Session 3
Despite the improvements, harsh environments also pose a challenge within the fibre optic sensing technology in many aspects, beyond material properties. Possible cable arrangements can be limited to the morphology of the region of interest (e.g., topography, ground coupling), which ultimately affects the quality of the data and the information that can be retrieved from it. Therefore, researchers in the field must also consider deployment, coupling, and cable arrangement to obtain as much information as possible from these unexplored regimes.
In this session, we welcome contributions that involve fibre optic sensing applications in extreme environments such as boreholes, deep ocean, acidic soil, space, and exoplanets. Contributions that explain the technical challenges of extreme locations, request solutions, and highlight the benefits of the existing, offering solutions for reducing costs and solving technical challenges, are particularly welcome.
Invited speaker: Marc-André Gutscher (Geo-Ocean, France)
Within the framework of the EU funded FOCUS project, we have established BOTDR (Brillouin Optical Time Domain Reflectometry) time series spanning up to 3 years on academic and commercial fiber-optic cables. Offshore Catania a 6-km-long dedicated fiber-optic cable (connected to a 29-km-long electro-optical cable), recorded natural and man-made strain signals of 40 - 250 microstrain at the seafloor (in 1800 - 2000 m water depths). The strongest natural signal (40 microstrain elongation) developed from 19 - 21 Nov. 2020, where the cable crosses a mapped submarine fault in the first of 4 locations. However, a network of 8 seafloor geodetic stations (acoustic beacons mounted on tripods) recorded no baseline changes, thus ruling out a tectonic movement. A simultaneous positive-negative strain doublet (+40 to -20 microstrain) observed 6 km from shore (in 300 m water depth), suggests a downslope current affected the shallow and deep portions of the fiber-optic cable path length. The 6-km long FOCUS cable includes a redundant, triple-loop, consisting of 1 loose and 2 tight optical fibers. (A second double-loop, consisting of 1 tight and 1 loose fiber is being monitored by a second BOTDR interrogator.) The tightly bound fibers typically record a strain signal twice as high as the loose fibers (40 vs 20 microstrain for the natural signal). Weight bag drops created man-made signals along four 120-m-long segments, with amplitudes of 80 - 250 microstrain (in the tight fibers), which gradually decay in the following months / years.
Baseline measurements were repeatedly taken on the 100-km-long Capo Passero (SE Sicily) electro-optical cable in Oct. 2022, March 2023, and Nov. 2023. The main purpose of the monitoring is to test the maximum range attainable with commercially available BOTDR interrogators. While no significant strain development has been measured on the optical path, we report that with an acquisition time of 2+ hours it is possible to extend the measurement range up to 80 km. This represents a benchmark for future BOTDR measurements over long distances.
In June 2022, in collaboration with the “Conseil Regional” of Guadeloupe and Orange, we began long-term monitoring of a network of unrepeated submarine telecom cables that links the islands of the Guadeloupe archipelago. We repeated the measurements of the same fiber segments (30 - 70 km length), in Dec. 2022, June 2023, Nov/ Dec. 2023, and finally May 2024 in order to identify strain or thermal signals along the cable during the 2-year period. We confirm that using the BOTDR technique, we detect significant shifts in the Brillouin frequency (2 - 5 MHz), which could represent substantial strain signals (40 - 100 micro-strain in amplitude) in several locations along the cable network. These signals, which can be positive (elongation) or negative (shortening) occur typically in areas of steep seafloor slopes (e.g. the shelf break) or in submarine valleys/canyons. Our preliminary interpretation is that stretching and shortening of the cable (representing about 1 cm over a few hundred meters) is occurring, most likely due to sea-bottom currents.
How to cite: Gutscher, M.-A., Quetel, L., Cappelli, G., Riccobene, G., Aurnia, S., Nativelle, C., Philippon, M., and Lebrun, J.-F.: Observing seafloor processes by distributed Fiber Optic Sensing: examples from academic cables offshore East Sicily (Italy) and a commercial telecom network in the Guadeloupe archipelago (Lesser Antilles)., Galileo conference: Fibre Optic Sensing in Geosciences, Catania, Italy, 16–20 Jun 2024, GC12-FibreOptic-58, https://doi.org/10.5194/egusphere-gc12-fibreoptic-58, 2024.
Active seismic experiments during the Apollo missions characterized the lunar regolith and crust, while passive monitoring suggested a thermal stress origin for the high-frequency lunar seismic noise. Deploying Distributed Acoustic Sensing (DAS) instruments, capable of withstanding the extreme lunar conditions, would allow to examine various lunar environments including permanently shadowed regions, which trap water ice due to their extremely cold temperatures. Benefiting from high spatial and temporal resolutions, DAS surveys would allow analyzing wave propagation, constructing 2D wave velocity sections, and potentially identifying ice-related velocity variations. How the DAS technology positions in terms of self-noise with respect to Apollo and modern sensors? We estimate the strain noise level of geophones to be around 1 pε/sqrt(Hz). For a 5-km long optic fiber with 10 meters gauge length, the typical self-noise of current DAS systems is around 1 pε/sqrt(Hz). This indicates that DAS instruments may achieve a low noise level on par with the best current geophysical technologies, which is crucial for precise and reliable exploration of lunar structure. We will discuss experiments that would be necessary for qualifying such an instrument for space applications.
How to cite: Tauzin, B., Lognonné, P., Kawamura, T., Panning, M., Jousset, P., Lanticq, V., Mercerat, D., Metaxian, J.-P., Hibert, C., De Raucourt, S., Coutant, O., and Almoric, E.: DAS system for the Moon, Galileo conference: Fibre Optic Sensing in Geosciences, Catania, Italy, 16–20 Jun 2024, GC12-FibreOptic-47, https://doi.org/10.5194/egusphere-gc12-fibreoptic-47, 2024.
