Shallow Water Acoustic Modeling Research Articles

Inversion of seabed attenuation by using single mode extracted by warping transform

Seabed is an important part of the marine environment and it has a significant influence on sound propagation. Considering the fact that geoacoustic parameters are directly acquired with difficulty and complexity, a lot of researchers have focused on the inversion of them. The seabed attenuation coefficient is insensitivity to the matching field. However it has great effects on the transmission loss, mode amplitude ratios, etc. It can be inverted from measurements of these quantities. In this paper, we present an inversion scheme based on warping transform technique for estimating the seabed attenuation coefficient. It utilizes an equivalent seabed model which is constructed by using a prior and posterior knowledge. The dispersion characteristics of normal modes can be observed using the time-frequency analysis of the explosive signal recorded. The dispersion curve can be used to invert the seabed sound speed and density. The results presented by other scholars in the same circle are cited in this paper that focuses on how to obtain the seabed attenuation. Warping transform technique is used to separate and extract the normal modes. The main advantage of warping transform is that it can transform the time-frequency spectrogram into linear relationship which makes it easier to extract the normal modes. The feature of this paper lies in determining the distance normalized normal mode transmission loss. If the depths of receiving hydrophone and the explosion source are constant, the plot of normalized normal mode transmission loss versus distance is a straight line from the normal modes theory, which can be used to obtain the attenuation factor of real part of pressure. Then the seabed attenuation coefficient of the shallow water acoustic model can be calculated. In order to verify the effectiveness of this method, the warping transformation technology is used to separate and extract the first three modes from the simulated Gaussian pulse signal which is obtained in a simulated environment which is similar to the real marine environment. The extracted results are completely consistent with the numerical results. After that, the impulsive signal data collected in the Yellow Sea are analyzed according to the scheme process, and the relationship between the seabed attenuation and frequency is =0.581fk1.86(dB/m) in a range from 150 Hz to 550 Hz. The results are in good agreement with those obtained by other scholars in the same circle. On the other hand, the inversion results of seabed attenuation from different modes can be used for comparison at the same frequency, which can be a good support for the result.

Three-dimensional Gaussian beam tracing for shallow-water applications

Gaussian beam tracing is a ray-based method of acoustic wave propagation that overcomes some of the implementation problems of conventional ray methods, while retaining a speed advantage over wave theory approaches. A fan of Gaussian beams are propagated from a source, according to the standard ray equations, so that the pressure at any given point can be approximated by the sum of contributions from each beam. Eigenray computations, perfect shadows, and infinite caustics associated with standard ray methods are thereby eliminated, and the applicability to lower-frequency problems is improved. Gaussian beam tracing is particularly well suited for three-dimensional problems, for which eigenray computations are costly. The effectiveness of a three-dimensional Gaussian beam model [Bucker, J. Acoust. Soc. Am. 95, 2437–2440 (1994)] for predicting acoustic propagation in shallow water is demonstrated. At low frequencies, Gaussian beam and wave solutions are compared for the ASA benchmark wedge problem and the Shallow Water Acoustic Modeling 1999 Workshop Gaussian canyon problem. The use of the model for the analysis of three-dimensional bathymetric effects in real data will also be demonstrated. At high frequency, model predictions of impulse responses will be compared to measured data for a number of acoustic communications experiments. [Work supported by ONR.]

MULTIPLICATIVE PADÉ PE FORMULATION APPLIED TO SWAM'99 TEST CASES

Accurate forward modeling of acoustic propagation is crucial in underwater sound applications that rely on coherent field predictions, such as source localization and geoacoustic inversion based on matched field processing concepts. As acoustic propagation in shallow water environments becomes important in recent years, range-dependent modeling due to environmental changes has to be considered of which parabolic equation (PE) method has received widespread use because they are accurate and relatively fast. In this paper, Seoul National University parabolic equation (SNUPE) employing a multiplicative Padé formulation is developed. Linearization of the depth direction operator is achieved via expansion into a multiplication form of Padé approximation. To approximate the depth directional equation, Galerkin's method is used with partial collocation to achieve computational efficiency. To approximate the range directional equation, Crank–Nicolson's method is used. Finally, numerical self-starter has been used to initiate the near-field solution. The Shallow Water Acoustic Modeling (SWAM'99) Workshop provides an opportunity to test SNUPE's accuracy and compare its results with others for a variety of synthetic environments. In this paper, the numerical implementation and accuracy of SNUPE is tested by comparing with RAM12 results for the SWAM'99 test cases. Numerical experiments for SWAM'99 test cases give satisfactory results in accuracy for SNUPE and show the importance of the bottom information in the shallow water acoustic modeling.

