scholarly journals Urban Distributed Acoustic Sensing Using In-Situ Fibre Beneath Bern, Switzerland

2020 ◽  
Author(s):  
Krystyna Smolinski ◽  
Patrick Paitz ◽  
Daniel Bowden ◽  
Pascal Edme ◽  
Felix Kugler ◽  
...  
Keyword(s):  
Spatial Resolution ◽  
Seismic Waves ◽  
Velocity Structure ◽  
Road Traffic ◽  
Hazard Analysis ◽  
Noise Sources ◽  
Acoustic Sensing ◽  
Wide Range ◽  
Distributed Acoustic Sensing

<p>Anticipating the risks natural hazards pose to an urban environment requires an understanding of the shallow Earth structure of the region. While urban infrastructure often hinders the deployment of a traditional seismic array, Distributed Acoustic Sensing (DAS) technology facilitates the use of existing telecommunication fibre-optic cables for seismic observation, with spatial resolution down to the metre scale.</p><p>Through collaboration with the SWITCH foundation, we were able to use existing, in-situ fibres beneath Bern, Switzerland for seismic data acquisition over two weeks, covering a distance of 6 km with a spatial resolution of 2 m. This allowed for not only real-time visualisation of anthropogenic noise sources (e.g. road traffic), but also of the propagation of resulting seismic waves.</p><p>Data is analysed in the time and frequency domain to explore the range of signals captured and to assess the consistency of data quality along the cable. The local velocity structure can be constrained using both noise correlations and deterministic signals excited by traffic.</p><p>Initial results reveal the ability of DAS to capture signals over a wide range of frequencies and distances, and show promise for utilising urban DAS data to perform urban seismic tomography and hazard analysis.</p>

Distributed Acoustic Sensing Turns Fiber‐Optic Cables into Sensitive Seismic Antennas

2019 ◽  
Vol 91 (1) ◽  
pp. 1-15 ◽  
Author(s):  
Zhongwen Zhan
Keyword(s):  
Seismic Waves ◽  
Fiber Optic ◽  
Glass Fibers ◽  
Ocean Bottom ◽  
Thin Glass ◽  
Acoustic Sensing ◽  
Wide Range ◽  
Solar System Bodies ◽  
Distributed Acoustic Sensing ◽  
Seismic Networks

Abstract Distributed acoustic sensing (DAS) is a new, relatively inexpensive technology that is rapidly demonstrating its promise for recording earthquake waves and other seismic signals in a wide range of research and public safety arenas. It should significantly augment present seismic networks. For several important applications, it should be superior. It employs ordinary fiber‐optic cables, but not as channels for data among separate sophisticated instruments. With DAS, the hair‐thin glass fibers themselves are the sensors. Internal natural flaws serve as seismic strainmeters, kinds of seismic detector. Unused or dark fibers are common in fiber cables widespread around the globe, or in dedicated cables designed for special application, are appropriate for DAS. They can sample passing seismic waves at locations every few meters or closer along paths stretching for tens of kilometers. DAS arrays should enrich the three major areas of local and regional seismology: earthquake monitoring, imaging of faults and many other geologic formations, and hazard assessment. Recent laboratory and field results from DAS tests underscore its broad bandwidth and high‐waveform fidelity. Thus, while still in its infancy, DAS already has shown itself as the working heart—or perhaps ear drums—of a valuable new seismic listening tool. My colleagues and I expect rapid growth of applications. We further expect it to spread into such frontiers as ocean‐bottom seismology, glacial and related cryoseismology, and seismology on other solar system bodies.

scholarly journals Acoustic Energy Harvesting in Nigeria: Prospects, Technical Problems and Socio-Economic Obstacles

2020 ◽  
pp. 16-33
Author(s):  
Michael U. Onuu
Keyword(s):  
Energy Harvesting ◽  
Road Traffic ◽  
Acoustic Energy ◽  
Road Traffic Noise ◽  
Noise Power ◽  
Noise Levels ◽  
Noise Sources ◽  
Technical Problems ◽  
Wide Range ◽  
Acoustic Energy Harvesting

