Acoustique sous-marine

Résumé

vignette|Simulation acoustique dans un environnement océanique simple. L'acoustique sous-marine est l'étude de la propagation du son dans l'eau et de l'interaction des ondes mécaniques constituant le son avec l'eau, son contenu et ses frontières. L'eau peut être l'océan, un lac, une rivière ou un réservoir. Les fréquences typiques de l'acoustique sous-marine sont comprises entre 10 Hz et 1 MHz. La propagation du son dans l'océan à des fréquences inférieures à se poursuit dans les fonds marins, tandis que les fréquences supérieures à sont rarement utilisées car elles sont absorbées très rapidement. L'acoustique sous-marine est parfois connue sous le terme hydroacoustique. Ce domaine est étroitement lié à d'autres domaines d'études acoustiques, tels que le sonar, la transduction, le traitement du signal acoustique et la bioacoustique. Histoire Les mammifères marins utilisent le son sous-marin depuis probablement des millions d'années. L'étude de l'acoustique sous-marine c

Source officielle

https://fr.wikipedia.org/wiki/Acoustique_sous-marine

À propos de ce résultat

Cette page est générée automatiquement et peut contenir des informations qui ne sont pas correctes, complètes, à jour ou pertinentes par rapport à votre recherche. Il en va de même pour toutes les autres pages de ce site. Veillez à vérifier les informations auprès des sources officielles de l'EPFL.

Publications associées (3)

A survey of techniques and challenges in underwater localization

Marc Waldmeyer

Underwater Wireless Sensor Networks (UWSNs) are expected to support a variety of civilian and military applications. Sensed data can only be interpreted meaningfully when referenced to the location of the sensor, making localization an important problem. While global positioning system (GPS) receivers are commonly used in terrestrial WSNs to achieve this, this is infeasible in UWSNs as GPS signals do not propagate through water. Acoustic communications is the most promising mode of communication underwater. However, underwater acoustic channels are characterized by harsh physical layer conditions with low bandwidth, high propagation delay and high bit error rate. Moreover, the variable speed of sound and the non-negligible node mobility due to water currents pose a unique set of challenges for localization in UWSNs. In this paper, we provide a survey of techniques and challenges in localization specifically for UWSNs. We categorize them into (i) range-based vs. range-free techniques; (ii) techniques that rely on static reference nodes vs. those who also rely on mobile reference nodes, and (iii) single-stage vs. multi-stage schemes. We compare the schemes in terms of localization speed, accuracy, coverage and communication costs. Finally, we provide an outlook on the challenges that should be, but have yet been, addressed. (C) 2011 Elsevier Ltd. All rights reserved.

2011

Chargement

, ,

Monte Carlo light transport simulations often lack robustness in scenes containing specular or near-specular materials. Widely used uni- and bidirectional sampling strategies tend to find light paths involving such materials with insufficient probability, producing unusable images that are contaminated by significant variance. This article addresses the problem of sampling a light path connecting two given scene points via a single specular reflection or refraction, extending the range of scenes that can be robustly handled by unbiased path sampling techniques. Our technique enables efficient rendering of challenging transport phenomena caused by such paths, such as underwater caustics or caustics involving glossy metallic objects. We derive analytic expressions that predict the total radiance due to a single reflective or refractive triangle with a microfacet BSDF and we show that this reduces to the well known Lambert boundary integral for irradiance. We subsequently show how this can be leveraged to efficiently sample connections on meshes comprised of vast numbers of triangles. Our derivation builds on the theory of off-center microfacets and involves integrals in the space of surface slopes. Our approach straightforwardly applies to the related problem of rendering glints with high-resolution normal maps describing specular microstructure. Our formulation alleviates problems raised by singularities in filtering integrals and enables a generalization of previous work to perfectly specular materials. We also extend previous work to the case of GGX distributions and introduce new techniques to improve accuracy and performance.

ASSOC COMPUTING MACHINERY2020

Chargement

A Study on MoS2 Nanolayer Coated Etched Fiber Bragg Grating Strain Sensor

Suneetha Sebastian

In this paper, we report on the comprehensive study on Molybdenum disulfide (MoS2) nanolayer coated etched Fiber Bragg Grating (eFBG) strain sensor. MoS2 nanolayer is coated using Physical Vapor Deposition (PVD) of Molybdenum (Mo) on eFBGs followed by sulfurization of the same in an inert atmosphere at 450 degrees C. Such coating technique provides a direct control over the coating thickness of MoS2, thereby enabling a study based on the effect of nanolayer coating thickness on the intrinsic strain sensitivity as well as the power of the back reflected Bragg wavelength of eFBG in the 0.78eV spectral region. High uniformity of MoS2 nanolayer coating ensures consistent, repeatable and highly linear FBG strain sensors with a correlation coefficient of 0.988 in the range of 0 to 2500 mu epsilon. A maximum intrinsic strain sensitivity of similar to 6.65 pm/mu epsilon with a resolution of similar to 150 n epsilon have been achieved with optimized MoS2 coated eFBG sensors. This kind of consistent, highly sensitive and linear strain sensors when incorporated with proper packaging schemes can be particularly useful for applications demanding high sensitivity of FBG sensors such detection of seismic vibrations, underwater acoustic signals, low amplitude accelerations, etc.

IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC2021

Chargement

Personnes associées

Aucun résultat

Unités associées

Aucun résultat

Concepts associés (19)

Concepts associés

Chargement

Cours associés (4)

Cours associés

Chargement

Séances de cours associées (9)

Séances de cours associées

Chargement