Yann Stephan

Yann Stephan
Service hydrographique et océanographique de la marine | SHOM · HOM

PhD, HDR

About

120
Publications
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729
Citations

Publications

Publications (120)
Article
Shipping noise has been identified as a threat on underwater ecosystems. In particular, several impacts have been documented on cetaceans, e.g., communication’s masking and stress increasing. To assess the risk related to such anthropogenic noise requires both quantifying the noise levels and estimating the distribution of the cetaceans’ population...
Article
Full-text available
In a recent paper [Pinson et al., J. Acoust. Soc. Am. 143, 2622–2631], theoretical interface echo scintillation, time-of-arrival variance, and angle-of-arrival variance have been derived as a function of the roughness autocorrelation function. Those parameters have been obtained under the Kirchhoff and small-roughness approximation by including int...
Article
Underwater soundscape may be seen as an intrinsic feature of the environment in which it is recorded. In fact, underwater soundscape is a complex combination of sounds from a variety of acoustic sources, whether from natural or from human origin. When the distances between the sources and the receivers are sufficiently large, the received signals a...
Article
Full-text available
Integral solutions for wave scattering over slightly rough surfaces generally include the source and receiver directivity. In this paper, it is shown that integrating the point source, point receiver solution over the source and receiver apertures leads to solutions with a clear physical interpretation. The scintillation, time-of-arrival, and direc...
Presentation
Full-text available
La solution intégrale de la réflexion d’une onde sur une surface légèrement rugueuse inclue généralement la directivité des transducteurs d’émission et de réception. Or, on peut montrer qu’en utilisant la solution intégrale pour une source et un récepteur ponctuels, puis en intégrant sur les surfaces des transducteurs, on obtient une solution avec...
Article
The management of underwater noise within the European Union's waters is a significant component (Descriptor 11) of the Marine Strategy Framework Directive (MSFD). The indicator related to continuous noise, is the noise levels in two one-third octave bands centered at 63 Hz and 125 Hz. This paper presents an analysis of underwater noise in the Celt...
Data
The shipping noise is a major component of the underwater soundscape at low frequency. The increase of the fleet size at world scale for several decades have arisen the potential impacts of noise pollution on marine ecosystems.Modeling the shipping noise levels at large scale became an important task of marine environmental policies. However, becau...
Data
The management of underwater anthropogenic noise is becoming a significant component of marine policies. Rules to limit noise exposure in a way that marine animals are not adversely affected are expected to be set up in the future. However, modeling or measuring underwaternoise levels (orother suitable metrics) can still be subject to a lot of unce...
Article
The management of underwater anthropogenic noise is becoming a significant component of marine policies. Rules to limit noise exposure in a way that marine animals are not adversely affected are expected to be set up in the future. However, modeling or measuring underwaternoise levels (orother suitable metrics) can still be subject to a lot of unce...
Article
The shipping noise is a major component of the underwater soundscape at low frequency. The increase of the fleet size at world scale for several decades have arisen the potential impacts of noise pollution on marine ecosystems.Modeling the shipping noise levels at large scale became an important task of marine environmental policies. However, becau...
Poster
Full-text available
The aim of the study is to perform quantitative imaging of the seafloor random parameters using a multibeam echosounder. More specifically we present in this communication a focus on the interface roughnesses with controlled parameters using a 3D modeling of a layered media with rough interfaces. The modeling consists of a sum of integrals over eac...
Presentation
Full-text available
Presentation of the workshop ”Fostering inter-regional cooperation in underwater noise monitoring and impact assessment in waters around Europe, within the context of the European Marine Strategy Framework Directive” organized by ACCOBAMS during ECS 2017
Presentation
Full-text available
The increase of the world fleet size for several decades may lead to a global increase of the traffic ambient noise levels in the oceans. The threat of an impact on biodiversity is high enough to promote the idea that potential harmful noise levels should be avoided, or at least controlled and regulated. For this purpose, it is necessary to estimat...
Conference Paper
Full-text available
The increase of the world fleet size for several decades may lead to a global increase of the traffic ambient noise levels in the oceans. The threat of an impact on biodiversity is high enough to promote the idea that potential harmful noise levels should be avoided, or at least controlled and regulated. For this purpose, it is necessary to estimat...