Optical fiber sensors constitute the biggest revolution in geophysical and environmental sensor technology since digitization. Although traditional sensors have been refined through decades of incremental progress, optical fiber sensors provide an entirely new lens with which to study fundamental processes. These sensors are particularly advantageous for systems that require high spatial and temporal resolution (i.e., on the order of 1-10m spatial scale and 100 s to 100 kHz sampling rate). The UW Fiber Lab has deployed these technologies in Antarctica, Greenland, Alaska, New Zealand, and at a dozen sites in Europe and the lower United States. The main focus of this research has been on studying Earth's cryosphere, submarine, urban, and otherwise difficult-to-instrument environments. This talk will focus specifically on use cases where basic knowledge has been gained regarding the calving front of large, ocean-terminating glaciers in Greenland, paleoclimatic history of the Antarctic ice sheet, monitoring of clean energy systems, and earthquake detection and ground motion hazard characterization. The presentation will conclude with a forward looking discussion regarding the rapid pace of development of basic optical physics and engineering, and the prospects for future growth at the intersection of optical fiber sensor technology and basic geoscience research.
How to cite: Lipovsky, B., Abadi, S., Denolle, M., Gaete Elgueta, V., Gräff, D., Manos, J.-M., Ni, Y., Shi, Q., Sprinkle, P., Wilcock, W., and Williams, E.: New Earth and Planetary Science Discoveries Enabled by the Optical Fiber Sensing Revolution, Galileo conference: Fibre Optic Sensing in Geosciences, Catania, Italy, 16–20 Jun 2024, GC12-FibreOptic-95, https://doi.org/10.5194/egusphere-gc12-fibreoptic-95, 2024.
I present the results of the Suboptic working group formed during the Suboptic 2023 conference to create a synergy between submarine cable owners and government institutions to improve safety for coastal communities.
Since discovery of sensing capabilities of operational submarine cables, a perfect storm of smart optical spectroscopic techniques enabled enhancement of cable security and environmental protection. We are looking for synergy between cable owners and government institutions to improve safety for coastal communities. In high seas, Subsea Environmental Sensing with Operational Submarine Cables (SESOSC) has a target to create industry wide collaboration to enable early warning of tsunami. As awareness of the importance and complexity of the ocean environment becomes increasingly clear, the need for improved sensing, with better spatial resolution and increased temporal coverage, is now pressing. Submarine cables developed to transmit information between continents can be used as sensors. Sensing with submarine cables was a topic of active discussion at the SubOptic 2023 Conference, where two dozen authors presented results convincing that sensing is a powerful tool to improve cable safety but also provides opportunities for environmental monitoring. Enormous opportunities of sensing with submarine cables are clear to many today, and need to be addressed from juridical and security perspectives. Fiber optic networks, both terrestrial and subsea, are a growing part of the information revolution. It is clear that sensing with telecom optical fibers creates a base for multiple applications, including earthquake and tsunami early warning. We discuss the next step for the submarine industry to improve cable safety and enhance environmental monitoring worldwide.
This paper contains a summary of Working Group results dedicated to DAS technology for coastal areas cable safety and environmental surveillance and sensing with trans-continental operational cables. We discuss the strategy to facilitate applications of operational submarine cables for sensing of earthquakes, water waves, and improvement of security of submarine cables. We also plan to provide a consolidated industry viewpoint on the considerations and opportunities afforded by existing and emerging cable-based technologies for sensing the marine environment. The Working Group envisions international cooperation between cable owners and government agencies to provide low frequency data to tsunami warning centers with an early alarm threshold established based on the research project. We are working on the development of the platform to summarize industry position on the technologies in the field of submarine cable-based environmental sensing. The Working Group does not cover the SMART submarine cables program as the Working Group deals with fiber as a sensor technologies that do not require modification of the wetplant. Optical transmission fibers are excellent sensors and operational submarine cables can provide additional value to submarine cable owners.
How to cite: Kamalov, V.: Subsea Environmental Sensing with Operational Submarine Cables, Galileo conference: Fibre Optic Sensing in Geosciences, Catania, Italy, 16–20 Jun 2024, GC12-FibreOptic-19, https://doi.org/10.5194/egusphere-gc12-fibreoptic-19, 2024.
Geothermal reservoirs require reliable well-completion techniques to reach well integrity. Well, integrity means there are no flow paths behind the casing at all. While constructing the well, the drilling mud must be fully displaced by uncontaminated cement, measured in displacement efficiency. Conventional real-time measurements show average pumping parameters to control the cement job's success. However, studies show issues with well integrity worldwide. We aim to improve well integrity by closing an information gap within the construction phase using continuous distributed fiber-optic sensing with dense spatial sampling.
This study investigated the primary cementing of an 874 m surface casing in Munich, Germany. A fiber optic cable deployed behind the casing enabled the measurement of distributed dynamic strain rate (DDSS or DAS) and distributed temperature (DTS) during cement placement. We used field data from the cementing service, developed a fluid displacement model, and compared the results with those of the fiber optics.
While we can trace only the rise of a cold front in the temperature data, the combined interpretation of DAS data shows features that allow comprehensive insights into the subsurface displacement process. We observed two rising velocities at a constant pumping rate. We were able to correlate them to the rise of different fluid interfaces. We conclude that the freshwater spacer does not displace the drilling mud but the first arrival of cement. Once the breakouts are filled, the succeeding cement seeks the path of least resistance without displacing cement in the breakouts again.
Our findings suggest the possibility of tracking the rise of different fluids and the stability of their interfaces in real-time with distributed dynamic strain sensing. Having sensors along the borehole to track the displacement efficiency enables on-site reactions to ensure the cement jobs' success.
How to cite: Hart, J., Polat, B., Schölderle, F., Ledig, T., Lipus, M., Wollin, C., Reinsch, T., and Krawczyk, C.: Closing an Information Gap in Geothermal Well Construction: Continuous Distributed Fiber-Optic Sensing for Improved Displacement Efficiency, Galileo conference: Fibre Optic Sensing in Geosciences, Catania, Italy, 16–20 Jun 2024, GC12-FibreOptic-22, https://doi.org/10.5194/egusphere-gc12-fibreoptic-22, 2024.
We present the results and current challenges of an experiment with Distributed Acoustic Sensing (DAS) on Grímsvötn volcano in Iceland, and its potential for improvements in source characterization using Full-Waveform Inversion (FWI).
