To retrieve information about physical changes along cables, current fiber optic sensing technologies can exploit the interaction between light and matter i.e., using conventional Rayleigh, Brillouin, and Raman scattering. Alternatively, observables can be measured via light interferometry or state of polarization sensing. Interrogators extract information from telecom-grade fibers, exploiting both telecom and non-telecom frequency bands, or from specialty fibers and multi-core designs.
Despite rapid progress, key challenges remain in converting distributed optical measurements into reliable geophysical observables. Translating fiber deformation into true geophysical observables via instrumental response demands improved deployment schemes encompassing cable and fiber embedment geometries, coupling between cable and medium, and quantitative models of cable-to-fiber strain transfer. In parallel, production of massive observable data volumes necessitates new solutions in edge computing, compression schemes, and machine learning to transform how datasets are acquired, reduced, and interpreted.
The session will cover contributions on technological and methodological breakthroughs that push the boundaries of what fiber optic sensors and sensing systems can measure and how they operate. We seek contributions addressing known as well as emerging sensing technology such as designs of next-generation interrogators and specialty fibers, quantifying and improving instrumental response through innovative cable design and ground coupling schemes, as well as extraction of diverse observables (including rotation, stress and strain tensor components). In addition, methodological advances in architectures for edge computing, processing and intelligent data management are welcome.
We invite instrument developers, telecom and optical engineers, as well as method innovators to showcase the developments that will define the next generation of fiber optic sensing tools for the geosciences.
Distributed acoustic sensing (DAS) turns fiber-optic cables into distributed, passive sensors suited for continuous, spatially extended ocean monitoring. Specifically, an optoelectronic interrogator injects laser pulses into the fiber and measures the phase modulation of Rayleigh backscattered light, which is caused by external acoustic wavefields inducing elastic strain over a gauge length. A DAS sensor (channel) is commonly considered a point sensor for signal processing, i.e., introduces no spatial coherence to the measured signal. However, DAS sensors have a non-negligible spatial extent due to the transfer function between the measured optical signal and the external acoustic field. The transfer function between optical and acoustic quantities is factorized into four terms, describing the filtering effect of the acquisition gauge window and the spatial averaging window, and of the acoustic wavenumber and direction of arrival. The resulting sensitivity as a function of frequency and angular direction of individual DAS sensors is related to the sensor’s equivalent spatial aperture. The spatial shape of an individual DAS sensor is derived theoretically, and is quantified in common array signal processing terms, such as equivalent spatial aperture, directivity, and beampattern. The shape of the spatial aperture determines the spatial coherence of DAS measurements in a diffuse acoustic wavefield, as demonstrated on publicly available data. The corresponding spatial coherence predicts the statistical characteristics of the speckle pattern in DAS.
How to cite: Xenaki, A. and Gerstoft, P.: Frequency-dependent directivity of distributed acoustic sensing in ocean acoustics, Galileo conference: Fibre Optic Sensing in Geosciences, Aussois, France, 31 Aug–4 Sep 2026, GC14-FibreOptic-51, https://doi.org/10.5194/egusphere-gc14-fibreoptic-51, 2026.
The strength of Distributed Acoustic Sensing (DAS) for vibration monitoring is the use of existing (telecom) fibre infrastructure. However, these cable geometries are typically not optimal for event localisation and beam-forming methods. Also, deployment (and thus ground coupling) is outside the control of geoscientists. To overcome these issues we designed and constructed the NORFOX array (NORwegian Fibre Optic eXperimental array) as a dedicated fibre-optic sensing testbed. NORFOX thus allows to investigate the opportunities DAS offers for both (array) processing and system-level characterization. The array comprises five fibre arms (~18 km total length, ~3 km aperture) and is co-located with the NORES seismic- and infrasound-array, enabling direct benchmarking against conventional instrumentation.
A key objective of NORFOX is to exploit DAS as a dense, continuous array for beamforming. Treating the fibre as thousands of spatially distributed channels, we demonstrate that DAS can retrieve coherent wavefield properties such as slowness and back-azimuth. The array geometry is specifically designed to balance directional sensitivity, robustness, and optical budget, providing improved azimuthal coverage compared to linear deployments. The design of NORFOX can be considered as best case scenario, and we can also simulate the impact of sub-optimal designs by reducing the geometry to various combinations of the 5 arms.
NORFOX also serves as a platform to calibrate fibre sensitivity. The installation includes both standard telecom fibres and enhanced backscatter cables, either directly buried in the ground or deployed inside a protective plastic conduit. This allows direct comparison of sensitivity, attenuation, and noise performance. In addition, multiple interrogators operating at different wavelengths (e.g., within the C- and L-bands) are tested, highlighting trade-offs between optical loss, backscatter efficiency, and signal-to-noise ratio. These comparisons are critical for understanding how hardware choices influence DAS data quality and array performance.
At the same time, NORFOX exposes key challenges in DAS. Cable-to-ground coupling strongly controls signal fidelity and varies with soil conditions and installation, leading to spatially heterogeneous noise. This variation occurs over both short-term (intra-day) and long-term (seasonal) timescales, leading to spatially heterogeneous noise conditions. DAS measurements are inherently directional and single-component, complicating beamforming and requiring adapted processing strategies. NORFOX records continuously with 250 Hz, 4 m spacing, and 20m gauge length, equivalent of about 4400 channels, and generating 93 GB data each day. It is possible to choose a secondary data-stream with different settings, or perform parallel measurements with other interrogators on additional. We present our considerations of for data management, data reduction, edge computing, and (long-term) storage.
By combining controlled array design, mixed fibre infrastructure, and multi-interrogator testing, NORFOX provides a unique experimental platform to investigate the full DAS sensing from fibre and interrogator physics to processing and interpretation. We here highlight the potential of fibre-optic arrays as next-generation sensing systems, while directly addressing the instrumental and methodological challenges limiting broader adoption.
How to cite: Wuestefeld, A., Baird, A., and Turquet, A.: NORFOX: A Fibre-Sensing Testbed for Seismo-Acoustic Monitoring, Galileo conference: Fibre Optic Sensing in Geosciences, Aussois, France, 31 Aug–4 Sep 2026, GC14-FibreOptic-40, https://doi.org/10.5194/egusphere-gc14-fibreoptic-40, 2026.
Distributed Acoustic Sensing (DAS) has become a key technology for downhole seismic monitoring over the past decade, owing to its dense spatial sampling, operational simplicity, and cost efficiency. By converting fibre‑optic cables into continuous seismic sensors, DAS enables full‑depth borehole measurements that significantly exceed the spatial coverage of conventional geophone arrays. However, the quality of DAS measurements is highly dependent on fibre–formation coupling, which in turn is controlled by the method used to deploy the fibre within the borehole.
