bluuebunny/crossref_metadata_2025 huggingface dataset:
Divergent biophysical responses of western United States forests to wildfire driven by eco-climatic gradients
Authors: Shrestha Surendra , Williams Christopher A. , Rogers Brendan M. , Rogan John , Kulakowski Dominik
Published: May 2024

Abstract. Understanding vegetation recovery after fire is critical for predicting vegetation-mediated ecological dynamics in future climates. However, information characterizing vegetation recovery patterns after fire and their determinants over large geographical extents is limited. This study uses Moderate Resolution Imaging Spectroradiometer (MODIS) leaf area index (LAI) and albedo to characterize patterns of post-fire biophysical dynamics across the western United States (US) and further examines the influence of topo-climatic variables on the recovery of LAI and albedo at two different time horizons, 10 and 20 years post-fire, using a random forest model. Recovery patterns were derived for all wildfires that occurred between 1986 and 2017 across seven forest types and 21 level III ecoregions of the western US. We found differences in the characteristic trajectories of post-fire vegetation recovery across forest types and eco-climatic settings. In some forest types, LAI had recovered to only 60 %–70 % of the pre-fire levels by 25 years after the fire, while it recovered to 120 %–150 % of the pre-fire levels in other forest types, with higher absolute post-fire changes observed in forest types and ecoregions that had a higher initial pre-fire LAI. Our random forest results showed very little influence of fire severity on the recovery of both summer LAI and albedo at both post-fire time horizons. Post-fire vegetation recovery was most strongly controlled by elevation, with faster rates of recovery at lower elevations. Similarly, annual precipitation and average summer temperature had significant impacts on the post-fire recovery of vegetation. Full recovery was seldom observed when annual precipitation was less than 500 mm and average summer temperature was above the optimal range, i.e., 15–20 °C. Climate influences, particularly annual precipitation, were a major driver of post-fire summer albedo change through its impact on ecological succession. This study provides quantitative measures of primary controls that could be used to improve the modeling of ecosystem dynamics post-fire.
21st century global glacier evolution under CMIP6 scenarios and the role of glacier-specific observations
Authors: Zekollari Harry , Huss Matthias , Schuster Lilian , Maussion Fabien , Rounce David R. , Aguayo Rodrigo , Champollion Nicolas , Compagno Loris , Hugonnet Romain , Marzeion Ben , Mojtabavi Seyedhamidreza , Farinotti Daniel
Published: May 2024

Abstract. Projecting the global evolution of glaciers is crucial to quantify future sea-level rise and changes in glacier-fed rivers. Recent intercomparison efforts have shown that a large part of the uncertainties in the projected glacier evolution is driven by the glacier model itself and by the data used for initial conditions and calibration. Here, we quantify the effect that mass balance observations, one of the most crucial data sources used in glacier modelling, have on glacier projections. For this, we model the 21st century global glacier evolution under CMIP6 climate scenarios with the Global Glacier Evolution Model (GloGEM) calibrated to match glacier-specific mass balance observations, as opposed to relying on regional mass balance observations. We find that the differences in modelled 21st century glacier changes can be large at the scale of individual glaciers (up to several tens of percent), but tend to average out at regional to global scales (a few percent at most). Our study thus indicates that the added value of relying on glacier-specific observations is at the subregional and local scale, which will increasingly allow projecting the glacier-specific evolution and local impacts for every individual glacier on Earth. To increase the ensemble of models that project global glacier evolution under CMIP6 scenarios, simulations are also performed with the Open Global Glacier Model (OGGM). We project the 2015–2100 global glacier loss to vary between 25±15 % (GloGEM) and 29±14 % (OGGM) under SSP1-2.6 to 46±26 % and 54±29 % under SSP5-8.5 (ensemble median, with 95 % confidence interval). Despite some differences at the regional scale and a slightly more pronounced sensitivity to changing climatic conditions, our results agree well with the recent projections by Rounce et al. (2023), thereby projecting, for any emission scenario, a higher 21st century mass loss than the current community estimate from the second phase of the Glacier Model Intercomparison Project (GlacierMIP2).
Seasonal Variation of Total Column Formaldehyde, Nitrogen Dioxide, and Ozone Over Various Pandora Spectrometer Sites with a Comparison of OMI and Diurnally Varying DSCOVR-EPIC Satellite Data
Authors: Herman Jay , Mao Jianping
Published: May 2024