We deployed a 12 km long fibre-optic cable for one month (May 2021) on Grímsvötn, Iceland’s most active volcano on a centennial time scale, which is covered by the Vatnajökull ice cap. The cable was trenched 50 cm into the ice, following the caldera rim and ending near the central point of the caldera on top of a subglacial lake.
We discover previously undetected levels of microseismicity, and we locate these events with first-arrival times and a probabilistic inversion using the Hamiltonian Monte Carlo algorithm. The ~2000 detected events have local magnitudes between -3.4 and 1.7, and their locations indicate clear clusters of activity. These appear near surface expressions of the caldera fault, such as fumaroles, and cauldrons. We use the results, combined with an initial velocity model, to set up an FWI workflow, that takes the complex topography and subsurface into account. We create the initial velocity model for the firn-ice transition by inverting a dispersion curve of the snow cat driving along the cable, and we combine this with homogeneous media for the bedrock, ice layer, and subglacial lake. We perform an initial forward modelling study for a selection of ~600 events in the frequency range of 1.5 – 3 Hz, combined with a least-squares inversion to obtain the moment tensor components of each event. Finally, we assess the resulting moment tensors and their resolution matrix in order to evaluate the potential to invert for source characteristics.
This research shows the results and potential of DAS on active subglacial volcanoes, and we hope that this research will contribute to the fields of volcano monitoring and DAS modelling.
How to cite: Klaasen, S., Noe, S., Thrastarson, S., Cubuk-Sabuncu, Y., Jónsdóttir, K., and Fichtner, A.: Moment Tensor inversion with Full-Waveform Inversion and Distributed Acoustic Sensing on a subglacial volcano: Grímsvötn, Iceland., Galileo conference: Fibre Optic Sensing in Geosciences, Catania, Italy, 16–20 Jun 2024, GC12-FibreOptic-25, https://doi.org/10.5194/egusphere-gc12-fibreoptic-25, 2024.
Scientific infrastructures cover areas worldwide to monitor Earth system processes. Most of these are installed on land, but land masses make up only about 30% of the Earth's surface. The oceans and particularly the ocean floor are difficult to access, and thus are not adequately instrumented and monitored. Since they play a critical role in regulating climate as a heat and carbon store, and are the site of deadly natural disasters including strong earthquakes, tsunamis, and volcanic eruptions, we are faced with a substantial gap in the monitoring of critical physical parameters in the near-coast and offshore domains. For seismology and geohazard assessment the global coverage is as essential as for oceanography and climate studies. Using a combination of established and novel technologies implemented in telecommunication infrastructure on the sea-floor and coastal areas will, without a doubt, prove to be a game changer in geosciences and Earth system understanding.
In recent years, three different and complementary fiber-optics-based technologies have gained at-tention as valuable tools for investigating Earth system processes: Distributed Fiber-Optic Sensing (DFOS), State of Polarization (SoP), and Science Monitoring and Reliable Telecommunications (SMART) cable systems. The first two technologies use the fiber-optic cable as the sensing element, while in the third technology type (SMART cable systems), independent sensors are integrated into fiber-optic cable repeaters, and the cable is used for power and data transmission. These technologies and their application to geoscientific problems are at different levels of maturity, and combining them with a FAIR data infrastructure into a demonstrator is the vision of the planned infrastructure project SAFAtor (see presentation by Cotton et al., this meeting).
We want to present and discuss in the framework of our planned SAFAtor initiative (SMART Cables And Fiber-optic Sensing Amphibious Demonstrator) the first experiments we performed in the testbeds foreseen at Mt. Etna, in the Marmara Sea, and in Chile. While Etna’s volcano-tectonic setting is complex (Jousset et al., Currenti et al.) and origin and spatial-temporal evolution of the volcanism and its relationship with the tectonic dynamics are still a matter of debate, its unstable eastern flank stretches far into the Ionian Sea with an average flank movement of 2-3 cm/yr. In the Marmara Sea, critical data on offshore fault structure and seismicity will enable efficient investigation of structure and seismic hazard underneath densely populated areas along the coast, especially in Istanbul where the major earthquake is overdue. This also holds for Chile, where ongoing subduction erosion and mature seismic gaps should be complemented by new monitoring efforts. Developing our SAFAtor activities in terms of adapted fibre-optics sensing and monitoring will thus help areas exposed to hazard at active plate boundaries and volcanic systems in coastal zones.
How to cite: Krawczyk, C., Cotton, F., Tilmann, F., Wallace, L., and Team, S.: Closing the Ocean Data Gap: near-coast fibre-optics sensing to monitor tectonic and volcanic events, Galileo conference: Fibre Optic Sensing in Geosciences, Catania, Italy, 16–20 Jun 2024, GC12-FibreOptic-41, https://doi.org/10.5194/egusphere-gc12-fibreoptic-41, 2024.
The INFN-LNS (Istituto Nazionale di Fisica Nucleare – Laboratori Nazionali del Sud) operates two deep-sea cabled infrastructures in Eastern Sicily.
The first infrastructure connects a shore laboratory in the port of Catania to two underwater sites in the Gulf of Catania. This connection is made through an electro-optical submarine cable, approximately 25 km long, which hosts 10 optical fibers. At a distance of 20 km from the shore laboratory, the cable splits into two branches via a Y-junction to reach two different cable termination frames: TSN (Test Site North) and TSS (Test Site South), both located at a depth of 2100 m.
The second infrastructure is situated 100 km southeast of Portopalo di Capo Passero at a depth of 3500m. The underwater site is connected to the shore laboratory in the harbor of Portopalo via two underwater electro-optical cables. These cables carry 20 and 48 optical fibers, respectively. The second cable, funded by the IDMAR PO-FESR project, was deployed between November 2020 and November 2022. Thanks to a Y-branching unit, the cable is split underwater into two different branches.
These two LNS fiber optic infrastructures have hosted several Italian and European projects, including Geoinquire, EMSO-ERIC, IPANEMA/ECCSEL-ERIC, and FOCUS-ERC in Catania; KM3NeT and EMSO in Portopalo di Capo Passero.
Specifically, within the FOCUS-ERC and Geoinquire projects, DAS (Distributed Acoustic Sensing) and BOTDR (Brillouin Optical Time Domain Reflectometer) measurements were acquired over a long period.
