Acoustic propagation trough internal gravity waves using normal-mode

4 pages, 8 figures.-- Contributed to: 33rd International Acoustical Conference (Strbske Pleso, Slovakia, Oct 4-6, 2006)In this paper we will interest ourselves on acoustic propagation through internal waves. This type of waves is generally due to variations of density on time scales of a few hours; they induce oscillations on the sound speed profile. We will discuss the effects of internal waves on acoustic propagation. We will use a one way-coupled mode approach to model our problem and present the results for two cases. In the first one, we will study the effects of the internal waves in a deep water problem. In the second one, we will present results for a shallow water case.Peer reviewe

Influencia del oleaje: entorno Peckeris y solución de alta frecuencia

6 pages, 4 figures.-- Comunicación presentada en: XXXV Congreso Español de Acústica – TecniAcústica 2004, IV Congreso Iberoamericano de Acústica, IV Congreso Ibérico de Acústica y EAA Symposium "Environmental and Architectural Acoustics" (Guimaraes, 14-17 Sep 2004).[EN] Acoustically shallow waters are those where the characteristics of the surface and the bottom, influence the final receiving acoustic field. Shallow waters form a sound channel in which the sound becomes trapped. A Peckeris environment comes defined by two parallel surfaces, both the surface and the bottom of the sea, the depth remains constant all around, as well as the sound speed. This paper shows how the sound field modifies when the sea state influence is considered. The receiving point is located at “r” meters from the surface, and the source radiates at a depth of “h-z0” meters. Geographically the shallow water matches many continental shelf zones (parallel to the coast line) and also inner water zones (bays, harbours, estuaries, etc,..); the depth of those waters, for sonar applications, can be established in 300 meters or less.[ES] Aguas poco profundas (acústicamente) son aquellas en las que las características de la superficie y del fondo son determinantes del campo acústico final en el punto de recepción. Las aguas poco profundas forman un canal sonoro entre superficie y fondo en el que el sonido queda atrapado. Un entorno Peckeris viene definido por dos superficies paralelas: fondo marino y superficie libre, en el que la profundidad es constante y la traza baty presenta una velocidad que también lo es. Este trabajo presenta cómo se modifica el campo acústico recibido, a un alcance “r”, y generado por una fuente a profundidad “h-z0”, cuando se introduce la influencia del oleaje, o si se quiere la altura media de la ola presenta en la zona. Bajo un punto de vista geográfico, las aguas poco profundas coinciden con la plataforma continental o zonas de aguas interiores (bahías, puertos, estuarios, etc.); las profundidades de estas aguas, para los sistemas sonar habituales, pueden situarse en aquellas inferiores a 300 m.Peer reviewe

Toward an automatic full-wave inversion: Synthetic study cases

Full-waveform inversion (FWI) in seismic scenarios continues to be a complex procedure for subsurface imaging that might require extensive human interaction in terms of model setup, constraints, and data preconditioning. The underlying reason is the strong nonlinearity of the problem that forces the addition of a priori knowledge (or bias) in order to obtain geologically sound results. In particular, when the use of a long-offset receiver is not possible or may not favor the reconstruction of the fine structure of the model, one needs to rely on reflection data. As a consequence, the inversion process is more prone to becoming stuck in local minima. Nevertheless, misfit functionals can be devised that can either cope with missing long-wavenumber features of initial models (e.g., cross-correlation-based misfit) or invert reflection-dominated data whenever the models are sufficiently good (e.g., normalized offset-limited least-squares misfit). By combining both, high-frequency data content with poor initial models can be successfully inverted. If one can figure out simple parameterizations for such functionals, the amount of uncertainty and manual work related to tuning FWI would be substantially reduced. Thus, FWI might become a semiautomatized imaging tool.We want to thank Repsol for funding this research by means of the Aurora project. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 644202. Additionally, the research leading to these results has received funding from the European Union’s Horizon 2020 Programme (2014-2020) and from Brazilian Ministry of Science, Technology and Innovation through Rede Nacional de Pesquisa (RNP) under the HPC4E Project (www.hpc4e.eu), grant agreement No 689772. We acknowledge Chevron for the dataset that was used in our second example.Peer ReviewedPostprint (author's final draft