Presentation
Full-text available
Depuis 2008, la Directive Cadre Stratégique pour le Milieu Marin s’intéresse à définir le bon état écologique (BEE) dans les eaux européennes à travers onze descripteurs de pressions anthropiques, d’impacts et d’état du milieu. Le descripteur 11 (D 11) définit les pressions des sources d’énergie introduites par l’homme ; la pollution sonore y est r...
Article
Full-text available
Cet article presente un procede d'inversion geoacoustique passif a partir de signaux representatifs de vocalises de mammiferes marins et d'un unique hydrophone en milieux petits fonds. Notre methode utilise au mieux la propagation en multitrajets des vocalises et leur signature temps-frequence pour extraire un observable permettant d'estimer par in...
Article
Seismic velocities together with sediment/rock compaction models are of common use in the oil industry to predict reservoir pressures and to detect and identify any potential hazard associated with over-pressured formations. Excess pore pressure is a key parameter for geohazard assessment, nevertheless this approach is very seldom applied to shallo...
Article
Full-text available
To improve the performance prediction of low frequencies sonar (Anti Submarine Warfare)we can use geoacoustic information coming from different kind of sensors. However, geoacoustic and scattering properties estimation by inversion of received acoustic signals remains very difficult and strongly dependent on the system of measurement. Indeed the in...
Article
Full-text available
The scattering strength of isotropic and anisotropic rough surfaces was experimentally and theoretically investigated for high frequencies about 500 kHz. Emphasis was placed on studying the response from three two-dimensional rough sur-faces which roughness was either isotropic (characterized by a Gaussian distribution) or anisotropic (characterize...
Article
Full-text available
The first-order small slope approximation is applied to model the scattering strength from a rough surface in underwater acoustics to account for seafloor for high frequencies from 10 kHz to hundreds of kilohertz. Emphasis is placed on simulating the response from two-dimensional anisotropic rough surfaces. Several rough surfaces are described base...
Article
Full-text available
An inversion scheme is proposed, relying upon the inversion of the noise of a moving ship measured on a single distant hydrophone. The spectrogram of the measurements exhibits striations which depend on waveguide parameters. The periodic behavior of striations versus range are used to estimate the differences of radial wavenumber between couples of...
Technical Report
Full-text available
The European Maritime Strategy Framework imposes to each Member State to develop a strategy for its marine waters. The aim is to achieve or maintain a good environmental status. This strategy includes among others the initial assessment of underwater sonic pressures and impacts due to human activities. This report presents a synthesis of this asses...
Article
Full-text available
This paper presents a novel approach to synthesize realistic environment for ocean-acoustic parametric studies. In its current form, this methodology applies to internal waves and tides. Empirical orthogonal function (EOF) decomposition is applied to a temporal series of temperature profiles. It can be observed that the first two time-dependent exp...
Article
Full-text available
The objective of this work was to study the scattering strength depending on the receiver and sound source positions compared to an anisotropic surface. Roughness scattering by an anisotropic rough surface was studied under controlled laboratory conditions at a frequency of 500kHz. Two kinds of anisotropic rough surfaces were used, both with a heig...
Article
Full-text available
The Ushant thermal front is a seasonal phenomenon which occurs from May to October in a shallow water environment (100m) of the Iroise Sea (off the coast of the northwestern France). It corresponds to the boundary separating a well mixed inner shelf water from an open sea stratified water. To determine the dynamic of the front -or more basically th...
Article
This study consisted in the characterization of internal waves in the south of the Strait of Messina (Italy). The observational data consisted in thermistor string profiles from the Coastal Ocean Acoustic Changes at High frequencies (COACH06) sea trial.An empirical orthogonal function analysis is applied to the data. The first two spatial empirical...
Article
-------------------------------------------------------------------------------- One of the most challenging applications of time–frequency representations deals with the analysis of the signal issued from natural environment. Recently, the interest for passive underwater context increased, basically due to the rich information carried out by the n...
Article
Full-text available
Time-frequency representations constitute the main tool for analysis of nonstationary signals arising in real-life systems. One of the most challenging applications of time-frequency representations deal with the analysis of the underwater acoustic signals. Recently, the interest for dispersive channels increased mainly due to the presence of the w...
Article
The continuous monitoring of coastal processes presents a great interest both from the environmental and economic viewpoints. Passive acoustic tomography can be a good candidate to provide synoptic measurements over wide areas while a range-dependent inversion scheme allows to achieve a reasonable spatial resolution along each vertical slice sectio...