The optical network of the two deep-sea infrastructures and the available assets for geoscience will be described.
How to cite: Pulvirenti, S. and Viola, S.: The INFN-LNS Fibre optic infrastructure, Galileo conference: Fibre Optic Sensing in Geosciences, Catania, Italy, 16–20 Jun 2024, GC12-FibreOptic-10, https://doi.org/10.5194/egusphere-gc12-fibreoptic-10, 2024.
Distributed Acoustic Sensing (DAS) technology is a new photonic method that can convert several tens of kilometer-long seafloor fiber-optic telecommunication cables into dense arrays of strain sensors. With such spatial and temporal resolution, DAS appears as a potential future alternative to in-situ oceanographic measurements. Nevertheless, the DAS measurement needs to be calibrated because several factors can induce modifications to the measurements such as the structure of the cable or the level of burial in the sediments. In addition, the mechanisms through which the external stresses are conveyed to the fiber are still not well understood. An initial strategy involves analyzing the response of the DAS data to surface gravity waves as these are continuously present and well-characterized signals, that can be readily measured at shallow depth. From December 2020 to January 2021, an in-situ campaign was performed which involved deploying a pressure sensor at a depth of 15 meters for nearly 2 months next to the 50 km-long LSPM (Laboratoire Sous-marin Provence Méditerranée) seafloor cable in the bay of Les Sablettes, South of France. In the frequency band of surface gravity waves, we identify a remarkable linear correlation between the energy of the pressure sensor and that of the colocated DAS sensor, for various sea conditions. This result implies that the significant wave height can be reconstructed from DAS data at all points along the telecom cable, from the coast down to the cut-off depth of linear wave theory (roughly 100 meters in that region). From the linear wave potential theory, we derive an analytical transfer function linking the cable deformation and wave kinematic parameters. Even though this transfer function provides a first quantification of the effects related to waves and the cable response, it does not allow to distinguish between the different components of the wave spectrum (long-period, infragravity, surface gravity, ultra-gravity waves...), nor acknowledge the potential contribution of temperature variations. Also, the coupling processes between water, cable, and sediment remain to be included in this transfer function. In 2023, along the same telecom cable, we deployed 6 instrumented stations along the LSPM cable for 3 months. In particular, we installed instruments to measure seafloor pressure and temperature, the velocity components in the water column, as well as variations in the depth of sediments relative to a reference. These measurements will enable us to refine the analysis of the processes involved in the DAS response.
How to cite: Mohammedi, A., Sladen, A., Meulé, S., Pelaez-Quiñones, J., Bouchette, F., Ponte, A., and Ampuero, J.-P.: Reconstruction of nearshore surface gravity waves from Distributed Acoustic Sensing data, Galileo conference: Fibre Optic Sensing in Geosciences, Catania, Italy, 16–20 Jun 2024, GC12-FibreOptic-79, https://doi.org/10.5194/egusphere-gc12-fibreoptic-79, 2024.
Distributed Acoustic Sensing (DAS) offers unprecedented meter-scale spatial sampling of strain/strain-rate wavefields, enabling unaliased seismic event observations. DAS technology utilizes fiber optic cables (FOCs), extending seismological observations to extreme environments, including ocean floors. Given the logistical difficulties in deploying and maintaining traditional seismic stations in these contexts, seismological data near oceanic earthquake sources remain limited. On a positive note, telecommunication FOCs are often deployed on the ocean bottoms to connect urban areas on land, potentially bridging this observational gap.
Traditional seismological monitoring, which aims to locate earthquake sources, typically relies on phase picking and subsequent data inversion. In a standard seismometer network, automatically-retrieved arrival times can be manually validated by expert operators; however, this task becomes practically impossible with DAS due to the unprecedented data density it offers, which can easily reach tens of thousands channels, considering the current capabilities of interrogating cables up to 100 km. For the purpose of leveraging both data measurements close to the source (DAS) and the improved azimuthal coverage by land stations, DAS data flows must be automated. Potential solutions include accurately tuning automatic pickers for the specific FOC and/or employing data selection and weighing procedures. Recently, pickers based on machine learning have been tested for DAS as substitutes for standard pickers, offering promising results and efficient arrival time measurements. Despite these advancements, challenges persist in accurately estimating onsets due to spatial variability in DAS waveforms, arising from a) uniaxial signal polarization, b) sensitivity to site conditions, and c) heterogeneities in FOC coupling. These data uncertainties, in turn, affect event location accuracy.
We address this problem by conducting a preliminary comparison of two standard pickers (based on the actual amplitude-frequency content of each channel) with a machine-learning-derived picker. We focus on DAS recordings of six local earthquakes located on the ocean bottom between Fuerteventura and Gran Canaria islands during an experiment from November 2022 to April 2023. Each earthquake is provided with a reference location from the regional network of seismometers. Kurtosis and FilterPicker (standard pickers) and Phasenet-DAS (machine-learning picker) onsets are inverted for event location, with a focus on statistically comparing the solutions' uncertainty (scattering). To achieve this, we employed a Markov chain Monte Carlo method to estimate the Posterior Probability Densities (PPDs) of hypocentral parameters.
In a second stage, we test a data-weighing approach on absolute arrival times based on specific channel properties. The aim is to assess its effects on location PPDs, in comparison to the “not-weighed” inversion. We repurpose the same algorithm, previously used for the location comparison, to modify each entry of the covariance matrix in the Bayesian inversion scheme, thus enabling a differential weighting of the arrival times. These preliminary comparisons of the efficiency of automatic pickers and data weighting procedures are commonly employed for the evaluation of standard seismological networks. With DAS arrays, these approaches become even more crucial, given the reduced space for manual validation by experts.
How to cite: Bozzi, E., Piana Agostinetti, N., Ugalde, A., Latorre, H., Cubas Armas, M., Ventosa, S., Villaseñor, A., and Saccorotti, G.: Comparing location uncertainties with automatic pickers on DAS data: case studies from Canary Islands, Galileo conference: Fibre Optic Sensing in Geosciences, Catania, Italy, 16–20 Jun 2024, GC12-FibreOptic-17, https://doi.org/10.5194/egusphere-gc12-fibreoptic-17, 2024.
