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Arnestad, Håvard; Rindal, Ole Marius Hoel; Austeng, Andreas & Näsholm, Sven Peter
(2024).
Estimation of probability densities in ultrasound imaging.
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Han, Chaoran; Arnestad, Håvard; Austeng, Andreas & Näsholm, Sven Peter
(2024).
Spectral estimation inspired by a non-linear beamformer: Insights into null-subtraction imaging.
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Solberg, Celine Marie; Brissaud, Quentin & Näsholm, Sven Peter
(2024).
Preliminary assessments of the global detectability of venusquakes from a balloon platform.
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(presented on-site by Celine Marie Solberg)
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Brissaud, Quentin; Näsholm, Sven Peter & Solberg, Celine Marie
(2024).
Assumptions and uncertainties when simulating seismo-acoustic wave propagation on Venus.
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Sufayan, Mulani; Näsholm, Sven Peter & Austeng, Andreas
(2024).
Fourier Migration Based Beamforming Method For Medical Ultrasound Imaging.
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Sotoodeh Ziksari, Mahsa; Näsholm, Sven Peter & Austeng, Andreas
(2024).
Adaptive beamforming for high frame-rate ultrasound imaging.
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Giuliacci, Kety; Bailo, Daniele; Michalek, Jan; Paciello, Rossana; Vinciarelli, Valerio & Goffi, Claudio
[Vis alle 20 forfattere av denne artikkelen]
(2023).
A FAIR approach for the integration of scientific services in the Geo-INQUIRE initiative.
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In recent years, there has been a growing trend in science towards data integration, with the purpose of using multidisciplinary data and products to foster new methodological approaches and scientific discoveries. One of the many projects that have emerged is the Geosphere INfrastructures for QUestions into Integrated REsearch (Geo-INQUIRE).
Geo-INQUIRE started in October 2022 and benefits from a unique consortium of 51 partners consisting of major national research institutes, universities, national geological surveys, and European consortia.
Geo-INQUIRE aims to overcome cross-domain barriers, especially in land-sea-atmosphere environments. To achieve this goal, it has set out to integrate the resources and capacities of the major research infrastructures (RIs) involved with geosphere observations, namely EPOS, EMSO, ARISE, ECCSEL, and ChEESE.
By making available its enhanced data, product, and service portfolio, it will enable the next generation of scientists to carry out leading-edge research addressing societal challenges from a multidisciplinary perspective, making intelligent use of these resources to encourage curiosity-driven research.
In order to achieve curiosity-driven advanced scientific results across domains, the project aims at providing integrated access to harmonised data, data products, software and services from different RIs services to a broader community of users.
To identify services provided by RIs a comprehensive survey was conducted. The collected information included basic details, points of contact, and the technical status of the service (e.g., accessibility, API structure, response formats, data representations, and the standard of metadata describing the service). Furthermore, the survey also assessed the presence of licenses and documentation related to both the service and the provided data, ultimately providing an overview of the technology readiness level and the level of integrability of the services, with the goal of validating the “FAIRness of the services”.
This contribution describes the landscape analysis conducted and the technical solutions being adopted to integrate such a wealth of heterogeneous resources. These solutions are based on the FAIR metadata approach successfully applied in the EPOS context.
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Brissaud, Quentin; Näsholm, Sven Peter; Turquet, Antoine; Kaschwich, Tina & Solberg, Celine Marie
(2023).
The AIR project: Leveraging balloon pressure data for planetary exploration .
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Our understanding of Earth’s internal structure comes primarily from seismic waves that provide important constraints on subsurface seismic-velocity properties. However, traditional inversion methods cannot be implemented in regions of limited seismic-station coverage, in particular on Venus due to its harsh surface conditions but also in remote Earth regions. This lack of seismic data greatly limits our understanding of Venus’ origin and evolution and Earth’s subsurface. However, the mechanical coupling between the ground and its atmosphere enables the seismic energy to be transmitted into the atmosphere as low-frequency acoustic waves carrying information about the seismic source and the subsurface properties. While infrasound is traditionally recorded at ground-based stations, which suffers from the same in-situ deployment limitations as seismic stations, recent studies have demonstrated that balloon platforms can be used to monitor seismic activity from the atmosphere at a low operational cost. Balloon-borne seismology is a new dynamic field considered to be the only way to investigate Venus’ interior. However, inversion methods for balloon-borne infrasound data are lacking and the coupling between seismic and acoustic waves in realistic media is poorly understood. Taking advantage of historical balloon pressure data, the newly granted project Airborne Inversion of Rayleigh waves (AIR), will address these key theoretical and practical issues by analyzing and modeling these seismically-induced infrasound signatures to retrieve the source and subsurface properties. In this contribution, we will present the project objectives and recent progress in balloon seismology and infrasound modeling.
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Holm, Sverre; Chandrasekaran, Sri Nivas & Näsholm, Sven Peter
(2023).
Finding wave equations for sediment acoustics theories.
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The two main theories for wave propagation in sediments, the Extended Biot theory and the Viscous Grain Shearing (VGS) theory, have been formulated in terms of dispersion equations only. Some have considered the lack of a wave equation to be a weakness that may indicate lack of a physical basis for these theories. In the Biot theory, it is the frequency-dependent viscodynamic operator which models viscous boundary effects in pores that poses the problem. It can be formulated as a ratio of Bessel functions for circular pores and as a ratio of tanh-functions for a 2D parallel plane duct. There is no simple equivalent time domain operator for use in the wave equation. In both geometries, the factor may, however, be approximated well with (1 + icω)1/2, where c is a constant. This factor also appears in the Cole-Davidson dielectric theory for complex media. The equivalent time domain operator, the fractional pseudo-differential operator, enables the formulation of wave equations for all three wave modes. The same operator turns out to be central for transforming the dispersion relations of the VGS theory to time-space wave equations. These wave equations enable a closer study of properties of the medium models than that obtained from dispersion relations alone.
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Näsholm, Sven Peter; Arnestad, Håvard; Austeng, Andreas & Rindal, Ole Marius Hoel
(2023).
Calculating the generalized contrast-to-noise ratio using kernel density estimation.
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The histogram-based generalized contrast-to-noise ratio (gCNR) evaluates how well image regions with different intensity can be distinguished. The gCNR is defined as ‘one minus the overlap region’ of normalized histograms from two regions. Histogram-based gCNR depends on user parameters like bin size and bin offset, but there are also approaches to robustify the histogram calculation.
Kernel density estimation (KDE) is a well-established alternative to histograms to estimate probability density functions (PDFs), and is generally considered to be more robust. We suggest replacing histograms with KDE in gCNR calculations.
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Amezcua, Javier & Näsholm, Sven Peter
(2023).
Using satellite data assimilation techniques to combine infrasound observations and a full ray-tracing model to constrain atmospheric variables.
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Vorobeva, Ekaterina; Assink, Jelle D.; Chunchuzov, Igor; Renkwitz, Toralf; Espy, Patrick Joseph & Näsholm, Sven Peter
(2023).
Using infrasound from explosions for probing internal gravity waves in the middle atmosphere.