Conference Paper
A modern method for discrete underwater channel characterization is the passive tomography concept which takes advantage of the generated signals by the natural sources (opportunity sources). The main difficulty which appears in this field is due to the lack of any information about the received signals. In this paper, we present a method for under...
Article
Full-text available
Ocean modeling and forecasting require significant hydro-graphic and satellite measurements to provide accurate and valid results through assimilation methods. In coastal environment, this task is made more complex because of the strong coupling between state variables and forcing, the lack of data and the frequent model break. In addition, in the...
Article
Full-text available
The concept of basin scale ocean acoustic tomography, born thirty years ago, generated a strong enthusiasm in late twentieth century. This enthusiasm fall as the concept did not led to operational applications. Since a decade the interest for coastal areas, either for civilian or military applications rose again with the new concepts of rapid envir...
Article
Full-text available
This paper focus on the activities conducted at SHOM in ocean acoustics. These studies are mainly relative to the impact of the environment on the acoustic systems operated by naval forces as well the tomographic characterization of the environment. The major axes of research in this domain are presented and discussed.
Article
Full-text available
In September 2009, during two days, a geo-acoustic experiment, named ERATO-09, was conducted by SHOM in the Bay of Biscay. During the experiment, the presence of common dolphins (Delphinus delphis) has been noticed. In this paper, we retrospectively evaluate the feasibility of passive acoustic monitoring to derive interactions between active acoust...
Article
Full-text available
Monitoring the environment with non intrusive acoustic techniques is the subject of many research initiatives worldwide. In the framework of the scientific interest group "Europôle Mer (GIS-EM)", ENSIETA, SHOM and Océanopolis co-organized the SERENADE workshop in Brest. This workshop has enabled to provide a state of the art in the field of acousti...
Article
Full-text available
Cet article présente une vue prospective de la recherche au SHOM dans le domaine de l'environnement marin, pour l'ensemble de ses missions. S'il couvre essentiellement le domaine de l'océanographie militaire, il traite néanmoins aussi, mais avec un moindre niveau de détail, les autres mandats du SHOM qui concernent la sécurité de la navigation et l...
Article
Full-text available
Le concept de tomographie acoustique de bassin, né il y a une trentaine dʼannées, a suscité un engouement très fort à la fin du vingtième siècle. Cet engouement est sensiblement retombé depuis et le concept nʼa pas débouché sur de réelles applications opérationnelles. Lʼintérêt très fort suscité depuis une dizaine dʼannées pour les zones côtières,...
Article
Full-text available
In September 2009, during two days, a geo-acoustic experiment, named ERATO-09, was conducted by SHOM in the Bay of Biscay. During the experiment, the presence of common dolphins (Delphinus delphis) has been noticed. In this paper, we retrospectively evaluate the feasibility of passive acoustic monitoring to derive interactions between active acoust...
Article
Full-text available
We investigate a characterization of underwater acoustic signals using extracted time-scale features of the propagation channel model for medium-to-high frequency range. The underwater environment over these frequencies causes multipath and Doppler scale changes on the transmitted signal. This is the result of the time-varying nature of the channel...
Article
A single-hydrophone geoacoustic inversion procedure using a calibrated source is proposed and tested with experimental shallow water data. In a first step the number of sediment layers, their thicknesses and velocities are estimated using a conventional seismic approach. In a second step, the amplitude variations of each reflected arrival are used...
Article
The internal waves in the south of the Strait of Messina (Italy) are studied using observational data and numerical simulations. The observational data consisted of SAR images, XBT probes, CTD yoyos and thermistor string profiles from the Coastal Ocean Acoustic Changes at High Frequencies (COACH06) cruise. The numerical Lamb model was used to solve...
Article
Full-text available
We propose the use of discrete time-scale transformations of acoustic signals to characterize the wideband effect of underwater environment propagation. The representation depends on the Mellin transform, and it can be used to efficiently process the effect of the underwater environment. For sparse environments, we also consider a new approach with...
Article
Full-text available
The estimation of the impulse response (IR) of a propagation channel may be of great interest for a large number of underwater applications: underwater communications, sonar detection and localization, marine mammal monitoring, etc. It quantifies the distortions of the transmitted signal in the underwater channel and enables geoacoustic inversion....
Article
Full-text available
The estimation of the impulse response of a propagation channel is necessary for a large number of acoustic applications: underwater communication, detection and localization, etc. Basically, it informs us about the distortions of a transmitted signal in one channel. This operation is usually subject to additional distortions due to the motion of t...