Abstract. Both The OMI (Ozone Monitoring Instrument) satellite and the Pandora ground-based instruments operate with spectrometers that have similar characteristics in wavelength range and spectral resolution that enable them to retrieve total column amounts of formaldehyde TCHCHO, and nitrogen dioxide TCNO2, and ozone TCO at 13:30 ± 0:45 local time. At most sites, Pandora shows a strong seasonal dependence for TCO and TCHCHO and little seasonal dependence for TCNO2, while OMI sees little seasonal dependence for TCHCHO and TCNO2 but does see seasonal dependence for TCO. The seasonal behavior of TCHCHO is caused by plant growth and emissions from lakes that peak in the summer suggesting that OMI is not correctly retrieving TCHCHO all the way to the Earth’s boundary layer. Since the OMI retrieval is around 13:30 local equator crossing time ± 0:45 and tends to occur near the frequent minimum of the daily TCNO2 time series, OMI underestimates the amount of air pollution that occurs during each year. Better TCNO2 agreement occurs when the Pandora data is averaged between 13:00 and 14:00 hours local time. Comparisons of OMI total column NO2 and HCHO with Pandora daily time series show both agreement and disagreement at various sites and days. Similar comparisons of OMI TCO with those retrieved by Pandora show good agreement in most cases. Additional comparisons are shown of Pandora TCO with hourly retrievals during a day from EPIC (Earth Polychromatic Imaging Camera) spacecraft instrument orbiting the Earth-Sun Lagrange point L1.
Investigating the global and regional response of drought to idealized deforestation using multiple global climate models
Authors: Li Yan , Huang Bo , Tan Chunping , Zhang Xia , Cherubini Francesco , Rust Henning W.
Published: May 2024

Abstract. Land use change, particularly deforestation, significantly influences the global climate system. While various studies have explored how deforestation affects temperature and precipitation, its impact on drought remains less explored. Understanding these effects across different climate zones and time scales is crucial for crafting effective land use policies aimed at mitigating climate change. This study seeks to investigate how changes in forest cover affect drought across different time scales and climate zones using simulated deforestation scenarios, where forests are converted to grasslands. The study utilizes data from nine global climate models participating in the Land Use Model Intercomparison Project. Drought effects are assessed by examining changes in the Standardized Precipitation Evapotranspiration Index (SPEI). The results reveal that deforestation leads to negative shifts in global SPEIs, indicating increased dryness, particularly in tropical regions, while causing wetter conditions in dry regions. Moreover, the impact on drought indices becomes more pronounced with longer time scales, underscoring the lasting effects of deforestation on drought. Seasonally, deforestation exacerbates SPEI03 shifts during autumn and winter, especially affecting tropical and northern polar regions. Continental zones experience significant seasonal changes, becoming drier in winter and wetter in summer due to global deforestation, while the northern hemisphere's dry regions see increased wetter conditions, particularly in autumn. These findings deepen our understanding of the relationship between vegetation change and climate change, offering valuable insights for better resource management and mitigation strategies against future climate change impacts.
Graphical representation of global water models
Authors: Müller Schmied Hannes , Gosling Simon Newland , Garnsworthy Marlo , Müller Laura , Telteu Camelia-Eliza , Ahmed Atiq Kainan , Andersen Lauren Seaby , Boulange Julien , Burek Peter , Chang Jinfeng , Chen He , Grillakis Manolis , Guillaumot Luca , Hanasaki Naota , Koutroulis Aristeidis , Kumar Rohini , Leng Guoyong , Liu Junguo , Liu Xingcai , Menke Inga , Mishra Vimal , Pokhrel Yadu , Rakovec Oldrich , Samaniego Luis , Satoh Yusuke , Shah Harsh Lovekumar , Smilovic Mikhail , Stacke Tobias , Sutanudjaja Edwin , Thiery Wim , Tsilimigkras Athanasios , Wada Yoshihide , Wanders Niko , Yokohata Tokuta
Published: May 2024

