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Intelligent Underwater Systems: Sensing, Communication, Networking and Applications
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Intelligent Underwater Systems: Sensing, Communication, Networking and Applications

A special issue of Sensors (ISSN 1424-8220). This special issue belongs to the section "Sensor Networks".

Deadline for manuscript submissions: closed (30 September 2019) | Viewed by 63509

Special Issue Editor

Dr. Zheng Peng

E-Mail Website
Guest Editor
Department of Computer Science, NAC 8/203, Grove School of Engineering, City University of New York - City College, 160 Covent Avenue, New York, NY 10031, USA
Interests: Underwater Wireless Sensor Networks; Wireless Networking; Cross-layer Design and Optimization; Localization and Synchronization; Computer Architecture; Embedded System; Operating System; Cyber-Physical System; Autonomous Underwater Vehicle
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Following the success of the previous Special Issue on Underwater Sensing, Communication, Networking, and Systems , we are pleased to announce a new Special Issue on Intelligent Underwater Systems: Sensing, Communication, Networking, and Applications. It aims to encourage interdisciplinary and multidisciplinary research at the frontier of intelligent underwater systems.

The strategic significance of the ocean leads has inspired a growing interest in developing effective and efficient sensing, communication, and networking systems for underwater environments. New technology is being developed to meet the increasing need of exploring the mysteries of the deep sea. New research is being conducted to address new challenges posed by unique underwater environments. These efforts can transform the way we understand, explore, and utilize the largely unexplored ocean.

In this Special Issue, we welcome our fellow colleagues to present recent research outcomes in the areas of underwater sensing, communication, networking, and system designs. The topics of interests include, but are not limited to, the following:

  • Underwater sensing technology, including sensor design, sensing algorithms, data mining, data fusion, and dissemination;
  •  Underwater wireless communications, including acoustic, optical, RF, and magneto-inductive;
  • Underwater observatory, including wired and wireless observatory at coastal, regional, and global scales;
  • Underwater wireless networks, including networking theories, protocol designs, and architecture;
  • Underwater robotics, including autonomous underwater vehicles (AUV), underwater remotely operated underwater vehicles (ROV), and underwater unmanned vehicles (UUV);
  • Power harvesting and power systems, including alternative energy sources, renewable energy sources, underwater wireless charging, and low power design;
  • Hardware design, including sensor systems, system integration, prototype, software defined communication, and networking platform;
  • Modeling, simulation, and testbed design;
  • Underwater ranging, localization, and tracking;
  • Underwater cybersecurity and countermeasures;
  • System deployment and network planning;
  • Applications, case studies, field trials, and experiment results.

Dr. Zheng Peng
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

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. Sensors is an international peer-reviewed open access semimonthly 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.

Published Papers (19 papers)

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Research

28 pages, 5492 KiB  
Article
An Approach to Multi-Objective Path Planning Optimization for Underwater Gliders
by Carlos Lucas, Daniel Hernández-Sosa, David Greiner, Aleš Zamuda and Rui Caldeira
Sensors 2019, 19(24), 5506; https://doi.org/10.3390/s19245506 - 13 Dec 2019
Cited by 15 | Viewed by 4030
Abstract
Underwater gliders are energy-efficient vehicles that rely on changes in buoyancy in order to convert up and down movement into forward displacement. These vehicles are conceived as multi-sensor platforms, and can be used to collect ocean data for long periods in wide range [...] Read more.
Underwater gliders are energy-efficient vehicles that rely on changes in buoyancy in order to convert up and down movement into forward displacement. These vehicles are conceived as multi-sensor platforms, and can be used to collect ocean data for long periods in wide range areas. This endurance is achieved at the cost of low speed, which requires extensive planning to ensure vehicle safety and mission success, particularly when dealing with strong ocean currents. As gliders are often involved on missions that pursue multiple objectives (track events, reach a target point, avoid obstacles, sample specified areas, save energy), path planning requires a way to deal with several constraints at the same time; this makes glider path planning a multi-objective (MO) optimization problem. In this work, we analyse the usage of the non-dominated sorting genetic algorithm II (NSGA-II) to tackle a MO glider path planning application on a complex environment integrating 3D and time varying ocean currents. Multiple experiments using a glider kinematic simulator coupled with NSGA-II, combining different control parameters were carried out, to find the best parameter configuration that provided suitable paths for the desired mission. Ultimately, the system described in this work was able to optimize multi-objective trajectories, providing non dominated solutions. Such a planning tool could be of great interest in real mission planning, to assist glider pilots in selecting the most convenient paths for the vehicle, taking into account ocean forecasts and particular characteristics of the deployment location. Full article
(This article belongs to the Special Issue Intelligent Underwater Systems: Sensing, Communication, Networking and Applications)
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18 pages, 19347 KiB  
Article
Generation and Processing of Simulated Underwater Images for Infrastructure Visual Inspection with UUVs
by Olaya Álvarez-Tuñón, Alberto Jardón and Carlos Balaguer
Sensors 2019, 19(24), 5497; https://doi.org/10.3390/s19245497 - 12 Dec 2019
Cited by 19 | Viewed by 3537
Abstract
The development of computer vision algorithms for navigation or object detection is one of the key issues of underwater robotics. However, extracting features from underwater images is challenging due to the presence of lighting defects, which need to be counteracted. This requires good [...] Read more.