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Eggen, Mari Dahl; Midtfjord, Alise Danielle; Vorobeva, Ekaterina; Benth, Fred Espen; Hupe, Patrick & Brissaud, Quentin
[Vis alle 10 forfattere av denne artikkelen]
(2023).
Using a machine learning and stochastics-founded model to provide near real-time stratospheric polar vortex diagnostics based on high-latitude infrasound data.
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Acoustic waves below the frequency limit of human hearing - infrasound - can travel for thousands of kilometres in the atmosphere. The global propagation signature of infrasound is highly sensitive to the wind structure of the stratosphere.
This work exploits processed continuous data from three high-latitude infrasound stations to characterize an aspect of the stratospheric polar vortex. Concretely, a mapping is developed which takes the infrasound data from these three stations as input and outputs an estimate of the polar cap zonal mean wind averaged over 60-90 degrees in latitude at the 1 hPa pressure level. This stratospheric diagnostic information is relevant to, for example, sudden stratospheric warming assessment and sub-seasonal prediction.
The considered acoustic data is within a low-frequency regime globally dominated by so-called microbarom infrasound, which is continuously radiated into the atmosphere due to nonlinear interaction between counter-propagating ocean surface waves.
We trained a stochastics-based machine learning model (delay-SDE-net) to map between a time series of five years (2014-2018) of processed infrasound data and the ERA5 (reanalysis-based) daily average polar cap wind at 1 hPa for the same period. The ERA5 data was hence treated as ground-truth. In the prediction, the delay-SDE-net utilizes time-lagged inputs and their dependencies, as well as the day of the year to account for seasonal differences. In the validation phase, the input was the 2019 and 2020 infrasound time series, and the model inference results in an estimate of the daily average polar cap wind time-series. This result was then compared to the ERA5 representation of the stratospheric diagnostic time-series for the same period.
The applied machine learning model is based on stochastics and allows for an interpretable approach to estimate the aleatoric and epistemic prediction uncertainties. It is found that the mapping, which is only informed of the trained model, the day of year, and the infrasound data from three stations, generates a 1 hPa polar cap average wind estimate with a prediction error standard deviation of around 10 m/s compared to ERA5.
Focus should be put on the winter months because this is when the coupling between the stratosphere and the troposphere can mostly influence the surface conditions and provide additional prediction skill, in particular during strong and weak stratospheric polar vortex regimes. The infrasound data is available in real-time, and we discuss how the developed approach can be extended to provide near real-time stratospheric polar vortex diagnostics.
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Näsholm, Sven Peter; Amezcua, Javier; Assink, Jelle D.; Belova, Evgenia; Blixt, Mårten & Brissaud, Quentin
[Vis alle 16 forfattere av denne artikkelen]
(2023).
Summarizing the research of the MADEIRA project - Middle atmosphere dynamics: exploiting infrasound using a multidisciplinary approach at high latitudes.
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Forestier, Edouard; Näsholm, Sven Peter; Brissaud, Quentin & Pichon, Alexis Le
(2023).
Rapid estimation of ground-to-ground infrasonic transmission loss using a recurrent neural network (RNN) trained on simulations through realistic atmosphere model specifications.
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Näsholm, Sven Peter; Brissaud, Quentin; Vorobeva, Ekaterina & Eggen, Mari Dahl
(2023).
Introduction to Infrasound and Atmospheric Sensing.
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Brissaud, Quentin; Schweitzer, Johannes; Näsholm, Sven Peter; Vorobeva, Ekaterina & Eggen, Mari Dahl
(2023).
Infrasound arrays as probes for atmospheric and ice dynamics in polar regions.
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Hupe, Patrick; Vergoz, Julien; Listowski, Constantino; Pichon, Alexis Le; Milton A., Garcés & Marchetti, Emanuele
[Vis alle 16 forfattere av denne artikkelen]
(2023).
IMS observations of infrasound and acoustic-gravity waves produced by the January 2022 volcanic eruption of Hunga, Tonga: A global analysis.
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Vorobeva, Ekaterina; Assink, Jelle D.; Belova, Evgenia; Latteck, Ralph; Espy, Patrick Joseph & Baumgarten, Gerd
[Vis alle 9 forfattere av denne artikkelen]
(2023).
Probing internal gravity waves in the middle atmosphere using infrasound from explosions.
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Näsholm, Sven Peter
(2023).
Measuring winds we cannot measure using sound we cannot hear?
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Turquet, Antoine Leo; Brissaud, Quentin; Näsholm, Sven Peter; Alvizuri, Celso; Kero, Johan & Listowski, Constantino
[Vis alle 8 forfattere av denne artikkelen]
(2023).
Constraining Moment-Tensor and Source Depth of a Mine Quake Using Local Infrasound Data.
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Vergoz, Julien; Pichon, Alexis Le; Pilger, Christoph; Listowski, Constantino; Marchetti, Emanuele & Ceranna, Lars
[Vis alle 16 forfattere av denne artikkelen]
(2023).
International Monitoring System Observations of Infrasound and Acoustic Gravity Waves Produced by the January 2022 Volcanic Eruption of Hunga, Tonga: A Global Analysis.
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Arnestad, Håvard; Gereb, Gabor; Lønmo, Tor Inge Birkenes; Kirkebø, Jan Egil; Austeng, Andreas & Näsholm, Sven Peter
(2023).
Bounding the beampattern of acoustic arrays using interval arithmetic.
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Arnestad, Håvard; Gereb, Gabor; Lønmo, Tor Inge Birkenes; Kirkebø, Jan Egil; Austeng, Andreas & Näsholm, Sven Peter
(2022).
Bounding the beampattern of acoustic arrays using interval arithmetic.
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Arnestad, Håvard; Austeng, Andreas; Näsholm, Sven Peter & Rindal, Ole Marius Hoel
(2022).
The Effect of Retrospective Transmit Focusing on Minimum Variance Beamforming.
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Gereb, Gabor; Hansen, Roy Edgar; Austeng, Andreas; Lønmo, Tor Inge Birkenes; Näsholm, Sven Peter & Rindal, Ole Marius Hoel
(2022).
Ultrasound Beamformer Benchmarking Pipeline.
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Gereb, Gabor; Hansen, Roy Edgar; Lønmo, Tor Inge Birkenes; Näsholm, Sven Peter; Austeng, Andreas & Rindal, Ole Marius Hoel
(2022).
Improving Sonar Surveying of Subsea Cables and Pipelines with Adaptive Beamforming.
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Background, Motivation and Objective
Safe and efficient transportation of offshore energy requires well-maintained underwater infrastructure, no matter if the energy source is fossil, wind, sun, or wave. Subsea cables and pipelines can be efficiently surveyed using sonar systems mounted on surface or underwater vehicles. Adaptive array signal processing methods are increasingly explored to improve image quality and detection or estimation accuracy in specific survey scenarios. However, adaptive methods can be sensitive to the context they are used in. Therefore, choosing the right beamforming approach from the available candidates requires extensive testing in various scenarios, which is often not feasible out at sea.
