https://sam.ensam.eu:443 The DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material. Fri, 15 May 2026 02:23:51 GMT 2026-05-15T02:23:51Z http://hdl.handle.net/10985/8711 T-wave generation and propagation: A comparison between data and spectral element modeling JAMET, Guillaume; GUENNOU, Claude; GUILLON, Laurent; MAZOYER, Camille; ROYER, Jean-Yves T-waves are underwater acoustic waves generated by earthquakes. Modeling of their generation and propagation is a challenging problem. Using a spectral element code—SPECFEM2D, this paper presents the first realistic simulations of T-waves taking into account major aspects of this phenomenon: The radiation pattern of the source, the propagation of seismic waves in the crust, the seismic to acoustic conversion on a non-planar seafloor, and the propagation of acoustic waves in the water column. The simulated signals are compared with data from the mid-Atlantic Ridge recorded by an array of hydrophones. The crust/water interface is defined by the seafloor bathymetry. Different combinations of water sound-speed profiles and sub-seafloor seismic velocities, and frequency content of the source are tested. The relative amplitudes, main arrival-times, and durations of simulated T-phases are in good agreement with the observed data; differences in the spectrograms and early arrivals are likely due to too simplistic source signals and environmental model. These examples demonstrate the abilities of the SPECFEM2D code for modeling earthquake generated T-waves Tue, 01 Jan 2013 00:00:00 GMT http://hdl.handle.net/10985/8711 2013-01-01T00:00:00Z JAMET, Guillaume GUENNOU, Claude GUILLON, Laurent MAZOYER, Camille ROYER, Jean-Yves T-waves are underwater acoustic waves generated by earthquakes. Modeling of their generation and propagation is a challenging problem. Using a spectral element code—SPECFEM2D, this paper presents the first realistic simulations of T-waves taking into account major aspects of this phenomenon: The radiation pattern of the source, the propagation of seismic waves in the crust, the seismic to acoustic conversion on a non-planar seafloor, and the propagation of acoustic waves in the water column. The simulated signals are compared with data from the mid-Atlantic Ridge recorded by an array of hydrophones. The crust/water interface is defined by the seafloor bathymetry. Different combinations of water sound-speed profiles and sub-seafloor seismic velocities, and frequency content of the source are tested. The relative amplitudes, main arrival-times, and durations of simulated T-phases are in good agreement with the observed data; differences in the spectrograms and early arrivals are likely due to too simplistic source signals and environmental model. These examples demonstrate the abilities of the SPECFEM2D code for modeling earthquake generated T-waves http://hdl.handle.net/10985/8681 Image source detection for geoacoustic inversion by Teager-Kaiser energy operator DRIRA, Achraf; GUILLON, Laurent; BOUDRAA, Abdel-Ouahab This letter presents an improvement of the image source method (ISM) for geoacoustic inversion. The new algorithm is based on the Teager-Kaiser Energy Operator which ampli es the discontinuities in signals while the soft transitions are reduced. This property is exploited for accurate detection of time arrivals and thus for location of the image sources. The e ectiveness of the method is shown on both synthetic and real data and the inversion results are, overall, in good agreement with ground truth and other inversion results with a signi cant reduction of computation time. Wed, 01 Jan 2014 00:00:00 GMT http://hdl.handle.net/10985/8681 2014-01-01T00:00:00Z DRIRA, Achraf GUILLON, Laurent BOUDRAA, Abdel-Ouahab This letter presents an improvement of the image source method (ISM) for geoacoustic inversion. The new algorithm is based on the Teager-Kaiser Energy Operator which ampli es the discontinuities in signals while the soft transitions are reduced. This property is exploited for accurate detection of time arrivals and thus for location of the image sources. The e ectiveness of the method is shown on both synthetic and real data and the inversion results are, overall, in good agreement with ground truth and other inversion results with a signi cant reduction of computation time. http://hdl.handle.net/10985/15086 Antartic blue whale localization with ocean bottom seismometers in southern indian ocean DREO, Richard; BOUFFAUT, Léa; GUILLON, Laurent; LABAT, Valérie; BARRUOL, Guilhem; BOUDRAA, Abdel-Ouahab