The IPANEMA project, funded under the ECCSEL-ERIC activity, aims at studying the natural emissions of carbon dioxide in the Mediterranean region via acoustic detection. In the framework of IPANEMA INFN-LNS has designed two underwater stations equipped with hydrophones and CO2 sensors: a shallow water (20 m depth) autonomous and retrievable observatory, deployed offshore the Island of Panarea (Aeolian Islands, Tyrrhenian Sea) and a cabled deep sea observatory, to be deployed in offshore the Coast of Catania at 2000 m depth (Sicily, Western Ionian Sea). Both detectors are capable to monitor the sea soundscape from a few Hz to just under 100 kHz.
In this context, INFN is investigating the possibility to use Distributed Optical Fiber sensing (DOFS) to enable the measurement of biological and anthropogenic acoustic signals along the entire length of underwater electro-optical cables. Unlike conventional sensors that measure at specific points, DOFS systems provide distributed measurements along the fiber length with high spatial sampling, allowing for dense monitoring of large structures or environments in real time. In this work, we will focus on the application of DOFS in the monitoring of biological sounds emitted by fin whales, as demonstrated by recent researches in Isfjorden Sea, Norway.
During a campaign of measurements between November 9th and 16th, 2023, IFREMER interrogated with an ASN OptoDAS two seafloor electro-optical cables of the INFN-LNS marine infrastructure in Eastern Sicily. The Distributed Acoustic Sensor (DAS) system was first connected to the LNS-INFN electro-optical cable, extending 25 km from the port of Catania to its end at approximately 2100 m water depth. Another set of measurements was carried out at the LNS-INFN Capo Passero site, using a cable extending 100 km to the shore, reaching depths of around 3500 m. In this area a research study conducted by INFN-LNS between 2012 and 2013, using hydrophones on seafloor showed the presence of fin whales.
In this work we will present the analysis of DAS signals: custom codes for data reduction, noise filtering and search for the typical fin whale calls (20 Hz intermittent pulses) will be presented and results discussed.
How to cite: Idrissi, A., Aurnia, S., Di Mauro, L. S., Pulvirenti, S., Riccobene, G., Diego-Tortosa, D., Viola, S., Sanfilippo, S., Bonanno, D., Le Pape, F., Ker, S., Murphy, S., Cappelli, G., Quetel, L., and Gutscher, M.-A.: Search for fin whale calls and shipping noise in Western Ionian Sea using Distributed Acoustic Sensor, Galileo conference: Fibre Optic Sensing in Geosciences, Catania, Italy, 16–20 Jun 2024, GC12-FibreOptic-85, https://doi.org/10.5194/egusphere-gc12-fibreoptic-85, 2024.
Nowadays, fiber-optic telecommunication cables are serving a multitude of purposes beyond their conventional role. One such application is earthquake detection, which is particularly advantageous in submarine environments, where data acquisition is inherently more challenging and costly. Leveraging Distributed Acoustic Sensing (DAS) technology, these cables undergo a remarkable metamorphosis, transforming into a network of seismic sensors spaced just meters apart, and spanning remote and inaccessible environments with ease.
Nevertheless, the quality of DAS data relies on varios factors that surpass the interrogator’s performance, such as the seafloor topography and cable characteristics and coupling. Equally critical is the development of robust software capable of discerning earthquake waves amidst a cacophony of noise and a broad spectrum of signals in the submarine environment.
With this aim in mind, this study utilizes DAS data from a telecommunications fiber-optic cable linking the islands of Tenerife and Gran Canaria within the Canary Islands region. Our dataset spans approximately 2 months in 2020 and encompasses readings from both cable ends, each equipped with an interrogator, providing coverage of approximately 60 kilometers on each side. Situated between these islands lies a submarine volcano, which exhibits seismic activity nearly every day. Additionally, the recent installation of new land stations has enabled to observe an increase in seismicity to the east of Gran Canaria. Hence, this dark-fiber could enhance our ability to monitor the volcano and to accurately locate the source of this newfound seismic activity.
Leveraging the pre-trained PhaseNet-DAS model, we detect P and S waves of seismic events and compare our findings with those published by the National Geographic Institute (IGN) earthquake bulletin. Through comparative analysis of both cable ends, we ascertain their earthquake detection capabilities, delineating sensitivity levels and identifying cable segments with optimal event detection and minimal noise interference.
How to cite: Cubas Armas, M., Rodríguez, T., Latorre, H., Ventosa, S., Villaseñor, A., and Ugalde, A.: Assessing Submarine Earthquake Detectability with Fiber-Optic Cables in the Canary Islands , Galileo conference: Fibre Optic Sensing in Geosciences, Catania, Italy, 16–20 Jun 2024, GC12-FibreOptic-6, https://doi.org/10.5194/egusphere-gc12-fibreoptic-6, 2024.
Earthquake location schemes for regional oceanic earthquakes within archipelago regions
are limited by the azimuthal resolution that land stations provide for each specific event. Although
ocean bottom seismometers (OBS) can help, they are not suited for real time monitoring and thus
can only provide a posteriori improvements. An alternative approach to improve coverage, not
strictly limited to a temporal increase of onshore stations, is to use Distributed Acoustic Sensing
(DAS) on oceanic fiber-optic cables. With DAS, real time monitoring in areas up to 100 km
offshore is possible, which can potentially improve azimuthal resolution by reaching previously
inaccessible locations within the archipelago. A great example of such a region are the Canary
Islands, where land-based coverage is already phenomenal yet volcanic activity monitoring from
underwater sources still has poor coverage in some cases.
Recently, the deployment of additional land stations at the islands of Gran Canaria and
Fuerteventura has revealed existing seismicity between the two islands. When locating the source of
this seismicity, there is a considerable east-west bias on the azimuthal distribution of those stations.
An existing fiber-optic cable that connects the islands of Tenerife and Gran Canaria has been
interrogated with DAS before, on both sides. The most recent experiment, which was set up on the
Gran Canaria side, recorded such seismicity from late 2022 to early 2023.
This work attempts to use the DAS-recorded onsets of some events for location purposes.