The development of computer vision algorithms for navigation or object detection is one of the key issues of underwater robotics. However, extracting features from underwater images is challenging due to the presence of lighting defects, which need to be counteracted. This requires good environmental knowledge, either as a dataset or as a physic model. The lack of available data, and the high variability of the conditions, makes difficult the development of robust enhancement algorithms. A framework for the development of underwater computer vision algorithms is presented, consisting of a method for underwater imaging simulation, and an image enhancement algorithm, both integrated in the open-source robotics simulator UUV Simulator. The imaging simulation is based on a novel combination of the scattering model and style transfer techniques. The use of style transfer allows a realistic simulation of different environments without any prior knowledge of them. Moreover, an enhancement algorithm that successfully performs a correction of the imaging defects in any given scenario for either the real or synthetic images has been developed. The proposed approach showcases then a novel framework for the development of underwater computer vision algorithms for SLAM, navigation, or object detection in UUVs. Full article
(This article belongs to the Special Issue Intelligent Underwater Systems: Sensing, Communication, Networking and Applications)
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12 pages, 5516 KiB  
Article
Multicore-Processor Based Software-Defined Communication/Network Platform for Underwater Internet of Things
by Chaohui Luo, Biyun Ma, Fangjiong Chen, Quansheng Guan, Hua Yu and Fei Ji
Sensors 2019, 19(23), 5168; https://doi.org/10.3390/s19235168 - 26 Nov 2019
Cited by 8 | Viewed by 2499
Abstract
Software-defined acoustic modems (SDAMs) for underwater communication and networking have been an important research topic due to their flexibility and programmability. In this paper, we propose a reconfigurable platform for SDAMs based on the TI AM5728 processor, which integrates dual-core ARM Cortex-A15 CPUs [...] Read more.
Software-defined acoustic modems (SDAMs) for underwater communication and networking have been an important research topic due to their flexibility and programmability. In this paper, we propose a reconfigurable platform for SDAMs based on the TI AM5728 processor, which integrates dual-core ARM Cortex-A15 CPUs and two TI C66x DSP cores. The signal processing and A/D, D/A for physical-layer communication are implemented in the DSP cores. The networking protocols and the application programs are implemented in the ARM cores. The proposed platform has the following characteristics: (1) Due to the high-performance dual-ARM cores, the whole NS3 network simulator can be run in the ARM cores. Network protocols developed in a software simulation platform (e.g., NS3 platform) can be seamlessly migrated to a hardware platform without modification. (2) A new physical-layer module associated with real acoustic channel is developed, such that a data packet generated from the application layer will be transmitted through a real acoustic channel. The results of networking experiments with five nodes are presented to demonstrate the effectiveness of the proposed platform. Full article
(This article belongs to the Special Issue Intelligent Underwater Systems: Sensing, Communication, Networking and Applications)
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11 pages, 966 KiB  
Article
Estimation of Overspread Underwater Acoustic Channel Based on Low-Rank Matrix Recovery
by Jie Li, Fangjiong Chen, Songzuo Liu, Hua Yu and Fei Ji
Sensors 2019, 19(22), 4976; https://doi.org/10.3390/s19224976 - 15 Nov 2019
Cited by 4 | Viewed by 2135
Abstract
In this paper, the estimation of overspread, i.e., doubly spread underwater acoustic (UWA) channels of strong dispersion is considered. We show that although the UWA channel dispersion causes the degeneration of channel sparsity, it leads to a low-rank structure especially when the channel [...] Read more.
