Papers by Xavier Demoulin
Cette thèse est une contribution à la caractérisation des fonds sous-marins par des techniques ac... more Cette thèse est une contribution à la caractérisation des fonds sous-marins par des techniques acoustiques. On s'intéresse aux fonds sédimentaires, principalement sédiments sableux. Les fonds de sables sont en effet fréquemment rencontrés par petits fonds sous nos latitudes. Les procédés existants de caractérisation acoustique des fonds visent le plus souvent à qualifier la géométrie du sol ou du sous-sol: morphologie du fond, typologie des faciès sédimentaires, identification du toit rocheux ... Toutefois, les détails du sous-sol marin (stratification et composition des sables) nous échappent le plus souvent et on a alors recours à des sondages in-situ ponctuels, coûteux et souvent difficiles à réaliser. Afin de résoudre ce problème, nous avons développé SCAMPI (Système de Caractérisation Acoustique Marine Propagation Interface). C'est un dispositif de caractérisation géoacoustique breveté qui vise justement à réduire notre myopie chronique dans les premiers mètres des sous...
Seismo-acoustic wave propagation in the Rade of Hyères (France) generated by counter-mining of explosive devices: comparison between numerical simulations and real experiments
The Journal of the Acoustical Society of America, 2019
In order to study the impact of the potential explosion of WWII unexploded ordnances which are co... more In order to study the impact of the potential explosion of WWII unexploded ordnances which are commonly found along the French Mediterranean coast, a series of underwater explosions were conducted in December 2018 in the Rade of Hyeres in France. These explosions were realized within the framework of the POSA project, led by SHOM, and which includes LMA, Géoazur and LPG Nantes which addresses the upstream hazard management issue of such counter-mining operations in the marine field. From topographical and sedimentary measurements performed in this area, physical and geometrical characteristics of the marine seabed have been carefully selected to serve as input data for numerical simulations of seismo-acoustic wave propagation from the source to several seismometers deployed on the coast of Hyeres and surrounding islands. Numerical simulations were conducted using a spectral-element method in the time domain. The impact of the explosive device (source) charge and its location (on the...
Analyse de la dynamique d’un cyclone à l’aide d’un réseau d’OBS
HAL (Le Centre pour la Communication Scientifique Directe), Apr 11, 2022
Imagerie ultrasonore de l'intérieur des sédiments: premiers éléments du projet OSCARABIS
HAL (Le Centre pour la Communication Scientifique Directe), 2017
International audienc
High-frequency sediment sound speed and attenuation measurements during TREX13 (Target and Reverberation Experiment 2013) with a new portable velocimeter
Journal of the Acoustical Society of America, Nov 1, 2013
During the Target and Reverberation Experiment 2013 (TREX13), high-frequency measurements of sedi... more During the Target and Reverberation Experiment 2013 (TREX13), high-frequency measurements of sediment sound speed and attenuation were collected throughout the experiment site. These measurements were performed using the INSEA, a diver-portable array of sources and receivers conceived and developed by French companies in collaboration with research institutions. During each deployment of the instrument, the INSEA was inserted 10–15 cm into the sediment and narrow-band pulses covering the 70 to 350 kHz range were transmitted through the sediment. The sound speed is determined from the time-of-flight and attenuation is determined from the amplitude ratio of the transmissions through the sediment and through the water. The variability of the TREX13 site made it possible to collect data in several different sediment types including mud, silty-sand, and sand sediments each with low to high concentrations of shells. In addition to the acoustic measurements, diver cores and shell samples were also collected. The sound speed and attenuation measured in these sediments are presented and discussed. [Work supported by DGA, ONRG, and SERDP.]