This study investigates the impact of different fibre‑optic deployment strategies on the quality and detectability of active DAS signals in a geothermal context. Experiments were conducted at a newly developed geothermal test site in Pau, France, equipped with six shallow (130 m) boreholes supplying a heating and cooling system. Two deployment methods were tested during probe installation: fibre cemented alongside the geothermal probe and fibre installed inside the geothermal probe tube. Multiple fibre‑optic cables (Single‑Mode and Multi‑Mode) were deployed, with this study focusing on three wells instrumented with different cable types and geometries (cemented looped, cemented single‑pass, and retrievable looped inside the probe).
An active seismic Vertical Seismic Profiling (VSP) survey was conducted in September 2025 using a weight‑drop source, with 43 repeated shots stacked to enhance signal‑to‑noise ratio. DAS data were acquired with a 5 m gauge length, 1 kHz sampling rate, and 2.4 m spatial sampling, yielding over 500 measurement channels along a continuous 1.2 km fibre. Despite ongoing geothermal circulation during the experiment, coherent seismic energy was detected along all boreholes down to 130 m depth.
Preliminary analysis of the stacked DAS data reveals coherent seismic arrivals in all instrumented boreholes, with detectable signals down to 130 m depth. Two main wave types are observed across all configurations: a fast first‑arrival wave (~2,270 m/s) and a slower guided mode (~550 m/s). Qualitative comparisons between boreholes suggest that signal amplitude and continuity vary with fibre deployment configuration. Cemented fibres generally display clearer first arrivals, while fibres installed inside the HDPE probe show localized attenuation and reduced amplitudes, potentially linked to bending and coupling conditions. Further analysis will include wavefield separation and time-lapse analysis to help quantify the effects of fibre coupling and geothermal operations
How to cite: Chauvet, R., Nziengui Bâ, D., and Duret, F.: Comparison of Fiber-Optic Cable Deployment Strategies inside a Geothermal Borehole using Active DAS VSP , Galileo conference: Fibre Optic Sensing in Geosciences, Aussois, France, 31 Aug–4 Sep 2026, GC14-FibreOptic-24, https://doi.org/10.5194/egusphere-gc14-fibreoptic-24, 2026.
Fibre-optic telecommunication networks are increasingly emerging as pervasive sensing infrastructures for geophysical and environmental monitoring. Beyond their primary role in data transmission, optical fibres are intrinsically sensitive to external perturbations: mechanical strain induced by seismic waves modifies both the optical phase and the state of polarization of the propagating light. This property enables existing fibre networks to act as large-scale distributed or integrated sensors, offering a promising complement to conventional seismic instrumentation. In highly active volcanic and seismic areas, such as Campi Flegrei, dense and continuous monitoring is particularly relevant for improving event detection, risk assessment and early response. However, established fibre-sensing techniques often rely on dedicated fibres, specialized interrogators or highly stable laser sources, which may limit scalability and increase deployment costs. For this reason, low-complexity sensing approaches that can operate over in-service telecom infrastructure are of strong interest.
In this work, we present a multi-technology fibre-sensing testbed deployed over operational and production fibre infrastructure owned by the italian operator Open Fiber in the Campi Flegrei area. The testbed combines three complementary techniques: state-of-polarization (SOP) sensing, distributed acoustic sensing based on ϕ-OTDR, and interferometric phase sensing. As shown in figure, the SOP and phase measurements are implemented over FTTH links departing from the same point of presence and reaching street cabinets in Agnano and Posillipo, while the DAS reference is acquired over another 22 km FTTH dark fibre owned by another italian operator (Fibercop). The SOP system uses a low-tech polarization-beam-splitter-based receiver that measures the normalized difference between two orthogonal polarization components of an intensity-modulated telecom signal. This architecture avoids coherent receivers and ultrastable lasers, and it can operate by tapping only a small portion of the optical power, preserving compatibility with live data transmission.
The experimental campaign demonstrates that the low-tech SOP approach can detect local seismic events down to magnitude 1.9. Earthquakes recorded in November 2025 were analysed and compared against independent reference measurements from DAS, interferometric phase sensing when available, and INGV seismic stations. The SOP traces clearly capture seismic signatures associated with P- and S-wave arrivals, with waveform features and spectral content consistent with the established fibre-sensing techniques. In particular, consecutive M1.9 and M3.0 events were detected by the SOP system and validated against DAS and INGV seismic-station data, while an M3.3 event was jointly observed by SOP, interferometric phase sensing, DAS and the INGV seismic network. These results show that simple SOP monitoring over in-service FTTH links can provide reliable seismic information while significantly reducing system complexity and cost, paving the way for scalable and minimally invasive seismic monitoring using existing telecom networks.
How to cite: Virgillito, E., Notarstefano, F., Herrero, A., Currenti, G., Bianco, F., Corsaro, M., Prestifilippo, M., Bratovich, R., Corsini, R., Donadello, S., Clivati, C., Di Lena, F., Calonico, D., Hovsepyan, M., Carpentieri, F., and Curri, V.: Low-Tech State of Polarization Seismic Monitoring over Production FTTH Cable in Campi Flegrei, Galileo conference: Fibre Optic Sensing in Geosciences, Aussois, France, 31 Aug–4 Sep 2026, GC14-FibreOptic-94, https://doi.org/10.5194/egusphere-gc14-fibreoptic-94, 2026.
Traditional groundwater monitoring techniques lack the capabilities to measure groundwater fluxes at high spatial resolution over large distances. Breakthrough work by Simon et al. (2021) enabled the quantification of groundwater fluxes at high spatiotemporal resolution using actively heated fibre optic Distributed Temperature Sensing (A-DTS), establishing this as a promising hydrogeophysical method. However, current A-DTS interpretation methods, such as the analytical solution used to process A-DTS data, assume that groundwater flux is perpendicular to the cable. Yet, many field-based applications of A-DTS violate this assumption due to the multi-dimensional nature of groundwater flow. This study aims to characterise the effect of fibre optic cable orientation on the interpretation of groundwater fluxes, and determine the minimum angle for which the method remains applicable.
This study presents methodological advancements to A-DTS by characterising how cable orientation relative to flow direction affects groundwater flux estimates in a controlled environment. Estimating groundwater fluxes from A-DTS relies on the Moving Analytical Line Source (MILS) analytical model describing heat dissipation. A key assumption of the MILS model is that the flow is perpendicular to the cable angle, a condition frequently violated in field applications. To establish critical angle thresholds for reliable groundwater flux estimation, a large-scale experiment was conducted at the Site Contrôlé Expérimental de Recherche pour la réhabilitation des Eaux et des Sols (SCERES) platform in Strasbourg, France. This 25×12×3 m experimental tank represents an ~1000 m3 artificial porous aquifer designed to reduce potential boundary effects. This study allowed us to test some of the assumptions underlying the A-DTS method. A hybrid cable containing fibre optic strands and a steel armour for heating, was installed in a configuration with five sections at different orientations relative to the flow direction though the horizontal plane. The cable was buried within the saturated porous medium and different flux rates were imposed to establish the critical angle thresholds for reliable groundwater flux estimation. We will discuss the advantages and limitations of A-DTS for high-resolution groundwater flux monitoring under controlled yet field-representative conditions.