Aims: To investigate the prospects or potentials of acoustic energy harvesting in Nigeria as well as highlight technical problems and socio-economic obstacles. Study Design: The study re-examined existing data, noise levels and noise power, from road traffic, aircraft, industrial/occupational, outdoor and indoor noise sources. Noise levels and noise power obtained from recent measurements of such noise sources were also examined and analyzed. The data were compared with values from noise sources used for electricity in other countries of the world. Technical problems and socio-economic obstacles have been highlighted. Place and Duration of Study: The study was carried out in Abakaliki, Ebonyi State, Nigeria. The duration was one year: April, 2019 and April, 2020. Methodology: Wide range noise level measurements, analysis and re-examination of existing data on road traffic, aircraft, industrial/occupational, outdoor and indoor noise were conducted, in line with the objectives of the study, in cities, industries as well as homes with different noise features. Measurements were carried out using sound level meter, SLM, (Bruel and Kjaer 2203) with  – octave band filter and SLM, EXTECH 407750 with RS232, sound level recorder (B & K 7005), and noise level (statistical) analyzer (B & K 2121) to obtain noise levels and indices. Also, noise power was subsequently obtained for each of the various noise levels and indices. Results: Maximum noise levels, Lmax.; noise power, Wmax.; octave band pressure levels, BPLs; and other indices for the different noise sources were determined. Lmax. and Wmax for aircraft were as high as 116 dB and 0.4 W, respectively, while those for industry and road traffic ranged from 104.0 dB-131.0 dB and 67.5 dB-85.6 dB corresponding to 0.025 W-12.59 W and 0.0000056 W-0.00036 W, respectively. Spectral power of road traffic noise varied between 5.17 x 10-5 W and 9.69 x 10-3 W. Outdoor and household noise sources had Lmax. of up to 48.5 dB and 88.0 dB, that is, 0.000000071 W and 0.00063 W, for quiet and noisy periods, respectively. It was observed that road traffic noise has the highest potential for acoustic energy harvesting in Nigeria being reasonably steady over time, especially, on intra-city roads. Availability of tricycles/motorcycles in abundance and frequent use of horn by motorists support this assertion. The noise levels and noise power from these sources obtained in this investigation are higher than those that have been used as input to acoustic energy harvesters (AEHs) such as piezoelectric based and triboelectric nanogenerators (TRENGs) to achieve known efficiencies as reported elsewhere. Conclusion: The noise power is such that it could be used in powering microelectronic components, devices and in lighting light emitting diodes (LEDs). Power supply (PS) audio noise harvesters (ANHs) have been identified as potential noise energy sources since there is wide range use of air-conditioned by the political class, elites and government agencies in Nigeria where maximum temperature of 47.2°C is attainable. These findings show the viability of AEH in Nigeria and their addition to the existing body of knowledge in the emerging area of AEH will open a new window of research in AEH in this part of the world. Other prospects of AEH in Nigeria, technical problems and socio-economic obstacles are highlighted.

scholarly journals The seismic wavefield as seen by Distributed Acoustic Sensing (DAS) arrays: local, regional and teleseismic sources

2021 ◽  
Author(s):  
Brian Kennett
Keyword(s):  
Strain Rate ◽  
Seismic Waves ◽  
Strong Dependence ◽  
Laser Pulses ◽  
Gauge Length ◽  
Additional Contribution ◽  
Acoustic Sensing ◽  
Distributed Acoustic Sensing ◽  
The Difference ◽  
Seismic Wavefield

Distributed acoustic sensing (DAS) exploiting fibre optic cables provides a means for high-density sampling of the seismic wavefield. The scattered returns from multiple laser pulses provide local averages of strain rate over a finite gauge length, and the nature of the signal depends on the orientation of the cable with respect to the passing seismic waves. The properties of the wavefield in the slowness-frequency domain help to provide understanding of the nature of DAS recordings. For local events the dominant part of the strain rate can be extracted from the difference of ground velocity resolved along the fibre at the ends of the gauge interval, with an additional contribution just near the source. For more distant events the response at seismic frequencies can be represented as the acceleration along the fibre modulated by the horizontal slowness resolved in the same direction, which means there is a strong dependence on cable orientation. These representations of the wavefield provide insight into the character of the DAS wavefield in a range of situations from a local jump source, through a regional earthquake to teleseismic recording with different cable configurations and geographic locations. The slowness domain representation of the DAS signal allows analysis of the array response of cable configurations indicating the important role of the slowness weighting associated with the effect of gauge length. Unlike seismometer arrays the response is not described by a single generic stacking function. For high frequency waves, direct stacking enhances P, SV waves and Rayleigh waves; an azimuthal weighted stack provides retrieval of SH and Love waves at the cost of enhanced sidelobes in the array response.