Statement of Contribution/Methods
Realistic simulation of complex underwater scenarios has been previously demonstrated using the Field II Ultrasound Simulation Program in combination with the open access package UltraSound ToolBox (USTB). We use Field II to create digital twins of water column images from pipeline surveys, and then modify parameters such as the layout, depth, and SNR to extend the scope of testing. We add multiple realizations of random noise to the signal and then use USTB to beamform the data with different techniques. On the beamformed data we perform estimation of multiple parameters such as the position and size of the pipe and the seabed depth around it. Finally, using the known ground truth of the model, we compare the bias and variance of the estimations made using images reconstructed by different beamformers.
Results/Discussion
Following on the results of previous studies demonstrating the benefits of adaptive beamforming in sonar bathymetry, we present a benchmark study of adaptive beamforming techniques such as Low Complexity Adaptive (LCA) and Capon Minimum Variance (MVDR). Comparison with the Coherence Factor (CF) method is made as well. We use Delay-and-Sum (DAS) as a reference with various apodizations. We provide quantitative performance assessment based on the statistical distribution of the estimations with reference to the ground truth in different scenarios.
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Belova, Evgenia; Barabash, Victoria; Godin, Oleg A.; Kero, Johan; Näsholm, Sven Peter & Vorobeva, Ekaterina
[Vis alle 7 forfattere av denne artikkelen]
(2022).
Infrasound as a Probable Cause of Fast-travelling Polar Mesosphere Winter Echoes.
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Polar mesosphere winter echoes (PMWE) are relatively strong signals from 50-80 km altitudes observed by radars operating at a broad frequency range, at polar latitudes during the equinox and winter seasons. A majority of PMWE can be explained by the neutral air turbulence with or without the presence of charged small particles (presumably meteor smoke particles). However, in some cases strong, quasi-specular radar echoes with high horizontal speeds exceeding 350-400 m/s were observed (Kirkwood et al., 2006; Kirkwood, 2007). Since atmospheric scatterers moving with velocities of hundreds of m/s cannot be attributed to the atmospheric turbulence or nano particles moving with the wind, there is a need to understand what are the physical mechanisms that can generate such PMWE. We consider three recent PMWE events, when the signals travelling with high horizontal velocities above 300 m/s were measured by the 52 MHz atmospheric radar ESRAD located at Esrange, near Kiruna in northern Sweden. We propose four mechanisms of generation of such PMWE that involves microbaroms, i.e. infrasound waves at 0.1 - 0.35 Hz frequencies created by ocean swell. These mechanisms are (i) generation of viscous waves, (ii) generation of thermal waves, (iii) direct contributions of infrasound, and (iv) generation of secondary waves at sound dissipation and they necessarily accompany sound propagation in inhomogeneous, thermally conducting and viscous fluid (air). The infrasound measurements at the IS37 station located about 170 km north-west from the ESRAD radar, modelled maps of the microbarom sources, infrasound propagation conditions and ionospheric conditions for three PMWE events support the proposed mechanisms.
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Näsholm, Sven Peter
(2022).
Infralydbasert karakterisering av vind i den midtre atmosfæren.
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Lyd i lavere frekvenser enn mennesket kan høre – infralyd – forplanter seg over lange avstander (opp til tusenvis av kilometer) i den midtre atmosfæren og blir deretter registrert av et globalt nettverk av bakkebaserte instrumenter.
Disse akustiske bølgene bringer med seg informasjon om dynamikken i den øvre stratosfæren (opp til cirka 50 km høyde) der det er få andre muligheter å måle vind. Vi forteller om vår forskning knyttet til assimilering av infralyddata i atmosfæremodeller og vår ambisjon om å bidra til en forbedret langtidsværvarsling.
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Rindal, Ole Marius Hoel; Näsholm, Sven Peter; Hansen, Roy Edgar & Austeng, Andreas
(2022).
Compensating Dynamic Range Alterations from Adaptive Beamforming using Histogram Matching.
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Rindal, Ole Marius Hoel; Näsholm, Sven Peter; Hansen, Roy Edgar & Austeng, Andreas
(2022).
Image Enhancement Using Capon Minimum Variance Adaptive Beamforming in Synthetic Aperture Sonar.
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Austeng, Andreas; Näsholm, Sven Peter; Hansen, Roy Edgar & Rindal, Ole Marius Hoel
(2022).
Spatial Aperture Coherence with Synthetic Transmit Focusing in SAS.
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Dando, Benjamin; Iranpour, Kamran; Wüstefeld, Andreas; Näsholm, Sven Peter; Baird, Alan F. & Oye, Volker
(2022).
Designing the next generation of seismic arrays using fibre optic DAS.
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While seismic arrays have been in use since the 1950s and are currently a vital part of the IMS, they have fundamentally consisted of single or 3-component seismometers to measure the ground motion at a discrete set of locations known as the array elements. With the advent of Distributed Acoustic Sensing (DAS) within the last two decades, there is currently great interest in exploring the potential seismological applications. In contrast to traditional seismometers, DAS measures the deformation (e.g. strain-rate) along the length of a fibre optic cable with great flexibility in the number of measurements that can be taken and where they are taken along a given cable layout. Applying such technology to seismic arrays offers an exciting opportunity to design array configurations that were previously impractical with individual seismometers. However, the use of DAS requires special consideration of its unique signal characteristics, which include insensitivity of P-waves arriving broadside to the fibre optic cable.
In this paper we present a design study for the installation of a new fibre optical cable at the site of the existing NORES seismic array in Norway – a 1.4 km aperture array located within a subarray of IMS station PS27 (NOA). We demonstrate through the modelling of DAS-specific array response functions how to optimize a new seismic array for regional seismic monitoring, highlighting the importance of incorporating DAS directivity effects. The final design will be installed in 2022 supplementing the current NORES array and will provide a unique data set that could lead to a new generation of DAS seismic arrays for both regional and global seismic monitoring.
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Eggen, Mari Dahl; Dahl, Kristina Rognlien; Näsholm, Sven Peter & Mæland, Steffen
(2022).
Stochastic Modeling of Stratospheric Temperature.
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This study suggests a stochastic model for time series of daily zonal (circumpolar) mean stratospheric temperature at a given pressure level. It can be seen as an extension of previous studies which have developed stochastic models for surface temperatures. The proposed model is a combination of a deterministic seasonality function and a Lévy-driven multidimensional Ornstein–Uhlenbeck process, which is a mean-reverting stochastic process. More specifically, the deseasonalized temperature model is an order 4 continuous-time autoregressive model, meaning that the stratospheric temperature is modeled to be directly dependent on the temperature over four preceding days, while the model’s longer-range memory stems from its recursive nature. This study is based on temperature data from the European Centre for Medium-Range Weather Forecasts ERA-Interim reanalysis model product. The residuals of the autoregressive model are well represented by normal inverse Gaussian-distributed random variables scaled with a time-dependent volatility function. A monthly variability in speed of mean reversion of stratospheric temperature is found, hence suggesting a generalization of the fourth-order continuous-time autoregressive model. A stochastic stratospheric temperature model, as proposed in this paper, can be used in geophysical analyses to improve the understanding of stratospheric dynamics. In particular, such characterizations of stratospheric temperature may be a step towards greater insight in modeling and prediction of large-scale middle atmospheric events, such as sudden stratospheric warming. Through stratosphere–troposphere coupling, the stratosphere is hence a source of extended tropospheric predictability at weekly to monthly timescales, which is of great importance in several societal and industry sectors.