How to cite: Sai Louie, A., Moullec, C., Belfort, B., Reiller, H., Julien, A., Mace, S., and Bour, O.: Quantifying the influence of cable orientation on groundwater flux estimates from Active-Distributed Temperature Sensing, Galileo conference: Fibre Optic Sensing in Geosciences, Aussois, France, 31 Aug–4 Sep 2026, GC14-FibreOptic-61, https://doi.org/10.5194/egusphere-gc14-fibreoptic-61, 2026.
Distributed Acoustic Sensing (DAS), a photonic technology that converts a fibre-optic cable into a long (tens of kilometres), high–linear-density (with measurements every few metres) array of seismo-acoustic sensors, can provide high-density, high-resolution strain measurements along the entire cable. The potential of such distributed measurements has gained increasing attention in the seismological community for a wide range of applications.
It has been shown that DAS exhibits sub-wavelength sensitivity to heterogeneities near the fibre-optic cable. This sensitivity is related to the fact that DAS measures deformation, as opposed to the displacements measured by conventional seismometers. However, this sensitivity can also create difficulties for many DAS applications, such as source location or imaging at depth. Nevertheless, it can be advantageous for retrieving information about the subsurface in the immediate vicinity of the cable.
Here, we present a method to locate small heterogeneities near a fibre-optic cable by inverting an indicator of small-scale heterogeneities: the homogenised first-order corrector. We show that this first-order corrector can be used to locate heterogeneities near the fibre-optic cable with a precision on the order of the gauge length, independently of the wavelength.
We will first briefly present the homogenisation theory, making it possible to explain and interpret the link between small-scale heterogeneities and DAS data. We will then present the proposed method to retrieve information about small scales from DAS data, followed by several numerical and field-data application examples.
How to cite: Capdeville, Y., Mukumoto, K., Leparoux, D., Ikeda, T., Naruse, R., and Tsuji, T.: Locating sub-wavelength heterogeneities with DAS, Galileo conference: Fibre Optic Sensing in Geosciences, Aussois, France, 31 Aug–4 Sep 2026, GC14-FibreOptic-15, https://doi.org/10.5194/egusphere-gc14-fibreoptic-15, 2026.
Distributed dynamic strain sensing (DDSS) enables dense observations of seismic wavefields in complex environments such as active volcanoes, but records only axial strain along the fibre and therefore captures a limited projection of the full wavefield. Co-located rotational ground-motion measurements provide complementary constraints on wavefield geometry, propagation direction, and wave type.
We investigate the December 2025–January 2026 eruptive activity of Mount Etna using a combined dataset of distributed acoustic sensing and broadband rotational measurements at the Serra La Nave observatory. The work has been performed in the frame of ROTATIONAL-NIGHT project, a Transnational Access to the Eastern Sicily testbed supported by the EU project Geo-INQUIRE. Geo-INQUIRE is funded by the European Commission under project number 101058518 within the HORIZON-INFRA-2021-SERV-01 call.
The DDSS system comprises a ~300 m fibre-optic cable (10 m gauge length, 2 m channel spacing, 500 Hz sampling), complemented by a BlueSeis-3A rotational sensor. The dataset spans multiple eruptive phases, including pre-activation, escalating unrest, and the 27 December paroxysmal episode.
We track the evolving seismic wavefield by integrating spatially distributed strain observations with rotational constraints. Frequency–wavenumber (FK) analysis along the fibre resolves tremor propagation and apparent phase velocities, while rotational polarization analysis constrains dominant propagation directions and wavefield composition. Together, these measurements enable robust characterization of temporal changes in the wavefield during eruptive activity.
In addition, we analyze local volcano-tectonic (VT) events to investigate attenuation processes. By combining spatially distributed strain amplitudes with rotational constraints on propagation geometry, we explore the separation of intrinsic and scattering attenuation through frequency-dependent energy decay and wavefield characteristics.
Preliminarily results demonstrate that combining distributed strain sensing with rotational ground motion extends the observable seismic wavefield beyond the limitations of individual techniques, providing a pathway toward resolving source, path, and site effects within a unified framework.
How to cite: Izgi, G., Currenti, G., Eibl, E. P. S., Vollmer, D., Pellegrino, D., Pulvirenti, M., Alparone, S., Larocca, G., and Jousset, P.: Resolving seismic wavefield components using combined distributed strain and rotational measurements, Galileo conference: Fibre Optic Sensing in Geosciences, Aussois, France, 31 Aug–4 Sep 2026, GC14-FibreOptic-50, https://doi.org/10.5194/egusphere-gc14-fibreoptic-50, 2026.
Time-lapse monitoring is one of the main requirements for Carbon Capture and Storage sites. Seismic monitoring, the most used geophysical method for such purpose, is central to tracking subsurface changes during CO2 injection. However, as CCS deployment scales up, monitoring technologies must balance data quality, operational practicality, repeatability, and long-term cost-effectiveness. Distributed Acoustic Sensing (DAS) offers a viable alternative to conventional sensors for permanent installation and monitoring of large-scale CCS sites. However, as DAS is still considered an emergingtechnology, its performance must be evaluated against established instruments under controlled field conditions.
DAS provides many advantages, including requirement for electrical power only at one fibre end, dense spatial sampling, and the ability to record many channels over large coverage from a single interrogator. At the same time, DAS measurements can be affected by higher noise levels, directional sensitivity, gauge-length and pulse-width effects, and variable coupling between the fiber and the surrounding medium.
Here, we present a comparative study of surface and borehole fiber-optic seismic sensing during a CO₂ injection experiment at the Svelvik CO₂ Field Lab in May 2026. Injection was conducted in a central 65 m deep borehole, surrounded by four 100 m deep monitoring boreholes located 9–16 m from the injection well and instrumented with cemented fiber-optic cables. During the survey, a P-wave sparker source was deployed in the monitoring boreholes and on a surface in a prototype seismic source. The DAS system included straight and helically wound borehole fibers cemented outside of the monitoring wells, together with a prototype fiber optic surface sensor coupled to the ground with adjustable fluid mass loading. The entire fiber layout was interrogated simultaneously with an ASN OptoDAS interrogator. The DAS data are compared with measurements from borehole hydrophone strings, surface geophones, standalone seismic nodes, and a prototype of a optical MEMS-based accelerometer, allowing direct comparison of multiple sensors under identical field conditions.
We evaluate signal-to-noise ratio, repeatability metrics, stacking performance, quantitative signal attributes, and time-lapse response. The study provides a field-based assessment of how DAS-based seismic data can complement conventional and novel point seismic sensors for high-resolution monitoring of CO₂ injection and other shallow subsurface processes.