Seismo-acoustic wave propagation generated by the detonation of UXOs of large charge weights in a shallow water environment
HAL (Le Centre pour la Communication Scientifique Directe), Oct 24, 2022
IEEE Journal of Oceanic Engineering, Apr 1, 2022
The goal of the work presented in a two-companion paper is to pave the way for reliably assessing... more The goal of the work presented in a two-companion paper is to pave the way for reliably assessing the risks of damage to buildings on the shore, induced by the detonation of unexploded historical ordnance (UXO) of large weights in variable shallow water environments with a water depth less than 50 m. The risk assessment is quantified through the seismic magnitude on the Richter scale, induced by the detonation of charges of different weights (between 80-and 680-kg TNT-equivalent). This metric is investigated experimentally using a coupled seismo-acoustic approach within the framework of a UXO clearance (countermining) campaign in the Mediterranean Sea. Analysis of real acoustic and seismic data shows that, compared to a charge detonation in water, a similar detonation on the seabed generates seismic signals of lower frequencies and higher amplitudes that propagate in the seabed. The larger the charge weight, the higher the seismic amplitude. Besides the explosion-coast distance, the ground properties also Manuscript
Using hydrodynamic and thermodynamic equations appropriate for modelling internal tides, one can ... more Using hydrodynamic and thermodynamic equations appropriate for modelling internal tides, one can predict the current and temperature distributions associated with the ocean's dynamic modes. Comparing such predictions with observations from the INTIMATE'96 experiment, we find a high degree of correlation between the first 3 theoretically calculated dynamic modes and corresponding empirical orthogonal functions (EOF's) derived from an ensemble of temperature and current profiles. The implications are twofold. First, this implies that the dominant variability in the INTIMATE'96 experiment is indeed associated with internal tides. Secondly, it suggests that in future tidal experiments a theoretically generated basis may be used as effectively as an EOF basis (which requires more extensive oceanographic measurements). We have also used the set of dynamic modes to simulate the effect of the tides on acoustic propagation to understand the relative importance of the usual surface tide (barotropic) and the internal (baroclinic) tides.
Seismo-acoustic waves generated by the detonation of UXOs of large charge weights in a shallow water environment
International audienceLes travaux présentés s'inscrivent dans le projet RAPID BODAMM (Buried ... more International audienceLes travaux présentés s'inscrivent dans le projet RAPID BODAMM (Buried Objects Detection by Acoustics and Magnetics Methods) porté par la société RTSYS, l'ENSTA Bretagne, et la société MAREE. Ce projet a pour but la détection automatisée d'objets enfouis de type mines ou câbles sous-marinsà l'aide de techniques acoustiques et magnétiques mises en oeuvre depuis des drones sous-marins. L'objectif principal de la partie acoustique est la mise en place du portage du système SCAMPI (système léger de sismique réflexion breveté par MAREE) sur un AUV (Autonomous Underwater Vehicle). En effet, la détection de petits objets enfouis nécessite au préalable de déterminer avec la plus grande précision possible la stratification des premiers mètres du sous-sol. Deux grands axes ontété traités dans ce cadre : (1) le dimensionnement et l'analyse des contraintes du portage du système par l'AUV en fonction des objectifs du projet, (2) la mise en condit...
Dimensionnement du système SCAMPI pour AUV et détection d’objets enfouis
HAL (Le Centre pour la Communication Scientifique Directe), Apr 1, 2015
International audienc
Instrumentation and data management for geoacoustic characterization of shallow water sediments
OCEANS 2016 - Shanghai, 2016
In order to study the geoacoustic relations for shallow water sediments, a project has started in... more In order to study the geoacoustic relations for shallow water sediments, a project has started in 2014, bringing together French academic and industrial partners. One of this project objectives is to build a large database of acoustical and sedimentological parameters collected in-situ with specific devices. Therefore, an important task is to manage the data acquisition, storage, and exploitation. A two-step process has been designed to achieve this: first, a mobile application which helps the users during the measurements, and second a relational database system which gathers all the data and favors their exploitation. The first dataset come from extensive measurements on the French coastlines. The data acquisition, visualization, and exploitation have been considerably facilitated with this data management system.
Experimental Acoustic Inversion Methods for Exploration of the Shallow Water Environment, 2000
This paper presents an overview of the experiment INTIMATE96, carried out in June 1996 on the con... more This paper presents an overview of the experiment INTIMATE96, carried out in June 1996 on the continental shelf off the coast of Portugal and discusses the effects of internal tides on the acoustic propagation. A towed broadband acoustic source and a 4-hydrophone vertical array were used. Acoustic data were collected for 5 days, including legs where the source ship was moving and legs with the ship on station. Intensive environmental surveys (XBT, CDT, bottom and hull-mounted ADCP, thermistor chain, bathymetry, geoacoustic characteristics of the sediments) were also conducted. The central Y. STEPHAN ET AL. results of acoustic data processing is that several effects of the environment, including bottom influence, source range and depth and internal tides effects, can be clearly seen on the signals and they can be processed separately. The acoustical effect of tides enables to perform inversion with simple and fast methods. The results of INTIMATE96 confirm the efficiency of broadband analysis on a single hydrophone to infer the geophysical environment.