Abstract. Numerical models are simplified representations of the real world at a finite level of complexity. Global water models are used to simulate the global water cycle and their outputs contribute to the evaluation of important natural and societal issues, including water availability, flood risk and ecological functioning. Whilst global water modelling is an area of science that has developed over several decades, and individual model-specific descriptions exist for some models, there has to date been no attempt to visualize the ways that several models work, using a standardized visualisation framework. Here, we address this gap by presenting a set of visualizations of several global water models participating in the Inter-Sectoral Impact Model Intercomparison Project phase 2b (ISIMIP2b). The diagrams were co-produced between a graphics designer and 16 modelling teams, based on extensive discussions and pragmatic decision-making that balanced the need for accuracy and detail against the need for effective visualization. The model diagrams are based on a standardized "ideal" global water model that represents what is theoretically possible to represent in the current generation of state-of-the-art global water models participating in ISIMIP2b. Model-specific diagrams are then copies of the "ideal" model, with individual processes either included or greyed out. As well as serving an educational purpose, we envisage that the diagrams will help researchers in and outside of the global water model community to select the suitable model(s) for specific applications, stimulate a community learning process, and identify missing components to help direct future model developments.
Nitrate-nitrogen dynamics in response to forestry harvesting and climate variability: Four years of UV nitrate sensor data in a shallow, gravel aquifer
Authors: Wilkins Ben , Johns Tom , Mager Sarah
Published: May 2024

Abstract. The leaching of inorganic nitrogen can adversely affect groundwater and hydrologically connected streams and rivers. Traditionally, these effects have been assessed using discrete water quality measurements. However, it is difficult to characterise the complex biogeochemical processes that control nitrate-nitrogen dynamics in groundwater using temporally sparse data. In this study, we installed a continuous UV nitrate sensor, downgradient of forestry land use in a shallow, gravel aquifer to understand nitrate-nitrogen dynamics in groundwater. We found that there were two mechanisms of nitrate-nitrogen pulses in groundwater from the upgradient forestry land use. The most prevalent were nutrient losses during winter months when plant uptake is lower. Outside of winter months, we observed a higher nitrate-nitrogen concentration (12 mg L-1) as a result of changing biogeochemical conditions after trees were harvested, compared to 5.9 mg L-1 when there was no harvesting. We used a novel hysteresis approach, comparing nitrate-nitrogen concentrations and groundwater levels after rainfall recharge to understand event scale variability. First flush events in winter had a larger average area (more hysteresis) of 0.65 compared to 0.35 (less hysteresis) for subsequent events. Peak concentrations occurred earlier in events during 2021 (wetter) compared to 2020 (dryer), highlighting slower drainage pathways in years with less recharge. Through this analysis we also found evidence that the mobilisation of nitrate-nitrogen shifted from rainfall recharge to rising groundwater levels after the surface supply was depleted from successive recharge events. Finally, the nitrate-nitrogen load analysis indicates that the leaching and export occurs in pulses, that discrete sampling cannot accurately characterise. For example, in 2021, over 80 percent of the exported load occurred during a quarter of the year and discharged when there were base flow conditions in the nearby Hurunui River. These findings have implications for forestry land management, the understanding of inorganic nitrogen dynamics in groundwater in response to rainfall recharge and can be applied to future climate projections where periods of drought and storm events are more frequent.
A Framework for Bootstrapping Event Classification Datasets
Authors: Dumitru Vlad , Strasser Lisa , Lienhart Werner
Published: May 2024