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Vergoz, Julien; Le Pichon, Alexis; Listowski, Constantino; Hupe, Patrick; Pilger, Christian & Peter, Gaebler
[Vis alle 15 forfattere av denne artikkelen]
(2022).
A global analysis of deep infrasound produced by the January 2022 eruption of Hunga volcano.
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The eruption of Hunga volcano, Tonga is the most energetic event recorded by the infrasound component of the global International Monitoring System (IMS). Infrasound, acoustic-gravity and Lamb waves were recorded by all 53 operational stations after circling four times the globe. The atmospheric waves recorded globally exhibit amplitude and period comparable to the ones observed following the 1883 Krakatoa eruptions. In the context of the future verification of the Comprehensive Nuclear-Test-Ban Treaty, this event provides a prominent milestone for studying in detail infrasound propagation around the globe for almost one week as well as for calibrating the performance of the IMS network in a broad frequency band.
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Näsholm, Sven Peter; Iranpour, Kamran; Wüstefeld, Andreas; Dando, Benjamin; Baird, Alan F. & Oye, Volker
(2022).
Array signal processing on distributed acoustic sensing data: directivity effects in slowness space.
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Distributed Acoustic Sensing (DAS) involves the transmission of laser pulses along a fiber-optic cable. These pulses are backscattered at fiber inhomogeneities and again detected by the same interrogator unit that emits the pulses. Elastic deformation along the fiber causes phase shifts in the backscattered laser pulses which are converted to spatially averaged strain measurements, typically at regular fiber intervals.
DAS systems provide the potential to employ array processing algorithms. However, there are certain differences between DAS and conventional sensors. The current paper is focused on taking these differences into account. While seismic sensors typically record the directional particle displacement, velocity, or acceleration, the DAS axial strain is inherently proportional to the spatial gradient of the axial cable displacement. DAS is therefore insensitive to broadside displacement, e.g., broadside P-waves. In classical delay-and-sum beamforming, the array response function is the far-field response on a horizontal slowness (or wavenumber) grid. However, for geometrically non-linear DAS layouts, the angle between wavefront and cable varies, requiring the analysis of a steered response that varies with the direction of arrival. This contrasts with the traditional array response function which is given in terms of slowness difference between arrival and steering.
This paper provides a framework for DAS steered response estimation accounting also for cable directivity and gauge-length averaging – hereby demonstrating the applicability of DAS in array seismology and to assess DAS design aspects. It bridges a gap between DAS and array theory frameworks and communities, facilitating increased employment of DAS as a seismic array.
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Gereb, Gabor; Hansen, Roy Edgar; Lønmo, Tor Inge Birkenes; Näsholm, Sven Peter & Austeng, Andreas
(2022).
Underwater pipeline detection and localisation using multibeam echo sounder in a resolution limited case.
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Arnestad, Håvard; Gereb, Gabor; Birkenes Lønmo, Tor Inge; Kirkebø, Jan Egil; Austeng, Andreas & Näsholm, Sven Peter
(2022).
Sonar array beampattern bounds: tolerance analysis using interval arithmetic.
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The framework of interval arithmetic (IA) and its extension to complex numbers has in the last decade been applied as a tool for finding robust tolerance bounds of antenna arrays. The IA framework complements statistical methods, as inclusive upper and lower bounds of the beampattern are obtained directly, only assuming error bounds on specifically chosen array parameters.
Recently, beampattern synthesis for sonar arrays subject to amplitude excitation errors has been extended from linear arrays with omnidirectional elements to non-linear arrays with directive elements. In this work, we demonstrate that the analysis can be developed further to include both amplitude and phase errors. Moreover, we account for error bounds in element position and orientation, thus representing a more comprehensive method for evaluating the worst-case performance due to uncertainty bounds in a multitude of design parameters.
For this purpose, we have created an open-source MATLAB toolbox to calculate beampattern bounds for an array with bounded error tolerances. The toolbox features an object oriented library of interval classes and an interactive graphical user interface with easily configurable settings, where results for different interval representations are shown along with their corresponding bounds. The beampattern bounds of a sonar array is illustrated through an example.
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Amezcua, Javier; Näsholm, Sven Peter & Vera Rodriguez, Ismael
(2022).
Constraining middle and upper atmospheric variables by assimilating measurements from infrasound propagation.
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When an infrasound wave travels through the atmosphere, it is affected by the atmospheric variables it encounters (e.g. temperature and winds) in its path. When the wave is detected, the integrated effect of these variables along the trajectory of the wave affects measured quantities such as apparent velocity, backazimuth angle and travel time.
Data assimilation combines background atmospheric information with observations to get a better estimate (analysis) of atmospheric variables. In this work, we use the ensemble Kalman filter --with the 10-member ERA-5 reanalysis as background-- to assimilate integrated infrasound observations from the Hukkakero explosions detected by the ARCES array. This process helps get better estimates of atmospheric variables, specially in the stratosphere and lower mesosphere. For each explosion, this process has three steps: (i) the mapping of each of the 10 atmospheric profiles into observation space using the Infra-GA wave propagation model, (ii) the application of the filer equations in observation space, and (c) the mapping back to the space of model variables. The results of these experiments are compared to the Copernicus Artic Regional Reanalysis Service.
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Brissaud, Quentin; Näsholm, Sven Peter & Turquet, Antoine Leo
(2021).
Predicting infrasound transmission loss using deep learning.
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Modeling the spatial distribution of infrasound attenuation (or transmission loss, TL) from surface sources is key to understanding and interpreting observations at ground-based stations. Such predictions enable the reliable assessment of infrasound source characteristics such as ground pressure levels associated with earthquakes, volcanic explosion properties, yield of nuclear and non-nuclear explosions, and ocean-generated microbaroms wavefields. However, the computational cost associated with current full-waveform modeling tools, such as Parabolic Equation (PE) codes, often prevents the exploration of a large parameter space, i.e., variations in wind models, source frequency, and source location, when deriving reliable estimates of source or atmospheric properties — in particular for real-time and near-real-time applications. Therefore, many studies rely on analytical regression heuristic TL equations that neglect complex vertical wind variations and the range-dependent variation in the atmospheric properties. This introduces significant uncertainties in the predicted TL. In this contribution, we propose a deep-learning model trained on a large set of simulated wavefields using PE simulations and ERA5 re-analysis atmospheric models to predict infrasound amplitudes up to 1000 km from the source, also accounting for arbitrarily large vertical and horizontal wind variations. Given an atmospheric model, our new modeling framework provides a fast (0.05 s runtime) and reliable (<5 dB error on average, compared to PE simulations) estimate of the infrasound TL. This work paves the way for real-time monitoring and characterization of infrasound sources such as active volcanoes and man-made explosions. We also see a potential for this approach to be incorporated into frameworks that invert for infrasound source locations, and into studies where infrasound datasets are exploited to constrain atmospheric and numerical weather prediction models.