In this paper, the estimation of overspread, i.e., doubly spread underwater acoustic (UWA) channels of strong dispersion is considered. We show that although the UWA channel dispersion causes the degeneration of channel sparsity, it leads to a low-rank structure especially when the channel delay-Doppler-spread function is separable in delay and Doppler domain. Therefore, we introduce the low-rank criterion to estimate the UWA channels, which can help to improve the estimation performance in the case of strong dispersion. The estimator is based on the discrete delay-Doppler-spread function representation of channel, and is formulated as a low-rank matrix recovery problem which can be solved by the singular value projection technique. Simulation examples are carried out to demonstrate the effectiveness of the proposed low-rank-based channel estimator. Full article
(This article belongs to the Special Issue Intelligent Underwater Systems: Sensing, Communication, Networking and Applications)
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22 pages, 11208 KiB  
Article
A Sensing and Tracking Algorithm for Multiple Frequency Line Components in Underwater Acoustic Signals
by Xinwei Luo and Zihan Shen
Sensors 2019, 19(22), 4866; https://doi.org/10.3390/s19224866 - 8 Nov 2019
Cited by 11 | Viewed by 3477
Abstract
Reliable and efficient sensing and tracking of multiple weak or time-varying frequency line components in underwater acoustic signals is the topic of this paper. We propose a method for automatic detection and tracking of multiple frequency lines in lofargram based on hidden Markov [...] Read more.
Reliable and efficient sensing and tracking of multiple weak or time-varying frequency line components in underwater acoustic signals is the topic of this paper. We propose a method for automatic detection and tracking of multiple frequency lines in lofargram based on hidden Markov model (HMM). Instead of being directly subjected to frequency line tracking, the whole lofargram is first segmented into several sub-lofargrams. Then, the sub-lofargrams suspected to contain frequency lines are screened. In these sub-lofargrams, the HMM-based method is used for detection of multiple frequency lines. Using image stitching and statistical model method, the frequency lines with overlapping parts detected by different sub-lofargrams are merged to obtain the final detection results. The method can effectively detect multiple time-varying frequency lines of underwater acoustic signals while ensuring the performance under the condition of low signal-to-noise ratio (SNR). It can be concluded that the proposed algorithm can provide better multiple frequency lines sensing ability while greatly reducing the amount of calculations and providing potential techniques for feature sensing and tracking processing of unattended equipment such as sonar buoys and submerged buoys. Full article
(This article belongs to the Special Issue Intelligent Underwater Systems: Sensing, Communication, Networking and Applications)
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24 pages, 1602 KiB  
Article
Advanced Autonomous Underwater Vehicles Attitude Control with L 1 Backstepping Adaptive Control Strategy
by Yuqian Liu, Jiaxing Che and Chengyu Cao
Sensors 2019, 19(22), 4848; https://doi.org/10.3390/s19224848 - 7 Nov 2019
Cited by 7 | Viewed by 2454
Abstract
This paper presents a novel attitude control design, which combines L 1 adaptive control and backstepping control together, for Autonomous Underwater Vehicles (AUVs) in a highly dynamic and uncertain environment. The Euler angle representation is adopted in this paper to represent the attitude [...] Read more.
This paper presents a novel attitude control design, which combines L 1 adaptive control and backstepping control together, for Autonomous Underwater Vehicles (AUVs) in a highly dynamic and uncertain environment. The Euler angle representation is adopted in this paper to represent the attitude propagation. Kinematics and dynamics of the attitude are in the strict feedback form, which leads the backstepping control strategy serving as the baseline controller. Moreover, by bringing fast and robust adaptation into the backstepping control architecture, our controller is capable of dealing with time-varying uncertainties from modeling and external disturbances in dynamics. This attitude controller is proposed for coupled pitch-yaw channels. For inevitable roll excursions, a Lyapunov function-based optimum linearization method is presented to analyze the stability of the roll angle in the operation region. Theoretical analysis and simulation results are given to demonstrate the feasibility of the developed control strategy. Full article
(This article belongs to the Special Issue Intelligent Underwater Systems: Sensing, Communication, Networking and Applications)
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20 pages, 711 KiB  
Article
Blind Fractionally Spaced Channel Equalization for Shallow Water PPM Digital Communications Links
by Gaetano Scarano, Andrea Petroni, Mauro Biagi and Roberto Cusani
Sensors 2019, 19(21), 4604; https://doi.org/10.3390/s19214604 - 23 Oct 2019
Cited by 9 | Viewed by 2225
Abstract
Underwater acoustic digital communications suffer from inter-symbol interference deriving from signal distortions caused by the channel propagation. Facing such kind of impairment becomes particularly challenging when dealing with shallow water scenarios characterized by short channel coherence time and large delay spread caused by [...] Read more.