Machine learning models require large amounts of training samples: in most cases, thousands of unique instances are required for each class of events.
Constructing such a dataset is an extremely expensive task in terms of the time it takes to identify and label meaningful events.
Additionally, the large amount of data produced by DAS interrogator units makes storage prohibitively expensive: the mediums need to be both fast (storing one second of data should take less than one second), and of high capacity (spanning long periods of time, such that rarely-occurring events of interest can be captured). To alleviate these constraints, a typical approach is to only store "interesting" events. But how to know which events to store without having a classifier in the first place?
To solve this chicken-and-egg problem, we propose a framework for constructing datasets used to train classifiers of events detectable through the acoustic fingerprinting of DAS measurement data.
Our framework progressively builds up a dataset starting from one or more hard-coded anomaly detection rules (even as simple as energy thresholding) to solve the initial problem of managing limited storage space. This creates an intermediate dataset of unlabeled events.
The intermediate dataset is then evaluated by means of acoustic fingerprinting, which assigns a feature vector to each event. To facilitate further user input, the feature vectors are projected onto a two-dimensional space. Supervised clustering is performed on the projected representations, where users can select the granularity of the clustering process, and consequently the number of resulting intermediate classes.
By assigning labels to entire clusters instead of individual samples, the time required to annotate the dataset is significantly reduced.
We evaluate the outcomes of this framework on a dataset of more than 50000 events initially detected on an inner-city measurement line, and discuss the possibilities of developing more sophisticated models that can be bootstrapped from this approach.
Understanding DAS records and their response with full-waveform modelling
Authors: Celli Nicolas Luca , Bean Christopher J. , O'Brien Gareth
Published: May 2024

Distributed Acoustic Sensing (DAS) can provide unprecedented spatial resolution and sensitivity to a wide frequency band. The instrument response of the interrogated optical fibre cables, however, is largely unknown and difficult to separate from source, path, and directivity effects on seismic records. This prevents us from using DAS in many staple seismological techniques that require either absolute amplitude values or a complete understanding of the full waveform (e.g., earthquake magnitude estimation, waveform tomography).
Here we present a full-waveform simulation scheme developed to model the DAS instrument response using a particle-based Elastic Lattice Model (ELM-DAS). The scheme allows us to simulate a virtual cable embedded in the medium and made of a string of connected particles. By measuring the strain along these particles, we are able to replicate the axial strain natively measured by DAS as well as the effects of irregular cable geometries. Analysing synthetic DAS data allows us to focus on the main factors that are believed to determine the instrument response: cable-ground coupling and local site effects. The particle-based numerical scheme allows us to easily simulate complex properties of the material around the cable (e.g., unconsolidated sediments, nonlinear materials) as well as different degrees of cable-ground coupling.
By simulating DAS cables in 2D, we observe that at the meter scale, realistic DAS materials, cable-ground coupling, and the presence of unconsolidated trench materials around it dramatically affect wave propagation, each change affecting the synthetic DAS record, with differences exceeding at times the magnitude of the recorded signal. By expanding the scheme to 3D, we can accurately include the effects of realistic, complex–and at times sub-wavelength–cable geometries and how they influence DAS records. Our observations show that cable coupling and local site effects have to be considered both when designing a DAS deployment and analysing its data when either true or along-cable relative amplitudes are considered.
Distributed Sensing of Ocean-Earth Interface on Hadal-station deployed fiber-optic cable
Authors: Zhang Hanyu , Xu Tuanwei , Yu Chunliang , Deng Dimin , Chen Jun , Wu Shiguo
Published: May 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.
Shallow slow earthquake activity in the Nankai Trough after the 2024 M7.6 Noto Peninsula earthquake analyzed by distributed acoustic sensing data
Authors: Baba Satoru , Araki Eiichiro
Published: May 2024