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Turquet, Antoine Leo; Brissaud, Quentin; Kero, Johan; Näsholm, Sven Peter; Le Pichon, Alexis & Listowski, Constantino
[Vis alle 7 forfattere av denne artikkelen]
(2021).
Near and Far-Field Seismo-Acoustic Analysis of Mb 4.9 Mining Induced Earthquake Nearby Kiruna, Sweden .
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Turquet, Antoine Leo; Brissaud, Quentin; Kero, Johan; Näsholm, Sven Peter; Kværna, Tormod & Le Pichon, Alexis
[Vis alle 7 forfattere av denne artikkelen]
(2021).
Seismo-acoustic analysis of Mw 4.2 mining induced earthquake nearby Kiruna, Sweden.
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Turquet, Antoine Leo; Brissaud, Quentin; Näsholm, Sven Peter; Kero, Johan; Kværna, Tormod & Listowski, C.
[Vis alle 7 forfattere av denne artikkelen]
(2021).
Near and far-field seismo-acoustic analysis of mb 4.9 mining induced earthquake nearby Kiruna, Sweden.
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Eggen, Mari Dahl; Dahl, Kristina Rognlien; Näsholm, Sven Peter & Mæland, Steffen
(2021).
Stochastic modelling of stratospheric temperature.
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Vorobeva, Ekaterina; De Carlo, Marine; Näsholm, Sven Peter; Le Pichon, Alexis & Espy, Patrick Joseph
(2021).
A vespagram-based approach in application to atmospheric remote sensing.
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Vorobeva, Ekaterina; De Carlo, Marine; Näsholm, Sven Peter; Le Pichon, Alexis & Espy, Patrick Joseph
(2021).
A vespagram-based approach to assess microbarom radiation and propagation models.
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Vorobeva, Ekaterina; De Carlo, Marine; Näsholm, Sven Peter; Le Pichon, Alexis & Espy, Patrick Joseph
(2021).
Vespagram-based approach for microbarom radiation and propagation model assessment using infrasound recordings.
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Vera Rodriguez, Ismael; Näsholm, Sven Peter; Brissaud, Quentin; Turquet, Antoine Leo & Le Pichon, Alexis
(2021).
Estimation of infrasound-consistent wind and temperature atmospheric profiles from model ensembles in North Scandinavia.
Vis sammendrag
Atmospheric reanalysis models rely on the assimilation of direct and indirect measurements of different properties of the atmosphere. A better representation of the upper stratosphere in these models, especially for winds, can contribute to enhanced numerical weather predictions on weekly to monthly timescales. Thus, in the current work, we consider the problem of estimating an updated atmospheric model to become consistent with a set of infrasound array observations of travel-time, backazimuth, and apparent velocity.
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Amezcua, Javier; Näsholm, Sven Peter; Blixt, Erik Mårten & Charlton–Perez, Andrew
(2020).
Assimilation of Atmospheric Infrasound Data to Constrain Winds using an EnKF.
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Näsholm, Sven Peter
(2020).
Probing middle atmospheric winds using infrasound recorded at ground-based arrays.
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Näsholm, Sven Peter
(2020).
Probing middle atmospheric winds using infrasound recorded at ground-based arrays.
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Vera Rodriguez, Ismael; Näsholm, Sven Peter; Turquet, Antoine Leo & Evers, Läslo G.
(2020).
Climatology reflected by infrasound travel-times sampling the stratosphere in its transition between summer and winter.
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Belova, Evgenia; Näsholm, Sven Peter; Vorobeva, Ekaterina; Godin, Oleg A. & Barabash, Victoria
(2020).
Polar Mesosphere Winter Echoes and their relation to infrasound.
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Amezcua, Javier; Näsholm, Sven Peter; Blixt, Erik Mårten & Charlton-Perez, Andrew
(2020).
Assimilation of atmospheric infrasound data to constrain tropospheric and stratospheric winds.
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Vera Rodriguez, Ismael; Näsholm, Sven Peter & Le Pichon, Alexis
(2020).
Atmospheric model calibration using infrasound waves from explosions.
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Vorobeva, Ekaterina; De Carlo, Marine; Näsholm, Sven Peter & Le Pichon, Alexis
(2020).
Vespagram-based approach for benchmarking microbarom models and observations.
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Turquet, Antoine Léo; Kero, Johan; Brissaud, Quentin; Näsholm, Sven Peter; Kværna, Tormod & Le Pichon, Alexis
(2020).
In-depth seismo-acoustic analysis of mining-induced Mw 4.9 Kiruna earthquake.
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Millet, Christophe; Ribstein, Bruno & Näsholm, Sven Peter
(2019).
Learning about small-scale atmospheric structures through recurrent infrasound events.
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Le Pichon, Alexis; De Carlo, Marine; Vergoz, Julien; Näsholm, Sven Peter; Espy, Patrick Joseph & Hibbins, Robert
[Vis alle 7 forfattere av denne artikkelen]
(2019).
Characterizing middle atmosphere variability using ocean ambient noise as recorded by a regional infrasound network.
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Le Pichon, Alexis; De Carlo, Marine; Näsholm, Sven Peter; Kero, Johan; Ceranna, Lars & Hupe, Patrick
[Vis alle 7 forfattere av denne artikkelen]
(2019).
Characterizing ocean ambient noise using a regional infrasound network: a sensitivity analysis.
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Dinescu, Raluca; Chica, Daniela; Schweitzer, Johannes; Näsholm, Sven Peter; Popa, Michaela & Ionescu, Constantin
(2019).
Monitoring man-made hazards using data recorded with the Romanian seismic and infrasonic arrays.
Vis sammendrag
Seismic events observed with the Romanian Seismic Network, operated by the National Institute for Earth Physics, are produced by various sources: earthquakes, mining and quarry blasts, thunderstorms, atmospheric and underground explosions. To monitor man-made seismic sources, data recorded by the Romanian seismic and infrasonic arrays deployed at Plostina seismo-acoustic site (PLOR and IPLOR stations) and at Bucovina seismo-acoustic site (BURAR and BURARI stations) are jointly analyzed in order to build an efficient tool for discrimination between anthropogenic and natural events, i.e. between explosions and tectonic earthquakes. At the same time, our work supports the attempt to clean the Romanian seismic catalogue from non-tectonic events.
A specific methodology for the seismo-acoustic analysis has been developed. The main analysis steps consist of: (1) selection of natural and artificial reference events detected by seismo-acoustic arrays considered; (2) analysis of the infrasound detections using standard array processing methods – array data processing software “ep” – provided by NORSAR, in order to extract the signal features (backazimuth, apparent velocity, frequency content, amplitude, SNR); (3) analysis of the seismic detections using the same array data processing software, in order to extract the characteristics of their seismic signature (waveform shape, frequency content, amplitude, particle motion; (4) combination of the infrasonic detections with seismic ones in order to associate them with the reference events based on comparison of the backazimuth estimates and arrival time measurements with the theoretical/expected values and taking in account the effect of the atmospheric propagation conditions; (5) identification of the near-surface explosions produced in the local quarries using the analyzed seismo-acoustic signals and discrimination between these blasts and tectonic earthquakes.