First, we test DAS by itself, and subsequently, DAS in combination with land stations. Automatic picking methods are tested for this purpose, since manual picking of onsets is not feasible for DAS. The possibility of catalog revisions using just a few hand-picked onsets at
previously selected DAS channels is also considered, since there is a lot of redundancy in DAS data
and visual inspection is not unreasonable if limited to a number of channels.
How to cite: Latorre, H., Bozzi, E., Ventosa, S., Cubas Armas, M., Vidal-Moreno, P., Villaseñor, A., Bartolomé, R., and Ugalde, A.: Enhancing earthquake location in deep ocean environments with DAS, Galileo conference: Fibre Optic Sensing in Geosciences, Catania, Italy, 16–20 Jun 2024, GC12-FibreOptic-7, https://doi.org/10.5194/egusphere-gc12-fibreoptic-7, 2024.
Fiber-optic distributed acoustic sensing (DAS) has exhibited potential in ocean monitoring. However, its monitoring region depends upon preexisting submarine telecommunication cables. In this study, we used a fine-scale optical fiber array (FOFA) DAS to sense the deep-ocean environment and illuminate underwater shear velocity structure. On the R/V Tansuoyihao TS-37-2 expedition in 2023, we carried out a DAS experiment to monitor deep-sea microseism in the central rift zone of the Philippine Sea basin. By utilizing the Hadal station（H-Station）and remotely operated vehicles (ROV) for collaborative operations, we successfully deployed a 560-meter long, 3-mm diameter optic-fiber array on the seabed at a depth of 5,569 meters. We obtained continuous data of seafloor strain field with a spatial 400 channels and a resolution of 1.6 meters. Through the processing of DAS data from UTC November 11, 2023, between 19:00 PM and November 12, 2023, 02:30 AM, combined with previous observations from hydrophones and ocean bottom seismometer (OBS), the results indicate: 1) The submarine in the study area is quiet, with a less than 20×10-9 strain variation. 2) DAS can perceive microseism from solid media or water disturbances from fluid media within a wide frequency band (10,000 s ~ 250 Hz). In power spectra density (PSD) profile, the 0.32 Hz contains most of the energy, mainly originating from water disturbances. The second at 0.78 ~ 2.5 Hz exhibits multiple dispersion in the F-K domain, representing Scholte waves. The third is reaching 19.5 Hz, is a noise likely from rotating ship propellers near the water surface. Additionally, narrowband signals at 12.4 Hz, 24.8 Hz, 37.5 Hz, 56.1 Hz, and 62.4 Hz, which exhibit harmonic properties, may be related to local oscillator noise from H-station. 3) Based on Scholte waves and its 7th-order modes dispersion curves collected by DAS, we got deep-sea 1D sub-bottom shear-wave velocity structure. This study reveals deep-sea distributed strain fields at the meter-scale resolution for the first time, confirming the effectiveness of DAS in deep-sea environmental monitoring. It will provide new technical support for study on ocean-solid interactions, turbidity currents, earthquakes, and biological acoustic events, as well as Scholte wave velocity inversion.
How to cite: Zhang, H., Xu, T., Yu, C., Deng, D., Chen, J., and Wu, S.: Distributed Sensing of Ocean-Earth Interface on Hadal-station deployed fiber-optic cable, Galileo conference: Fibre Optic Sensing in Geosciences, Catania, Italy, 16–20 Jun 2024, GC12-FibreOptic-21, https://doi.org/10.5194/egusphere-gc12-fibreoptic-21, 2024.
With 70% of the earth underwater, seafloor geodesy provides a vital means of measuring tectonic deformation in a zone where terrestrial geodesy cannot reach. The expense of placing, maintaining and recovering instruments and data from seafloor sensors makes their widespread use prohibitive. Distributed fibre sensing techniques offer the opportunity to measure deformation along the seafloor at unprecedented spatial resolution and at a high sensitivity. An added advantage of this technology is that it can utilise pre-existing infrastructure such as telecommunication cables or cabled scientific seafloor observatories converting them into multi-node marine sensors. While much attention has focused on the application of DAS in seismology, the use of other distributed sensing techniques in the geosciences remains under studied.
Brillouin Optical Time Domain Reflectometry (BOTDR) provides a means of measuring relative changes in longitudinal strain and temperature on the order of a few meters with a sensitivity of micro-strain making it an ideal tool for marine geodesy. We will present a theoretical study investigating how it may be applied and what are challenges of using this technique. Using a dislocation model in linearly elastic half space media we demonstrate that the relationship between cable and fault geometry is a critical feature that needs to be accounted for when designing a geodetic survey. For example, in the case of a strike slip fault a cable at a 45° angle relative to the fault strike will be more sensitive compared to a cable traversing the same fault at 90° . We will also demonstrate what information on imaging tectonic slip could provide by cables through the calculation of resolution kernels for a variety of different faults.
Finally, we discuss some of the challenges to the use of BOTDR in marine environments. Using BOTDR data collected continuously over a period of 1.5 years starting in May 2021 on the INFN-LNS cable which extends offshore Catania, we demonstrate the effect seasonal water temperature plays on strain readings. We also discuss observations from laboratory geotechnical experiments that demonstrate the importance of accounting for phenomena such as cable buckling and coupling.
How to cite: Murphy, S., Palano, M., Garreau, P., Terzariol, M., Ker, S., Cappelli, G., Quetel, L., Riccobene, G., Aurnia, S., Viola, S., Pulvirenti, S., and Gutscher, M.-A.: Use of distributed fibre sensing in marine geodesy, Galileo conference: Fibre Optic Sensing in Geosciences, Catania, Italy, 16–20 Jun 2024, GC12-FibreOptic-30, https://doi.org/10.5194/egusphere-gc12-fibreoptic-30, 2024.
The oceans are a vast and dynamic part of our planet’s ecosystem, especially in a geophysical and oceanographic sense. The sea state is naturally constantly changing as a result of underlying currents, ocean surface waves and the tides. Alongside this, the acoustic and seismic noise fields are also highly diverse with a plethora of natural (marine wildlife, ocean microseisms, earthquakes) and anthropogenic (ship traffic, seafloor construction) sources. Distributed acoustic sensing (DAS) applied on submarine fibre optic cables offers a means of unprecedented spatial resolution within the ocean environment for detailed analysis of seismic and acoustic noise. With telecommunication optical fibres around the globe, there’s a wealth of information waiting to be tapped into.
