Underwater Acoustics and Digital Signal Processing

A special issue of Journal of Marine Science and Engineering (ISSN 2077-1312). This special issue belongs to the section "Ocean Engineering".

Deadline for manuscript submissions: closed (25 October 2023) | Viewed by 21409

Special Issue Editors


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Guest Editor
Head of the Department, Department of Mathematical Physics and Information Technology, Voronezh State University, Voronezh, Russia
Interests: underwater acoustics; acoustic holography; signal processing; computational physics; mathematical physics; wave propagation; ocean acoustics

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Guest Editor
Applied Mathematics and Numeical Analysis, University of Wuppertal, Wuppertal, Germany
Interests: computational finance; sparse grids; artificial boundaries; splitting methods
Special Issues, Collections and Topics in MDPI journals

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Guest Editor
V.I. Il'ichev Pacific Oceanological Institute, Far Eastern Branch Russian Academy of Sciences, 690041 Vladivostok, Russia
Interests: wave propagation; underwater acoustics; numerical simulation of waves in complex media; mathematical physics; asymptotic methods
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

We invite you to take part in the Special Issue “Underwater Acoustics and Digital Signal Processing” for the Journal of Marine Science and Engineering. This Special Issue is intended to provide the results of original research and reviews of advances in signal processing methods used in underwater acoustics. Both theoretical and experimental papers are encouraged. This Special Issue’s objective is to present theoretical and experimental research. This Special Issue includes, but is not limited to, the following research areas:

  • holography signal processing;
  • matched field processing (MFP);
  • linear and nonlinear time-warping;
  • physics-based signal processing;
  • adaptive signal processing;
  • signal processing for autonomous underwater vehicles (AUVs);
  • signal processing for marine mammals;
  • active and passive sonar signal processing;
  • signal processing in a non-stationary environment;
  • signal processing for scalar sensors, vector sensors, antennas;
  • signal processing for detection, localization and classification;
  • underwater acoustic communications;
  • experimental data signal processing results;
  • numerical modelling for signal processing.

Dr. Sergey Pereselkov
Prof. Dr. Matthias Ehrhardt
Dr. Pavel Petrov
Guest Editors

Manuscript Submission Information

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Journal of Marine Science and Engineering is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • underwater acoustics
  • signal processing, holography
  • matched field processing
  • nonlinear time-warping
  • autonomous underwater vehicles
  • marine mammals
  • active and passive sonar
  • detection, localization and classification
  • scalar and vector sensors
  • antennas
  • underwater communications

Published Papers (17 papers)

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Research

22 pages, 7083 KiB  
Article
The Formation of 2D Holograms of a Noise Source and Bearing Estimation by a Vector Scalar Receiver in the High-Frequency Band
by Sergey Pereselkov, Venedikt Kuz’kin, Matthias Ehrhardt, Yurii Matvienko, Sergey Tkachenko and Pavel Rybyanets
J. Mar. Sci. Eng. 2024, 12(5), 704; https://doi.org/10.3390/jmse12050704 - 25 Apr 2024
Viewed by 621
Abstract
The holographic signal-processing method for a single vector scalar receiver (VSR) in the high-frequency band in shallow water is developed in the paper. The aim of this paper is to present the results of the theoretical analysis, numerical modeling, and experimental verification of [...] Read more.
The holographic signal-processing method for a single vector scalar receiver (VSR) in the high-frequency band in shallow water is developed in the paper. The aim of this paper is to present the results of the theoretical analysis, numerical modeling, and experimental verification of holographic signal processing for a noise source by the VSR. The developed method is based on the formation of the 2D interferogram and 2D hologram of a noise source in a shallow-water waveguide. The 2D interferograms and 2D holograms for different channels of the VSR (P sound pressure and VX and VY vibration velocity components) are considered. It is shown that the 2D interferogram consists of parallel interference fingers in the presence of a moving noise source. As a result, the 2D hologram contains focal points located on a straight line, and the angular distribution of the holograms has the main extreme value. It is shown in the paper that the holographic signal-processing method allows detecting the source, estimating the source bearing, and filtering the useful signal from the noise. The results of the source detection, source bearing estimation, and noise filtering are presented within the framework of experimental data processing and numerical modeling. Full article
(This article belongs to the Special Issue Underwater Acoustics and Digital Signal Processing)
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22 pages, 38926 KiB  
Article
Real-Time Underwater Acoustic Homing Weapon Target Recognition Based on a Stacking Technique of Ensemble Learning
by Jianjing Deng, Xiangfeng Yang, Liwen Liu, Lei Shi, Yongsheng Li and Yunchuan Yang
J. Mar. Sci. Eng. 2023, 11(12), 2305; https://doi.org/10.3390/jmse11122305 - 5 Dec 2023
Viewed by 1032
Abstract
Underwater acoustic homing weapons (UAHWs) are formidable underwater weapons with the capability to detect, identify, and rapidly engage targets. Swift and precise target identification is crucial for the successful engagement of targets via UAHWs. This study presents a real-time target recognition method for [...] Read more.