In the future we aim to extract templates of the seismo-acoustic signals generated by the man-made explosions and compare them with the continuously recorded waveforms in order to develop an automatic event identification process.
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De Carlo, Marine; Le Pichon, Alexis; Ardhuin, Fabrice; Näsholm, Sven Peter & Smets, Pieter
(2019).
Evaluating microbaroms source models in finite ocean depth: comparison with IMS station observations.
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Blixt, Erik Mårten; Näsholm, Sven Peter; Gibbons, Steven John & Kværna, Tormod
(2019).
Estimating tropospheric and stratospheric large-scale wind components using infrasound from explosions.
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Blanc, Elisabeth; Hauchecorne, Alain; Keckhut, Philippe; Le Pichon, Alexis; Baumgarten, Gerd & Stober, Gunter
[Vis alle 23 forfattere av denne artikkelen]
(2019).
Atmospheric dynamics from near ground to near Earth space: The ARISE project.
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Blanc, Elisabeth; Le Pichon, Alexis; Pilger, Christoph; Hupe, Patrick; Ceranna, Lars & Marchetti, Emanuele
[Vis alle 12 forfattere av denne artikkelen]
(2019).
ARISE project: infrasound monitoring for civil applications.
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Näsholm, Sven Peter; Assink, Jelle; Blixt, Erik Mårten; De Carlo, Marine; Evers, Läslo Gerardus & Gibbons, Steven John
[Vis alle 11 forfattere av denne artikkelen]
(2019).
Observations of microbarom-generated infrasound in
Northern Norway during three different sudden stratospheric warmings
.
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Näsholm, Sven Peter
(2019).
Observations of microbarom-generated infrasound in Northern Norway during three different sudden stratospheric warmings.
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Gibbons, Steven John; Kværna, Tormod & Näsholm, Sven Peter
(2019).
CTBT Seismic Monitoring in Far East Asia using Coherent and Incoherent Array Processing.
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Marine, De Carlo; Le Pichon, Alexis; Vergoz, Julien; Ardhuin, Fabrice; Näsholm, Sven Peter & Ceranna, Lars
[Vis alle 8 forfattere av denne artikkelen]
(2019).
Characterizing coherent ambient noise in the North Atlantic and Barents sea regions.
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Blixt, Erik Mårten; Charlton–Perez, Andrew; Evers, Läslo Gerardus; Gibbons, Steven John; Kværna, Tormod & Näsholm, Sven Peter
[Vis alle 7 forfattere av denne artikkelen]
(2019).
Cross-wind effects on infrasound waves partially reflected at stratospheric altitudes.
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Näsholm, Sven Peter
(2019).
Exploiting low-frequency acoustic waves to probe middle atmospheric dynamics.
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Näsholm, Sven Peter
(2019).
NORSAR: Vi lytter til jorden for et sikrere samfunn.
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Näsholm, Sven Peter; Assink, Jelle; Blixt, Erik Mårten; De Carlo, Marine; Evers, Läslo G. & Gibbons, Steven John
[Vis alle 11 forfattere av denne artikkelen]
(2019).
Observations of microbarom-generated infrasound in Northern Norway during three different sudden stratospheric warmings .
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Näsholm, Sven Peter; Assink, Jelle; Blanc, Elisabeth; Blixt, Erik Mårten; Claud, Chantal & Gibbons, Steven John
[Vis alle 13 forfattere av denne artikkelen]
(2018).
Infrasonic signatures of polar lows - Comparing a decade of polar low tracks to infrasonic detection backazimuths.
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Näsholm, Sven Peter; Blixt, Erik Mårten; Gibbons, Steven John; Stettner, Felix Benedikt & Kværna, Tormod
(2018).
Interpreting explosive acoustic arrivals at the ARCES seismic array in the context of atmospheric cross-winds.
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Le Pichon, Alexis; Arnal, Thibault; Blixt, Erik Mårten; Näsholm, Sven Peter; Kero, Johan & Ceranna, Lars
[Vis alle 7 forfattere av denne artikkelen]
(2018).
Characterizing ocean ambient noise using a regional infrasound network.
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Gibbons, Steven John; Näsholm, Sven Peter; Blixt, Erik Mårten & Kværna, Tormod
(2018).
Measuring infrasonic wavefronts over large aperture sensor arrays.
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Blixt, Erik Mårten; Näsholm, Sven Peter; Stettner, Felix Benedikt & Kværna, Tormod
(2018).
Cross-wind effects on infrasound propagation.
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Blixt, Erik Mårten; Näsholm, Sven Peter; Kværna, Tormod & Gibbons, Steven John
(2018).
Multi-station study of the cross-wind effect on infrasound propagation.
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Gibbons, Steven John; Kværna, Tormod; Näsholm, Sven Peter & Mykkeltveit, Svein
(2018).
Seismic Monitoring of the North Korea Nuclear Test-Site to Low Magnitude Using Seismic Pattern Detectors .
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Kühn, Daniela; Heimann, Sebastian; Näsholm, Sven Peter; Dando, Benjamin; Gharti, Hom Nath & Ruigrok, Elmer
(2017).
Uncertainties in moment tensor estimation for induced earthquakes illustrated at the example of the Groningen gas field, Netherlands.
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Lambert, Simon; Chatelin, Simon; Näsholm, Sven Peter; Jugé, Lauriane; Garteiser, Philippe & ter Beek, Leon
[Vis alle 12 forfattere av denne artikkelen]
(2013).
Sub-Voxel Micro-Architecture Assessment by Scattering of Mechanical Shear Waves.
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Lambert, Simon; Chatelin, Simon; Näsholm, Sven Peter; Jugé, Lauriane; Garteiser, Philippe & ter Beek, Leon
[Vis alle 12 forfattere av denne artikkelen]
(2012).
Sub-Voxel Micro-Architecture Assessment by Scattering of Mechanical Shear.
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Chatelin, Simon; Lambert, Simon; Jugé, Lauriane; Cai, Xing; Näsholm, Sven Peter & Vilgrain, Valérie
[Vis alle 12 forfattere av denne artikkelen]
(2012).
Measured elasticity and its frequency dependence are sensitive to tissue microarchitecture in MR Elastography.
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Lambert, Simon; Chatelin, Simon; Näsholm, Sven Peter; Holm, Sverre & Sinkus, Ralph
(2012).
Sub-Voxel Micro-Architecture Assessment by Diffusion of Mechanical Shear.
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Näsholm, Sven Peter & Holm, Sverre
(2012).
A Fractional Acoustic Wave Equation from Multiple Relaxation Loss and Conservation Laws.
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Holm, Sverre; Näsholm, Sven Peter & Sinkus, Ralph
(2012).
Fractional acoustic wave equations from constitutive equations.
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Prieur, Fabrice Jean Gabriel; Näsholm, Sven Peter; Austeng, Andreas & Holm, Sverre
(2011).
Second harmonic imaging with echo-sounders: measurements and preliminary results.
