Seabed geoacoustic characterization and classification by multisonar fusion

International audienceThis paper deals with potentialities of improvement of seabed geoacoustic properties characterization and classification by multisensor fusion. The aim of this work is to improve the performance prediction of low frequencies sonar (Anti Submarine Warfare). Geoacoustic and scattering properties estimation by inversion of received acoustic signals remains very difficult and strongly dependent on the system of measurement. Indeed the interaction between an acoustic wave and the sediment is heavily dependent on frequency, measurement angle and micro roughness of seafloor. The fusion of geoacoustic models inverted from different sonar systems with wide diversity of insonification angles and frequencies (single beam echosounder, multibeam echosounder, sidescan sonar and subbottom profiler) allow an extended description of the acoustic properties of the seafloor and the first sediment layers. A characterization method based on the Dempster Shafer theory of evidence is used to fuse geoacoustic models in order to classify the seafloor in three homogeneous acoustic zones (scattered solid, reflective fluid and absorbent fluid). Then, estimation of the geoacoustic parameters is conducted on each zone

Studying and modeling of submerged aquatic vegetation environments seen by a single beam echosounder

International audienceFor both environmental and economic reasons, it is important to map the distribution of submerged aquatic vegetation. Acoustic technologies seem to be the more efficient and cost effective methods for that. Many papers have been published on underwater vegetation detection using an acoustic echo-sounder. However, few general studies have been performed to quantitatively understand the acoustic process of scattering from underwater vegetation. First, the effect of fields of vegetation on the temporal signal of the echo-sounder is studied. Real echo-sounder data obtained from different sites and different kinds of submerged aquatic vegetation was used. In most cases, the vegetation signal has a relatively strong backscatter signal before the bottom detection time and a less abrupt leading edge. However, different species-dependant behaviors were found. In order to explain this phenomenon and to characterize underwater vegetation, a model, based on the sonar equation, is developed to highlight the interaction between the acoustic wave and the environment composed of underwater vegetation. The result is a submerged aquatic vegetation apparent scattering index which can be used to help to characterize underwater vegetation

Contribution of automatic classification of sonar images for long term registration

This issue handles the ability of using segmentation results of sidescan sonar images for long term registration. This study take a part of AUV (Autonomous Underwater Vehicle) navigation problems, particularly to correct the drift of navigation sensors. Principle of images formation with this type of engines and the main properties are first reminded. Some images are shown, which allows us to understand difficulties of this type of data to realise AUV positioning. Then, we decide that segmentation results of sidescan images provide us landscapes on which registration will be able. Segmentation is then explained. It is supervised type on five classes, rocks, ripples, sand, mud and shadow. Using Gabor filters provides classifying parameters and classification is realised by the nearest neighbour. This is made step by step, refining step by step the segmentation. In order to know which landscapes may be extracted to enable the positioning, a statement is then realised on the obtained results. The registration methodology is then quickly explained and several results are commented. This allows us to realise a final conclusion on the ability to use results of segmentation of sonar images to make registration and to give possibilities and limits of this type of positioning system.Cet article aborde la possibilité d’utiliser les résultats de segmentation d’images issues d’un sonar latéral pour effectuer un recalage à long terme. Ce travail s’inscrit dans les problématiques liées à la navigation des AUV (Autonomous Underwater Vehicle). Ceux-ci, navigant généralement à l’estime, subissent une dérive qu’il est nécessaire de régulièrement contrecarrer. Le principe de formation des images à l’aide d’un tel engin est alors rappelé, ainsi que ses propriétés principales. Quelques exemples d’images sont également montrés, ce qui nous permet d’appréhender les difficultés liées à l’utilisation de telles données pour effectuer le positionnement. Nous décidons alors que les résultats de segmentation des images sonar fourniront les amers sur lesquels on pourra se recaler. La segmentation des images est alors expliquée. Elle est de type supervisé sur cinq classes, roches, rides, sable, vase et ombre. Le filtrage par ondelettes de Gabor fournit les paramètres classifiants et la classification est réalisée par le plus proche voisin. Celle-ci est alors effectuée pas à pas, en affinant peu à peu la segmentation alors obtenue. Un état des lieux est ensuite réalisé sur les résultats obtenus, permettant de savoir quels amers peuvent être extraits pour permettre le positionnement. La méthode de recalage est ensuite rapidement expliquée, et plusieurs résultats obtenus sont commentés en détail. Cela permet alors d’effectuer un bilan final sur la possibilité d’utiliser les résultats de segmentation d’images sonar pour effectuer un recalage et indiquer les possibilités et les limitations de l’utilisation d’un tel système de positionnement

Marine observations with a harmonic single-beam echo-sounder

International audienceTo characterise the seabed or water-column targets with acoustics, it is common to use multiple frequencies and therefore several sonar transducers or echo-sounders. The single beam echo-sounder we present here is able, thanks to non-linearity of the sea water, to generate more than three harmonics above its fundamental transmitted frequency, in effect producing four distinct frequencies with a single echo-sounder. In addition, all transmitted signals are perfectly in phase because they are carried by the same pulse, which has obvious benefits for further processing of the echoes. In this presentation, after a short review of the entire system, its application to seabed characterisation using the reflectivity level (acoustic backscattering strength from the seafloor) will be exposed. Further developments of plans to use this echo-sounder for fishery acoustics will then be highlighted, based on datasets acquired in the Bay of Brest (France). (Project funded by ANR and DGA / ANR-14-ASTR-0022-00)