How to cite: Duda, M., Długosz, S., Wilczyński, Z., Ligas, E., Pantaleo, G., Meneghini, F., and Mithassel, B.: Quantitative comparison of DAS and point seismic sensors at Svelvik CO2 Field Lab , Galileo conference: Fibre Optic Sensing in Geosciences, Aussois, France, 31 Aug–4 Sep 2026, GC14-FibreOptic-110, https://doi.org/10.5194/egusphere-gc14-fibreoptic-110, 2026.
Optical sensing technologies are increasingly pivotal in geosciences and planetary exploration, where ultra-precise displacement measurements are essential for understanding seismic activity, subsurface dynamics, and environmental monitoring. This work presents a comparative analysis of two advanced optical measurement techniques developed in parallel by MAAGM: the LOKI optical interrogator — enabling all-optical, remote interrogation of electronics-free sensors based on a technology transfer from ESEO — and a planetary seismometer developed in collaboration with IPGP and funded by CNES. Both systems rely on optical distance measurements but employ distinct modulation schemes: phase modulation within an interferometer for the planetary seismometer, and optical frequency modulation upstream of the interferometer for LOKI. These approaches are positioned within the broader landscape of state-of-the-art optical displacement sensing, with emphasis on their respective interrogation architectures, sensitivity, robustness, and adaptability to harsh or remote environments — attributes directly relevant to next-generation fiber optic interrogator design.
The core of this study is an experimental campaign designed to cross-calibrate and compare the performance of these two optical methods. This work reflects a unique interdisciplinary collaboration between MAAGM, IPGP — a leader in planetary seismology — and ESEO, renowned for its expertise in optical sensing technologies. A single mechanical oscillator, originally developed by IPGP for planetary seismology, was instrumented with two phase-based optical sensors and one wavelength-based optical sensor, alongside a reference STS-2 seismometer. This setup enabled direct comparison of intrinsic noise levels and sensitivity, with particular focus on meeting the stringent requirements of lunar missions, where ambient noise is significantly lower than on Earth. The target sensitivity for such applications is 10⁻¹¹ m·s⁻²/√Hz at 0.1 Hz, necessitating exceptionally low self-noise instrumentation (cf. EGU26-13434).
Preliminary results demonstrate the noise performance of each interrogation method under controlled conditions, providing quantitative insights into their suitability for both planetary and terrestrial applications. Beyond planetology, these optical interrogation techniques show strong potential for instrumenting diverse geophysical transducers — including pressiometers, borehole seismometers, strainmeters, and rotational seismometers (cf. EGU26-18427) — thereby broadening the scope of retrievable observables in distributed and point optical sensing systems. The findings contribute to informing the design of next-generation optical interrogators optimized for deployment across a wide range of geoscience sensing contexts.
How to cite: Daddi Hammou, I., Feuilloy, M., Menard, P., Leleux, A., Nébut, T., Pagès, G., Robert, O., Ménigot, S., Leray, V., de Raucourt, S., and Guattari, F.: Comparative Study of Ultra-Precise Optical Displacement Sensing Techniques: From Planetary Seismology to Geosciences Applications, Galileo conference: Fibre Optic Sensing in Geosciences, Aussois, France, 31 Aug–4 Sep 2026, GC14-FibreOptic-115, https://doi.org/10.5194/egusphere-gc14-fibreoptic-115, 2026.
Distributed Acoustic Sensing (DAS) has emerged as a powerful tool for monitoring strain and temperature variations along fiber cables. Up to now, DAS has been most often used to track processes with frequencies above 1 Hz, originating either from anthropogenic sources (such as railway lines or highways, water and power distribution lines, vibrational modes of large civil infrastructures, etc.) or strain waves triggered by natural events such as earthquakes. However, many natural processes of interest (such as magma migrations in volcanoes, tidal or infra-gravity waves, tsunamis, slow ground motions, etc.) present relevant features at frequencies well below 1 Hz. As such, there is an increasing interest in monitoring this range of very low frequencies, which so far has been rather scarcely explored in DAS measurements.
In this very low-frequency range, the sensitivity of DAS systems is largely dominated by 1/f noise. This noise emerges as a fundamental limitation linked not only to laser instability but also to the inherently differential (relative) measurement principle of DAS. Phase or strain is not measured in DAS in an absolute sense; instead, it is continuously estimated with respect to a dynamically updated reference. This repeated referencing introduces cumulative error because each update step carries residual uncertainty arising from both system noise and environmental perturbations. Over time, these small errors integrate, producing a noise spectrum that increases toward low frequencies, leading to the characteristic 1/f behavior of strain noise in DAS measurements. In other words, the relative nature of DAS effectively is at the heart of this dominant low-frequency noise floor. Addressing 1/f noise in DAS therefore requires not only reducing underlying hardware noise sources but also rethinking referencing schemes.
Different DAS technologies on the market employ distinct methodologies to measure strain and temperature variations. Focusing on optical time-domain reflectometry-based DAS, some techniques measure the optical phase to infer strain, whereas others, such as chirped-pulse DAS (CP-DAS), measure strain by estimating the local spectral shift in the fiber response. In recent years, the performance advantages of CP-DAS have been well-documented, its primary advantages being related to larger strain dynamic range and uniform response along the fiber. The larger strain dynamic range and local nature of the measurement given by CP-DAS also lead to less frequent reference updating and superior performance at low frequencies. Strategies to almost completely cancel reference updates in CP-DAS have been explored in the literature.
In this work, we experimentally demonstrate a commercial platform with a strain sensitivity of < 10-9 ε/√Hz (and down to pε/√Hz for ~1 Hz and the upper band), essentially limited by ambient noise, across the entire millihertz band on a conventional fiber. The common phase DAS system tested shows a strain sensitivity performance in this band ~2 orders of magnitude worse in equivalent conditions. To the best of our knowledge, this represents the highest sensitivity reported to date in this frequency range. Such performance specifications demonstrate the significant potential of CP-DAS for integration into advanced early warning systems as well as monitoring a wide range of environmental phenomena.
How to cite: Preciado-Garbayo, J., Canudo, J., Gella, D., Garcia, J. M., Ramirez, J. A., Martins, H. F., and Gonzalez-Herraez, M.: Unlocking the low frequency band in DAS measurements: a chirped-pulse DAS with < 10-9 ε/√Hz sensitivity in the milli-Hertz band, Galileo conference: Fibre Optic Sensing in Geosciences, Aussois, France, 31 Aug–4 Sep 2026, GC14-FibreOptic-58, https://doi.org/10.5194/egusphere-gc14-fibreoptic-58, 2026.
We present a microwave-frequency optical time-domain reflectometry (MF-OTDR) scheme for distributed acoustic sensing (DAS) of large strain-rate mechanical perturbations, supported by both theoretical analysis and experimental demonstration. The system employs microwave-modulated optical probe pulses injected into the fiber, where large external mechanical perturbations induce localized phase changes on the backscattered signal at the microwave frequency, and the resulting beat encodes group delay variations from which strain signals are efficiently recovered through phase demodulation, even under large strain-rate conditions.