scholarly journals High-resolution inventory to capture glacier disintegration in the Austrian Silvretta

2021 ◽  
Author(s):  
Andrea Fischer ◽  
Bernd Seiser ◽  
Kay Helfricht ◽  
Martin Stocker-Waldhuber
Keyword(s):  
High Resolution ◽  
Spatial Resolution ◽  
Ice Age ◽  
Surface Elevation ◽  
Glacier Changes ◽  
Wide Range ◽  
Elevation Data ◽  
Glacier Ice ◽  
Geodetic Mass Balance

Abstract. Eastern Alpine glaciers have been receding since the LIA maximum, but the majority of glacier margins could be delineated unambiguously for the last Austrian glacier inventories. Even debris-covered termini, changes in slope, colour or the position of englacial streams enabled at least an in situ survey of glacier outlines. Today the outlines of totally debris-covered glacier ice are fuzzy and raise the theoretical discussion if these glaciogenic features are still glaciers and should be part of the respective inventory – or part of an inventory of transient cryogenic landforms. A new high-resolution glacier inventory (area and surface elevation) was compiled for the years 2017 and 2018 to quantify glacier changes for the Austrian Silvretta region in full. Glacier outlines were mapped manually, based on orthophotos and elevation models and patterns of volume change of 1 to 0.5 m spatial resolution. The vertical accuracy of the DEMs generated from 6 to 8 LiDAR points per m2 is in the order of centimetres. calculated in relation to the previous inventories dating from 2004/2006 (LiDAR), 2002, 1969 (photogrammetry) and to the Little Ice Age maximum extent (moraines). Between 2004/06 and 2017/2018, the 46 glaciers of the Austrian Silvretta lost −29 ± 4 % of their area and now cover 13.1 ± 0.4 km2. This is only 32 ± 2 % of their LIA extent of 40.9 ± 4.1 km2. The area change rate increased from −0.6 %/year (1969–2002) to −2.4 %/year (2004/06–2017/18). The annual geodetic mass balance showed a loss increasing from −0.2 ± 0.1 m w.e./year (1969–2002) to –0.8 m ±0.1 w.e./year (2004/06–2017/18) with an interim peak in 2002–2004/06 at −1.5 ± 0.7 m w.e./year. Identifying the glacier outlines offers a wide range of possible interpretations of former glaciers that have evolved into small and now totally debris-covered cryogenic geomorphological structures. Only the patterns and amounts of volume changes allow us to estimate the area of the buried glacier remnants. To keep track of the buried ice and its fate, and to distinguish increasing debris cover from ice loss, we recommend inventory repeat frequencies of three to five years and surface elevation data with a spatial resolution of one metre.

Borehole Seismic: Essential Contributions Over the Oilfield Lifecycle

2021 ◽  
Author(s):  
Rajeev Kumar ◽  
Pierre Bettinelli
Keyword(s):  
Hydraulic Fracturing ◽  
Real Time ◽  
Depth Information ◽  
Acoustic Sensing ◽  
Seismic Profiling ◽  
Production Phase ◽  
Vertical Seismic Profiling ◽  
Wide Range ◽  
Distributed Acoustic Sensing ◽  
Borehole Seismic