While visual survey of whales requires substantial means for limited areas, passive acoustic monitoring (PAM) offers larger scale coverage for long periods and less costs. It usually provides information about species behavior, e.g. seasonal movements, but tools are needed to detail the individuals' behavior. From October 2012 to November 2013 as part of the German-French "RHUM-RUM" (Réunion Hotspot and Upper Mantle - Réunion Unterer Mantel) seismic experiment, a 70km by 40km array of 8 Ocean Bottom Seismometers (OBS) was deployed in Southern Indian Ocean in a mountainous area, with depths from 2500 to 5500 meters. The [0-50] Hz-frequency band covered by the OBS's hydrophone provides observations about whales. Each source-OBS path has its own acoustic propagation. Indeed, closest OBS can be reached by direct rays, while remote OBS can only be reached by multi-reflected rays. Therefore, the localization problem cannot be solved directly using a classical Time Difference Of Arrival (TDOA) algorithm. In this work, the TDOA problem is solved in the case of long range detection, even with mountainous relief, enabling localization and tracking of whales. For each point of the spatial matrix representing the area, Times Of Arrival (TOA) of signal on the OBS are computed with a ray tracing algorithm (BELLHOP), taking into account the bottom profile. The theoretical corresponding TDOA are then compared to measured ones using a loss function. The obtained results, using L1, L2, cross-correlation cost functions, show the effectiveness of the proposed strategy to track whales on their calls. For example, an Antarctic blue whale is tracked during 10 hours from 40 kilometers south of the array center to 40 kilometers north where the mean speed is close to 10 km/h on a straight trajectory. Sun, 01 Jan 2017 00:00:00 GMT http://hdl.handle.net/10985/15086 2017-01-01T00:00:00Z DREO, Richard BOUFFAUT, Léa GUILLON, Laurent LABAT, Valérie BARRUOL, Guilhem BOUDRAA, Abdel-Ouahab While visual survey of whales requires substantial means for limited areas, passive acoustic monitoring (PAM) offers larger scale coverage for long periods and less costs. It usually provides information about species behavior, e.g. seasonal movements, but tools are needed to detail the individuals' behavior. From October 2012 to November 2013 as part of the German-French "RHUM-RUM" (Réunion Hotspot and Upper Mantle - Réunion Unterer Mantel) seismic experiment, a 70km by 40km array of 8 Ocean Bottom Seismometers (OBS) was deployed in Southern Indian Ocean in a mountainous area, with depths from 2500 to 5500 meters. The [0-50] Hz-frequency band covered by the OBS's hydrophone provides observations about whales. Each source-OBS path has its own acoustic propagation. Indeed, closest OBS can be reached by direct rays, while remote OBS can only be reached by multi-reflected rays. Therefore, the localization problem cannot be solved directly using a classical Time Difference Of Arrival (TDOA) algorithm. In this work, the TDOA problem is solved in the case of long range detection, even with mountainous relief, enabling localization and tracking of whales. For each point of the spatial matrix representing the area, Times Of Arrival (TOA) of signal on the OBS are computed with a ray tracing algorithm (BELLHOP), taking into account the bottom profile. The theoretical corresponding TDOA are then compared to measured ones using a loss function. The obtained results, using L1, L2, cross-correlation cost functions, show the effectiveness of the proposed strategy to track whales on their calls. For example, an Antarctic blue whale is tracked during 10 hours from 40 kilometers south of the array center to 40 kilometers north where the mean speed is close to 10 km/h on a straight trajectory. http://hdl.handle.net/10985/8679 Sound speed profile characterization by the image source method PINSON, Samuel; GUILLON, Laurent This paper presents the first results of an imaging technique that measures the geoacoustic structure of a seafloor in shallow water areas. The devices used were a broadband 100 Hz–6 kHz acoustic source towed by a ship and a vertical array. Among all the acoustic paths existing in the water column, two are used: the direct one and the seabed-reflected one, the latter being composed of the reflections from the seafloor’s surface as well as that from each buried layer. Due to the good time resolution of the signal and to the short range configuration, the reflected signal can be modeled as a sum of