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Prieur, Fabrice Jean Gabriel; Näsholm, Sven Peter; Austeng, Andreas & Holm, Sverre
(2010).
Second harmonic imaging a possibility with sonar?
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Prieur, Fabrice Jean Gabriel; Näsholm, Sven Peter; Austeng, Andreas & Holm, Sverre
(2010).
Exploiting nonlinear propagation in echo sounders and sonar.
Fulltekst i vitenarkiv
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Måsøy, Svein-Erik; Tangen, Thor Andreas; Standal, Øyvind; Deibele, Jochen; Näsholm, Sven Peter & Hansen, Rune
[Vis alle 8 forfattere av denne artikkelen]
(2009).
SURF imaging - Acoustics from a dual-frequency band annular array.
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Måsøy, Svein-Erik; Tangen, Thor Andreas; Standal, Øyvind; Deibele, Jochen; Näsholm, Sven Peter & Hansen, Rune
[Vis alle 8 forfattere av denne artikkelen]
(2009).
SURF imaging - A real time dual-frequency band ultrasound system.
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Måsøy, Svein-Erik; Tangen, Thor Andreas; Standal, Øyvind; Deibele, Jochen; Näsholm, Sven Peter & Hansen, Rune
[Vis alle 8 forfattere av denne artikkelen]
(2009).
SURF imaging - Acoustics from a dual-frequency band annular array.
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Måsøy, Svein-Erik; Tangen, Thor Andreas; Standal, Øyvind; Deibele, Jochen; Näsholm, Sven Peter & Hansen, Rune
[Vis alle 8 forfattere av denne artikkelen]
(2009).
SURF imaging - A real time dual-frequency band ultrasound system.
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Näsholm, Sven Peter; Kaupang, Halvard; Måsøy, Svein-Erik; Hansen, Rune & Angelsen, Bjørn Atle J.
(2008).
A simulation study on SURF reverberation suppression in an aberrating medium.
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Måsøy, Svein-Erik; Hansen, Rune; Angelsen, Anders; Kaupang, Halvard; Tangen, Thor Andreas & Standal, Øyvind
[Vis alle 9 forfattere av denne artikkelen]
(2008).
SURF IMAGING – High-frequency ultrasound contrast agent imaging in patients with prostate cancer.
Vis sammendrag
A dual-band method for ultrasound contrast agent detection is demonstrated in vivo in patients with prostate cancer. The method is named Second-Order UltRasound Field Imaging, with the acronym SURF Imaging. It relies on simultaneously transmitting two ultrasound pulses with a large separation in frequency. Here, a low-frequency pulse of 0.9 MHz is combined with a high-frequency pulse of 7.5 MHz. The low-frequency pulse is used to manipulate the properties of the contrast agent, and the high-frequency pulse is used for high-resolution contrast imaging. An annular array capable of transmitting the low- and high-frequency pulses simultaneously was constructed and fitted to a mechanically scanned probe used in a GE Vingmed System 5 ultrasound scanner. The scanner was modified and adapted for the dual-band transmit technique. In-house software was written for post-processing of recorded IQ-data, thus real-time imaging was not possible.
Generally, the method decouples the contrast agent detection frequency from the resonance frequency of the microbubbles, allowing imaging at clinically-high frequencies. The low-frequency pulse is used (e.g. 0.5-2 MHz) to manipulate the properties of the contrast agent around its resonance frequency, changing the back-scattering from the high-frequency pulse (e.g. 3-14 MHz) which is used for high-resolution detection. The general principle of insonifying ultrasound contrast agents with the above described pulse complex is also known as Radial Modulation Imaging in the literature. Here, the name SURF Imaging is used to recognize the fact that transmitting such a pulse complex also infers changes in the forward generated tissue nonlinearities which needs to be accounted for. The low-frequency manipulation pulse generates a local change in the speed of sound experienced by the high-frequency pulse. In the data presented here, this effect is estimated and compensated in the obtained images.
The results present contrast-processed B-mode images from patients enrolled in an ongoing pilot study aimed at imaging prostate cancer using ultrasound contrast agents. The study is approved by the local ethics committee and the patients provide written informed consent. The obtained images show contrast agent detection in the prostate with a transmit frequency of 7.5 MHz, demonstrating that SURF imaging works well in a clinical setting. Due to scanner limitations in IQ-data storage, wash-in curves were not possible to obtain. Images displaying Maximum Intensity Projections (MIP) are presented, demonstrating areas of high contrast activity in regions with positive biopsy findings in patients with locally advanced prostate cancer (T3) and aggressive growth patterns (Gleason score 9).
The results demonstrate the potential of SURF Imaging as an ultrasound contrast detection technique in a clinical setting for high ultrasound frequencies.
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Måsøy, Svein-Erik; Kaupang, Halvard; Tangen, Thor Andreas; Standal, Øyvind; Näsholm, Sven Peter & Johansen, Tonni Franke
[Vis alle 8 forfattere av denne artikkelen]
(2007).
SURF IMAGING – IN VIVO DEMONSTRATION OF AN ULTRASOUND CONTRAST AGENT DETECTION TECHNIQUE IN PATIENTS WITH PROSTATE CANCER AND THYROID NODULES.
Vis sammendrag
A dual-band method for ultrasound contrast agent detection is demonstrated in vivo in patients with prostate cancer and thyroid nodules. The method is named Second-Order UltRasound Field Imaging, with the acronym SURF Imaging. It relies on simultaneously transmitting two ultrasound pulses with a large separation in frequency. Here, a low-frequency pulse of 0.9 MHz is combined with a high-frequency pulse of 7.5 MHz. The low-frequency pulse is used to manipulate the properties of the contrast agent, and the high-frequency pulse is used for high-resolution contrast imaging. An annular array capable of transmitting the low- and high-frequency pulses simultaneously was constructed and fitted to a mechanically scanned probe used in a GE Vingmed System 5 ultrasound scanner. The scanner was modified and adapted for the dual-band transmit technique. In-house software was written for post-processing of recorded IQ-data, thus real-time imaging was not possible.
Generally, the method decouples the contrast agent detection frequency from the resonance frequency of the microbubbles, allowing imaging at clinically-high frequencies. The low-frequency pulse is used (e.g. 0.5-2 MHz) to manipulate the properties of the contrast agent around its resonance frequency, changing the back-scattering from the high-frequency pulse (e.g. 3-14 MHz) which is used for high-resolution detection. The general principle of insonifying ultrasound contrast agents with the above described pulse complex is also known as Radial Modulation Imaging in the literature. Here, the name SURF Imaging is used to recognize the fact that transmitting such a pulse complex also infers changes in the forward generated tissue nonlinearities which needs to be accounted for. The low-frequency manipulation pulse generates a local change in the speed of sound experienced by the high-frequency pulse. In the data presented here, this effect is estimated and compensated in the obtained images.