Underwater acoustic digital communications suffer from inter-symbol interference deriving from signal distortions caused by the channel propagation. Facing such kind of impairment becomes particularly challenging when dealing with shallow water scenarios characterized by short channel coherence time and large delay spread caused by time-varying multipath effects. Channel equalization operated on the received signal represents a crucial issue in order to mitigate the effect of inter-symbol interference and improve the link reliability. In this direction, this contribution presents a preliminary performance analysis of acoustic digital links adopting pulse position modulation in severe multipath scenarios. First, we show how the spectral redundancy offered by pulse position modulated signals can be fruitfully exploited when using fractional sampling at the receiver side, which is an interesting approach rarely addressed by the current literature. In this context, a novel blind equalization scheme is devised. Specifically, the equalizer is blindly designed according to a suitably modified Bussgang scheme in which the zero-memory nonlinearity is replaced by a M-memory nonlinearity, M being the pulse position modulation order. Numerical results not only confirm the feasibility of the technique described here, but also assess the quality of its performance. An extension to a very interesting complex case is also provided. Full article
(This article belongs to the Special Issue Intelligent Underwater Systems: Sensing, Communication, Networking and Applications)
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20 pages, 2032 KiB  
Article
Passive Source Localization Using Compressive Sensing
by Hangfang Zhao, M. Jehanzeb Irshad, Huihong Shi and Wen Xu
Sensors 2019, 19(20), 4522; https://doi.org/10.3390/s19204522 - 17 Oct 2019
Cited by 6 | Viewed by 2777
Abstract
This paper presents an underwater passive source localization method by forming an underdetermined linear inversion problem. The signal strength on a specified grid is evaluated using sparse reconstruction algorithms by exploiting the spatial sparsity of the source signals. Our strategy leads to a [...] Read more.
This paper presents an underwater passive source localization method by forming an underdetermined linear inversion problem. The signal strength on a specified grid is evaluated using sparse reconstruction algorithms by exploiting the spatial sparsity of the source signals. Our strategy leads to a high ratio of measurements to sparsity (RMS), an increase in the peak sharpness with a low side lobe level, and minimization of the dimensionality of the problem due to the formulation of the system equation of the multiple snapshots based on the data correlation matrix. Furthermore, to reduce the computational burden, pre-locating with Bartlett is presented. Our proposed technique can perform close to Bartlet and white noise gain constraint processes in the single-source scenario, but it can give slightly better results while localizing multiple sources. It exhibits the respective characteristics of traditionally used Bartlett and white noise gain constraint methods, such as robustness to environmental/system mismatch and high resolution. Both the simulated and experimental data are processed to demonstrate the effectiveness of the method for underwater source localization. Full article
(This article belongs to the Special Issue Intelligent Underwater Systems: Sensing, Communication, Networking and Applications)
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22 pages, 1309 KiB  
Article
A Mobile Anchor Node Assisted RSSI Localization Scheme in Underwater Wireless Sensor Networks
by Yanlong Sun, Yazhou Yuan, Qimin Xu, Changchun Hua and Xinping Guan
Sensors 2019, 19(20), 4369; https://doi.org/10.3390/s19204369 - 10 Oct 2019
Cited by 25 | Viewed by 3003
Abstract
In this paper, a mobile anchor node assisted RSSI localization scheme in underwater wireless sensor networks (UWSNs) is proposed, which aims to improve location accuracy and shorten location time. First, to improve location accuracy, we design a support vector regression (SVR) based interpolation [...] Read more.
In this paper, a mobile anchor node assisted RSSI localization scheme in underwater wireless sensor networks (UWSNs) is proposed, which aims to improve location accuracy and shorten location time. First, to improve location accuracy, we design a support vector regression (SVR) based interpolation method to estimate the projection of sensor nodes on the linear trajectory of the mobile anchor node. The proposed method increases the accuracy of the nonlinear regression model of noisy measured data and synchronously decreases the estimation error caused by the discreteness of measured data. Second, to shorten location time, we develop a curve matching method to obtain the perpendicular distance from sensor nodes to the linear trajectory of the mobile anchor node. The location of the sensor node can be calculated based on the projection and the perpendicular distance. Compared with existing schemes that require the anchor node to travel at least two trajectories, the proposed scheme only needs one-time trajectory to locate sensor nodes, and the location time is shortened with the reduction in the number of trajectories. Finally, simulation results prove that the proposed scheme can obtain more accurate sensor node location in less time compared with the existing schemes. Full article
(This article belongs to the Special Issue Intelligent Underwater Systems: Sensing, Communication, Networking and Applications)
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19 pages, 24102 KiB  
Article
An Energy-Efficient Redundant Transmission Control Clustering Approach for Underwater Acoustic Networks
by Gulnaz Ahmed, Xi Zhao, Mian Muhammad Sadiq Fareed and Muhammad Zeeshan Fareed
Sensors 2019, 19(19), 4241; https://doi.org/10.3390/s19194241 - 30 Sep 2019
Cited by 19 | Viewed by 2712
Abstract
Underwater Acoustic Network (UAN) is an emerging technology with attractive applications. In such type of networks, the control-overhead, redundant inner-network transmissions management, and data-similarity are still very challenging. The cluster-based frameworks manage the control-overhead and redundant inner-network transmissions persuasively. However, the current clustering [...] Read more.