Proceedings of Meetings on Acoustics, 2012
The knowledge of geoacoustic parameters of the seafloor, especially the sound speed, can be obtai... more The knowledge of geoacoustic parameters of the seafloor, especially the sound speed, can be obtained by geoacoustic inversion methods or by direct measurements done in-situ or on cores. The relation between geotechnical parameters such as grain size and acoustical parameters is either given by empirical relations or by theoretical models. The presented work is a part of CARASEDIM, an experimental project devoted to refine these geoacoustic relations in marine sediments, including coarse sands. In this paper, we focus on a velocimeter prototype that is developed for this purpose. It is designed for both laboratory and in-situ measurements, and is light enough to be used by a single diver. It is equipped with two emitting and two receiving transducers. The distance between emitters and receivers can be adjusted between 5 and 40 cm and their depth can vary from 0 to 15 cm. The frequency band is 40 kHz to 400 kHz and any type of signal can be used. We discuss about the processing techniques, the protocol of measurement, and the first results obtained. Some laboratory results are presented in both real coarse sands and artificial glass beads. They are compared with theoretical predictions based on grain-shearing model.
Proc. of …, 1997
The INTIMATE (INternal Tide Investigation by Means of Acoustic Tomography Experiment) project is ... more The INTIMATE (INternal Tide Investigation by Means of Acoustic Tomography Experiment) project is devoted to the study of internal tides by use of acoustic tomography. The first exploratory experiment was carried out in June 1996 on the continental shelf off the coast ...
High-frequency sediment sound speed and attenuation measurements during TREX13 (Target and Reverberation Experiment 2013) with a new portable velocimeter
The Journal of the Acoustical Society of America, 2013
During the Target and Reverberation Experiment 2013 (TREX13), high-frequency measurements of sedi... more During the Target and Reverberation Experiment 2013 (TREX13), high-frequency measurements of sediment sound speed and attenuation were collected throughout the experiment site. These measurements were performed using the INSEA, a diver-portable array of sources and receivers conceived and developed by French companies in collaboration with research institutions. During each deployment of the instrument, the INSEA was inserted 10–15 cm into the sediment and narrow-band pulses covering the 70 to 350 kHz range were transmitted through the sediment. The sound speed is determined from the time-of-flight and attenuation is determined from the amplitude ratio of the transmissions through the sediment and through the water. The variability of the TREX13 site made it possible to collect data in several different sediment types including mud, silty-sand, and sand sediments each with low to high concentrations of shells. In addition to the acoustic measurements, diver cores and shell samples w...
A simple and fast approach to retrieve equivalent geoacoustic parameters is presented in this pap... more A simple and fast approach to retrieve equivalent geoacoustic parameters is presented in this paper. The method is based upon the processing of 300-800 Hz broadband signals on a single hydrophone.Two stable characteristics of the impulse response of the shallow water waveguide are estimated: the time dispersion and the bottom reflection amplitudes. This two features are analytically linked to the compressional speed and to the attenuation coefficient of the medium. The inversion of the two latter geoacoustic parameters is straightforwa rd since it relies on an analytical expression. The method is tested on INTIMATE96 data. The results show an excellent agreement between the reflection of the true medium and the reflection coefficient of the equivalent medium.
Bedload transport monitoring at sea still remains a challenge for sedimentologists and coastal en... more Bedload transport monitoring at sea still remains a challenge for sedimentologists and coastal engineers. Indeed, data and instrumental techniques that establish a detailed link between boundary layer turbulence and sediment mixture dynamics are scarce. The passive acoustic method, based on hydrophones measuring self-generated noise due to inter-particle collisions, has been mostly developed in laboratories on coarse particles during the past decades. It has been shown that the amplitude and the frequency spectrum of the monitored signals are linked to bedload fluxes and grain size distribution. This technique shows numerous advantages: it is not disruptive to the flow field, easy to handle and cost effective. One experiment at sea is reported here. It was conducted on a sandy dune subject to strong tidal currents. Hydrodynamic parameters near the bed have been provided by Doppler velocimeters. Signal processing was adapted to distinguish the useful information, bedload self-generat...
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Papers by Xavier Demoulin