contributions coming from image sources relative to the seabed layers. The seabed geometry and the sound speed profile can then be recovered with the detection and localization of these image sources. The map of the image sources is obtained by a function that combines back-propagation of signals and knowledge of the emitted pulse. The thickness and sound-speed of each layer is finally obtained by a position analysis of the image sources. The results obtained by this data-driven algorithm on both at-sea and synthetic data are satisfactory. Fri, 01 Jan 2010 00:00:00 GMT http://hdl.handle.net/10985/8679 2010-01-01T00:00:00Z PINSON, Samuel GUILLON, Laurent This paper presents the first results of an imaging technique that measures the geoacoustic structure of a seafloor in shallow water areas. The devices used were a broadband 100 Hz–6 kHz acoustic source towed by a ship and a vertical array. Among all the acoustic paths existing in the water column, two are used: the direct one and the seabed-reflected one, the latter being composed of the reflections from the seafloor’s surface as well as that from each buried layer. Due to the good time resolution of the signal and to the short range configuration, the reflected signal can be modeled as a sum of contributions coming from image sources relative to the seabed layers. The seabed geometry and the sound speed profile can then be recovered with the detection and localization of these image sources. The map of the image sources is obtained by a function that combines back-propagation of signals and knowledge of the emitted pulse. The thickness and sound-speed of each layer is finally obtained by a position analysis of the image sources. The results obtained by this data-driven algorithm on both at-sea and synthetic data are satisfactory. http://hdl.handle.net/10985/8677 Range dependent sediment sound speed profile measurements using the image source method PINSON, Samuel; GUILLON, Laurent; HOLLAND, Charles This paper presents a range dependent sediment sound speed profile measurement obtained using the image source method. This technique is based on the analysis of the seafloor reflected acoustic wave as a collection of image sources which positions are linked with the thick-nesses and the sound speed of the sediment stack. The data used were acquired by the NURC in 2009 during the Clutter09 experiment. The equipment used was an autonomous undersea vehicle towing a 1600–3500 Hz frequency band source and a 32 m horizontal line array of 32 hydrophones at 12m above the seabed. Under the assumption of locally range independent seabed properties, the moving horizontal array provides successive range independent sediment sound speed profiles along a track to obtain the range and depth dependent structure of the seafloor. Two key steps include recovery of the time-varying unknown array shape from the data and spatial filtering of the successive sound speed profiles. A comparison of the image source method result and seismic data along nearly the same 14 km track indicates that the seabed stratigraphy is correctly mapped by this method. Tue, 01 Jan 2013 00:00:00 GMT http://hdl.handle.net/10985/8677 2013-01-01T00:00:00Z PINSON, Samuel GUILLON, Laurent HOLLAND, Charles This paper presents a range dependent sediment sound speed profile measurement obtained using the image source method. This technique is based on the analysis of the seafloor reflected acoustic wave as a collection of image sources which positions are linked with the thick-nesses and the sound speed of the sediment stack. The data used were acquired by the NURC in 2009 during the Clutter09 experiment. The equipment used was an autonomous undersea vehicle towing a 1600–3500 Hz frequency band source and a 32 m horizontal line array of 32 hydrophones at 12m above the seabed. Under the assumption of locally range independent seabed properties, the moving horizontal array provides successive range independent sediment sound speed profiles along a track to obtain the range and depth dependent structure of the seafloor. Two key steps include recovery of the time-varying unknown array shape from the data and spatial filtering of the successive sound speed profiles. A comparison of the image source method result and seismic data along nearly the same 14 km track indicates that the seabed stratigraphy is correctly mapped by this method. http://hdl.handle.net/10985/11332 Spherical wave reflection in layered media with rough interfaces: Three-dimensional modeling