-to-noise ratios and distances. We have detected, tracked, and identified whales, storms, ships, and earthquakes. We live-streamed 250 TB of DAS data from Svalbard to mid-Norway via Uninett’s research network over 44 days; a first step towards real-time processing and distribution. Our findings demonstrate the potential for a global Earth-Ocean-Atmosphere-Space DAS monitoring network with multiple applications, e.g. marine mammal forecasting combined with ship tracking, to avoid ship strikes. By including automated processing and fusion with other remote-sensing data (automated identification systems, satellites, etc.), a low-cost ubiquitous real-time monitoring network with vastly improved coverage and resolution is within reach. We anticipate that this is a game-changer in establishing a global observatory for Ocean-Earth sciences that will mitigate current spatial sampling gaps. Our pilot test confirms the viability of this ‘cloud-observatory’ concept.

R. A. Rørstadbotnen et al, “Simultaneous tracking of multiple whales using two fiber-optic cables in the Arctic”, Frontiers in Marine Science, Vol 10 (2023).
https://doi.org/10.3389/fmars.2023.1130898

Abstract

Climate change is impacting the Arctic faster than anywhere else in the world. As a response, ecosystems are rapidly changing. As a result, we can expect rapid shifts in whale migration and habitat use concurrent with changes in human patterns. In this context, responsible management and conservation requires improved monitoring of whale presence and movement over large ranges, at fine scales and in near-real-time compared to legacy tools. We demonstrate that this could be enabled by Distributed Acoustic Sensing (DAS). DAS converts an existing fiber optic telecommunication cable into a widespread, densely sampled acoustic sensing array capable of recording low-frequency whale vocalizations. This work proposes and compares two independent methods to estimate whale positions and tracks; a brute-force grid search and a Bayesian filter. The methods are applied to data from two 260 km long, nearly parallel telecommunication cables offshore Svalbard, Norway. First, our two methods are validated using a dedicated active air gun experiment, from which we deduce that the localization errors of both methods are 100 m. Then, using fin whale songs, we demonstrate the methods’ capability to estimate the positions and tracks of eight fin whales over a period of five hours along a cable section between 40 and 95 km from the interrogator unit, constrained by increasing noise with range, variability in the coupling of the cable to the sea floor and water depths. The methods produce similar and consistent tracks, where the main difference arises from the Bayesian filter incorporating knowledge of previously estimated locations, inferring information on speed, and heading. This work demonstrates the simultaneous localization of several whales over a 800 km area, with a relatively low infrastructural investment. This approach could promptly inform management and stakeholders of whale presence and movement and be used to mitigate negative human-whale interaction.

L. Thiem et al, “Ship Noise Characterization for Marine Traffic Monitoring Using Distributed Acoustic Sensing”, 2023 IEEE International workshop on Metrology for the Sea, Malta 2023, pp 334-339
https://dx.doi.org/10.1109/MetroSea58055.2023.10317227

Abstract

We investigate the feasibility of distributed acoustic sensing (DAS) for marine traffic monitoring in the Trondheimsfjord, Norway. We deployed a DAS system on a fiber-optic telecommunication cable trenched at the seabed of the fjord and recorded continuous acoustic signals generated by passing vessels. In this study, we investigate if an alternative method and workflow can be used to monitor marine traffic despite the noisy environment and poor coupling of the cable to the surrounding seabed sediments. We apply 2D image processing techniques and various signal processing filters to the data to achieve further noise reduction. We analyzed the data using a method named persistent homology to detect direct arrivals of vessel signals. Inverting for the traveltimes of the detected P-wave arrivals enables us to localize the acoustic source. Our results show that persistent homology can be an effective tool for analyzing continuous signals. It is a promising data processing technology for detecting and tracking vessels in coastal areas. We compared our localization results for a vessel to the GPS locations logged by the automatic identification system (AIS) and found good agreement. Furthermore, we demonstrate the ability of the method to localize successfully a previously undetected vessel within reasonable positioning errors, that was not sending an AIS signal. These findings demonstrate the potential of our presented method which has significant implications for maritime security and environmental protection. While other research studies have focused on localizing vessels and marine mammals in calm and deep water, we present an approach that allows localizing vessels (and potentially other objects) in noisy, shallow waters. Overall, our study highlights the valuable capabilities of DAS for marine traffic monitoring but underscores the need for continued research to fully realize its potential in this area.