Underwater acoustic homing weapons (UAHWs) are formidable underwater weapons with the capability to detect, identify, and rapidly engage targets. Swift and precise target identification is crucial for the successful engagement of targets via UAHWs. This study presents a real-time target recognition method for UAHWs based on stacking ensemble technology. UAHWs emit active broadband detection signals that manifest distinct reflection characteristics on the target. Consequently, we have extracted energy and spatial distribution features from the target’s broadband correlation detection output. To address the problem of imbalanced original sea trial data, we employed the SMOTE algorithm to generate a relatively balanced dataset. Then, we established a stacking ensemble model and performed training and testing on both the original dataset and relatively balanced dataset separately. In conclusion, we deployed the stacking ensemble model on an embedded system. The proposed method was validated using real underwater acoustic homing weapon sea trial data. The experiment utilized 5-fold cross-validation. The results indicate that the method presented in this study achieved an average accuracy of 93.3%, surpassing that of individual classifiers. The model’s single-cycle inference time was 15 ms, meeting real-time requirements. Full article
(This article belongs to the Special Issue Underwater Acoustics and Digital Signal Processing)
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17 pages, 3870 KiB  
Article
Particle Filtering for Source Depth and Water Depth Joint Tracking in Shallow Water
by Yuyuan Zhou, Chao Sun and Lei Xie
J. Mar. Sci. Eng. 2023, 11(12), 2213; https://doi.org/10.3390/jmse11122213 - 22 Nov 2023
Viewed by 725
Abstract
Environmental mismatch degrades the performance of source localization and tracking methods in shallow water. One solution is to estimate source parameters and the key environmental parameters simultaneously from the acoustic data. In this paper, an unconventional approach of joint tracking source depth and [...] Read more.
Environmental mismatch degrades the performance of source localization and tracking methods in shallow water. One solution is to estimate source parameters and the key environmental parameters simultaneously from the acoustic data. In this paper, an unconventional approach of joint tracking source depth and water depth parameters by a particle filter is proposed. This approach is free of prior environmental knowledge and numerical calculation of any forward model. First, a state-space model based on modal nature behavior is established driving the shallow-water propagation, instead of modeling in time or space, as was done previous works. Subsequently, particle filtering is employed for joint tracking, in which the evolution with mode-order of vertical wavenumbers and the relationship between state parameters and beam-wavenumber outputs transformed from the data are exploited. Final, the particle smoother reduces the uncertainty of state parameters at initial steps, and improves the overall tracking accuracy. Our approach is demonstrated using simulated data in an ideal waveguide and applied to shallow-water SWellEx-96 experimental data to substantiate its superior performance. Full article
(This article belongs to the Special Issue Underwater Acoustics and Digital Signal Processing)
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15 pages, 2090 KiB  
Article
Design and Implementation of a Multi-Function Hydrophone for Underwater Acoustic Application
by Rong Wang, Yuehai Zhou, Xiaoyu Yang, Feng Tong and Jianming Wu
J. Mar. Sci. Eng. 2023, 11(11), 2203; https://doi.org/10.3390/jmse11112203 - 20 Nov 2023
Viewed by 1481
Abstract
In recent years, underwater acoustic applications have attracted much attention, for example, for underwater environmental monitoring, underwater exploration, etc. Hydrophones play a particularly important role. Although hydrophone design has been in multifarious application forms, it still needs to consider increasing demand for low-cost, [...] Read more.