Abstract During the evolution of the petroleum industry, surface seismic imaging has played a critical role in reservoir characterization. In the early days, borehole seismic (BHS) was developed to complement surface seismic. However, in the last few decades, a wide range of BHS surveys has been introduced to cater to new and unique objectives over the oilfield lifecycle. In the exploration phase, vertical seismic profiling (VSP) provides critical time-depth information to bridge time indexed subsurface images to log/reservoir properties in depth. This information can be obtained using several methods like conventional wireline checkshot or zero-offset vertical seismic profiling (ZVSP), seismic while drilling (SWD) or distributed acoustic sensing (DAS) techniques. SWD is a relatively new technique to record real-time data using tool deployed in the bottomhole assembly without disturbing the drilling. It helps to improve decision making for safer drilling especially in new areas in a cost-effective manner. Recently, a breakthrough technology, distributed acoustic sensing (DAS), has been introduced, where data are recorded using a fiber-optic cable with lots of saving. ZVSP also provides several parameters like, attenuation coefficient (Q), multiples prediction, impedance, reflectivity etc., which helps with characterizing the subsurface and seismic reprocessing. In the appraisal phase, BHS applications vary from velocity model update, anisotropy estimation, well- tie to imaging VSPs. The three-component VSP data is best suited for imaging and amplitude variation with offset (AVO) due to several factors like less noise interference due to quiet downhole environment, higher frequency bandwidth, proximity to the reflector, etc. Different type of VSP surveys (offset, walkaway, walkaround etc.) were designed to fulfill objectives like imaging, AVO, Q, anisotropy, and fracture mapping. In the development phase, high-resolution images (3D VSP, walkaway, or crosswell) from BHS surveys can assist with optimizing the drilling of new wells and, hence reduce costs. it can help with landing point selection, horizontal section placement, and refining interpretation for reserve calculation. BHS offers a wide range of surveys to assist the oilfield lifecycle during the production phase. Microseismic monitoring is an industry-known service to optimize hydraulic fracturing and is the only technique that captures the induced seismicity generated by hydraulic fracturing and estimate the fracture geometry (height, width, and azimuth) and in real time. During enhanced oil recovery (EOR) projects, BHS can be useful to optimize the hydrocarbon drainage strategies by mapping the fluid movement (CO2, water, steam) using time-lapse surveys like walkaway, 3D VSP and/or crosswell. DAS has brought a new dimension to provide vital information on injection or production evaluation, leak detection, flow behind tubing, crossflow diagnosis, and cement evaluation during production phase. This paper highlights the usage of BHS over the lifecycle of the oilfield.

Road traffic estimation using in-situ acoustic sensing

2010 ◽  
Vol 40 (4) ◽  
pp. 431-432 ◽  
Author(s):  
C. Viven Rajendra ◽  
Purushottam Kulkarni
Keyword(s):  
Road Traffic ◽  
Acoustic Sensing ◽  
Traffic Estimation

Seafloor seismology with Distributed Acoustic Sensing in Monterey Bay

2020 ◽  
Author(s):  
Nathaniel Lindsey ◽  
Jonathan Ajo-Franklin ◽  
Craig Dawe ◽  
Lise Retailleau ◽  
Biondo Biondi ◽  
...  
Keyword(s):  
Solid Earth ◽  
Wavelet Transforms ◽  
Seismic Waves ◽  
Wind Waves ◽  
Thickness Distribution ◽  
Wave Interaction ◽  
Monterey Bay ◽  
S Wave ◽  
Acoustic Sensing ◽  
Distributed Acoustic Sensing