Publisher: IEEE

S. Wienecke et al, “New Advances in Fiber Optic Technology for Environmental Monitoring, Safety, and Risk Management Applications“,2023 IEEE International workshop on Metrology for the Sea, Malta 2023, pp 316-321
https://dx.doi.org/10.1109/MetroSea58055.2023.10317494

Summary

The concept of long-range DAS interrogation utilizing existing telecommunication cables for oceanic monitoring has been successfully demonstrated in several field trials. Real-time monitoring capabilities, low instrument noise, high spatial resolution and extended aperture are beneficial for the development of new DAS applications to observe cetacean and other marine fauna, to monitor marine traffic, to detect earthquakes, tele-seismic events, and microseism signals. Furthermore, DAS interrogation in coexistence with live telecom traffic was validated in high-capacity telecommunication networks. The results show that the DAS measurements are provided within the same range, sensitivity, and high fidelity as with DAS interrogation on dark fibers, importantly without interference to live telecom traffic. These new technology advances allow the full utilization of existing telecommunication infrastructure providing a smart surveillance tool of the oceanic environment. It will be a window opener to less explored areas with sparse data coverage because the infrastructure of submarine fiber optic cables covers nearly all oceans around the globe.

Publisher: IEEE

C. Sagary et al, “Seabed DAS PP image on Johan-Sverdrup field: a good surprise with the wrong sensor”, EAGE GeoTech 2024 Fourth EAGE Workshop on Practical Reservoir Monitoring, 4, Volume 2024, p.1 – 5
https://doi.org/10.3997/2214-4609.202430022

Summary

Equinor conducted a Distributed Acoustic Sensing (DAS) field trial by acquiring active DAS and Permanent Reservoir Monitoring (PRM) conventional accelerometer and hydrophone seismic data simultaneously along the same 9-km long cable, over the Johan Sverdrup field. The quality of both DAS and PRM inline acceleration along the X horizontal axis (AX) PP images was unexpected. Why was it a surprise? Because the power of stacking on final signal-to-noise ratio was underestimated and observation of pre-stack data might have been misleading. The amplitudes recorded on these sensors a priori wrong for PP reflection recording are very weak on individual seismic traces and invisible on pre-stack data but focus effectively to the stack. Mirror imaging improves the overall quality of DAS and PRM AX PP images, thanks to higher fold and better noise attenuation by stacking. The noises that have the greatest impact on image quality are the Scholte waves and associated back-scattered waves. Their filtering is much more effective on DAS data than on PRM AX data thanks to the very fine spatial sampling of DAS data down to 2 meters, compared to the PRM AX sampling of 50 meters.

©EAGE Publications BV

J. K. Brenne et al, “Non-Intrusive DAS Coexisting in Telecom Networks,” 2024 Optical Fiber Communications Conference and Exhibition (OFC), San Diego, USA, 2024, pp. 1-3.
https://ieeexplore.ieee.org/document/10526675

Abstract

We describe DAS interrogation for non-intrusive coexistence with live C-band WDM channels. The scheme facilitates consistent high sensing sensitivity range >100 km. Surface vessels, seabed fishing gear and earthquakes are localized from the 2Africa network.

©2024 The Author(s)

J. P. Morten et al, “Sensing enabled submarine telecom networks for seismology”, EGU General Assembly 2024, Session: SM-3.1: fiber-optic point and distributed sensing, April 2024, Vienna
https://doi.org/10.5194/egusphere-egu24-16375

Summary

Distributed acoustic sensing (DAS) on submarine fiber optic cables will contribute to resilient societies by significantly enhancing environment and hazard monitoring. Recent studies have emphasized applications to earthquake and tsunami early warning, volcanic eruptive events observation, and characterizing climate change effects. Widespread deployment of DAS instrumentation on the existing cable networks traversing the coastal zones and oceans can vastly expand data coverage with real-time capabilities at low cost.

The use of DAS in existing long-haul telecommunication systems has so far been limited since most DAS interrogators rely on optical wavelengths that interfere with the existing telecom traffic. Recent developments in DAS technology enable co-existence of telecom traffic with the sensing application. Lab and field investigations have demonstrated that there is no detrimental effect from the interrogation on the transmission line performance when the DAS instrument is configured to operate at sufficiently separated wavelength channels. Thus, it is possible to utilize all existing cable networks for sensing applications in unison with continued telecom transmission without sacrificing any capacity in the link and maintaining high-quality DAS measurements.

This study describes a DAS deployment on a submarine cable system with live telecom traffic. The interrogation scheme facilitates consistent high sensing sensitivity exceeding 120 km range. The data quality and interrogator performance are quantified, and the localization and characterization for a representative set of environmental and anthropic signal sources is shown. We will describe real-time processing and detection implementations that transform such sensing enabled submarine telecom networks into measurement arrays suitable for seismic monitoring. Moreover, the technical solutions for DAS installation with existing terminal equipment and the practical aspects of data sharing will be described.