The performance is validated by both theoretical analysis and proof-of-concept experiments, demonstrating high-fidelity recovery of strain amplitudes up to the microstrain level, reaching 1.8 microstrains, and dynamic frequencies up to the kilohertz range over multi-kilometer distances, currently demonstrated over 4 km. Compared with conventional phase-demodulation DAS, the proposed scheme extends the measurable strain range by up to four orders of magnitude at the same spatial resolution. In particular, direct detection enables linear strain quantification up to 1000-fold the saturation limit of conventional DAS under identical performance conditions. Meanwhile, the proposed scheme has a system architecture and hardware requirements highly similar to existing phase-sensitive OTDR configurations, making the two approaches complementary for constructing a sensing system that simultaneously offers high sensitivity and high dynamic range.
Such an experimentally verified increase in saturation level is especially important for earthquake early warning (EEW), where near-field strong motions may generate extremely large strain-rate signals. Peak ground strain rate is known to scale approximately exponentially with earthquake magnitude, implying that a three- to four-order-of-magnitude increase in measurable strain-rate amplitude can correspond to an increase of several magnitude units. In practical terms, while conventional DAS systems may saturate for events on the order of M3 at distances of ~10 km, the enhanced dynamic range demonstrated here could in principle extend measurable conditions toward much larger-magnitude events, thereby substantially reducing signal saturation in near-field strong-motion scenarios. The proposed MF-OTDR scheme is therefore a promising solution for distributed sensing of large strain-rate dynamic events, including strong ground motions in EEW scenarios.
To enable such performance under large strain-rate conditions, a key challenge must also be addressed: direct detection of the microwave beat introduces phase distortion within the perturbed region, as well as amplitude fluctuations and phase deviations after the perturbation, including irregular π phase jumps. The underlying mechanism of this issue is theoretically analyzed, and a corresponding data processing strategy is developed, which is experimentally implemented and addressed by a dedicated processing procedure involving phase-jump correction and smoothing to suppress amplitude anomalies. This ensures accurate phase demodulation and strain reconstruction.
How to cite: Ren, Y., Fernández-Ruiz, M. R., Martin-Lopez, S., Costa, L., Zhan, Z., and Gonzalez-Herraez, M.: Microwave-Frequency OTDR for Distributed Sensing of Large Strain-Rate Perturbations, Galileo conference: Fibre Optic Sensing in Geosciences, Aussois, France, 31 Aug–4 Sep 2026, GC14-FibreOptic-35, https://doi.org/10.5194/egusphere-gc14-fibreoptic-35, 2026.
As in many scientific fields, seismologists have a long history of developing and distributing domain-specific software. Some of the earliest packages were written in C and Fortran and were primarily used via the command line or through shell scripting. The emergence of a new generation of programming languages, such as Python, R, MATLAB, and Julia, has led to a growing ecosystem of seismological software, lowering the barrier to conducting research and improving interoperability with the broader scientific community. Python, in particular, has become especially popular among seismologists, and several foundational DAS packages have emerged, each with distinct strengths and feature sets. However, compatibility between these packages is not guaranteed. In this talk, I compare the design and capabilities of the existing libraries and provide guidance for researchers and package developers to help reduce ecosystem fragmentation. I also highlight key gaps and opportunities for future contributions within the nascent open-source DAS ecosystem. Finally, I explore the implications of emerging, highly capable coding agents and how they may reshape seismic research and software development. To demonstrate, I present several new experimental projects that illustrate both the dramatic increase in development velocity and the enhanced capabilities enabled by this new generation of tools.
How to cite: Chambers, D.: The Open-Source DAS Python Ecosystem, Galileo conference: Fibre Optic Sensing in Geosciences, Aussois, France, 31 Aug–4 Sep 2026, GC14-FibreOptic-9, https://doi.org/10.5194/egusphere-gc14-fibreoptic-9, 2026.
Massive Fiber-Optic Distributed Acoustic Sensing (FO-DAS) data streams pose major challenges in archiving, dissemination, and exploitation due to their enormous volumes and high spatio-temporal resolution. Efficient storage is constrained by bandwidth, cost, and metadata standardization, while dissemination is limited by network capacity, data discoverability and data format diversity. Scientific exploitation is further hindered by the need for scalable preprocessing, real-time analytics, and robust noise characterization to extract actionable signals from petabyte-scale, heterogeneous datasets.
This contribution showcases the DATA TERRA (FormaTerre, Odatis, THEIA) approach to describe, store, disseminate and exploit massive FO-DAS datasets, through the GAIA-Data distributed data and computing infrastructure. Key infrastructure aspects are presented allowing to construct a national/european and analysis-ready FO-DAS dataspace. This infrastructure allows easy and interactive discovery and exploitation of massive FO-DAS data for various applications in all domains of the Earth exploration (e.g. seismological source identification, event characterization and seismic parameter estimation generalizing across volcanoes, glaciers, fault zones, landslides, and urban areas).
Examples of resource-intensive processing on HPC infra and AI-ready workspaces are presented. FO-DAS bottlenecks are addressed via AI-driven compression (e.g. variational autoencoders), selective archiving, and data augmentation to ensure scalable monitoring. Integration of the dataspace in the DATA TERRA EOSC node will ensure interoperability with other national (NFDI4DEarth) and European research infrastructures (EPOS, EMSO, eLTER).
How to cite: Mouchené, M., Caer, G., Malet, J.-P., Hibert, C., Ramage, K., Boderé, E., Cunin, A., and Chaljub, E.: The GAIA Data Platform for Fiber Optic Distributed Acoustic Sensing Data Discovery and Processing, Galileo conference: Fibre Optic Sensing in Geosciences, Aussois, France, 31 Aug–4 Sep 2026, GC14-FibreOptic-69, https://doi.org/10.5194/egusphere-gc14-fibreoptic-69, 2026.
The rapid adoption of distributed acoustic sensing (DAS) retrofitted on submarine cables has enabled sensor coverage for seismology applications over vast oceanic regions that were previously lacking real-time sensors. The data integration into operational use in seismic networks often involves significant data downsampling and independent processing of single-cable data streams. However, a sparse set of pre-processed measurements from virtual seismic stations along the cable can be very valuable for earthquake early warning and location. Going forward, significantly scaling up data coverage and density is possible with recently introduced DAS technologies. Real-time DAS data from full-resolution cable networks will greatly enhance measurement geometries to improve location accuracy, and advance advanced processing and analysis making use of amplitude information.
When instrumenting multiple cables and jointly processing the data, the limitations of linear cable routing can be overcome to improve location accuracy. This is supported by DAS multiplexing that allows a single instrument to connect to fibres from multiple cables that may be available at a cable landing station. Further range extension of the DAS system will also contribute to geometrical coverage, in particular when reaching the non-straight routing segments tracking seabed topologies off the continental shelf. We will discuss the implications for seismology of recently introduced DAS technologies that extend the spatial coverage.