Underwater Acoustic Network (UAN) is an emerging technology with attractive applications. In such type of networks, the control-overhead, redundant inner-network transmissions management, and data-similarity are still very challenging. The cluster-based frameworks manage the control-overhead and redundant inner-network transmissions persuasively. However, the current clustering protocols consume a big part of their energy resources in data-similarity as these protocols periodically sense and forward the same information. In this paper, we introduce a novel two-level Redundant Transmission Control (RTC) approach that ensures the data-similarity using some statistical tests with an appropriate degree of confidence. Later, the Cluster Head (CH) and the Region Head (RH) remove the data-similarity from the original data before forwarding it to the next level. We also introduce a new spatiotemporal and dynamic CH role rotation technique which is capable to adjust the drifted field nodes because of water current movements. The beauty of the proposed model is that the RH controls the communications and redundant transmission between the CH and Mobile Sink (MS), while the CH controls the redundant inner-network transmissions and data-similarity between the cluster members. We conduct simulations to evaluate the performance of our designed framework under different criteria such as average end-to-end delay, the packet delivery ratio, and energy consumption of the network with respect to the recent schemes. The presented results reveal that the proposed model outperforms the current approaches in terms of the selected metrics. Full article
(This article belongs to the Special Issue Intelligent Underwater Systems: Sensing, Communication, Networking and Applications)
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17 pages, 486 KiB  
Article
Design and Analysis of Handshake-Based MAC with Delay Variations in Underwater Acoustic Networks
by Chao Dong, Yankun Chen, Quansheng Guan, Fei Ji, Hua Yu and Fangjiong Chen
Sensors 2019, 19(19), 4159; https://doi.org/10.3390/s19194159 - 25 Sep 2019
Cited by 5 | Viewed by 2171
Abstract
The long propagation delay in underwater acoustic channels has attracted tremendous attentions in designing Medium Access Control (MAC). The low acoustic propagation speed and wide area of the acoustic communication range led to a wide range of variations in the propagation delay. This [...] Read more.
The long propagation delay in underwater acoustic channels has attracted tremendous attentions in designing Medium Access Control (MAC). The low acoustic propagation speed and wide area of the acoustic communication range led to a wide range of variations in the propagation delay. This paper identifies an important characteristic of two-scale delay variations by field test results. We carry out simulations to study the impact of delay variations on MAC, and the results suggest a slot length adaptation scheme for the handshake and slotting based MAC. We further model an absorbing Markov chain to derive the closed-form equation for the throughput of MAC with adaptive slot length. Both the analytical and simulation results show that our proposed slot length adaptation improves significantly the throughput of MAC in underwater acoustic networks. Particularly, the Slotted-FAMA with an adaptive slot length achieves more than double the throughput than the Slotted-FAMA with a fixed slot length in a network with six nodes. Full article
(This article belongs to the Special Issue Intelligent Underwater Systems: Sensing, Communication, Networking and Applications)
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25 pages, 1534 KiB  
Article
A Pheromone-Inspired Monitoring Strategy Using a Swarm of Underwater Robots
by Guannan Li, Chao Chen, Chao Geng, Meng Li, Hongli Xu and Yang Lin
Sensors 2019, 19(19), 4089; https://doi.org/10.3390/s19194089 - 21 Sep 2019
Cited by 10 | Viewed by 3276
Abstract
The advent of the swarm makes it feasible to dynamically monitor a wide area for maritime applications. The crucial problems of underwater swarm monitoring are communication and behavior coordination. To tackle these problems, we propose a wide area monitoring strategy that searches for [...] Read more.