J. P. Morten et al, “Ocean Space Surveillance Using Distributed Acoustic Sensing on Submarine Networks”, Seismological Society of America, Photonic Seismology conference in Vancouver, Canada, 7-10 October 2024

Summary

Technology developments have realized long-range distributed acoustic sensing (DAS) that can coexist with transmission in submarine telecommunication networks. The fiber optic cable measurements can be used for multiple purposes contributing to enhancing environment and hazard monitoring, and resilient societies. The seismology community has rapidly adopted the technology to improve earthquake monitoring and early warning capabilities, and the enhanced marine data coverage is advancing ocean sciences.

In this presentation we will focus on surveillance using submarine cables. We have carried out long-term monitoring on a Southern North Sea telecom cable. During a three-year period, we have detected and analysed regional impulsive source events from sources located in the water column, onshore and in the air. The recordings show clear arrivals of seismic, hydroacoustic and infrasound waves. The long propagation range and sensitivity on the fiber optic cable measurements show that by instrumenting only a few cables, it is possible to achieve a coastline-scale surveillance capacity.

The observations from underwater detonation of ordnance, and onshore blasts show that it is possible to augment the seismometer-based networks for regional explosion monitoring. The signal characteristics also show how it is possible to determine the type of source to quickly assess an event and contribute to situational awareness.

We discuss how a real-time processing system can extract important event parameters. Source localization is limited by the single-component nature of the data. However, curvature in the cable path can be exploited since cable sections with different orientations are sensitive to different parts of the wavefield. Moreover, it is feasible to instrument multiple cables thereby achieving area coverage from simultaneous and coordinated interrogation on linear cables.

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Pipeline monitoring

Flow in a subsea pipeline (bringing the resource to shore) or in flowlines (connecting wellheads to the platform) will generate acoustic noise that can be picked up by an optical cable installed on the seabed nearby. Such noise will generate seabed surface waves imposing strain modulations on the cable observable by DAS measurements.

The picture shows recordings along a section of a subsea cable crossing the flowline (water injection) at the 24 km cable position. The surface waves are visible more than one km away from the crossing point.

By utilizing a fibre in an optical seabed cable, health monitoring (flow rate, leakages) of subsea flowlines can be performed with DAS interrogation.

Pipeline monitoring

Localisation of electrical failure

Some of the electrical energy released in a partial discharge (PD) transforms to acoustic energy. The generated acoustic emission will depend on surrounding materials of the void discharge. The main acoustic energy is at ultrasonic frequencies, but some energy is also emitted at much lower frequencies (suitable for long-range DAS monitoring).

DAS can be used for on-line monitoring of partial discharge in HVDC cables providing an instant location of the failure position. Although partial discharge effects occur quite seldom, an on-line OptoDAS system enables significantly faster repair and reduced period of lost revenue when a failure occurs.

OptoDAS can monitor power cables in excess of 300 km length (by monitoring from both ends). The figure illustrates background noise level measured over more than 160 km in an optical cable attached to an HVDC subsea cable. The figure also includes estimated DAS signals in case of a partial discharge. These signal levels are based on experimental results.

Localization of electrical failures

Trawl monitoring

When a trawl hits the sea floor, acoustic waves (propagating along the seabed) will be excited. Such waves will induce strain in an optical cable installed on the seabed. Detectable strain is distributed over several kilometers along the cable (depending on the distance between the trawl and cable).

Data have been recorded from trawl activities in a fishing area in the North Sea at cable positions 55 – 60 km from the shore end. Trawls on the seabed are recorded within 1-2 km distances from the cable.

Real-time processing software provides continuous localization and tracking of trawl activities by using the optical cable as a coherent DAS antenna. The software issues warnings to the telecom operator when trawls are approaching the cable. Vessel identification can be made through the use of AIS data.

Trawl monitoring
Alain Biston

Alain Biston

President & CEO

Alain has been working for more than 25 years in telecoms, with Nortel, then Alcatel-Lucent / Nokia, holding management and leadership positions in R&D, Product Line, Industrial Operations, Sales & Marketing, Business Unit P&L accountability.

He brings to ASN his thorough knowledge of the telecoms industry, his extensive international management background with several postings overseas, and his field-proven customer-facing acumen.

Since 2016, as a Nokia executive, Alain has been Senior VP Customer Operations End2End and until now Senior Vice President in charge of Mobile Network business management.

Alain holds a degree in Information Technology from INSA, Rennes, France. He was also honored with the National Order of Merit in 2006 from the French Minister of Industry.

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