Distributed acoustic sensing (DAS), one of the fiber-optic sensing technologies, measures the temporal change in strain or strain rate along a fiber-optic cable from the backscattering phase differences. Because DAS can measure spatial variation in strain along a fiber-optic cable with a meter-scale interval, DAS has been used for seismic observation recently. We have been conducting a DAS observation off the Cape Muroto in the Nankai Trough since January 2022. Off the Cape Muroto, the coseismic slip area of historical megathrust earthquakes and slow earthquake area is adjacent along the dip direction. Slow earthquakes can have the potential to trigger megathrust earthquakes; therefore, the investigation of slow earthquake activity is important to understand tectonic conditions on the plate boundary. Baba et al. (2023) detected shallow tremors, a type of slow earthquake observed in 2–8 Hz, by the DAS observation off the Cape Muroto. They located these tremors using DAS and broadband seismogram data from Dense Oceanfloor Network system for Earthquake and Tsunami (DONET). They located these tremors mainly around 134.7ºE and 32.8ºN, which is updip of a subducted seamount.
On January 1st, 2024, the M7.6 Noto Peninsula earthquake occurred at 16:10:22 (JST). After this earthquake, 13 tremors occurred off the Cape Muroto between 19:00 on January 1st and 4:00 on January 2nd. These tremors were observed by DAS data with a 120-km long fiber-optic cable and G-node stations of DONET. The signals of these tremors propagated from south to north and amplitudes are larger in the southern part near the trench of the DAS cable. We located these tremors based on the amplitude variation at each channel. For tremor activity in 2022, the maximum velocity amplitudes of tremors in DONET decreased by approximately 2.6 orders as the hypocentral distance increased by one order. We converted maximum strain amplitudes measured by DAS in tremors in 2024 to velocity amplitudes based on the amplitude difference between DONET and DAS at a similar hypocentral distance for tremors in 2022. Then we located the tremors in 2024 at the grid point where the attenuation by distance is closest to the case of tremors in 2022 by a grid search. As a result, tremors in 2024 were located in 134.2–134.6ºE and 32.3–32.5ºN near the Nankai Trough. In the future, we discuss the mechanism of the activation of these tremors after the Noto Peninsula earthquake.
This tremor activity after the Noto Peninsula earthquake was reported in a risk assessment by the Japanese government. Now we are constructing an earthquake monitoring system using DAS and DONET data in the Nankai Trough based on the automatic location of regular and slow earthquakes. In this presentation, we will also introduce the conception of this system.
Advancing Seismic Monitoring using Interferometric Data Recorded on Telecom Fiber Networks
Authors: Herrero Andre , Govoni Aladino , Margheriti Lucia , Vassallo Maurizio , donatello Simone , Clivati Cecilia , Brenda Daniele , Hovsepyan Marianna , Bertacco Elio , Concas Roberto , Levi Filippo , Mura Alberto , Carpentieri Francesco , Calonico Davide
Published: May 2024

The MEGLIO project aims to observe seismic waves using coherent laser interferometry on an active telecommunication fiber network. Open Fiber, one of Italy's leading optic fiber infrastructure providers, promoted this experiment on a buried optic cable connecting Ascoli Piceno and Teramo, Italy, spanning approximately 30 km.
The cable's route, passing through roads with moderate traffic, bridges, viaducts, and urban areas, poses challenges due to anthropogenic noise. However, one of the goals of the experiment aims to demonstrate the sensitivity of the measurement technique in real-world telecommunication networks. Nevertheless, many earthquakes with Ml2+ magnitudes have been recorded at different distances from the fiber optic cable.
The physical quantity measured here is the time variation of a phase-shift, i.e. an angle. The objective of the presentation is to show the waveform signatures of seismic waves on this type of measure and their frequency spectra from a seismological perspective. We also may quantify seismological attributes such as seismic phase arrival times, frequency content, and earthquake magnitudes. Furthermore, we compare the interferometric data with traditional seismic recordings from nearby velocimeter sensors.
In essence, the MEGLIO experiment seeks to advance seismic monitoring capabilities by leveraging existing telecommunication infrastructure. Through comprehensive waveform analysis and seismological attribute measurement, valuable insights into earthquake characteristics can be obtained, contributing to improved our seismic monitoring efforts.
Using DAS with an Optical Fibre Cable in Galway Bay for Ocean Noise Monitoring
Authors: Berry-Walshe Leon , Tary Jean-Baptiste , Le Pape Florian , Piana Agostinetti Nicola , Bean Christopher J. , Garcia Gomez Clara , MacCraith Eoin
Published: May 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).
Distributed Acoustic Sensing of Formation Poroelastic Deformation for Water Resources and Geothermal Energy
Authors: Becker Matthew W.
Published: May 2024