Scaling up DAS coverage to cable networks and transferring full-resolution data significantly increases requirements to bandwidth capacity and transmission protocols for high-datarate streaming. Users of DAS technologies in the energy sector have faced this challenge and suitable implementations can be adapted for seismology applications. These capacity expansions will support centralized processing at data centres for events recorded on multiple cables, even involving disparate interrogator locations. We describe how the requirements to timing concurrency and data contract management is supported.
While advanced protocols and increased network bandwidth are important enabling technologies for full-resolution DAS monitoring on cable networks, the significant increase in data volumes must also be tackled by developing edge processing techniques that can compute compact pre-processed data products. Recently introduced techniques for sub-array beamforming on pre-defined linear segments of the cable can considerably compress the data. These data products are then used for earthquake location processing at a centralized computing facility with access to the data from all cables in the DAS cable network. We discuss numerically efficient implementations of such edge processing techniques and the potential for relieving data transmission requirements.
How to cite: Morten, J. P. and Brenne, J. K.: DAS full-resolution cable networks in seismology, Galileo conference: Fibre Optic Sensing in Geosciences, Aussois, France, 31 Aug–4 Sep 2026, GC14-FibreOptic-43, https://doi.org/10.5194/egusphere-gc14-fibreoptic-43, 2026.
Distributed Acoustic Sensing (DAS) has rapidly evolved from an experimental sensing approach into a practical operational technology for seismic imaging and reservoir monitoring in geoscience applications due to its ability to transform fibre optic infrastructure into dense arrays of seismic receivers. DAS systems enable high-resolution measurements in boreholes, trenches, and subsea environments, supporting applications such as vertical seismic profiling (VSP), 3D and 4D reservoir monitoring, and near-surface imaging. As DAS deployments continue to scale, the efficient management of large distributed datasets and the automation of acquisition and processing workflows have become increasingly important for reliable field operations and timely geophysical interpretation.
This presentation provides a practical overview of operational best practices for DAS-based geoscience surveys, focusing on automated processing workflows, real-time quality control, and scalable acquisition architectures. The discussion covers the end-to-end operational workflow from survey planning and equipment preparation through acquisition, data handling, processing, visualization, and delivery. Workflows for both active and passive acoustic monitoring are presented, including continuous recording, triggered acquisition, automated event and shot extraction, and real-time operational QC.
Particular emphasis is placed on the DAS interrogators, auxiliary acquisition systems, networking infrastructure, and real-time processing environments to support efficient field deployment and remote operations. Practical quality control methodologies are also discussed, including automated monitoring of acquisition health, timing synchronization, data integrity, signal consistency, and operational performance throughout survey execution.
In addition, the presentation explores the growing role of edge-based processing and intelligent data handling within DAS acquisition systems. Real-time visualization, data reduction workflows, and remote operational support are discussed as emerging requirements for modern fibre optic sensing deployments, particularly where large data volumes and several distrusted systems are involved.
By consolidating operational experience from a range of DAS deployments, this work demonstrates how robust acquisition design, automated processing workflows, and scalable operational architectures can improve acquisition reliability and maximize the value of fibre optic sensing technologies for geoscience applications.
How to cite: Chalari, A. and Clarke, A.: Survey Design, Processing Workflows, and Operational Best Practice for Distributed Acoustic Sensing in Geoscience Applications, Galileo conference: Fibre Optic Sensing in Geosciences, Aussois, France, 31 Aug–4 Sep 2026, GC14-FibreOptic-96, https://doi.org/10.5194/egusphere-gc14-fibreoptic-96, 2026.
Over the past decade, studies involving fibre optic sensing (FOS) have increased substantially, and consequentialy, optical fibres have become a prominent option for seismo-acoustic data acquisition. FOS can leverage existing telecom infrastructure in locations where installing conventional seismic stations is difficult, while providing dense measurements at high spatial and temporal sampling rates. However, replacing conventional sensor workflows with fibre optic sensing introduces major practical challenges such as: very large data volumes, heterogeneous native formats, high computational demand for fast processing and visualisation, and the need for intuitive yet flexible programming interfaces.
Several open-source tools such as DASPy, DASCore and Xdas already address parts of these challenges. Here we present FoBench as a complementary architecture focused on practical, reproducible end-to-end workflows for FOS data handling and baseline signal processing. FoBench is designed to ease transition from conventional seismo-acoustic workflows by adopting usage patterns familiar to ObsPy and Pyrocko users. It supports native formats (I/O) from multiple interrogator manufacturers, provides high-speed interactive plotting for seamless data inspection, and organises campaign-scale archives through a structured Project-Unit-Dataset model.
FoBench also targets operational scalability. It includes discontinuity-aware dataset handling, configurable processing pipelines, and memory-efficient greater-than-memory workflows via chunked outputs, with four interchangeable parallel wrappers (multiprocessing, MPI, Dask, and Process Pools). In addition, FoBench’s architecture is aligned with the in-development Geo-INQUIRE proposed metadata scheme to improve consistency and interoperability across archives.
We present the design principles of FoBench, illustrate representative processing workflows on seismo-acoustic FOS datasets, and discuss benchmark comparisons against available toolboxes. Our goal is not to replace existing ecosystems, but to provide a lightweight, interoperable, and user-oriented framework that bridges the gap between raw FOS files and reproducible scientific products.
How to cite: Diaz-Meza, S., Pätzel, J., Wollin, C., Hart, J., and Hillmann, L.: FoBench: A Python toolbox for Fibre Optic Sensing signal processing and data handling., Galileo conference: Fibre Optic Sensing in Geosciences, Aussois, France, 31 Aug–4 Sep 2026, GC14-FibreOptic-48, https://doi.org/10.5194/egusphere-gc14-fibreoptic-48, 2026.
Optical fiber sensing has become increasingly important to provide continuous monitoring of optical fiber cables as well as their surrounding environment. In this context, Distributed Acoustic Sensing (DAS), based on Rayleigh scattering, has gained momentum and is now widely used to detect vibrational events for infrastructure monitoring and security, characterization of geophysical phenomena, or industrial process monitoring in energy, oil and gas, and smart city environments…
Our work focuses on multi-parameter estimation to detect and characterize a wider range of perturbations and gain knowledge about their nature. Using a coded-interrogation Multiple-Input-Multiple-Output Distributed Acoustic Sensing (MIMO-DAS) architecture, we estimate the Jones matrices describing the round-trip propagation along the optical fiber. From these matrices, we extract through post-processing two parameters of interest for each fiber section of 1.3m on average, independently of adjacent sections. These quantities are the common or polarization-averaged differential phase, representing the phase delay introduced by the fiber section and common to both polarization tributaries, and the retardance, corresponding to the phase shift between the two eigenpolarizations introduced by the fiber section, proportional to the effective birefringence magnitude.
