Normal modes, virtual modes, and alternative representations in the theory of surface‐duct sound propagation

1973 ◽  
Vol 53 (4) ◽  
pp. 1137-1147 ◽  
Author(s):  
Frank M. Labianca
Keyword(s):  
Sound Propagation ◽  
Normal Modes

scholarly journals A Chebyshev-Tau spectral method for normal modes of underwater sound propagation with a layered marine environment

2021 ◽  
Vol 492 ◽  
pp. 115784
Author(s):  
Houwang Tu ◽  
Yongxian Wang ◽  
Qiang Lan ◽  
Wei Liu ◽  
Wenbin Xiao ◽  
...  
Keyword(s):  
Spectral Method ◽  
Marine Environment ◽  
Sound Propagation ◽  
Normal Modes ◽  
Underwater Sound

Range‐dependent normal modes in underwater sound propagation: Application to the wedge‐shaped ocean

1975 ◽  
Vol 58 (6) ◽  
pp. 1171-1177 ◽  
Author(s):  
R. D. Graves ◽  
Anton Nagl ◽  
H. Überall ◽  
G. L. Zarur
Keyword(s):  
Sound Propagation ◽  
Normal Modes ◽  
Underwater Sound

A DEDISPERSION TRANSFORM FOR SOUND PROPAGATION IN SHALLOW WATER WAVEGUIDE

2010 ◽  
Vol 18 (03) ◽  
pp. 245-257 ◽  
Author(s):  
DA ZHI GAO ◽  
NING WANG ◽  
HAO ZHONG WANG
Keyword(s):  
Fourier Transform ◽  
Data Processing ◽  
Shallow Water ◽  
Sound Propagation ◽  
Normal Modes ◽  
Real Data ◽  
Present Approach ◽  
Dispersive Effect

For sound propagation in a shallow water waveguide, a dedispersion transform which can remove the dispersive effect of signal is described in this paper. The transform is a modified Fourier transform with two variables: translation and dispersion. Dispersive effect of signal for normal modes can be removed when these two variables match to real parameters. The validity of the present approach is verified in simulation and real data processing.

scholarly journals Improving the Performance of Mode-Based Sound Propagation Models by Using Perturbation Formulae for Eigenvalues and Eigenfunctions

2021 ◽  
Vol 9 (9) ◽  
pp. 934
Author(s):  
Alena Zakharenko ◽  
Mikhail Trofimov ◽  
Pavel Petrov
Keyword(s):  
Sound Propagation ◽  
Underwater Acoustics ◽  
Computational Cost ◽  
Normal Modes ◽  
Sound Field ◽  
Field Calculation ◽  
Combined Model ◽  
Eigenvalues And Eigenfunctions ◽  
Propagation Models ◽  
Area Of Interest

Numerous sound propagation models in underwater acoustics are based on the representation of a sound field in the form of a decomposition over normal modes. In the framework of such models, the calculation of the field in a range-dependent waveguide (as well as in the case of 3D problems) requires the computation of normal modes for every point within the area of interest (that is, for each pair of horizontal coordinates x,y). This procedure is often responsible for the lion’s share of total computational cost of the field simulation. In this study, we present formulae for perturbation of eigenvalues and eigenfunctions of normal modes under the water depth variations in a shallow-water waveguide. These formulae can reduce the total number of mode computation instances required for a field calculation by a factor of 5–10. We also discuss how these formulae can be used in a combination with a wide-angle mode parabolic equation. The accuracy of such combined model is validated in a series of numerical examples.

Underwater sound propagation described by range‐dependent normal modes

1975 ◽  
Vol 57 (S1) ◽  
pp. S64-S64
Author(s):  
R. Graves ◽  
A. Nagl ◽  
H. Überall ◽  
G. Zarur
Keyword(s):  
Sound Propagation ◽  
Normal Modes ◽  
Underwater Sound

scholarly journals The Effect of Mesoscale Eddy on the Characteristic of Sound Propagation

2021 ◽  
Vol 9 (8) ◽  
pp. 787
Author(s):  
Jiaqi Liu ◽  
Shengchun Piao ◽  
Lijia Gong ◽  
Minghui Zhang ◽  
Yongchao Guo ◽  
...  
Keyword(s):  
Coupling Coefficient ◽  
Satellite Images ◽  
Sound Propagation ◽  
Mesoscale Eddy ◽  
Normal Modes ◽  
Acoustic Energy ◽  
Acoustic Source ◽  
Acoustic Characteristics ◽  
North Pacific Region ◽  
Oceanic Eddy

A mesoscale eddy is detected and tracked in the western North Pacific region. Within the life cycle of the cyclonic eddies, the intensities of eddies make a difference. Satellite images indicate the oceanic eddy keeps westward-moving until it disappears. Oceanographic and acoustic characteristics of the eddy are studied. The acoustic energy distribution results from the different intensity of both modelled eddy and measured eddy are calculated. With sound propagation through the cyclonic eddy and anticyclonic eddy, the position of convergence zone moves away from and towards the acoustic source compared with the sound propagation through background hydrography. The coupling coefficient of different orders of normal modes changes significantly. The closer to the centre of the eddy, the stronger the coupling coefficient.

A 2-D DESCRIPTION OF SOUND PROPAGATION IN A HORIZONTALLY-INHOMOGENEOUS OCEAN

2002 ◽  
Vol 10 (01) ◽  
pp. 123-151 ◽  
Author(s):  
OLEG A. GODIN
Keyword(s):  
Travel Time ◽  
Sound Propagation ◽  
Environmental Gradients ◽  
Normal Modes ◽  
Approximate Expression ◽  
Underwater Sound ◽  
Mode Amplitude ◽  
Geometrical Acoustics ◽  
Horizontal Refraction ◽  
Horizontally Inhomogeneous

Effects of horizontal refraction on underwater sound propagation in deep and shallow water are considered within geometrical acoustics and adiabatic normal modes approximations. Several distinct formulations of the adiabatic approximation have been proposed in the literature on modal propagation. These formulations differ in the predicted values of mode amplitudes and, hence, in their reciprocity and energy-conserving properties. The formulations are compared with respect to their accuracy and domain of validity, assuming small and smooth variation of mode propagation constants characteristic of underwater acoustic waveguides. Perturbation theory for horizontal (modal) rays is used in the analysis. An approximate expression for the adiabatic mode amplitude in 3-D problems is derived which requires environmental information only along the source-receiver radial and which has greater accuracy than previous formulations. It is shown that the uncoupled azimuth approximation, also known as the N × 2-D approximation, overestimates travel times of ray arrivals as well as phases of adiabatic normal modes in a horizontally-inhomogeneous ocean. The travel time and phase biases rapidly increase with the value of cross-range environmental gradients and propagation range. Simple and explicit expressions for leading-order corrections to the travel time and the phase are found in terms of path-averaged cross-range environmental gradients. Implications on applicability of the uncoupled azimuth approximation for sound propagation modeling in a horizontally-inhomogeneous ocean are discussed. A perfect-wedge model of the coastal ocean is chosen to illustrate the importance of the travel-time and phase biases due to horizontal refraction.

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