Geomechanical strain resulting from fluid pressure changes is generally called poroelasticity and its theoretical underpinnings are well known.  However, the application of theory to real-world problems is often limited by the measurement of subsurface poroelastic heterogeneity.  The nanostrain resolution of DAS presents an opportunity to study poroelastic and hydraulic behavior in the subsurface in unprecedented detail.  Ultra-low frequency response in DAS data can be used to monitor the poroelastic behavior during dynamic hydraulic tests either in single or cross-hole testing mode.  We will present results from multiple field sites in which we have used DAS as a distributed dynamic strain meter to elucidate poroelastic behavior in consolidated and unconsolidated formations, for water resource and geothermal energy applications.
Single well hydraulic tests in alluvium were monitored with DAS fiber strapped to the screened well casing and mechanically coupled to the aquifer formation via a gravel pack.   In a short-screen interval well, DAS demonstrated the non-radial behavior of poroelastic response to extraction of water.  In a test conducted in an aquifer with a long (235 m) well screen, DAS-measured formation expansion and contraction in response to fluid injection were several hundred nanostrain.  Strain, and the implied storage distribution, was highly localized in specific strata and demonstrated complex hydromechanical behavior.  In a crystalline bedrock, DAS observed nanometer fracture displacements in response to injection at a companion well, 30 meters away.  The strain response was consistent with expected flow in sparse fracture networks.  Geomechanical response indicated some shear along the fractures.  An installation of fiber in a 3000 m deep geothermal borehole is characterizing hydraulic connectivity during flow recirculation.  These geothermal experiments are ongoing, but early DAS data show strain in response to recirculation tests between laterals separated by 100 m.
MIMO-DFS for detection-localization-identification of mechanical threats over existing telecom networks
Authors: Dorize Christian
Published: May 2024

Multiple input multiple output (MIMO) distributed fiber Sensing (DFS) is an innovative digital approach to phase-OTDR derived from technologies used in long-haul transmission over both terrestrial and submarine telecom networks. The probing signal is composed of digital codes that modulate in phase a highly coherent laser source over two orthogonal polarization axes, and the Rayleigh backscattered optical field is captured by a coherent mixer set in a homodyne configuration. This technique estimates, after digital processing, the backscattered signal without polarization fading effect and under a Jones matrix form, so giving access to the intensity, the local phase and the state of polarization along the fiber link under test. The link is continuously probed, which allows to monitor the local phase changes induced by mechanical events occurring in the fiber vicinity over a maximal bandwidth given by length of the monitored fiber link. We demonstrated the MIMO-DFS capabilities over links up to 100km with a gauge length of 10 meters and a capture of events linearly to disturbance pressure, in a microphone-like way, over a 200Hz bandwidth.  The detection threshold, or noise floor, increases along the fiber length and was shown to be drastically lowered compared with standard DFS techniques which probe the fiber over one polarization axis only. The 100km figure achieved will be further improved soon by enhancing the stability of the laser source.
The MIMO-DFS technique has been designed to be compliant with telecom networks in a way so that a fiber can be monitored using one WDM channel without impacting the traffic rate propagating over adjacent WDM channels. We recently conducted a field trial using a telecom operator active network in Saudi Arabia. The purpose was to early detect mechanical threats that may lead to a traffic disruption. We provoked mechanical events by means of jackhammer and excavator in the vicinity of a 57km deployed cable buried two meters depth, both in a city area and in the desert, at distance of 15 and 30km from the fiber start respectively.  The aim of the paper is to highlight the ability to detect, localize and even recognize the various noise sources under test in the context of a realistic deployed network, thanks to the outstanding sensitivity of the sensing technique. Beyond early detection of human induced threats for telecom networks integrity, the MIMO-DFS approach is also suited to detect much more critical environmental threats such as seisms with potential impact on people safety.
High resolution seismometers and strainmeters at the termination of plurikilometric fibers : a new brand of fiber optic sensors for harsh environment 
Authors: Bernard Pascal , Plantier Guy , Ménard Philippe , Feuilloy Mathieu , Savaton Guillaume , Feron Romain , Biagioli Francesco , Bouin Marie-Paule , Ripepe Maurizio , Stutzmann Eleonore , Metaxian Jean-Philippe , Hello Yann , Moretti Roberto , DeChabalier Jean-Bernard
Published: May 2024

