Browsing Reprints by Subject "Acoustic models"
Now showing items 21-40 of 59
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Critical angle and seabed scattering issues for active-sonar performance predictions in shallow water
(NATO. SACLANTCEN, 1997)Active sonar performance predictions (0.75 to 3 kHz) are examined in summer shallow-water environments to quantify the impact of variable seabed and watermass properties on detection. Scattering is computed with an ... -
Deterministic methods of sound field computation
(NATO. SACLANTCEN, 1975/10)Models for acoustic propagation in the ocean environment have matured to a level where they are used routinely to estimate deterministic phenomena and, most recently, have been applied to the investigation of stochastic ... -
Deterministic propagation modelling: Part 1: Fundamental principles *Part 2: Numerical results
(NATO. SACLANTCEN, 1981/06)The physics of sound propagation in the ocean is briefly reviewed. The wave equation is presented and a set of solutions under a variety of approximations is discussed. The consistency among these solutions is illustrated. -
Evaluation of experimental techniques for determining the plane wave reflection coefficient at the sea floor
(NATO. SACLANTCEN, 1986/06)One of the most commonly used techniques for determinati on of the geoacoustical properties of the sea bed is the measurement of plane wave reflection coefficients at the ocean bottom. An incident field is pr oduced by ... -
Extracting acoustic source information of shipping noise for dynamic ambient noise modelling
(CMRE, 2019/05)Shipping traffic is one of the largest contributors to anthropogenic noise in the ocean. Noise generated by merchant ships elevates natural occurring ambient noise level by 20-30 dB in many areas of the world?s ocean. In ... -
Geoacoustic modeling of the seabed at higher frequencies
(NATO. SACLANTCEN, 1997)In propagation at higher frequencies, local fluid motion in "hidden coordinate" systems and local discontinuities due to gas bubbles and bioturbation have a perturbing effect on the wave field. To model these effects, a ... -
High-speed simulation of an underwater acoustic field using an array processor
(NATO. SACLANTCEN, 1979/12)A computer model PAREQ for simulating the acoustic field of sound propagating in a complicated ocean environment has been installed on a realtime computer system (HP MX21) which includes an array processor (MAP 300). The ... -
Influence of background-noise spatial coherence on high-resolution passive method
(NATO. SACLANTCEN, 1982/06)New signal processing methods for passive listening have appeared recently : they are called "high resolution" methods because they have theoretically a better resolving power than conventional or adaptive beamforming . ... -
Le programme Ulysse: réseau de bouées pour l'étude statistique du bruit ambiant sous-marin
(NATO. SACLANTCEN, 1982/06) -
Measurements of normal-mode amplitude functions in a nearly-stratified medium
(NATO. SACLANTCEN, 1975/10)In normal-mode treatments of acoustic propagation in nearly-stratified media, calculations are frequently based on the perfectly-stratified medium model, in which symmetry permits separation of the wave equationo In these ... -
Model for the frequency spread of backscattered underwater sound based on the facet model of the rough sea surface
(NATO. SACLANTCEN, 1978/11)A theoretical model for the doppler spread of backscattered acoustic waves from the rough sea surface is described on the basis of the decomposition of the continuous sea-surface spectrum that leads to the concept of facets. ... -
Multipath field representation for seabed parameter extraction using backscatter data from shadow zones
(NATO. SACLANTCEN, 1997)Inversion strategies for bottom parameter estimation in shallow water impose stringent requirements on accuracy and speed of acoustic models. We highlight the importance of second order effects as first order determinants ... -
Notes on the interpretation of ambient noise statistics
(NATO. SACLANTCEN, 1982/06)Interpretation of statements about the character of ambient sea noise, as well as schemes to measure or model noise, are sensitive to the context or underlying view of what is essentially a stochastic process. A framework ... -
Numerical modeling results for mode propagation in a wedge
(NATO. SACLANTCEN, 1987/11)A PE (parabolic equation) code is used to study propagation in a shallow water wedge with a penetrable bottom. Particular attention is given to "wedge modes" that have wave fronts that are arcs of circles centered on the ... -
Numerical modelling of acoustic scattering by smooth inclusions in a layered fluid-solid medium
(NATO. SACLANTCEN, 1997)A boundary integral equation (BIE) method as descnbed for computing the scattering of a monofrequent acoustic field by a smooth, rigid 30 object in a layered range-independent fluid-solid medium. The BIE is discretized ... -
Obtaining the ocean index of refraction spectrum from the acoustic amplitude fluctuations
(NATO. SACLANTCEN, 1997)The feasibility of using acoustic measurements to determine the properties of a shallow water internal wave field is investigated through numerical simulations. The random intemal wave field is modeled by a generalized ... -
Ocean-basin reverberation from large underwater explosions: part 1: source-level and propagation-loss modelling
(NATO. SACLANTCEN, 1975/10)Predicting the reverberant returns from ocean basin reflectors requires describing acoustic source levels for large, conventional underwater explosions, defining the two way propagation loss and signal spreading from the ... -
Ocean-basin reverberation from large underwater explosions: part 2: computer model for reverberation
(NATO. SACLANTCEN, 1975/10)Following detonation of an underwater explosion, sound reverberates from the ocean surface and bottom and from scatterers within the medium. In addition, the boundaries of the ocean basin and obstructions within it, such ... -
Ocean-bottom reflectivity (a point of view)
(NATO. SACLANTCEN, 1975/10)The analysis procedures for extracting bottom loss values from pulsed acoustic signals that have interacted with the ocean bottom do not inherently consider sub-bottom refraction and reflection of sound, which are important ... -
Random temperature structure as a factor in long-range propagation
(NATO. SACLANTCEN, 1975/10)A statistical description of horizontal thermal microstructure in anosotropic turbulence is developed for application with an existing acoustic propagation theory. The model predicts a temperature power density spectrum ...