The results present contrast-processed B-mode images from patients enrolled in two ongoing pilot studies, aimed at imaging prostate cancer and thyroid nodules respectively. The studies are approved by the local ethics committee and the patients provide written informed consent. The obtained images show contrast agent detection in both cases, demonstrating that SURF imaging works well in a clinical setting. For the studied thyroid nodules, contrast-to-tissue ratios ranging from 15-20 dB was obtained, and wash-in curves of contrast agents within a region-of-interest are presented. For the prostate cases, due to scanner limitations in IQ-data storage, wash-in curves were not possible to obtain. Images displaying Maximum Intensity Projections are shown for both categories of patients.
The results demonstrate the potential of SURF Imaging as an ultrasound contrast detection technique in a clinical setting for high ultrasound frequencies.
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Hansen, Rune; Måsøy, Svein-Erik; Näsholm, Sven Peter; Standal, Øyvind; Johansen, Tonni Franke & Angelsen, Bjørn Atle J.
(2007).
SURF imaging for ultrasound contrast agents.
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Hansen, Rune; Måsøy, Svein-Erik; Standal, Øyvind; Näsholm, Sven Peter; Johansen, Tonni Franke & Angelsen, Bjørn Atle J.
(2007).
Improving contrast agent detection with SURF imaging.
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Kaupang, Halvard; Näsholm, Sven Peter; Måsøy, Svein-Erik & Angelsen, Bjørn Atle J.
(2007).
Sound Field Simulation Activities.
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Hansen, Rune; Johansen, Tonni Franke; Måsøy, Svein-Erik; Näsholm, Sven Peter; Standal, Øyvind & Angelsen, Bjørn Atle J.
(2006).
SURF - A better method to detect ultrasound contrast agents and micro-calcifications.
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Måsøy, Svein-Erik; Hansen, Rune; Näsholm, Sven Peter; Standal, Øyvind; Johansen, Tonni Franke & Angelsen, Bjørn Atle J.
(2006).
SURF IMAGING – A METHOD FOR HIGH FREQUENCY ULTRASOUND CONTRAST AGENT DETECTION.
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Måsøy, Svein-Erik; Näsholm, Sven Peter; Standal, Øyvind; Johansen, Tonni Franke; Hansen, Rune & Angelsen, Bjørn Atle J.
(2006).
ACOUSTIC NOISE IN MEDICAL ULTRASOUND IMAGING – CHALLENGES AND SOLUTIONS.
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Näsholm, Sven Peter; Hansen, Rune; Måsøy, Svein-Erik; Standal, Øyvind; Johansen, Tonni Franke & Angelsen, Bjørn
(2006).
Reverberation suppression using SURF as an alternative to second harmonic.
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Näsholm, Sven Peter; Johansen, Tonni Franke & Angelsen, Bjørn Atle J.
(2004).
Effect of a Curved Dome on the Effective Foci of an Annular Array - Numerical Simulations and Experimental Measurements.
Vis sammendrag
A numerical method to estimate the {effective focus} and {effective aperture} changes when a geometrically pre-focused ultrasound annular array is placed inside a curved fluid filled dome is developed. The method is based on ray tracing.
The {effective element} hypothesis and our numerical method to calculate it are verified by comparing simulated ultrasound fields for the following two cases:
1) The {real elements} in the inhomogeneous dome fluid/dome plastic/tissue medium.
2) The {effective elements} in a homogeneous medium.
The ultrasonic fields both along the x- and z axes are found to be very similar within each array element's active region. The focus moving effect prediction from the effective element model is verified by water tank ultrasound field hydrophone measurements of the on-axis z fields from elements of an array disposed in a fluid filled dome.
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Kühn, Daniela; Goertz-Allmann, Bettina; Albaric, Julie; Bohloli, Bahman; Braathen, A. & Brenguier, Florent
[Vis alle 22 forfattere av denne artikkelen]
(2017).
Final project report to KMB project 224880: SafeCO2 II 2013-2016
Investigation of induced seismicity and aseismic deformation in response to CO2 injection and related pressure changes
.
Final project report to industry partners, NORSAR report no. 16-022.
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Näsholm, Sven Peter & Angelsen, Bjørn Atle J.
(2008).
Ultralydstråler for forbedret bildekvalitet.
Norges teknisk-naturvitenskapelige universitet, Det medisinske fakultet.
ISSN 978-82-471-9144-6.
Vis sammendrag
Bildekvaliteten ved bruk av ultralyd i medisinsk diagnostikk varierer mellom ulike organer og fra pasient til pasient. Bedre bildekvalitet forbedrer diagnosepresisjonen og kan føre til mer utbredt anvendelse av ultralyd for eksempel ved bryst- og prostatadiagnose.
Utralydpulser genereres av en piezo-elektrisk transduser, som ofte er oppdelt i flere elementer. Den konverterer elektrisk spenning til vibrasjoner som sendes inn i kroppen. Tilbakespredt lyd mottas av transduseren og tolkes til bilder.
Mange egenskaper hos et ultralyd-avbildingssystem kan forutsies fra dets sender- og mottakerstråler.
I avhandlingen presenteres og analyseres en ny metode for design av annulære (ringformede) transduserelementer. I stedet for at alle elementer er geometrisk fokusert til samme dybde, er fokuseringen ulik fra element til element. Metoden er gunstig for kombinasjon av store mottakeraperturer og høy lydfrekvens som gir god bildeoppløsning. Samtidig dekker bildet et stort dybdeområde. Et arrayforslag designet med metoden vises, og dets mottakerstråler er beregnet numerisk.
En metode, kalt SURF, for generering av senderstråler som undertrykker reverberasjons-støy blir også analysert. Støyen oppstår pga.\ uønskede multiple ekkoer når lyd vandrer frem og tilbake mellom sterke reflektorer i vevet. De plukkes opp i det mottatte signalet og kan gjøre bildet tåkete. SURF-metoden er basert på samtidig utsendelse av en høyfrekvent bildepuls og en lavfrekvent manipulasjonspuls. På grunn av en ikke-lineær effekt forandrer den lavfrekvente pulsen lydhastigheten som bildepulsen beveger seg med. Numeriske simuleringer indikerer at SURF-sendestråler kan dannes både i et homogent propagasjonsmedium og når en modell av en sterkt ikke-homogen kroppsvegg er tilstede. Simulerte sendestråler sammenlignes både med stråler ved standard fundamentalavbildning og ved pulsinversjon. I tillegg presenteres en metode for å prosessere motatte SURF-signaler i ettertid til å forandre dybden for maksimal reverberasjonsundertrykkelse. uten at ny utsendelse av lydpulser trengs.
Resultatene som vises er funnet ved numerisk simulering og teoretisk analyse. De innbyr til utprøving av hvordan metodene yter ved bildedannelse in vivo. Til dette kreves nye typer av transduserarrayer. Reverberasjonsundertrykkelse ved SURF bør ytterligere analyseres ved simuleringsmetoder for bølgeforplanting som tar hensyn til multippel spredning.
Samlet bidrar avhandlingen til videreutvikling av metoder for å forbedre bildekvaliteten ved medisinsk ultralydundersøkelse.
Sven Peter Näsholm, Institutt for sirkulasjon og bildediagnostikk
Veileder: Bjørn A.J. Angelsen
Finansieringskilde: Norges Forskningsråd, programmet for medisin og helse