Compared to conventional differential phase Optical Time-Domain Reflectometry (ΔΦ-OTDR) that focuses solely on differential phase estimation or Polarization Optical Time-Domain Reflectometry (P-OTDR) that considers polarization-related properties only, our approach aims at providing further information on environmental events by allowing a joint estimation of phase and polarization effects. Moreover, the coded-interrogation scheme eliminates the need to send several input State of Polarization (SOPs) and enables the coexistence of sensing and data transmission.
First, we demonstrate the detection and localization of dynamic strain events of frequency up to 3 kHz on standard single-mode fibers with a mean spatial resolution of 1.3m, and show the ability to discriminate between purely axisymmetric strains and anisotropic strains. Indeed, while the differential phase is sensitive to both kinds of events, the retardance is only responsive to perturbations that break cylindrical symmetry. Second, we validate our model through experiments in two scenarios: in the presence of longitudinal strain and anisotropic transverse strain. In addition, we use our system to estimate the effective birefringence magnitude along the fiber length in static conditions, providing insights into the fiber characteristics and its surrounding environment. In the future, we foresee exploring the advantages of our technique over various field-deployed fiber cable configurations.
How to cite: Prato, D., Gabet, R., and Awwad, É.: Joint phase and birefringence estimation in MIMO-DAS for dynamic strain anisotropy discrimination and static fiber characterization, Galileo conference: Fibre Optic Sensing in Geosciences, Aussois, France, 31 Aug–4 Sep 2026, GC14-FibreOptic-68, https://doi.org/10.5194/egusphere-gc14-fibreoptic-68, 2026.
In recent years, significant technological progress has demonstrated the feasibility of using the long distance fiber optic links as large-scale distributed networks for environmental sensing [1]. The French national research infrastructure REFIMEVE [2] currently distributes an ultra-stable optical frequency reference (ultranarrow linewidth laser referenced to a metrological source at 1542 nm) across more than 9000 km of fibre links connecting laboratories throughout France and Europe. The optical reference is transferred through RENATER fibre network using bi-directional optical amplifiers and regeneration laser stations [3]. The light propagates back and forth in the same fiber enabling to maximize the cancellation of the noise induced by the optical link. The infrastructure has demonstrated strong potential for geophysical studies [4] as the cancelled noises are linked to the seismic noise integrated along the fibers. In this context, the European project SENSEI (Smart European Networks for Sensing the Environment and Internet Quality) [5] aims to harness this potential by developing the next generation photonic technologies for detecting both natural phenomena, such as earthquakes, volcano activity, and anthropogenic events including construction activity or vehicular traffic.
Within this framework, one of our objectives is to develop a coherent optical frequency domain reflectometry (C-OFDR) [6] sensing device based on a low noise laser in order to extend the sensing range of existing setups and add location capability to our previous result. In our setup, the output of a low noise laser is frequency modulated and a fibre under test is measured in a Michelson interferometer configuration. By analysing the Rayleigh backscattered signal along the fibre, the system enables detailed diagnostics of the fibre. As a first demonstration, we tested a prototype over a long-range fibre link extending up to 410 km. The system successfully identified the location of the optical amplifier and a PC connector placed at the end of the fibre with km scale spatial resolution. In future work, we plan to implement a transportable acquisition setup and deploy the C-OFDR system on an operational fiber network to evaluate its performance under real field conditions.
References:
[1] G. Marra et al., Science 361 (2018), https://doi.org/10.1126/science.aat4458
[2] REFIMEVE, https://www.refimeve.fr/en/homepage/
[3] O. Lopez et al., Opt. Express 20, 23518-23526 (2012) https://doi.org/10.1364/OE.20.023518
[4] M. B. K. Tønnes, Thesis (2022), https://hal.science/tel-03984045v1
[5] SENSEI, https://senseiproject.eu/
[6] C. Liang et al., IEEE Access. 9 (2021), DOI : 10.1109/ACCESS.2021.3061250
How to cite: Hilico, A., Show, D., Dutta, B., Lopez, O., Amy-Klein, A., Chardonnet, C., Pottie, P.-E., and Cantin, E.: Long range Coherent-Optical Frequency Domain Reflectometry for large scale fibre sensing, Galileo conference: Fibre Optic Sensing in Geosciences, Aussois, France, 31 Aug–4 Sep 2026, GC14-FibreOptic-95, https://doi.org/10.5194/egusphere-gc14-fibreoptic-95, 2026.
The deployment of ultra-stable optical frequency dissemination networks over existing telecommunication infrastructure opens new perspectives for large-scale fiber sensing. In France, the REFIMEVE network distributes ultra-stable optical reference signals through more than 5000 km of actively operated telecom fibers. Initially developed for frequency metrology applications, such infrastructures also provide an opportunity to investigate fiber-based environmental sensing at unprecedented spatial scales. The objective is to exploit existing permanent telecommunication infrastructures as large-scale environmental sensing systems for geophysical applications.
The originality of our approach relies on the use of ultra-stable optical carriers exhibiting sub-hertz linewidths and coherence lengths exceeding terrestrial scales. These properties enable highly coherent interferometric measurements over very long distances. These motivate the development of new photonic instrumentation dedicated to long-range sensing, potentially extending from continental to transoceanic links.
Previous experiments performed on REFIMEVE demonstrated the capability of the network to detect large seismic events (magnitude > 5) through phase perturbations accumulated along the optical path. However, these first demonstrations relied on integrated measurements with sampling times on the order of one second, limiting temporal resolution and hence event localization capabilities. In contrast with conventional distributed dynamic fiber sensing (DDFS) techniques, the measured signal corresponds to the integrated phase noise of the entire optical link, preventing direct spatial discrimination of perturbations.
Within the European project SENSEI, we investigate new coherent sensing architectures intended to combine long-range operation with improved spatial resolution. In this work, we present ongoing developments of a photonic sensing instrument based on repeater laser stations, capable of phase-locking onto the disseminated ultra-stable optical carrier. Once locked, the repeater station can introduce controlled phase modulation onto the transmitted optical field using a phase modulator. The sensing information is retrieved through coherent demodulation at the laser station (for backscattered light). We discuss the main principles underlying the proposed architecture, including modulation and demodulation strategies compatible with long-haul coherent propagation on active telecom networks.
Particular attention is given to polarization-related effects. We discuss approaches under investigation to mitigate polarization diversity and associated fading mechanisms. In addition, we examine the possibility of exploiting the evolution of the optical state of polarization itself as an additional sensing observable in such systems, potentially providing complementary information on environmental perturbations affecting the fiber link and complementary to the observations made in coherent telecommunication networks.
How to cite: Coget, G., Majek, C., Desruelle, B., and Pottie, P.-E.: Development of Photonic Instrumentation for Long-Range Fiber Sensing on Ultra-Stable Optical Frequency Networks, Galileo conference: Fibre Optic Sensing in Geosciences, Aussois, France, 31 Aug–4 Sep 2026, GC14-FibreOptic-105, https://doi.org/10.5194/egusphere-gc14-fibreoptic-105, 2026.