In recent years, underwater acoustic applications have attracted much attention, for example, for underwater environmental monitoring, underwater exploration, etc. Hydrophones play a particularly important role. Although hydrophone design has been in multifarious application forms, it still needs to consider increasing demand for low-cost, low-consumption, and multiple-function devices, as well as issues around miniaturization, lossless data collection, etc. In this paper, we design a compact underwater acoustic device that has the capability of underwater acoustic signal storage, underwater acoustic signal transmission via the Internet, and decoding based on the direct sequences spread spectrum (DSSS). The key problem is how to implement multiple functions in only one micro-controller unit (MCU). The hardware and software of the proposed multi-function hydrophone are described in detail. In particular, the MCU, the pre-amplifier with gain control, and the analog-to-digital integrated chip are introduced. Moreover, underwater acoustic data storage, underwater acoustic transmission, and the DSSS receiver are depicted in terms of software. The different functions of the hydrophone are verified in sea trial experiments. The results show that the proposed multi-function hydrophone is able to sample underwater acoustic data at high quality. In addition, to demonstrate configurable parameters, the DSSS receiver with different carrier frequencies is provided. The proposed multi-function hydrophone realizes zero bit error rate (BER) when carrier frequency fc=9 kHz, and the BER with 103 order of magnitude when carrier frequency fc=15.5 kHz. The results show that the proposed multi-function hydrophone has great potential to explore the ocean. Full article
(This article belongs to the Special Issue Underwater Acoustics and Digital Signal Processing)
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15 pages, 4523 KiB  
Article
A Cross-Medium Uplink Communication Model Merging Acoustic and Millimeter Waves
by Yu Gai, Qi Tan, Yating Zhang, Zhengyi Zhao, Yiguang Yang, Yanyan Liu, Ruitao Zhang and Jianquan Yao
J. Mar. Sci. Eng. 2023, 11(11), 2102; https://doi.org/10.3390/jmse11112102 - 2 Nov 2023
Viewed by 1114
Abstract
Uplink communication across the water–air interface holds great potential for offshore oil surveys and military applications. Among the various methods available for implementing uplink communication, translational acoustic-RF (TARF) communication stands out due to its ability to withstand wave interference and exhibit low absorption [...] Read more.
Uplink communication across the water–air interface holds great potential for offshore oil surveys and military applications. Among the various methods available for implementing uplink communication, translational acoustic-RF (TARF) communication stands out due to its ability to withstand wave interference and exhibit low absorption losses. However, the physical processes underlying such systems are currently under-researched, and channel models for evaluating its communication performance indicators are lacking. Herein, we propose a signal-to-noise ratio (SNR) channel model for evaluating the performance metrics of an uplink communication system combining acoustic and millimeter waves for the first time and validate the accuracy of the proposed model through experiments. Specifically, in the process of model construction, the physical process of the communication system was deeply studied, and the corrections of multipath effects, box vibrations, and second-order nonlinear coefficients of the amplitude of the water surface were realized. The water-to-air cross-medium communication system was built, and communication experiments were conducted to validate the feasibility of combining acoustic and millimeter wave communication. This research provides a theoretical and experimental foundation for the design and evaluation of TARF communication systems, providing valuable guidance for enhancing the system’s performance metrics and promising an innovative approach for modern seaborne communication. Full article
(This article belongs to the Special Issue Underwater Acoustics and Digital Signal Processing)
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15 pages, 4239 KiB  
Article
A Sparse Bayesian Learning Method for Direction of Arrival Estimation in Underwater Maneuvering Platform Noise
by Yan Wang, Lei Zhao, Longhao Qiu, Jinjin Wang and Chenmu Li
J. Mar. Sci. Eng. 2023, 11(10), 1879; https://doi.org/10.3390/jmse11101879 - 27 Sep 2023
Viewed by 814
Abstract
The underwater maneuvering platform generates self-noise when sailing, which shows spatial directionality to the arrays fixed on the platform. In this paper, it is called spatially colored noise (SCN). The direction of arrival (DOA) estimation results are often influenced by this self-noise, leading [...] Read more.