Comparison of methods employed to extract information contained in seafloor backscatter

International audienceSeabed maps are based on quantities extracted from measurements of the seafloor‘s acoustic response by sonar systems such as single-beam echo-sounders (SBES), multibeam echo-sounders (MBES) or sidescan sonars (SSS). In this paper, a comparison of various strategies to estimate the backscattering strength (BS) from recorded time-series, i.e. seabed echoes extracted from pings, is presented. The work hypotheses are based on processed data from a SBES designed to be tilted mechanically. Ideal survey conditions are taken into account and the seafloor is supposed to be rough so that BS is assumed to be equivalent to the Rayleigh probability density function parameter. Classical methods such as averaging corrected (sonar equation) backscattered single values over a set of pings to estimate BS are compared to other methods exploiting several time-samples being part of pings. Simulated data is considered to estimate BS in different situations (several estimators, natural/squared values, number of samples and pings). The best estimator to reach a 0.1dB uncertainty is proposed, and a formula governing the number of time-samples and pings needed to reach an accurate BS estimation according to the measurement conditions is derived

Metrology of the Acoustic Seafloor Response:How to accurately estimate backscatter and its intrinsic uncertainty using single-beam echosounder

Its measurements have been widely extended in hydrography using predominantly bathymetric echosounders, and they are used in diverse applications such as habitat mapping, seabed characterisation or classification. In recent decades, numerous theoretical models have also been developed to study its link with physical or heuristic bottom parameters. While analysing how these three domains (measurement, application, and theory) deal with the seafloor acoustic response, it appeared that the nature itself of the seafloor acoustic response is equivocal.The work presented here proposes a relationship between the three uses of the seafloor acoustic response. Based on statistical and physical hypotheses, a metrological method is established, connecting seafloor response measurements, applications and theory. In particular, the deterministic backscatter parameter derived theoretically is usefully linked to the stochastic nature observed in practice during backscatter measurements. This yieldsa method for accurately estimating backscatter values from bathymetric echosounder data: the best choice of backscatter estimator is justified based on analytical calculations, and ways to represent its uncertainties are proposed. Theoretical hypotheses are validated using real data from handmade single-beam echosounders tested at ENSTA Bretagne (France) and at the University of Bath (UK). After application of the method to survey data, its benefits, limits, and future implementation are discussed

Metrology of the Acoustic Seafloor Response:How to accurately estimate backscatter and its intrinsic uncertainty using single-beam echosounder

Its measurements have been widely extended in hydrography using predominantly bathymetric echosounders, and they are used in diverse applications such as habitat mapping, seabed characterisation or classification. In recent decades, numerous theoretical models have also been developed to study its link with physical or heuristic bottom parameters. While analysing how these three domains (measurement, application, and theory) deal with the seafloor acoustic response, it appeared that the nature itself of the seafloor acoustic response is equivocal.The work presented here proposes a relationship between the three uses of the seafloor acoustic response. Based on statistical and physical hypotheses, a metrological method is established, connecting seafloor response measurements, applications and theory. In particular, the deterministic backscatter parameter derived theoretically is usefully linked to the stochastic nature observed in practice during backscatter measurements. This yieldsa method for accurately estimating backscatter values from bathymetric echosounder data: the best choice of backscatter estimator is justified based on analytical calculations, and ways to represent its uncertainties are proposed. Theoretical hypotheses are validated using real data from handmade single-beam echosounders tested at ENSTA Bretagne (France) and at the University of Bath (UK). After application of the method to survey data, its benefits, limits, and future implementation are discussed

Imaging sensors in underwaters robotics: present and future trends

The two main visual sensors in underwater robotics are sonar and video. In a first part, we present the fundamentals of acoustic imagery. If some technics are well known, others, like synthetic aperture antenna, interferometry and parametric array are still research topics. In a second part, acoustic image processing techniques are presented. They are mainly applied to sea bottom characterization and robot navigation. The third part addresses video technology and processing. This sensor is complementary to sonar, due to its high resolution and the ease of interpretation of the images.Les deux principaux instruments utilisés comme capteurs de perception en robotique sous-marine sont le sonar et la vidéo. Dans une première partie, nous présentons les principes utilisés en imagerie acoustique. Si certaines techniques sont classiques, d'autres, telles que l'antenne synthétique, l'interférométrie et l'antenne paramétrique sont encore du domaine de la recherche appliquée. Dans une seconde partie, les applications de l'imagerie acoustique sont évoquées. Elles sont essentiellement axées sur la caractérisation des fonds sous-marins et sur l'aide que l'image peut apporter à la navigation du robot. Enfin, la troisième partie évoque les technologies et les traitements vidéo. Ce capteur s'avère très complémentaire du sonar grâce à sa haute résolution et à la facilité d'interprétation des images