<p>Emerging distributed fiber-optic sensing technology coupled to existing subsea telecommunications cables enable access to meterscale, multi-kilometer aperture, broadband seismic array observations of ocean and solid earth phenomena. In this talk, we report on two multi-day Distributed Acoustic Sensing (DAS) campaigns conducted in 2018 and 2019 with the Monterey Accelerated Research System (MARS) observatory tether cable. In both experiments, a DAS instrument located on shore was connected to a fiber inside the buried MARS cable and recorded a ~10,000-component, 20-kilometer-long, strain-rate array. We use the 8 TB DAS dataset to address three questions:</p><p>1. How can seafloor DAS earthquake records inform offshore seismic hazard assessments? Offshore seismic hazards are poorly characterized despite dense coastal populations. The MARS DAS array captured multiple unaliased earthquake recordings, which document phase conversions and abrupt S-wave delays of 0.25 s at mapped (and unmapped) faults that transect the cable. Minor earthquakes in Northern California produce seismic waves in the range 0.5 - 50 Hz, which interact with submarine faults lying just offshore. Spectral ratios and wavefield synthetics are used to explore how seismic waves from well-characterized earthquakes interact with poorly-characterized subsea faults.</p><p>2. How are ocean microseisms and other coastal processes recorded by subsea DAS? Horizontal seabed ambient noise recorded with the MARS DAS array matches the expected dispersion of primary microseisms (f~0.05-0.15 Hz) induced by shoaling ocean surface waves, but at a higher band than onshore observations. Separation of incoming and outgoing waves recorded over the DAS array validates the Longuet-Higgins-Hasselmann theory that bi-directional ocean wind-waves undergo nonlinear wave interaction, producing secondary microseisms (f~0.4-1.5 Hz), even when the outgoing energy is observed to be <1% of the incoming energy. Continuous wavelet transforms of sea state observations from buoys, onshore broadband seismometers, and subsea DAS provide insight into the physics of microseism generation and ocean-solid earth coupling. Additionally, DAS provides observation of post-low-tide tidal bores (f~1-5 Hz), storm-induced sediment transport (f~0.8-10 Hz), infragravity waves (f~0.01-0.05 Hz), and breaking internal waves (f~0.001 Hz) consistent with previous point sensor observations in Monterey Bay. </p><p>3. How is the coastal seafloor structure organized from shore to shelf break? The northern continental shelf of Monterey Bay is comprised of allochthonous Cretaceous granite overlain by marine sediments of varying thickness, and is crosscut by abandoned (and subsequently filled) paleochannels. Noise interferometry applied to the full MARS DAS dataset in the 0.25 - 5 Hz range retrieves Scholte waves, which are dispersive and coherent over 2 - 6 kilometers. We apply fundamental mode dispersion (1.5D) imaging to subarray noise correlations in order to understand the sediment thickness distribution across the shelf. Our model is compared with recent seismic reflection profiling conducted by the USGS California Seafloor Mapping Program.</p>

Observing avalanche dynamics with Distributed Acoustic Sensing

2021 ◽  
Author(s):  
Andreas Fichtner ◽  
Pascal Edme ◽  
Patrick Paitz ◽  
Nadja Lindner ◽  
Michael Hohl ◽  
...  
Keyword(s):  
Spatial Resolution ◽  
Flow Regimes ◽  
Dynamic Strain ◽  
Seismic Signals ◽  
Fibre Optic ◽  
Snow Avalanches ◽  
Acoustic Sensing ◽  
Fibre Optic Cable ◽  
Distributed Acoustic Sensing ◽  
Seismic Instrumentation

<p><span>Avalanche research requires comprehensive measurements of sudden and rapid snow mass movement that is hard to predict. Automatic cameras, radar and infrasound sensors provide valuable observations of avalanche structure and dynamic parameters, such as velocity. Recently, seismic sensors have also gained popularity, because they can monitor avalanche activity over larger spatial scales. Moreover, seismic signals elucidate rheological properties, which can be used to distinguish different types of avalanches and flow regimes. To date, however, seismic instrumentation in avalanche terrain is sparse. This limits the spatial resolution of avalanche details, needed to characterise flow regimes and maximise detection accuracy for avalanche warning.</span></p><p><span>As an alternative to conventional seismic instrumentation, we propose Distributed Acoustic Sensing (DAS) to measure avalanche-induced ground motion. DAS is based on fibre-optic technology, which has previously been used already for environmental monitoring, e.g., of snow avalanches. Thanks to recent technological advances, modern DAS interrogators allow us to measure dynamic strain along a fibre-optic cable with unprecedented temporal and spatial resolution. It therefore becomes possible to record seismic signals along many kilometres of fibre-optic cables, with a spatial resolution of a few metres, thereby creating large arrays of seismic receivers. We test this approach at an avalanche test site in the Valleé de la Sionne, in the Swiss Alps, using an existing 700 m long fibre-optic cable that is permanently installed underground for the purpose of data transfer of other, independent avalanche measurements.</span></p><p><span>During winter 2020/2021, we recorded numerous snow avalanches, including several which reached the valley bottom, travelling directly over the cable during runout. The DAS recordings show clear seismic signatures revealing individual flow surges and various phases/modes that may be associated with roll waves and avalanche arrest. We compare our observations to state-of-the-art radar and seismic measurements which ideally complement the DAS data.</span></p><p><span>Our initial analysis highlights the suitability of DAS-based monitoring and research for avalanches and other hazardous granular flows. Moreover, the clear detectability of avalanche signals using existing fibre-optic infrastructure of telecommunication networks opens the opportunity for unrivalled warning capabilities in Alpine environments.</span></p>