The underwater maneuvering platform generates self-noise when sailing, which shows spatial directionality to the arrays fixed on the platform. In this paper, it is called spatially colored noise (SCN). The direction of arrival (DOA) estimation results are often influenced by this self-noise, leading to a decrease in estimation accuracy and to the appearance of spurious peaks. To resolve this problem, a sparse Bayesian learning (SBL) method adapted to underwater maneuvering platform noise is proposed in this paper. The SBL framework with unknown SCN is established first. Then, the SCN covariance matrix is estimated by projecting the received data covariance matrix into the noise subspace, and the DOA estimation results are finally obtained through multiple iterations. The simulation results show that the proposed method avoids spurious peaks, and compared to the existing methods, the proposed method achieves a higher accuracy in the case of low SNRs and small snapshot numbers. The sea trial data processing results show that the proposed method provides lower and flatter noise spectrum levels without spurious peaks. Full article
(This article belongs to the Special Issue Underwater Acoustics and Digital Signal Processing)
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20 pages, 10676 KiB  
Article
A Study of Combined Graphical Acoustic Computing and the Depth Peeling Technique on Acoustic Backscattering of Multiple-Layered Structures
by Yang Zhang, Qiang Gui, Yuzheng Yang and Wei Li
J. Mar. Sci. Eng. 2023, 11(9), 1801; https://doi.org/10.3390/jmse11091801 - 15 Sep 2023
Viewed by 863
Abstract
An efficient graphical acoustic computing (GRACO) method is introduced. Referring to the rendering of semi-transparent objects, the depth peeling (DP) technique is compounded with the GRACO method, forming a combined GRACO and DP method (GRACO–DP) to consider the backscattering of multiple-layered structures in [...] Read more.
An efficient graphical acoustic computing (GRACO) method is introduced. Referring to the rendering of semi-transparent objects, the depth peeling (DP) technique is compounded with the GRACO method, forming a combined GRACO and DP method (GRACO–DP) to consider the backscattering of multiple-layered structures in which the contributions of inner structures are included. After that, some examples of GRACO and GRACO–DP are tested to evaluate the accuracy and efficiency of such methods. Through the examples of impedance sphere and benchmark models, GRACO can acquire results with higher efficiency and good consistency compared to the traditional KA method. Also, the TS of a pair of circular plates is determined by GRACO, GRACO–DP, and the finite element method (FEM). The results show that GRACO–DP can fit better with the FEM results. Moreover, the TS of a ribbed double shell is predicted by both GRACO and GRACO–DP; the features of a Bragg wave scattered by the periodically arranged inner ribs can be spotted from the result of GRACO–DP. Full article
(This article belongs to the Special Issue Underwater Acoustics and Digital Signal Processing)
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22 pages, 11618 KiB  
Article
A Coupled Overlapping Finite Element Method for Analyzing Underwater Acoustic Scattering Problems
by Bin Jiang, Jian Yu, Wei Li, Yingbin Chai and Qiang Gui
J. Mar. Sci. Eng. 2023, 11(9), 1676; https://doi.org/10.3390/jmse11091676 - 25 Aug 2023
Cited by 1 | Viewed by 1032
Abstract
It is found that the classic finite element method (FEM) requires much time for adequate meshes to acquire satisfactory numerical solutions, and is restricted to acoustic problems with low and middle frequencies. In this work, a coupled overlapping finite element method (OFEM) is [...] Read more.