The advent of the swarm makes it feasible to dynamically monitor a wide area for maritime applications. The crucial problems of underwater swarm monitoring are communication and behavior coordination. To tackle these problems, we propose a wide area monitoring strategy that searches for static targets of interest simultaneously. Traditionally, an underwater robot adopts either acoustic communication or optical communication. However, the former is low in bandwidth and the latter is short in communication range. Our strategy coordinates underwater robots through indirect communication, which is inspired by social insects that exchange information by pheromone. The indirect communication is established with the help of a set of underwater communication nodes. We adopt a virtual pheromone-based controller and provide a set of rules to integrate the area of interest into the pheromone. Based on the information in the virtual pheromone, behavior laws are developed to guide the swarm to monitor and search with nearby information. In addition, a robot can improve its performance when using additional far-away pheromone information. The monitoring strategy is further improved by adopting a swarm evolution scheme which automatically adjusts the visiting period. Experimental results show that our strategy is superior to the random strategy in most cases. Full article
(This article belongs to the Special Issue Intelligent Underwater Systems: Sensing, Communication, Networking and Applications)
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14 pages, 4134 KiB  
Article
Ultrasonic Power and Data Transfer through Multiple Curved Layers Applied to Pipe Instrumentation
by Victor L. Takahashi, Alan C. Kubrusly, Arthur M. B. Braga, Sully M. M. Quintero, Sávio W. O. Figueiredo and Ana B. Domingues
Sensors 2019, 19(19), 4074; https://doi.org/10.3390/s19194074 - 20 Sep 2019
Cited by 11 | Viewed by 3647
Abstract
Ultrasonic power and data transfer through multilayered curved walls was investigated using numerical and experimental analysis. The acoustic channel used in this paper was formed by two concentric pipes filled with water, aiming for applications that involve powering and monitoring sensors installed behind [...] Read more.
Ultrasonic power and data transfer through multilayered curved walls was investigated using numerical and experimental analysis. The acoustic channel used in this paper was formed by two concentric pipes filled with water, aiming for applications that involve powering and monitoring sensors installed behind the pipe walls. The analysis was carried out in the frequency and time domains using numerical and experimental models. Power and data were effectively simultaneously transferred through the channel. A remote temperature and pressure sensor was powered and interrogated throughout all the layers, and the power insertion loss was 10.72 dB with a data transmission rate of 1200 bps using an amplitude modulated scheme with Manchester coding. The efficiency of the channel was evaluated through an experimental analysis of the bit error rate (BER) with different values of signal-to-noise ratio (SNR), showing a decrease in the number of errors compared with detection without Manchester coding. Full article
(This article belongs to the Special Issue Intelligent Underwater Systems: Sensing, Communication, Networking and Applications)
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17 pages, 4014 KiB  
Article
M-ary Cyclic Shift Keying Spread Spectrum Underwater Acoustic Communications Based on Virtual Time-Reversal Mirror
by Feng Zhou, Bing Liu, Donghu Nie, Guang Yang, Wenbo Zhang and Dongdong Ma
Sensors 2019, 19(16), 3577; https://doi.org/10.3390/s19163577 - 16 Aug 2019
Cited by 21 | Viewed by 3160
Abstract
Underwater acoustic communications are challenging because channels are complex, and acoustic waves when propagating in the ocean are subjected to a variety of interferences, such as noise, reflections, scattering and so on. Spread spectrum technique thus has been widely used in underwater acoustic [...] Read more.
Underwater acoustic communications are challenging because channels are complex, and acoustic waves when propagating in the ocean are subjected to a variety of interferences, such as noise, reflections, scattering and so on. Spread spectrum technique thus has been widely used in underwater acoustic communications for its strong anti-interference ability and good confidentiality. Underwater acoustic channels are typical coherent multipath channels, in which the inter-symbol interference seriously affects the performance of underwater acoustic communications. Time-reversal mirror technique utilizes this physical characteristic of underwater acoustic channels to restrain the inter-symbol interference by reconstructing multipath signals and reduce the influence of channel fading by spatial focusing. This paper presents an M-ary cyclic shift keying spread spectrum underwater acoustic communication scheme based on the virtual time-reversal mirror. Compared to the traditional spread spectrum techniques, this method is more robust, for it uses the M-ary cyclic shift keying spread spectrum to improve the communication rate and uses the virtual time-reversal mirror to ensure a low bit error rate. The performance of this method is verified by simulations and pool experiments. Full article
(This article belongs to the Special Issue Intelligent Underwater Systems: Sensing, Communication, Networking and Applications)
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15 pages, 2483 KiB  
Article
Acoustic Classification of Surface and Underwater Vessels in the Ocean Using Supervised Machine Learning
by Jongkwon Choi, Youngmin Choo and Keunhwa Lee
Sensors 2019, 19(16), 3492; https://doi.org/10.3390/s19163492 - 9 Aug 2019
Cited by 37 | Viewed by 4953
Abstract
Four data-driven methods—random forest (RF), support vector machine (SVM), feed-forward neural network (FNN), and convolutional neural network (CNN)—are applied to discriminate surface and underwater vessels in the ocean using low-frequency acoustic pressure data. Acoustic data are modeled considering a vertical line array by [...] Read more.