Multiplicative Padé PE Formulation Applied to SWAM'99 Test Cases

Accurate forward modeling of acoustic propagation is crucial in underwater sound applications that rely on coherent field predictions, such as source localization and geoacoustic inversion based on matched field processing concepts. As acoustic propagation in shallow water environments becomes important in recent years, range-dependent modeling due to environmental changes has to be considered of which parabolic equation (PE) method has received widespread use because they are accurate and relatively fast. In this paper, Seoul National University parabolic equation (SNUPE) employing a multiplicative Pade formulation is developed. Linearization of the depth direction operator is achieved via expansion into a multiplication form of Pade approximation. To approximate the depth directional equation, Galerkin's method is used with partial collocation to achieve computational efficiency. To approximate the range directional equation, Crank–Nicolson's method is used. Finally, numerical self-starter has been used to initiate the near-field solution. The Shallow Water Acoustic Modeling (SWAM'99) Workshop provides an opportunity to test SNUPE's accuracy and compare its results with others for a variety of synthetic environments. In this paper, the numerical implementation and accuracy of SNUPE is tested by comparing with RAM12 results for the SWAM'99 test cases. Numerical experiments for SWAM'99 test cases give satisfactory results in accuracy for SNUPE and show the importance of the bottom information in the shallow water acoustic modeling.

THREE-DIMENSIONAL EFFECTS ON SOUND PROPAGATION AND MATCHED-FIELD PROCESSOR PERFORMANCE

The most recent 2-D split-step Padé parabolic-equation model was modified to include narrow-angle azimuthal coupling. This model was developed and applied to the Santa Barbara channel to assess the effect of 3-D propagation on the performance of a matched-field processor. These results, plus those from the Shallow Water Acoustic Modeling (SWAM) workshop's 3-D wedge and the Gaussian canyon cases, will demonstrate the importance of azimuthal coupling to sound propagation in littoral regions and its effect on the performance of a matched-field processor. Special emphasis is given to model limitations and suitable selection of model parameters that could be automated to achieve accurate predictions during production runs.

The SWAM'99 Workshop - An Overview

The SWAM'99 (Shallow Water Acoustic Modeling, 1999) workshop on the topic of benchmarking shallow water range-dependent propagation modeling was held in Monterey CA in September No specific benchmarks were generated. Rather, each participant offered his (her) Transmission Loss curves for comparison with other results. This overview article will: • discuss the six (6) test cases; • discuss each individual's contribution to this benchmarking effort (see the associated articles in this Special issue for full details); • conclude with suggestions for future efforts.

THE SWAM'99 WORKSHOP — AN OVERVIEW

The SWAM'99 (Shallow Water Acoustic Modeling, 1999) workshop on the topic of benchmarking shallow water range-dependent propagation modeling was held in Monterey CA in September No specific benchmarks were generated. Rather, each participant offered his (her) Transmission Loss curves for comparison with other results. This overview article will: • discuss the six (6) test cases; • discuss each individual's contribution to this benchmarking effort (see the associated articles in this Special issue for full details); • conclude with suggestions for future efforts.

Convergence, Stability, and Variability of Shallow Water Acoustic Predictions Using a Split-Step Fourier Parabolic Equation Model

The Shallow Water Acoustic Modeling (SWAM'99) Workshop was organized to examine the ability of various acoustic propagation models to accurately predict sound transmission in a variety of shallow water environments designed with realistic perturbations. In order to quantify this, tests of reciprocity, convergence, and stability must be considered. This paper presents the results of an established parabolic equation model based on the split-step Fourier algorithm. The test cases examined in this paper include a simple isospeed water column over a flat bottom with geoacoustic parameter variations, a randomly sloping bottom with geoacoustic parameter variations, and a canonical shallow water profile perturbed by internal waves over a flat, homogeneous bottom. Source configurations were generally held constant but numerous single frequency and broadband runs were performed. Model testing is emphasized with specific criteria for accurate solutions being specified. Random perturbations are added to one test case to examine the influence of environmental uncertainty on the details of the propagation. The results indicate that point-wise accurate solutions to the acoustic field in shallow water cannot be achieved beyond a few kilometers. This is partly due to the inaccuracies of the split-step Fourier algorithm employed in these shallow water scenarios and the treatment of the bottom interface boundary conditions, but also due to the inherent variability caused by uncertain environmental specification. Thus, more general features of the acoustic field should be emphasized at longer ranges.