It is found that the classic finite element method (FEM) requires much time for adequate meshes to acquire satisfactory numerical solutions, and is restricted to acoustic problems with low and middle frequencies. In this work, a coupled overlapping finite element method (OFEM) is employed by combining the overlapping finite element and the modified Dirichlet-to-Neumann (mDtN) boundary condition to solve underwater acoustic scattering problems. The main difference between the OFEM and the FEM lies in the construction of the local field approximation. In the OFEM, virtual nodes are utilized to form the partition of unity functions while no degree of freedom is assigned to these virtual nodes, which suppresses the linear dependence issue in other generalized finite element methods. Moreover, the user-defined enrichment functions can be flexibly utilized in the local field, and thus the numerical dispersions can be significantly mitigated. To truncate the infinite problem domain and satisfy the Sommerfeld radiation condition, an artificial boundary is constructed by incorporating the mDtN technique. Several numerical examples are studied and it is shown that the proposed method can greatly diminish the numerical error and is insensitive to distorted meshes, indicating that the proposed method is promising in predicting underwater acoustic scattering. Full article
(This article belongs to the Special Issue Underwater Acoustics and Digital Signal Processing)
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16 pages, 7657 KiB  
Article
Fast Calibration of Superdirective Ultra-Short Baseline Array
by Ruoyu Hu, Yingqiang Wang, Wencheng Yang, Ying Chen and S. H. Huang
J. Mar. Sci. Eng. 2023, 11(9), 1665; https://doi.org/10.3390/jmse11091665 - 24 Aug 2023
Viewed by 949
Abstract
Array calibration can effectively ensure the positioning accuracy of the ultra-short baseline (USBL) system. Traditional USBL array calibration methods focus on measuring the geometric position of the array elements. However, directional phase differences on the receive path are often ignored in the current [...] Read more.
Array calibration can effectively ensure the positioning accuracy of the ultra-short baseline (USBL) system. Traditional USBL array calibration methods focus on measuring the geometric position of the array elements. However, directional phase differences on the receive path are often ignored in the current calibration process, which can also cause array mismatch, especially when using the superdirective beamforming (SDB) technique. To further improve the calibration accuracy and convenience of the USBL using the SDB technique, a fast calibration method is proposed in this paper. In the new method, the hydrophone geometry error and the receiver path phase error are jointly considered. Then, two calibration models with different complexity are presented, and the conventional beamforming (CBF) beam output is deconvoluted with the calibrated beam pattern. The results of anechoic tank experiments show that the bearing root mean square error (RMSE) can be reduced from 1.663° to 0.081°, and the calibration time can be reduced from hours to tens of minutes. Full article
(This article belongs to the Special Issue Underwater Acoustics and Digital Signal Processing)
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17 pages, 5878 KiB  
Article
Frequency Shift Keying-Based Long-Range Underwater Communication for Consecutive Channel Estimation and Compensation Using Chirp Waveform Symbol Signals
by Jongmin Ahn, Dong-Hun Lee, Sangkug Lee and Wanjin Kim
J. Mar. Sci. Eng. 2023, 11(9), 1637; https://doi.org/10.3390/jmse11091637 - 22 Aug 2023
Viewed by 1072
Abstract
Currently, the demand for long-range underwater communication (UWC) is increasing. Conventional long-range UWC studies utilize vertical line array (VLA) and equalization techniques such as TRM and DFE to mitigate the long multi-path delay. However, recently developed underwater platforms such as unmanned underwater vehicles [...] Read more.
Currently, the demand for long-range underwater communication (UWC) is increasing. Conventional long-range UWC studies utilize vertical line array (VLA) and equalization techniques such as TRM and DFE to mitigate the long multi-path delay. However, recently developed underwater platforms such as unmanned underwater vehicles (UUVs) utilize a single hydrophone, and it is hard to apply the conventional long-range UWC system to these platforms. This paper proposes frequency shifting-based modulation to overcome the large multi-path delay without any optimization or training symbol. Unlike FSK, the proposed modulation method transmits the data using linear frequency modulation (LFM). The proposed demodulation method estimates the multi-path delay using data-modulated LFM and utilizes the estimated multi-path to compensate for the subsequent data signal. Therefore, the proposed method has better BER performance than FSK, and it is demonstrated through a simulation and ocean experiment with a single hydrophone. Full article
(This article belongs to the Special Issue Underwater Acoustics and Digital Signal Processing)
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18 pages, 2789 KiB  
Article
Self-Interference Suppression of Unmanned Underwater Vehicle with Vector Hydrophone Array Based on an Improved Autoencoder
by Jin Fu, Wenfeng Dong, Longhao Qiu, Chunpeng Zhao and Zherui Wang
J. Mar. Sci. Eng. 2023, 11(7), 1358; https://doi.org/10.3390/jmse11071358 - 3 Jul 2023
Viewed by 989
Abstract
The self-interference of an unmanned underwater vehicle (UUV) weakens its ability to detect targets of interest. Due to limitations in the size of the sonar array and the complexity of the interference, the performance of existing self-interference suppression methods in practical applications is [...] Read more.