Four data-driven methods—random forest (RF), support vector machine (SVM), feed-forward neural network (FNN), and convolutional neural network (CNN)—are applied to discriminate surface and underwater vessels in the ocean using low-frequency acoustic pressure data. Acoustic data are modeled considering a vertical line array by a Monte Carlo simulation using the underwater acoustic propagation model, KRAKEN, in the ocean environment of East Sea in Korea. The raw data are preprocessed and reorganized into the phone-space cross-spectral density matrix (pCSDM) and mode-space cross-spectral density matrix (mCSDM). Two additional matrices are generated using the absolute values of matrix elements in each CSDM. Each of these four matrices is used as input data for supervised machine learning. Binary classification is performed by using RF, SVM, FNN, and CNN, and the obtained results are compared. All machine-learning algorithms show an accuracy of >95% for three types of input data—the pCSDM, mCSDM, and mCSDM with the absolute matrix elements. The CNN is the best in terms of low percent error. In particular, the result using the complex pCSDM is encouraging because these data-driven methods inherently do not require environmental information. This work demonstrates the potential of machine learning to discriminate between surface and underwater vessels in the ocean. Full article
(This article belongs to the Special Issue Intelligent Underwater Systems: Sensing, Communication, Networking and Applications)
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17 pages, 473 KiB  
Article
An Efficient RSS Localization for Underwater Wireless Sensor Networks
by Thu L. N. Nguyen and Yoan Shin
Sensors 2019, 19(14), 3105; https://doi.org/10.3390/s19143105 - 13 Jul 2019
Cited by 35 | Viewed by 3601
Abstract
Localization is a key-enabling technology for many applications in underwater wireless sensor networks. Traditional approaches for received signal strength (RSS)-based localization often require uniform distribution for anchor nodes and suffer from poor estimates according to unpredictable and uncontrollable noise conditions. In this paper, [...] Read more.
Localization is a key-enabling technology for many applications in underwater wireless sensor networks. Traditional approaches for received signal strength (RSS)-based localization often require uniform distribution for anchor nodes and suffer from poor estimates according to unpredictable and uncontrollable noise conditions. In this paper, we establish an RSS-based localization scheme to determine the location of an unknown normal sensor from a certain measurement set of potential anchor nodes. First, we present a practical path loss model for wireless communication in underwater acoustic environments, where anchor nodes are deployed in a random circumstance. For a given area of interest, the RSS data collection is performed dynamically, where the measurement noises and the correlation among them are taken into account. For a pair of transmitter and receiver, we approximate the geometry distance between them according to a linear regression model. Thus, we can obtain a quick access for the range information, while keeping the error, the communication head and the response time low. We also present a method to correct noises in the distance estimate. Simulation results demonstrate that our localization scheme achieves a better performance for certain scenario settings. The successful localization probability can be up to 90%, where the anchor rate is fixed at 10%. Full article
(This article belongs to the Special Issue Intelligent Underwater Systems: Sensing, Communication, Networking and Applications)
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19 pages, 3178 KiB  
Article
Filtered Multitone Modulation Underwater Acoustic Communications Using Low-Complexity Channel-Estimation-Based MMSE Turbo Equalization
by Lin Sun, Mei Wang, Guoheng Zhang, Haisen Li and Lan Huang
Sensors 2019, 19(12), 2714; https://doi.org/10.3390/s19122714 - 17 Jun 2019
Cited by 5 | Viewed by 2612
Abstract
Filtered multitone (FMT) modulation divides the communication band into several subbands to shorten the span of symbols affected by multipath in underwater acoustic (UWA) communications. However, there is still intersymbol interference (ISI) in each subband of FMT modulation degrading communication performance. Therefore, ISI [...] Read more.