Deployed telecommunication fiber optic cables and distributed acoustic sensing (DAS) are increasingly emerging as a versatile sensing platform in geosciences, offering high-resolution dynamic environmental monitoring across large areas. However, in practical deployments, the measured DAS signals are not entirely determined by the event source. Variations in geological conditions, fiber optic cable installation, and fiber-medium coupling can significantly alter the recorded waveform, complicating the interpretation of vibration signals.
This study aims to investigate the differences in DAS signals under different ground conditions during the same controlled impact event. We analyzed repeated-impact experiments using ∆ϕ-OTDR (Differential Phase Optical Time Domain Reflectometry) measurements acquired from deployed telecommunication fiber optic cables under three different ground conditions. By integrating time-domain and frequency-domain features, we extract discriminative patterns from raw signal fluctuations. We employed metrics such as Euclidean distance, dynamic time warping, and Area Under the Receiver Operating Characteristic Curve (AUC-ROC) to compare these differences. Based on these distance metrics, we present preliminary classification attempts for ground type configuration by applying a K-Nearest Neighbors (KNN) algorithm.
While these initial classification attempts show promise, extracting physically meaningful features from DAS data remains a challenge. We propose a novel feature extraction method that leverages the spatio-temporal coherence of DAS signals through correlation matrices used in a previous work to identify fiber layout. Here, we use it for a new target: identification of the ground configuration. This proposed approach effectively demonstrates the ability to locate known impact events and reveals unique wave propagation patterns across different ground configurations.
This preliminary study highlights the potential of coherence-based feature extraction for DAS signal analysis under different ground configurations. Future work will focus on expanding datasets, optimizing feature extraction pipelines, and integrating further machine-learning techniques for classification.
How to cite: Luo, J., Pruvost, P., Irurozki, E., Jaouën, Y., and Awwad, É.: How Do Ground Conditions Shape DAS Signals? An Experimental Study with Telecom Fibers and Machine Learning., Galileo conference: Fibre Optic Sensing in Geosciences, Aussois, France, 31 Aug–4 Sep 2026, GC14-FibreOptic-72, https://doi.org/10.5194/egusphere-gc14-fibreoptic-72, 2026.
Optical fiber sensing method, such as Distributed Acoustic Sensing (DAS), are increasingly emerging as a versatile sensing platform in geosciences, offering high-resolution, continuous monitoring across large areas. Leveraging existing deployed fibers from telecommunication networks provides a cost-effective solution for large-scale applications, ranging from seismic monitoring and environmental surveillance to structural health assessment.
However, when utilizing pre-existing near-surface fiber infrastructure, the mechanical coupling between the fiber cable and the surrounding medium is highly variable and completely uncontrolled. This fluctuating coupling strongly influences the detected signal amplitude and frequency domain response. While it presents a challenge for quantization of amplitude analysis, assessing these local variations also offers a unique opportunity to probe and characterize the immediate shallow surroundings of the cable.
In this study, we investigate the impact of local environmental conditions on DAS signal using an urban telecommunication fiber network. Controlled surface seismic experiments were conducted across various deployment configurations, including sections buried in sand, passing through technical chambers (manholes), and embedded beneath asphalt. The acquired active-source data were analyzed in both the time and frequency domains to isolate the signatures of each distinct environment and extract the specific acoustic response of the cable’s surroundings.
Our preliminary results demonstrate that different deployment media introduce distinct spectral fingerprints and attenuation patterns in the DAS records. This analysis provides valuable insights into how unconstrained coupling filters the seismic wavefield. Ongoing and future work will focus on expanding the dataset, refining the transfer functions between the soil and the cable, and decoupling the intrinsic cable properties from the medium response to improve the reliability of urban DAS ambient noise and event monitoring.
How to cite: Pruvost, P., Jaouën, Y., and Awwad, É.: Characterizing the Surrounding Medium of an Optical Fiber Network Using Distributed Acoustic Sensing (DAS), Galileo conference: Fibre Optic Sensing in Geosciences, Aussois, France, 31 Aug–4 Sep 2026, GC14-FibreOptic-73, https://doi.org/10.5194/egusphere-gc14-fibreoptic-73, 2026.
Distributed Acoustic Sensing (DAS) has established itself as a robust technology for detecting thermal and mechanical variations along fiber-optic cables. Historically, DAS applications have predominantly targeted dynamic processes above 1 Hz, such as anthropogenic noise (e.g., traffic, railway monitoring, or structural health engineering) and high-frequency seismic waves from earthquakes. Conversely, many critical geophysical phenomena that characteristically manifest at frequencies well below 1 Hz —including volcanic magma migration, tidal fluctuations, ocean infra-gravity waves, and slow crustal deformation— can also be measured by DAS. Consequently, there is a growing scientific interest in exploring this ultra-low frequency spectrum, an area that remains largely understudied in distributed sensing frameworks.
Commercial DAS interrogators utilize diverse optical principles to quantify strain. Within phase-sensitive optical time-domain reflectometry (φ-OTDR), some systems extract the raw optical phase to calculate deformation, while alternative approaches, such as chirped-pulse DAS (CP-DAS), derive strain by tracking local spectral shifts in the fiber's backscattered response. Recent literature highlights the distinct metrological advantages of CP-DAS, particularly its wider dynamic range, uniform longitudinal sensitivity, and localized measurement principle. These features minimize the need for frequent reference updates and significantly enhance instrument stability at lower frequencies.
To evaluate these capabilities under optimal low-frequency conditions, a specialized experimental setup was deployed at the Black Forest Observatory (BFO). Here, eight single-mode patch fibers were rigidly coupled to the surrounding medium by cementing them into a 250-meter-long groove excavated directly into the gallery's concrete floor. The utilized cables comprise a standard 9 um core, 125 mm cladding, 250 mm coating, and a 900 mm tight buffer, resulting in a total outer diameter of 0.9 mm. This high-rigidity installation ensures near-ideal strain transfer from the host rock to the fiber core. Operating as a controlled geophysical test-bed, this layout allows for a cross-comparison between the DAS channels and BFO’s permanent Invar-wire strainmeter array, facilitating a precise evaluation of signal fidelity.
In this work, we present a comprehensive time- and frequency-domain intercomparison between a commercial CP DAS interrogator platform and the reference strainmeter array during periods of microseismic activity and teleseismic wave arrivals. Our experimental results demonstrate highly equivalent performance across both domains, validating the quantitative reliability of the distributed optical approach for broadband geophysical monitoring.
How to cite: Ramirez, J., Preciado-Garbayo, J., Forbriger, T., Canudo, J., Gella, D., del Ponzo, J., Martins, H., and Gonzalez-Herraez, M.: Time and Frequency analysis of DAS in cemented fibers: Insights from the Black Forest Observatory test-bed, Galileo conference: Fibre Optic Sensing in Geosciences, Aussois, France, 31 Aug–4 Sep 2026, GC14-FibreOptic-121, https://doi.org/10.5194/egusphere-gc14-fibreoptic-121, 2026.