The self-interference of an unmanned underwater vehicle (UUV) weakens its ability to detect targets of interest. Due to limitations in the size of the sonar array and the complexity of the interference, the performance of existing self-interference suppression methods in practical applications is unsatisfactory. Our research focuses on analyzing the influence of near-field interferences on the sample covariance matrix (SCM) and proposes an interference suppression algorithm based on an improved autoencoder. The proposed algorithm effectively learns the feature distribution of near-field interferences within the covariance domain and reconstructs the pure signal covariance matrix through the cancellation of the near-field interference features. Moreover, the proposed algorithm can meet the requirements of real-time processing and does not require prior knowledge about the positions or propagation of interference. Simulations demonstrate that the proposed algorithm outperforms comparison methods, particularly in scenarios with low signal-to-interference ratios and a limited number of sensors. Furthermore, lake experiments provide additional evidence of the proposed algorithm’s good performance in practical applications. Full article
(This article belongs to the Special Issue Underwater Acoustics and Digital Signal Processing)
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18 pages, 4217 KiB  
Article
Low-Resource Generation Method for Few-Shot Dolphin Whistle Signal Based on Generative Adversarial Network
by Huiyuan Wang, Xiaojun Wu, Zirui Wang, Yukun Hao, Chengpeng Hao, Xinyi He and Qiao Hu
J. Mar. Sci. Eng. 2023, 11(5), 1086; https://doi.org/10.3390/jmse11051086 - 22 May 2023
Viewed by 1486
Abstract
Dolphin signals are effective carriers for underwater covert detection and communication. However, the environmental and cost constraints terribly limit the amount of data available in dolphin signal datasets are often limited. Meanwhile, due to the low computational power and resource sensitivity of Unmanned [...] Read more.
Dolphin signals are effective carriers for underwater covert detection and communication. However, the environmental and cost constraints terribly limit the amount of data available in dolphin signal datasets are often limited. Meanwhile, due to the low computational power and resource sensitivity of Unmanned Underwater Vehicles (UUVs), current methods for real-time generation of dolphin signals with favorable results are still subject to several challenges. To this end, a Masked AutoEncoder Generative Adversarial Network (MAE-GAN) model is hereby proposed. First, considering the few-shot condition, the dataset is extended by using data augmentation techniques. Then, to meet the low arithmetic constraint, a denoising autoencoder with a mask is used to obtain latent codes through self-supervised learning. These latent codes are then utilized in Conditional Wasserstein Generative Adversarial Network-Gradient Penalty (CWGAN-GP) to generate a whistle signal model for the target dataset, fully demonstrating the effectiveness of the proposed method for enhancing dolphin signal generation in data-limited scenarios. The whistle signals generated by the MAE-GAN and baseline models are compared with actual dolphin signals, and the findings indicate that the proposed approach achieves a discriminative score of 0.074, which is 28.8% higher than that of the current state-of-the-art techniques. Furthermore, it requires only 30.2% of the computational resources of the baseline model. Overall, this paper presents a novel approach to generating high-quality dolphin signals in data-limited situations, which can also be deployed on low-resource devices. The proposed MAE-GAN methods provide a promising solution to address the challenges of limited data and computational power in generating dolphin signals. Full article
(This article belongs to the Special Issue Underwater Acoustics and Digital Signal Processing)
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21 pages, 1593 KiB  
Article
Adaptive Beamforming with Hydrophone Arrays Based on Oblique Projection in the Presence of the Steering Vector Mismatch
by Yan Dai and Chao Sun
J. Mar. Sci. Eng. 2023, 11(4), 876; https://doi.org/10.3390/jmse11040876 - 20 Apr 2023
Viewed by 1542
Abstract
In sonar systems, the performance of adaptive beamformers severely degrades when mismatches occur between the actual and presumed steering vectors of the desired signal, mainly due to hydrophone position errors, amplitude-phase errors, and the scattered effect of arrays. Similarly, an inadequate number of [...] Read more.