We have recently qualified in situ innovative high resolution optical seismometers and strainmeters. Designed and constructed by ESEO, they consist of a purely mechanical sensors, depleted from electronics, connected through a plurikilometric fiber to an optical interrogator based on Fabry-Perot interferometry. For the seismometer, the optical cavity is the centimetric gap between the collimator at the termination of the fiber and the mirror fixed on the mobile mass, which reflects the laser beam into the fiber towards the interrogator. The latter interferes with the primary laser beam reflected on the collimator interface. For the strainmeter, the optical cavity is a simple monomode fiber, of plurimetric size. The large distance between these sensors and their interrogator allows to install the former under harsh environmental conditions, as on active volcanos, on ocean bottom, in deep borehole, keeping the interrogator in a safe, accessible place providing facilities for powering (6 W for 4 channels), real-time telemetry, and easier maintenance. Such monitoring would be a difficult if not impossible task in the long run for most commercial instruments, due to much higher cost and/or risk for the installation and for the maintenance for the latter. These instruments may also prove usefull in (geo)-industrial contexts with high temperature or high radiation conditions. Here we present the basic features and overall performance of two prototype sensors: an optical ocean bottom seismometer installed 5 km offshore Les Saintes, Guadeloupe, and optical strainmeters installed on the slope of the Stromboli volcano, since 2021. For the Stromboli, we will describe its specific installation modality, with 5 m long sensing fibers buried in trenches, and compare the strain records of ordinary explosions to those of colocated instruments: a broadband seismometer, an optical fiber interrogated by DAS, and a borehole tiltmeter. Focussing on the strain records of several major explosions, we will show the potential of this strainmeter to better characterize the pressure source at the origin of these events and to contribute to improve the short term alert of major and paroxysmal explosions. We will finally present our projects of new installations of this optical strainmeter, with the objective or recording slow slip transients within tectonic fault systems, in the context of induced and natural seismicity.
Monitoring groundwater dynamics in the Crepieux-Charmy water catchment using DAS-based surface wave tomography
Authors: Nziengui Bâ Destin , Coutant Olivier , Jestin Camille , Lanticq Vincent
Published: May 2024

Ambient noise interferometry applied to Distributed Acoustic Sensing (DAS) arrays is an increasingly common approach to subsurface investigations. In this study, we show that analysis of urban seismic noise acquired on a DAS array can be used to track velocity variations caused by groundwater level changes in an alluvial aquifer.
We apply our methodology to the Crépieux-Charmy aquifer, a strategic site for the city of Lyon, France. This site provides more than 90% of the city's drinking water and uses a Managed Aquifer Recharge (MAR) system, which allows controlled recharge of the aquifer through infiltration basins. We analyzed four weeks of DAS ambient noise data recorded on a 3 km spiral DAS array surrounding an infiltration basin.  During this period, a controlled water infiltration experiment was conducted by the site operators. 
We used traffic noise in the 2-5 Hz frequency band and performed DAS-based time-lapse surface wave tomography of velocity variations in the area. We were then able to map relative changes in seismic velocity in the vadose zone. Comparison of point-scale water level measurements from piezometers and adjacent cells in the velocity variation maps shows good agreement between the two observables. These velocity variations are directly related to the water table variations and to residual water saturation changes within the unsaturated zone.
This pilot application demonstrates the potential for groundwater monitoring in aquifer systems using DAS combined with seismic interferometry.
Geophysical characterization using optical fiber measurements: PREMISE2 experiment in LSBB, first results on the effect of fiber coupling conditions
Authors: Carrillo-Barra Vanessa , Sladen Anthony , Mercerat Diego , Vallage Amaury , Sèbe Olivier , Jean-Paul Ampuero
Published: May 2024