PINSON, Samuel; CORDIOLI, Julio; GUILLON, Laurent In the context of sediment characterization, layer interface roughnesses may be responsible for sound-speed profile measurement uncertainties. To study the roughness influence, a three-dimensional (3D) modeling of a layered seafloor with rough interfaces is necessary. Although roughness scattering has an abundant literature, 3D modeling of spherical wave reflection on rough interfaces is generally limited to a single interface (using Kirchhoff-Helmholtz integral) or computationally expensive techniques (finite difference or finite element method). In this work, it is demonstrated that the wave reflection over a layered medium with irregular interfaces can be modeled as a sum of integrals over each interface. The main approximations of the method are the tangent-plane approximation, the Born approximation (multiple reflection between interfaces are neglected) and flat-interface approximation for the transmitted waves into the sediment. The integration over layer interfaces results in a method with reasonable computation cost. The authors would like to thank Derek Olson for his help on the rough surface simulation Fri, 01 Jan 2016 00:00:00 GMT http://hdl.handle.net/10985/11332 2016-01-01T00:00:00Z PINSON, Samuel CORDIOLI, Julio GUILLON, Laurent In the context of sediment characterization, layer interface roughnesses may be responsible for sound-speed profile measurement uncertainties. To study the roughness influence, a three-dimensional (3D) modeling of a layered seafloor with rough interfaces is necessary. Although roughness scattering has an abundant literature, 3D modeling of spherical wave reflection on rough interfaces is generally limited to a single interface (using Kirchhoff-Helmholtz integral) or computationally expensive techniques (finite difference or finite element method). In this work, it is demonstrated that the wave reflection over a layered medium with irregular interfaces can be modeled as a sum of integrals over each interface. The main approximations of the method are the tangent-plane approximation, the Born approximation (multiple reflection between interfaces are neglected) and flat-interface approximation for the transmitted waves into the sediment. The integration over layer interfaces results in a method with reasonable computation cost. http://hdl.handle.net/10985/8768 Cross-Spectral Analysis of Midfrequency Acoustic Waves Reflected by the Seafloor GUILLON, Laurent; HOLLAND, Charles; BARBER, Christopher Direct path measurements of a single-bottom interacting path on a vertical array are used to probe the seabed structure. The phase of the cross-spectrum, commonly used in engineering acoustics, permits examination of the importance of subbottom paths. When the cross-spectral phase is linear with frequency it implies that source to receiver propagation is dominated by a single path. A linear cross-spectral phase would also satisfy the linear seabed reflection coefficient phase approximation sometimes employed in forward modeling and geoacoustic inversion approaches. Shallow water measurements of the cross-spectrum, however, evidence a strongly nonlinear phase, below about 1500 Hz at one site, and 600 Hz at another site, implying that: 1) the subbottom structure plays an important role (i.e., a seabed half-space approximation would be inappropriate); and 2) the linear reflection phase approximation would be violated at those frequencies Sat, 01 Jan 2011 00:00:00 GMT http://hdl.handle.net/10985/8768 2011-01-01T00:00:00Z GUILLON, Laurent HOLLAND, Charles BARBER, Christopher Direct path measurements of a single-bottom interacting path on a vertical array are used to probe the seabed structure. The phase of the cross-spectrum, commonly used in engineering acoustics, permits examination of the importance of subbottom paths. When the cross-spectral phase is linear with frequency it implies that source to receiver propagation is dominated by a single path. A linear cross-spectral phase would also satisfy the linear seabed reflection coefficient phase approximation sometimes employed in forward modeling and geoacoustic inversion approaches. Shallow water measurements of the cross-spectrum, however, evidence a strongly nonlinear phase, below about 1500 Hz at one site, and 600 Hz at another site, implying that: 1) the subbottom structure plays an important role (i.e., a seabed half-space approximation would be inappropriate); and 2) the linear reflection phase approximation would be violated at those frequencies