In sonar systems, the performance of adaptive beamformers severely degrades when mismatches occur between the actual and presumed steering vectors of the desired signal, mainly due to hydrophone position errors, amplitude-phase errors, and the scattered effect of arrays. Similarly, an inadequate number of “training” samples can lead to performance degradations similar to those caused by mismatches. In this paper, an adaptive beamforming algorithm based on oblique projection (OP-ABF) mismatch compensation is proposed to remove the degradation caused by the arbitrary-type steering vector mismatch of the desired signal. The proposed algorithm is motivated by the fact that the weight vector of adaptive beamforming can be represented as a linear combination of the optimal one and the oblique projection (OP) vector, which is generated by the steering vector mismatch and does not exist without this. Our algorithm was developed by constructing the oblique projection mismatch compensation vector (OPMCV) to provide the minimum variance distortionless response (MVDR) beamformer. Then, the algorithm could be implemented by the solution of the OP matrix with the formulation of the covariance matrix loading (CML). The simulation results of a uniform linear array (ULA) and a half-cylindrical conformal array (HCCA) show that the OP-ABF can optimize the original weight vector as much as possible without sacrificing the output signal-to-interference-plus-noise ratio (SINR) under different conditions. Experimental results for the HCCA also confirm the effectiveness of this algorithm. Full article
(This article belongs to the Special Issue Underwater Acoustics and Digital Signal Processing)
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21 pages, 8778 KiB  
Article
Application of a Deep Neural Network for Acoustic Source Localization Inside a Cavitation Tunnel
by Bo-Jie Lin, Pai-Chen Guan, Hung-Tang Chang, Hong-Wun Hsiao and Jung-Hsiang Lin
J. Mar. Sci. Eng. 2023, 11(4), 773; https://doi.org/10.3390/jmse11040773 - 1 Apr 2023
Cited by 1 | Viewed by 1655
Abstract
Navigating with low noise is the key capability in the submarine design considerations, and noise reduction is also one of the most critical issues in the related fields. Therefore, it is necessary to identify the source of noise during design stage to improve [...] Read more.
Navigating with low noise is the key capability in the submarine design considerations, and noise reduction is also one of the most critical issues in the related fields. Therefore, it is necessary to identify the source of noise during design stage to improve the survivability of the submarines. The main objective of this research is using the supervised neural network to construct the system of noise localization to identify noise source in the large acoustic tunnel. Firstly, we started our proposed method by improving the Yangzhou’s method and Shunsuke’s method. In the test results, we find that the errors of the both can be reduced by using the min-max normalization to highlight the data characteristics of the low amplitude in some frequency. And Yangzhou’s method has higher accuracy than Shunsuke’s method. Then, we reset the diagonal numbers of the cross spectral matrix in Yangzhou’s method to zero and replace mean absolute error to be the loss function for improving the stability of training, and get the most suitable neural network construction for our research. After our optimization, the error decreases from 0.315 m to 0.008 m in cuboid model test. Finally, we apply our method to the cavitation tunnel model. A total of 100 data sets were used for training, 10 sets for verification, and 5 for testing. The average error of the test result is 0.13 m. For the model test in cavitation tunnel in National Taiwan Ocean University, the length of ship model is around 7 m. And the average error is sufficient to determine the noise source position. Full article
(This article belongs to the Special Issue Underwater Acoustics and Digital Signal Processing)
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20 pages, 9149 KiB  
Article
Effects of Internal Waves on Acoustic Temporal Coherence in the South China Sea
by Fei Gao, Ping Hu, Fanghua Xu, Zhenglin Li and Jixing Qin
J. Mar. Sci. Eng. 2023, 11(2), 374; https://doi.org/10.3390/jmse11020374 - 8 Feb 2023
Cited by 2 | Viewed by 1533
Abstract
An acoustic experiment to measure the sound field during internal wave activity was conducted in the South China Sea. During the experiment, a train of strong internal solitary waves (ISWs) moved from the acoustic source to the receiver array along the acoustic path, [...] Read more.