Filtered multitone (FMT) modulation divides the communication band into several subbands to shorten the span of symbols affected by multipath in underwater acoustic (UWA) communications. However, there is still intersymbol interference (ISI) in each subband of FMT modulation degrading communication performance. Therefore, ISI suppression techniques must be applied to FMT modulation UWA communications. The suppression performance of traditional adaptive equalization methods often exploited in FMT modulation UWA communications is limited when the effect of ISI spans tens of symbols or large constellation sizes are used. Turbo equalization consisting of adaptive equalization and channel decoding can improve equalization performance through information exchanging and iterative processes. To overcome the shortcoming of traditional minimum mean square error (MMSE) equalization and effectively suppress the ISI with relatively low computation complexity, an FMT modulation UWA communication using low-complexity channel-estimation-based (CE-based) MMSE turbo equalization is proposed in this paper. In the proposed method, turbo equalization is first exploited to suppress the ISI in FMT modulation UWA communications, and the equalizer coefficients of turbo equalization are adjusted using the low-complexity CE-based MMSE algorithm. The proposed method is analyzed in theory and verified by simulation analysis and real data collected in the experiment carried out in a pool with multipath propagation. The results demonstrate that the proposed method can achieve better communication performance with a higher bit rate than the FMT modulation UWA communication using traditional MMSE adaptive equalization. Full article
(This article belongs to the Special Issue Intelligent Underwater Systems: Sensing, Communication, Networking and Applications)
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19 pages, 24206 KiB  
Article
Visual Navigation for Recovering an AUV by Another AUV in Shallow Water
by Shuang Liu, Hongli Xu, Yang Lin and Lei Gao
Sensors 2019, 19(8), 1889; https://doi.org/10.3390/s19081889 - 20 Apr 2019
Cited by 36 | Viewed by 5177
Abstract
Autonomous underwater vehicles (AUVs) play very important roles in underwater missions. However, the reliability of the automated recovery of AUVs has still not been well addressed. We propose a vision-based framework for automatically recovering an AUV by another AUV in shallow water. The [...] Read more.
Autonomous underwater vehicles (AUVs) play very important roles in underwater missions. However, the reliability of the automated recovery of AUVs has still not been well addressed. We propose a vision-based framework for automatically recovering an AUV by another AUV in shallow water. The proposed framework contains a detection phase for the robust detection of underwater landmarks mounted on the docking station in shallow water and a pose-estimation phase for estimating the pose between AUVs and underwater landmarks. We propose a Laplacian-of-Gaussian-based coarse-to-fine blockwise (LCB) method for the detection of underwater landmarks to overcome ambient light and nonuniform spreading, which are the two main problems in shallow water. We propose a novel method for pose estimation in practical cases where landmarks are broken or covered by biofouling. In the experiments, we show that our proposed LCB method outperforms the state-of-the-art method in terms of remote landmark detection. We then combine our proposed vision-based framework with acoustic sensors in field experiments to demonstrate its effectiveness in the automated recovery of AUVs. Full article
(This article belongs to the Special Issue Intelligent Underwater Systems: Sensing, Communication, Networking and Applications)
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19 pages, 4183 KiB  
Article
Real-Time Monocular Visual Odometry for Turbid and Dynamic Underwater Environments
by Maxime Ferrera, Julien Moras, Pauline Trouvé-Peloux and Vincent Creuze
Sensors 2019, 19(3), 687; https://doi.org/10.3390/s19030687 - 8 Feb 2019
Cited by 47 | Viewed by 5143
Abstract
In the context of underwater robotics, the visual degradation induced by the medium properties make difficult the exclusive use of cameras for localization purpose. Hence, many underwater localization methods are based on expensive navigation sensors associated with acoustic positioning. On the other hand, [...] Read more.
In the context of underwater robotics, the visual degradation induced by the medium properties make difficult the exclusive use of cameras for localization purpose. Hence, many underwater localization methods are based on expensive navigation sensors associated with acoustic positioning. On the other hand, pure visual localization methods have shown great potential in underwater localization but the challenging conditions, such as the presence of turbidity and dynamism, remain complex to tackle. In this paper, we propose a new visual odometry method designed to be robust to these visual perturbations. The proposed algorithm has been assessed on both simulated and real underwater datasets and outperforms state-of-the-art terrestrial visual SLAM methods under many of the most challenging conditions. The main application of this work is the localization of Remotely Operated Vehicles used for underwater archaeological missions, but the developed system can be used in any other applications as long as visual information is available. Full article
(This article belongs to the Special Issue Intelligent Underwater Systems: Sensing, Communication, Networking and Applications)
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