Within this research project a 10 day long DAS dataset, acquired using a Febus Optics interrogator, from an optical fibre (5.56km length) connected to the Galway SmartBay offshore laboratory is being studied to characterise the submarine seismic and acoustic noise fields. In order to understand the cable sensitivity to seismic and acoustic signals present in the bay during the experiment, we compare the DAS data with data from other instruments such as seismometers (Irish National Seismic Network), hydrophones and wave buoys (both Galway SmartBay and Marine Institute Ireland).
The spectrum of the noise field is being studied through generating spectrograms for the entire acquisition period for various channels along the cable, showing the strongest signal in the 0.1-0.2Hz frequency band, which can be attributed to ocean surface gravity waves. Analysis in the frequency-wavenumber domain is also being employed to separate the seaward and landward travelling waves. This analysis has also shown the presence of weaker signals in the 0.5-1.5Hz and 3.5-5.5Hz frequency bands which were not apparent in the initial spectrograms and could be evidence of high frequency seismic noise (>1Hz).
How to cite: Berry-Walshe, L., Tary, J.-B., Le Pape, F., Piana Agostinetti, N., Bean, C. J., Garcia Gomez, C., and MacCraith, E.: Using DAS with an Optical Fibre Cable in Galway Bay for Ocean Noise Monitoring, Galileo conference: Fibre Optic Sensing in Geosciences, Catania, Italy, 16–20 Jun 2024, GC12-FibreOptic-44, https://doi.org/10.5194/egusphere-gc12-fibreoptic-44, 2024.
In November 2023, DAS (Distributed Acoustic Sensing) data were acquired along few fibers of the MEOC cable of the INFN-LNS submarine infrastructure, extending circa 29 km off the coast of Catania; one of these fibers is terminated with a further 6km-long optical fiber layed on the seafloor in the context of the FOCUS-ERC project. In addition another set of measurements were conducted using the INFN-LNS MEOC cable deployed offshore Capo Passero, probing a 200 km loop implemented on a pair of fibers. With almost 2 weeks of recordings, the DAS interrogator captured multiple types of signals from ocean waves to earthquakes and even volcanic tremors linked with an eruption phase of Etna. Here, we investigate in particular the ambient seismic noise associated to the sea state that was recorded on each cable. With the goal to identify and locate noise sources for using passive seismic imaging in the area, there is a need to differentiate seismic noise related to wind waves from other overlapping signals at similar frequencies (e.g. tremors from Etna). First, long-term trends in the DAS data are investigated using spectrograms for specific channels along each cable. In addition to continuous low frequency seismic noise, the data highlight the presence of short-term high frequency (>1Hz) events which also seem connected to the wind wave activity in the area. Taking advantage of the dense spatial sampling of the DAS data, spectral profiles and f-k analysis are applied on shorter time windows over different sections of the cables to decompose both ocean waves and seismic wavefields in more details (e.g. landward vs seaward separation of signals) and better characterize the mechanisms behind those events. Both cables show some differences in the seismic noise wavefield that imply a change in local noise sources but also highlight the influence of site effects from each cable. Whereas the wind waves signature is limited to the shallower sections of the cables, we also observe that microseisms are present over the whole length of each cable, with their energy fluctuating as a function of water depth but also the cable coupling with the seafloor. In particular, along the Capo Passero cable, we observe significant stronger microseisms energy far out at sea.
How to cite: Le Pape, F., Ker, S., Murphy, S., Riccobene, G., Viola, S., Aurnia, S., Pulvirenti, S., and Gutscher, M.-A.: Insights from the DAS analysis of ambient seismic noise recorded off the coast of Sicily, Galileo conference: Fibre Optic Sensing in Geosciences, Catania, Italy, 16–20 Jun 2024, GC12-FibreOptic-49, https://doi.org/10.5194/egusphere-gc12-fibreoptic-49, 2024.
The continuous Earth ground vibrations known as microseisms that are produced by wind driven surface gravity waves dominate the seismic noise spectrum and are closely tied to storm activity. Distributed Acoustic Sensing (DAS) technology exploits the backscattering properties of fibre optic cables to acquire strain rate data which represent high-fidelity measurements of acoustic and seismic waveforms. It enables acquisition over large distances of cables acting as a densely distributed arrays for acoustic and seismic data collection on the seafloor. In particular, being sensitive to both wind waves and microseisms at the same time, DAS has shown great potential for further understanding of ocean secondary microseisms that are generated due to the head-on collision of opposing wind wave systems of same period. DAS provides new ways of studying with high resolution the microseisms’ fingerprint at the seafloor and connect deep ocean microseisms events with land observations.
Here, five days of DAS data collected in October 2020 along a circa 29km long section of the fibre optic cable of the INFN-LNS subsea infrastructure, offshore Catania, Sicily in parallel to the FOCUS-ERC project was analysed to investigate the microseisms in the area. We focus on the study of a major secondary microseism event associated with high winds moving over Sicily, crossing the Mediterranean Sea from NW to SE. The spatiotemporal variations of the microseism energy are correlated with the local sea state variations in the area, confirming the influence of local weather conditions on microseisms generation. Whereas ocean wave model data highlight a dominant secondary microseism source located SE of Sicily, the F-K analysis shows that the associated seismic noise recorded with the DAS is propagating both in the landward and seaward directions, suggesting the potential presence of 3D path effects affecting the microseism wavefield. Finally, the DAS data is compared with nearby land broadband seismic stations to study its sensitivity and to assess the amount of microseism energy transmitted to land.
How to cite: Vijayan, A., Le Pape, F., Bean, C. J., Murphy, S., Ker, S., Jousset, P., Riccobene, G., Viola, S., Gutscher, M., Currenti, G., Aurnia, S., and Pulvirenti, S.: Secondary microseism event characterisation offshore Catania using DAS Data, Galileo conference: Fibre Optic Sensing in Geosciences, Catania, Italy, 16–20 Jun 2024, GC12-FibreOptic-62, https://doi.org/10.5194/egusphere-gc12-fibreoptic-62, 2024.