An acoustic experiment to measure the sound field during internal wave activity was conducted in the South China Sea. During the experiment, a train of strong internal solitary waves (ISWs) moved from the acoustic source to the receiver array along the acoustic path, and the propagation direction of the ISWs train was almost parallel to the acoustic path. Here, a study of the characteristics and physical mechanisms of the acoustic temporal coherence in this scenario is reported. The temporal coherence was analyzed by using the simulation results and experimental data. The results show that the temporal correlation coefficients oscillate quasi-periodically with both time and time delay, and the predominant oscillation periods are the same as the periods of the ISWs. The predominant fluctuation frequencies of the sound field correspond to some specific modes and lead to the periodicity of the temporal correlation coefficients. In the shallow layer, the spectrum structures of the temporal correlation coefficients are simpler because of the fewer effective modes. Full article
(This article belongs to the Special Issue Underwater Acoustics and Digital Signal Processing)
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15 pages, 1337 KiB  
Article
Variational Bayesian Inference Time Delay Estimation for Passive Sonars
by Feilong Ding, Cheng Chi, Yu Li and Haining Huang
J. Mar. Sci. Eng. 2023, 11(1), 194; https://doi.org/10.3390/jmse11010194 - 12 Jan 2023
Cited by 1 | Viewed by 1386
Abstract
In passive sonars, distance and depth estimation of underwater targets is often limited by the accuracy of time delay estimations. The estimation accuracy of the existing methods of time delay estimation is limited by the uniform discrete grid (signal sampling rate). When a [...] Read more.
In passive sonars, distance and depth estimation of underwater targets is often limited by the accuracy of time delay estimations. The estimation accuracy of the existing methods of time delay estimation is limited by the uniform discrete grid (signal sampling rate). When a true time delay is out of the grid, the estimation accuracy deteriorates due to the mismatch between the real-time delay and the discrete grid. This paper proposes a new method for time delay estimation, which realizes the time delay estimation under the framework of variational Bayesian inference. The proposed method is grid-less, that is, continuous in the time domain. Unlike the popular grid-less compressive time delay estimation method, this method does not require parameter adjustment, and can automatically estimate the number of time delays, noise variance, and amplitude variance. The simulation results showed that the performance of the proposed method was superior to the reference state-of-the-art time delay estimation methods. Full article
(This article belongs to the Special Issue Underwater Acoustics and Digital Signal Processing)
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16 pages, 4755 KiB  
Article
Waveform Design Using Coprime Frequency-Modulated Pulse Trains for Reverberation Suppression of Active Sonar
by Xiaobin Cui, Cheng Chi, Shuqiu Li, Zigao Li, Yu Li and Haining Huang
J. Mar. Sci. Eng. 2023, 11(1), 28; https://doi.org/10.3390/jmse11010028 - 26 Dec 2022
Cited by 1 | Viewed by 1556
Abstract
Over the last two decades, low-frequency active sonar has become an attractive tool for underwater target detection. The reverberation to signal ratio (RSR) of transmitted waveforms is an important factor affecting the detection capability of low-frequency active sonar. Therefore, reasonable waveform design for [...] Read more.
Over the last two decades, low-frequency active sonar has become an attractive tool for underwater target detection. The reverberation to signal ratio (RSR) of transmitted waveforms is an important factor affecting the detection capability of low-frequency active sonar. Therefore, reasonable waveform design for reverberation suppression of active sonar is an important topic. Pulse trains of linear frequency-modulated (PTFM) waveforms have been proposed and manifested their good performance in suppressing reverberation. The number of sub-pulses is positively related to the reverberation to signal ratio; the lower the number of sub-pulses, the lower the reverberation to signal ratio. However, to avoid ambiguity in a Doppler measurement, the PTFM waveforms have a requirement for the number of sub-pulses to be satisfied, which prevents its reverberation suppression performance from being further improved. In this paper, we propose a coprime pulse train of linear frequency-modulated (CPTFM) waveform, which reduces the number of sub-pulses to some extent. Therefore, the ability of reverberation suppression of the CPTFM waveform can be improved. The RSR was chosen as the metric to evaluate the waveform’s ability to suppress reverberation, and the theoretical formula for the RSR of the CPTFM waveform was derived in zone A and B. With the overlap of zones A and B brought about by the decrease in the number of sub-pulses, the average RSR of zones A and B is used in this paper to evaluate the reverberation suppression ability of the waveform. The simulation experiment shows that the proposed CPTFM waveform decreases the average RSR by 7 dB and 20 dB in comparison to the reference PTFM waveform and continuous waveform (CW), which is consistent with the theoretical results by the derived formulas. Full article
(This article belongs to the Special Issue Underwater Acoustics and Digital Signal Processing)
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