Synthetic Modeling for an Acoustic Exploration System for Physical Oceanography

10 pages, 6 figures, 1 tableMarine multichannel seismic (MCS) data, used to obtain structural reflection images of the earth¿s subsurface, can also be used in physical oceanography exploration. This method provides vertical and lateral resolutions of O(10¿100) m, covering the existing observational gap in oceanic exploration. All MCS data used so far in physical oceanography studies have been acquired using conventional seismic instrumentation originally designed for geological exploration. This work presents the proof of concept of an alternative MCS system that is better adapted to physical oceanography and has two goals: 1) to have an environmentally low-impact acoustic source to minimize any potential disturbance to marine life and 2) to be light and portable, thus being installed on midsize oceanographic vessels. The synthetic experiments simulate the main variables of the source, shooting, and streamer involved in the MCS technique. The proposed system utilizes a 5-s-long exponential chirp source of 208 dB relative to 1 ¿Pa at 1 m with a frequency content of 20¿100 Hz and a relatively short 500-m-long streamer with 100 channels. This study exemplifies through numerical simulations that the 5-s-long chirp source can reduce the peak of the pressure signal by 26 dB with respect to equivalent air gun¿based sources by spreading the energy in time, greatly reducing the impact to marine life. Additionally, the proposed system could be transported and installed in midsize oceanographic vessels, opening new horizons in acoustic oceanography researchThe first author’s work has been supported by the European Commission through Marie Curie Actions FP7-PEOPLE-2010-IOF-271936 and FP7-PEOPLE-2012-COFUND-600407. This work has been done in the framework of the Spanish project POSEIDON (CTM2010-25169) and the Italian National Flagship Programme RITMARE (Programma Nazionale della Ricerca 2011-2013 MIUR). We want to acknowledge the team of GO project funded by the EU (015603-GO-STREP)Peer Reviewe

Geophysical data integration for a joint interpretation in a shallow gypsiferous context

As every geophysical technique suffers from its own limitation, a proper survey has to combine different geophysical methods. The integration of different geophysical data in order to derive a joint geological interpretation is complicated beyond qualitative (subjective) correlations. We propose a new numerical method (less subjective) to integrate three separated datasets: seismics, electrics and well logging. The study area is the shallow subsurface of a planned singular facility in Villar de Cañas (Cuenca, Central Spain). Lithology down to 100 m deep consists of a transition from shale to massive gypsum. In 2013, we acquired a3D Traveltime Tomography to characterize this transition. After data processing, the velocity model showed, in general, a good correlation with geological profiles, being able to identify the three main layers: shales, transition gypsum and massive gypsum. The correlation for the massive gypsum limit (high velocity contrast) is very good, but is not that good for the transition shale-gypsum (low velocity contrast).Research supports: CGL2014-56548-P, 2009-SGR-1595 , CGL2013-47412-C2-1-PPeer Reviewe

Synthetic modelling of acoustical propagation applied to seismic oceanography experiments

Recent work shows that multichannel seismic (MCS) systems provide detailed information on the oceans' finestructure. The aim of this paper is to analyze if high order numerical algorithms are suitable to accurately model the extremely weak wavefield scattered by the oceans' finestructures. For this purpose, we generate synthetic shot records along a coincident seismic and oceanographic profile acquired across a Mediterranean salt lens in the Gulf of Cadiz. We apply a 2D finite-difference time-domain propagation model, together with second-order Complex Frequency Shifted Perfectly Matched Layers at the numerical boundaries, using as reference a realistic sound speed map with the lateral resolution of the seismic data. We show that our numerical propagator creates an acoustical image of the ocean finestructures including the salt lens that reproduces with outstanding detail the real acquired on

Acceleration strategies for elastic full waveform inversion workflows in 2D and 3D