The Reykjanes Peninsula, due to its active volcanism, has been subject of numerous studies. The eruption of Mount Fagradalsfjall in March 2021 followed a series of crustal inflation and subsidence cycles in 2020, as documented by GNSS stations. In this work, we monitor the crust in Reykjanes over a period of 5.5 months during the 2020 unrest with distributed dynamic strain sensing (also called DAS). At first, empirical Green’s functions are extracted through cross-correlation of ambient seismic noise (0.5 – 0.9 Hz). Subsequently, we apply coda wave interferometry to measure seismic velocity variations over time and space. We show that wavelength-dependent spatial stacking of DAS data prior to cross-correlation substantially enhances the time resolution and spatio-temporal coherency of measurements. Using this workflow, we reveal a compelling correlation between seismic velocity changes and both vertical and horizontal static ground deformation. This suggests a strong link between our measurements and geological processes. Measured velocity variations may be related to the infiltration of magmatic fluids into a shallow aquifer, although a comprehensive interpretation is impeded by the complexity of the tectonic setting, alongside increased seismic activity (>20,000 local earthquakes) and the existence of geothermal regions. Furthermore, discrepancies observed between results from causal and acausal sides of cross-correlations suggest that measurements are affected by the noise source distribution, which raises questions about the extent to which measurements are solely attributable to structural and dynamic changes of the crust. Our work not only demonstrates how the spatial sampling of DAS can be exploited to enhance seismic monitoring strategies, but also highlights conceptual limitations that need to be confronted in future investigations.
How to cite: Maass, R., Schippkus, S., Hadziioannou, C., Schwarz, B., Jousset, P., and Krawczyk, C.: Link between seismic velocity changes and the 2020 unrest in Reykjanes revealed by wavelength-dependent spatial stacking of distributed dynamic strain, Galileo conference: Fibre Optic Sensing in Geosciences, Catania, Italy, 16–20 Jun 2024, GC12-FibreOptic-70, https://doi.org/10.5194/egusphere-gc12-fibreoptic-70, 2024.
Laboratori Nazionali del Sud dell’INFN owns and manages a deep sea infrastructure situated in Portopalo di Capo Passero where theARCA KM3NeT infrastructure is installed.
The KM3NeT ARCA telescope is being installed at a depth of about 3500 m and the distance to the control station on shore is about 100 kilometers.
The telescope will comprise more than 4000 optical modules in the detector arrays with a point-to-point optical connection to the control station onshore. In particular, the detector is optimized for the detection of cosmic neutrinos with energies above about 1 TeV.
The expected maximum data rate is 200 Mbps per optical module. The implemented optical data transport system matches the layouts of the networks of electro-optical cables and junction boxes in the deep sea.
For efficient use of the fibers in the system the technology of Dense Wavelength Division Multiplexing is applied.
To comply with the scientific goals of KM3NeT , the implementation of the detectors has been subdivided into two phases in order to adapt to the time lines of funding sources and procurement procedures and to allow for adaptation or replacement of obsolete technical parts. The first implementation phase foresees the construction of 32 detection units for ARCA where synchronization is achieved by communication between a White Rabbit master onshore and a White Rabbit slave unit inside the optical modules. For the second phase of the project - adaptations are foreseen in order to have better scalability, reliability and standardization based on a full White Rabbit capable architecture (WWRS).
The KM3NeT broadcast and WWRS optical data transport system will be presented.
How to cite: Pulvirenti, S., Schmelling, J.-W., and D'Amico, A.: KM3NeT/ARCA Optical Network , Galileo conference: Fibre Optic Sensing in Geosciences, Catania, Italy, 16–20 Jun 2024, GC12-FibreOptic-84, https://doi.org/10.5194/egusphere-gc12-fibreoptic-84, 2024.
DAS technology has emerged as a transformative technology with a vast range of applications, both on land and at sea. These applications span from oil and gas exploration to geophysical data collection, infrastructure monitoring, security, and environmental hazard monitoring, including earthquake and tsunami early warning systems (Landrø et al., 2022; Gorshkov et al., 2022).
The unique properties of DAS systems can bring high benefits to the demanding field of seismology, as it provides a significant increment in the spatial information that can be obtained from a seismic event. Moreover, the widespread deployment of optical fiber across the Earth's surface, coupled with the relatively low cost per monitoring point for extended distances, has rendered DAS an appealing alternative to traditional seismographs (Li et al., 2023). This is especially true for subsea applications, where the capability of remote sensing is particularly attractive. Remote sensing enables the placement of systems far from harsh environments, often difficult to access, enhancing the feasibility and effectiveness of monitoring efforts.
In this work, it was employed a DAS equipment on a dark telecommunication fiber was installed exclusively for research purposes, named GEOLAB, located on the island of Madeira. This fiber spans approximately 50 km, where the initial tests were conducted using a DAS from January 31 to February 14, 2023. The equipment utilized is the HDAS provided by the IO-CSIC. The signal of the fiber was collected with a spatial resolution (or gauge length) of 10 m, resulting in total of 5000 channels, with a temporal acquisition with a frequency of 50 Hz. The DAS system has a chirped pulsed laser as the optical source, generating pulses with a width of 100 ns. These pulses were then amplified using a semiconductor optical amplifier to mitigate intra-band coherent noise.
A total of 19 seismic events were detected, and then characterized by performing two-dimensional linear bandpass filtering. We will present the initial findings, particularly the seismic activity resulting from the earthquakes with epicenters near the city of Gaziantep, located in Turkey. These events occurred on February 6, 2023, with magnitudes of 7.5 and 7.8 on the Richter scale.
How to cite: Cunha, C., Monteiro, C., Martins, H., Carrilho, F., Silva, S., and Frazão, O.: DAS System for the Evaluation of Subsea Seismic Data from GEOLAB cable in Madeira Island, Galileo conference: Fibre Optic Sensing in Geosciences, Catania, Italy, 16–20 Jun 2024, GC12-FibreOptic-92, https://doi.org/10.5194/egusphere-gc12-fibreoptic-92, 2024.