CONVERGENCE, STABILITY, AND VARIABILITY OF SHALLOW WATER ACOUSTIC PREDICTIONS USING A SPLIT-STEP FOURIER PARABOLIC EQUATION MODEL

The Shallow Water Acoustic Modeling (SWAM'99) Workshop was organized to examine the ability of various acoustic propagation models to accurately predict sound transmission in a variety of shallow water environments designed with realistic perturbations. In order to quantify this, tests of reciprocity, convergence, and stability must be considered. This paper presents the results of an established parabolic equation model based on the split-step Fourier algorithm. The test cases examined in this paper include a simple isospeed water column over a flat bottom with geoacoustic parameter variations, a randomly sloping bottom with geoacoustic parameter variations, and a canonical shallow water profile perturbed by internal waves over a flat, homogeneous bottom. Source configurations were generally held constant but numerous single frequency and broadband runs were performed. Model testing is emphasized with specific criteria for accurate solutions being specified. Random perturbations are added to one test case to examine the influence of environmental uncertainty on the details of the propagation. The results indicate that point-wise accurate solutions to the acoustic field in shallow water cannot be achieved beyond a few kilometers. This is partly due to the inaccuracies of the split-step Fourier algorithm employed in these shallow water scenarios and the treatment of the bottom interface boundary conditions, but also due to the inherent variability caused by uncertain environmental specification. Thus, more general features of the acoustic field should be emphasized at longer ranges.

Three-Dimensional Effects on Sound Propagation and Matched-Field Processor Performance

Journal of Computational AcousticsVol. 09, No. 01, pp. 17-39 (2001) No AccessTHREE-DIMENSIONAL EFFECTS ON SOUND PROPAGATION AND MATCHED-FIELD PROCESSOR PERFORMANCEJUAN I. ARVELO and ALLAN P. ROSENBERGJUAN I. ARVELOJohns Hopkins University, Applied Physics Laboratory, 11100 Johns Hopkins Road, Laurel, MD 20723-6099, USA Search for more papers by this author and ALLAN P. ROSENBERGJohns Hopkins University, Applied Physics Laboratory, 11100 Johns Hopkins Road, Laurel, MD 20723-6099, USA Search for more papers by this author https://doi.org/10.1142/S0218396X01000413Cited by:11 PreviousNext AboutSectionsPDF/EPUB ToolsAdd to favoritesDownload CitationsTrack CitationsRecommend to Library ShareShare onFacebookTwitterLinked InRedditEmail AbstractThe most recent 2-D split-step Padé parabolic-equation model was modified to include narrow-angle azimuthal coupling. This model was developed and applied to the Santa Barbara channel to assess the effect of 3-D propagation on the performance of a matched-field processor. These results, plus those from the Shallow Water Acoustic Modeling (SWAM) workshop's 3-D wedge and the Gaussian canyon cases, will demonstrate the importance of azimuthal coupling to sound propagation in littoral regions and its effect on the performance of a matched-field processor. Special emphasis is given to model limitations and suitable selection of model parameters that could be automated to achieve accurate predictions during production runs. FiguresReferencesRelatedDetailsCited By 11Measurements and modeling of acoustic propagation in a scale model canyonMegan S. Ballard and Jason D. Sagers1 Sep 2019 | The Journal of the Acoustical Society of America, Vol. 146, No. 3Developments of parabolic equation method in the period of 2000–2016Chuan-Xiu Xu, Jun Tang, Sheng-Chun Piao, Jia-Qi Liu and Shi-Zhao Zhang29 November 2016 | Chinese Physics B, Vol. 25, No. 12Leading-order cross term correction of three-dimensional parabolic equation modelsFrédéric Sturm1 Jan 2016 | The Journal of the Acoustical Society of America, Vol. 139, No. 1Normal Mode Analysis of Three-Dimensional Propagation Over a Small-Slope Cosine Shaped HillMegan S. Ballard, Benjamin M. Goldsberry, and Marcia J. Isakson25 June 2015 | Journal of Computational Acoustics, Vol. 23, No. 03A three dimensional parabolic equation method for sound propagation in moving inhomogeneous mediaRui Cheng, Philip J. Morris and Kenneth S. Brentner1 Jan 2009 | The Journal of the Acoustical Society of America, Vol. 126, No. 4INVESTIGATION OF 3D ACOUSTICAL EFFECTS USING A MULTIPROCESSING PARABOLIC EQUATION BASED ALGORITHMK. CASTOR and F. STURM21 November 2011 | Journal of Computational Acoustics, Vol. 16, No. 02ACCURATE TREATMENT OF A GENERAL SLOPING INTERFACE IN A FINITE-ELEMENT 3D NARROW-ANGLE PE MODELFRÉDÉRIC STURM and NIKOLAOS A. KAMPANIS21 November 2011 | Journal of Computational Acoustics, Vol. 15, No. 03A 3D Parabolic Equation Method for Sound Propagation in Moving Inhomogeneous MediaRui Cheng, Philip Morris and Kenneth Brentner4 November 2007A 3D Parabolic Equation Method for Wind Turbine Noise Propagation in Moving Inhomogeneous AtmosphereRui Cheng, Philip Morris and Kenneth Brentner11 November 2006Numerical study of broadband sound pulse propagation in three-dimensional oceanic waveguidesFrédéric Sturm1 Mar 2005 | The Journal of the Acoustical Society of America, Vol. 117, No. 3On the use of higher-order azimuthal schemes in 3-D PE modelingFrédéric Sturm and John A. Fawcett1 Jan 2003 | The Journal of the Acoustical Society of America, Vol. 113, No. 6 Recommended Vol. 09, No. 01 Metrics History Received 1 January 2000 Revised 1 June 2000 PDF download