Santé et sécurité du travail et formation professionnelle : Prochaine cible d’intérêt

Cette étude porte sur les événements accidentels associés à une blessure sans égard à sa gravité, survenus en cours de formation professionnelle, et sur les symptômes typiques d’une exposition professionnelle ressentis par les élèves. La population étudiée compte 327 élèves du programme d’entretien d’équipement motorisé. Tous les événements accidentels survenus en atelier à l’automne 2003 ont été documentés et un questionnaire sur des symptômes ressentis en lien avec l’exposition professionnelle en atelier de formation a été rempli par 213 élèves. Pour la période de septembre à décembre 2003, 72 événements ont été répertoriés (taux d’événements accidentels = 22 %). De ces derniers, 83,4 % sont survenus dans les spécialités mécanique automobile et carrosserie qui accueillaient 62,9 % des élèves inscrits, alors que les spécialités mécanique de véhicules lourds et engins de chantiers cumulaient 16,7 % des événements bien qu’elles comptaient 37 % des effectifs. Le questionnaire sur les symptômes a révélé que 11,3 % des répondants éprouvaient des douleurs au bas du dos et 16,0 % déclaraient avoir des problèmes cutanés qu’ils attribuaient, notamment, à leur exposition en atelier professionnel. Enfin, 29,6 % des répondants ont déclaré ressentir de la fatigue, avoir des difficultés de concentration ou des maux de tête sur une base régulière. Les résultats fournissent des indications importantes pour le Centre de formation professionnelle participant. La direction et les enseignants de ce CFP peuvent repérer des activités et des produits à risques et mettre de l’avant des mesures préventives appropriées. La nature exploratoire de l’étude ne permet pas de généraliser les résultats à l’ensemble des ateliers professionnels, mais témoigne de l’importance de documenter les questions de santé et de sécurité en milieu de formation professionnelle.This study investigates the accident events associated with an injury, without considering its severity, that occurred during vocational training, as well as the typical symptoms of the students’ occupational exposure. In the participating school, 327 students are enrolled in the motorized equipment maintenance program. All the accident events that occurred during the 2003 fall session were documented, and 213 students completed a questionnaire on the symptoms related to occupational exposure in a training workshop. Between September and December 2003, 72 accident events were documented (accident event rate of 22%). Of these, 83.4% occurred in automotive mechanics and body repair. These specialties accounted for 62.9% of the enrolled students. However, the heavy truck mechanics and heavy construction vehicle specialties accounted for 16.3% of the accident events while representing 37% of the population under study. The symptom questionnaire revealed that 11.3% of the respondents had low back pain and 16.0% had skin problems that they mainly attributed to their exposure in a vocational workshop. Finally, 29.6% reported that they regularly felt tired, had difficulty concentrating or had headaches. The results provide important indications about the situation prevailing in the participating professional school. Management and teachers from this vocational establishment can identify risky activities and hazardous products, as well as propose the appropriate preventive measures. Although the exploratory nature of the study prevents any generalization to all other vocational workshops, it highlights the importance of documenting the occupational health and safety question in vocational training environments.Este estudio se refiere a eventos accidentales asociados a una herida (sin tomar en cuenta su gravedad) que se produjo durante la formación profesional, y sobre los síntomas típicos de la exposición profesional sentidos por los alumnos. La población estudiada cuenta 327 estudiantes del programa de mantenimiento de equipo motorizado. Se documentaron todos los eventos accidentales que se produjeron en el taller durante el otoño 2003. Además, los estudiantes del programa fueron invitados a completar un cuestionario sobre los síntomas de problemas de salud relacionados con su exposición profesional en el taller de formación profesional. Este cuestionario fue respondido por 213 estudiantes. Durante el período de septiembre a diciembre 2003, ocurrieron 72 eventos (tasa de eventos accidentales = 22 %). De estos últimos, 83,4 % se produjeron en las especialidades de mecánica automóvil y carrocería que acogen 62,9 % de los alumnos inscritos. Las especialidades de mecánica de vehículos pesados y de maquinaria de construcción acumulaban 16,7 % de los eventos a pesar que cuentan con 37 % de los alumnos. El cuestionario sobre los síntomas reveló que 11,3 % de los participantes sentían dolores en la parte baja de la espalda y 16,0 % declaraban tener problemas cutáneos que atribuían particularmente a su exposición en los talleres de formación profesional. Finalmente, 29,6 % de los participantes dijeron sentir fatiga, tener dificultades de concentración y dolores de cabeza regularmente. Los resultados dan indicaciones importantes para el Centro de formación profesional participante. La dirección y los profesores de este CFP pueden identificar actividades y productos riesgosos y establecer las medidas preventivas apropiadas. La naturaleza exploratoria del estudio no permite generalizar los resultados al conjunto de los talleres de enseñanza profesional, pero atesta sobre la importancia de documentar las cuestiones de salud y de seguridad en los establecimientos de formación profesional