Full waveform inversion (FWI) is one of the most challenging procedures to obtain quantitative information of the subsurface. For elastic inversions, when both compressional and shear velocities have to be inverted, the algorithmic issue becomes also a computational challenge due to the high cost related to modelling elastic rather than acoustic waves. This shortcoming has been moderately mitigated by using high-performance computing to accelerate 3D elastic FWI kernels. Nevertheless, there is room in the FWI workflows for obtaining large speedups at the cost of proper grid pre-processing and data decimation techniques. In the present work, we show how by making full use of frequency-adapted grids, composite shot lists and a novel dynamic offset control strategy, we can reduce by several orders of magnitude the compute time while improving the convergence of the method in the studied cases, regardless of the forward and adjoint compute kernels used.The authors thank REPSOL for the permission to publish the present research and for funding through the AURORA project. J. Kormann also thankfully acknowledges the computer resources, technical expertise and assistance provided by the Barcelona Supercomputing Center - Centro Nacional de Supercomputacti ´on together with the Spanish Supercomputing Network (RES) through grant FI-2014-2-0009. This project has received funding from the European Union’s Horizon 2020, research and innovation programme under the Marie Skłodowska-Curie grant agreement no. 644202. The research leading to these results has received funding from the European Union’s Horizon 2020 Programme (2014–2020) and from the Brazilian Ministry of Science, Technology and Innovation through Rede Nacional de Pesquisa (RNP) under the HPC4E Project (www.hpc4e.eu), grant agreement no. 689772.We further want to thank the Editor Clint N. Dawson for his help, and Andreas Fichtner and an anonymous reviewer for their comments and suggestions to improve the manuscript.Peer ReviewedPostprint (published version

The deal.II Library, Version 9.0

This paper provides an overview of the new features of the finite element library deal.II version 9.0

A quadruply imaged quasar with an optical Einstein ring candidate: 1RXS J113155.4-123155

We report the discovery of a new quadruply imaged quasar surrounded by an optical Einstein ring candidate. Spectra of the different components of 1RXS J113155.4-123155 reveal a source at z=0.658. Up to now, this object is the closest known gravitationally lensed quasar. The lensing galaxy is clearly detected. Its redshift is measured to be z=0.295. Additionally, the total V magnitude of the system has varied by 0.3 mag between two epochs separated by 33 weeks. The measured relative astrometry of the lensed images is best fitted with an SIS model plus shear. This modeling suggests very high magnification of the source (up to 50 for the total magnification) and predicts flux ratios between the lensed images significantly different from what is actually observed. This suggests that the lensed images may be affected by a combination of micro or milli-lensing and dust extinction effects.Comment: 4 pages, 3 figures, published in A&

Safety and feasibility of intranasal heroin-assisted treatment: 4-week preliminary findings from a Swiss multicentre observational study

Background: Heroin-assisted treatment (HAT) is effective for individuals with severe opioid use disorder (OUD) who do not respond sufficiently to other opioid agonist treatments. It is mostly offered with injectable diacetylmorphine (DAM) or DAM tablets creating a barrier for individuals who need the rapid onset of action but are either unable or unwilling to inject, or primarily snort opioids. To explore another route of administration, we evaluated the safety and feasibility of intranasal (IN) DAM. Methods: This is a multicentre observational cohort study among patients in Swiss HAT. All patients planning to receive IN DAM within the treatment centres were eligible to participate. Participants were either completely switched to IN DAM or received IN DAM in addition to other DAM formulations or opioid agonists. Patients were followed up for four weeks. Sociodemographic characteristics, current HAT regimen, reasons for starting IN DAM, IN DAM doses, number of injection events in the sample, IN DAM continuation rate, and appearance of adverse events and nose-related problems were evaluated. Results: Participants (n = 52) reported vein damage, preference for nasal route of administration, and desire of a stronger effect or for a less harmful route of administration as primary reasons for switching to IN DAM. After four weeks, 90.4% of participants (n = 47) still received IN DAM. Weekly average realised injection events decreased by 44.4% from the month before IN DAM initiation to the month following. No severe adverse events were reported. Conclusions: After four weeks, IN DAM was a feasible and safe alternative to other routes of administration for patients with severe OUD in HAT. It addressed the needs of individuals with OUD and reduced injection behaviour. More long-term research efforts are needed to systematically assess efficacy of and patient satisfaction with IN DAM