Optical fiber measurements have been demonstrated to be useful in assessing geophysical near-surface parameters and in detecting seismological events in newly accessible regions (e.g. cities, ocean floor, highways) by leveraging the existing fiber-optic infrastructure. In particular, laser interferometry performed with DAS systems (Distributed Acoustic Sensing) allows measuring the cable axial strain related to passing seismo-acoustic waves, at any point along the cable and over tens of kilometers of cable.
However, there is a critical need to better understand how the measurements are influenced by the nature of the fiber optic cable, its coupling to the ground. To assess this issue, I will present results from the active seismic experiment PREMISE2 which was carried out in southeastern France in 2020, in an underground laboratory, the LSBB tunnel (Laboratoire Sous-terrain Bas Bruit, https://lsbb.cnrs.fr/). Multiple active shots were recorded both with a 4 km long underground optical fiber and with traditional seismic sensors. Different optical fiber cables and different types of coupling were tested along this 4 km optical fiber, besides the use of a pre-installed vertical fiber. This experiment brings a unique opportunity to examine in detail the possible variations in the strain signals recovered from DAS data in diverse deployment conditions (sealed, sandbag weighted, freely posed), with the utmost aim to understand the potential implications of these conditions for the geophysical characterization of sites of interest in the next stages of this research.
Hydroacoustic and tsunami observations by a seafloor fiber optic strain meter
Authors: Matsumoto Hiroyuki , Araki Eiichiro , Yokobiki Takashi , Ariyoshi Keisuke , Takahashi Narumi
Published: May 2024

The authors have developed a strain meter using a 200-m fiber optic cable detecting tiny strain change by optic interferometry technique, i.e., measurement of optic phase change with respect to a reference fiber (Araki et al., 2022). Three fiber optic strain meters have been deployed with forming like an array at the seafloor in the Nankai Trough seismogenic zone, and real-time dataset are acquired via the DONET seafloor observatory network. A series of submarine earthquakes in October 2023 occurred near Torishima Island, a volcanic island of the Izu-Ogasawara (Izu-Bonin) Islands had generated unexpected tsunamis, remaining their earthquake magnitude unknown. At a series of the earthquakes, fourteen hydroacoustic signals, i.e., T-phases, followed by a dispersive tsunami were detected by the fiber optic strain meters. Amplitudes of T-phases and the tsunami detected by the fiber strain meters were 0.07 to 0.2 micro-strain and 0.003 micro-strain, respectively. Likewise, a DONET pressure gauge located about 3 km away from the fiber optic strain meters detected pressure fluctuations with their amplitude of 100 to 500 Pa and 140 Pa, respectively. It has been confirmed that the frequency contents of T-phases and the tsunami detected by the fiber optic strain meters consistent with those of the nearby DONET pressure gauge. The fact that a fiber optic strain meter detected a tsunami signal suggests that hydro-static loading associated with tsunami can cause strain change at the seafloor.
Enhancing earthquake location in deep ocean environments with DAS
Authors: Latorre Hugo , Bozzi Emanuele , Ventosa Sergi , Cubas Armas Melania , Vidal-Moreno Pedro , Villaseñor Antonio , Bartolomé Rafael , Ugalde Arantza
Published: May 2024

Earthquake location schemes for regional oceanic earthquakes within archipelago regionsare limited by the azimuthal resolution that land stations provide for each specific event. Althoughocean bottom seismometers (OBS) can help, they are not suited for real time monitoring and thuscan only provide a posteriori improvements. An alternative approach to improve coverage, notstrictly 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 kmoffshore is possible, which can potentially improve azimuthal resolution by reaching previouslyinaccessible locations within the archipelago. A great example of such a region are the CanaryIslands, where land-based coverage is already phenomenal yet volcanic activity monitoring fromunderwater sources still has poor coverage in some cases.Recently, the deployment of additional land stations at the islands of Gran Canaria andFuerteventura has revealed existing seismicity between the two islands. When locating the source ofthis 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 beeninterrogated with DAS before, on both sides. The most recent experiment, which was set up on theGran 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 atpreviously selected DAS channels is also considered, since there is a lot of redundancy in DAS dataand visual inspection is not unreasonable if limited to a number of channels.
Link between seismic velocity changes and the 2020 unrest in Reykjanes revealed by wavelength-dependent spatial stacking of distributed dynamic strain
Authors: Maass Regina , Schippkus Sven , Hadziioannou Céline , Schwarz Benjamin , Jousset Philippe , Krawczyk Charlotte
Published: May 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.
 KM3NeT/ARCA Optical Network 
Authors: Pulvirenti Sara , Schmelling Jan-Willem , D'Amico Antonio
Published: May 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. 