Article
Full-text available
Underwater channel is an example of a natural environment potentially characterized by signals generated by various sources : underwater mammals, human activity noise, etc. In order to take advantage of these sources, the concept of passive acoustic tomography has been introduced. According to this concept, the environment parameters could be extra...
Conference Paper
Oceanic modeling and prediction are highly dependent on the availability of satellite remote sensing and hydrographic in situ measurements to provide reliable and accurate results. In coastal environments the data assimilation is a difficult problem due to the lack of data, the strong coupling between state variables and forcing and the frequent mo...
Article
The estimation of an impulse response of a propagation channel is necessary for a large number of underwater applications: underwater communication, sonar detection and localization, marine mammal monitoring, etc. Basically it informs us about the distortions of transmitted signal in underwater channels and enables geoacoustic inversion. The propag...
Conference Paper
Full-text available
The estimation of the impulse response (IR) of a propagation channel is necessary for a large number of acoustic applications: underwater communication, detection and localization, etc. Basically, it informs us about the distortions of a transmitted signal in one channel. This operation is usually subject to additional distortions due to the motion...
Conference Paper
This work presents a feasibility test of acoustic data assimilation in a basic feature model of the Ushant front, west off Brittany, enabling the tracking of the principal characteristics of the front. Two monitoring applications are presented for tracking the tidal variations of the front and its seasonal variations (from April to July). The data...
Article
Full-text available
Subbottom profilers are commonly used to explore the first sediment layers below the seafloor. Recent narrowbeam profilers achieve improved performances in terms of signal-to-noise ratio (SNR) and resolution. Thus, the potential of these systems for near real-time geoacoustic characterization of sediments is high and is worth being specifically exp...
Article
Full-text available
Developing operational oceanographic models for coastal environment is an exciting challenge for the next decades. The typical sparsity of assimilated in-situ observations often creates biases in the model predictions reducing the overall accuracy of the forecasting. In such a highly dynamic environment, acoustic tomography can be a good candidate...
Article
The most recent subbottom profilers present good performances in term of signal to noise ratio, resolution and penetration. These devices can thus be used to infer quantitatively the geoacoustic parameters of the seafloor. We have previously developed inversion methods which aim to estimate absorption, reflection, penetration, impedance contrast an...
Article
In the context of the passive geoacoustic inversion, this manuscript proposes a new Inversion Method suitable for very shallow water environments (10 to 30 m) from the broadband noise produced by ships of opportunity. The solution is dedicated to a small number of hydrophones and is easy to implement. The interference patterns generated by the ship...
Article
We propose a new method to localize low-frequency calls in 2D in shallow waters from a sparse array of hydrophones using modal propagation modelling. An analysis of modal propagation modelling of transients signals in shallow water environment shows that the dispersive behaviour of the waveguide can be exploited to design a robust localization sche...
Article
In the context of the passive geoacoustic inversion, this manuscript proposes a new Inversion Method suitable for very shallow water environments (10 to 30 m) from the broadband noise produced by ships of opportunity. The solution is dedicated to a small number of hydrophones and is easy to implement. The interference patterns generated by the ship...
Article
Full-text available
SHORT ABSTRACT: This paper describes the development of a real time geoacoustic inversion tool devoted to broad band signals. The aim of this tool is to automatically infer geoacoustic bottom characteristics from transmission sound field pressure measurements in a deep ocean medium. The first part of the article is devoted to the direct problem. It...
Article
This paper presents the new concept of passive acoustic tomography which allows ocean data collection with a passive acoustic remote sensing process. The originality lies in using acoustic sources of opportunity such as surface noise, radiated ship noise and marine mammal calls. Such use of passive tomography is a promising way to reduce acoustic e...
Article
Full-text available
Ocean Acoustic Tomography (OAT) uses powerful active emissions of repetitive signals causing problems when acoustic discretion is required as in military operations. In this paper, we propose to develop a new concept of OAT, called Discreet Acoustic Tomography (DAT), which is based on a stealthy acoustic signals emission. An appropriate global proc...
Article
Full-text available
Processing marine-mammal signals for passive oceanic acoustic tomography or species classification and monitoring are problems that have recently attracted attention in scientific literature. For these purposes, it is necessary to use a method which could be able to extract the useful information about the processed data, knowing that the underwate...