Quantitative Electron Holography Of Magnetic Materials

1999 ◽  
Vol 5 (S2) ◽  
pp. 32-33
Author(s):  
M. R. McCartney
Keyword(s):  
Spatial Resolution ◽  
Nanometer Scale ◽  
Objective Lens ◽  
Electron Holography ◽  
Field Versus ◽  
Wide Range ◽  
Phase Images ◽  
Phase Resolution ◽  
Range Of Values

Off-axis electron holography is a powerful method for providing quantitative micromagnetic structure to nanometer-scale resolution. One of the main challenges in determining magnetic induction from reconstructed phase images is the separation of phase shifts due to electrostatic and thickness effects from magnetostatic effects. We have used in-situ magnetization reversal to remove electrostatic and thickness effects which would otherwise prevent quantification of the induction. The Philips CM200-FEG microscope which was used for the holography described here is equipped with a powerful mini-lens below the specimen enabling 2nm spatial resolution (∼5nm phase resolution) and only a small residual field at the sample. In addition, the objective lens field versus current has been calibrated so that external vertical fields over a wide range of values may be applied to the sample. Tilting the sample in the presence of the vertical field has the effect of ‘applying an inplane component. This combination of high spatial resolution, quantitative analysis and in situ capabilities allows for the study of individual defects and provides experimental input for comparison with simulations.

scholarly journals Fiducial Reference Measurements for Vegetation Bio-Geophysical Variables: An End-to-End Uncertainty Evaluation Framework

2021 ◽  
Vol 13 (16) ◽  
pp. 3194
Author(s):  
Luke A. Brown ◽  
Fernando Camacho ◽  
Vicente García-Santos ◽  
Niall Origo ◽  
Beatriz Fuster ◽  
...  
Keyword(s):  
Spatial Resolution ◽  
Reference Data ◽  
High Spatial Resolution ◽  
Evaluation Framework ◽  
Uncertainty Evaluation ◽  
Uncertainty Estimates ◽  
Wide Range ◽  
End To End ◽  
Reference Measurements

With a wide range of satellite-derived vegetation bio-geophysical products now available to users, validation efforts are required to assess their accuracy and fitness for purpose. Substantial progress in the validation of such products has been made over the last two decades, but quantification of the uncertainties associated with in situ reference measurements is rarely performed, and the incorporation of uncertainties within upscaling procedures is cursory at best. Since current validation practices assume that reference data represent the truth, our ability to reliably demonstrate compliance with product uncertainty requirements through conformity testing is limited. The Fiducial Reference Measurements for Vegetation (FRM4VEG) project, initiated by the European Space Agency, is aiming to address this challenge by applying metrological principles to vegetation and surface reflectance product validation. Following FRM principles, and in accordance with the International Standards Organisation’s (ISO) Guide to the Expression of Uncertainty in Measurement (GUM), for the first time, we describe an end-to-end uncertainty evaluation framework for reference data of two key vegetation bio-geophysical variables: the fraction of absorbed photosynthetically active radiation (FAPAR) and canopy chlorophyll content (CCC). The process involves quantifying the uncertainties associated with individual in situ reference measurements and incorporating these uncertainties within the upscaling procedure (as well as those associated with the high-spatial-resolution imagery used for upscaling). The framework was demonstrated in two field campaigns covering agricultural crops (Las Tiesas–Barrax, Spain) and deciduous broadleaf forest (Wytham Woods, UK). Providing high-spatial-resolution reference maps with per-pixel uncertainty estimates, the framework is applicable to a range of other bio-geophysical variables including leaf area index (LAI), the fraction of vegetation cover (FCOVER), and canopy water content (CWC). The proposed procedures will facilitate conformity testing of moderate spatial resolution vegetation bio-geophysical products in future validation exercises.

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