PECan A Canadian Parabolic Equation Model for Underwater Sound Propagation

PECan is a Canadian N×2D/3D parabolic equation (PE) underwater sound propagation model that was developed for matched-field processing applications. It is based on standard square-root operator and/or propagator approximations that lead to an alternating direction solution of the 3-D problem. A 2-D split-step Pade approximation is employed for propagation in range. The 3-D azimuthal corrections are computed using either a split-step Fourier method or a Crank–Nicolson finite-difference approximation. It features a heterogeneous formulation of the differential operators on an offset vertical grid, energy conservation, a choice of initial field including self-starter, and both absorbing and nonlocal boundary conditions. Losses due to shear wave conversion in an elastic bottom are handled in the context of a complex density approximation. In this paper, PECan is described and validated against some standard benchmark solutions to underwater acoustics problems. Subsequently, PECan is applied to several single-frequency test cases that were offered for numerical consideration at the SWAM'99 Shallow Water Acoustic Modeling workshop.

PECAN: A CANADIAN PARABOLIC EQUATION MODEL FOR UNDERWATER SOUND PROPAGATION

PECan is a Canadian N× 2D/3D parabolic equation (PE) underwater sound propagation model that was developed for matched-field processing applications. It is based on standard square-root operator and/or propagator approximations that lead to an alternating direction solution of the 3-D problem. A 2-D split-step Padé approximation is employed for propagation in range. The 3-D azimuthal corrections are computed using either a split-step Fourier method or a Crank–Nicolson finite-difference approximation. It features a heterogeneous formulation of the differential operators on an offset vertical grid, energy conservation, a choice of initial field including self-starter, and both absorbing and nonlocal boundary conditions. Losses due to shear wave conversion in an elastic bottom are handled in the context of a complex density approximation. In this paper, PECan is described and validated against some standard benchmark solutions to underwater acoustics problems. Subsequently, PECan is applied to several single-frequency test cases that were offered for numerical consideration at the SWAM'99 Shallow Water Acoustic Modeling workshop.

Shallow water acoustic modeling over a sloping bottom

Ray theory with beam displacement gives an approximate method of finding the acoustic field in shallow water. It was shown to be quite accurate for a horizontally stratified two fluid (Pekeris) model by comparison with normal mode results. [C. T. Tindle, J. Acoust. Soc. Am. 73, 1581–1586 (1983)]. The method is extended to the sloping bottom situation by simple geometric arguments and without further approximation. Results show that even small bottom slopes have a dramatic effect on the sound field. The results are compared with those for the adiabatic normal mode approximation and agreement is good for higher frequencies. At lower frequencies differences are attributed to normal modes passing through cutoff, a process which is ignored in simple adiabatic mode theory.