Mobile Underwater Research Articles

A Novel Paradigm for Underwater Monitoring Using Mobile Sensor Networks.

This paper presents a novel autonomous environmental monitoring methodology based on collaboration and collective decision-making among robotic agents in a heterogeneous swarm developed within the project subCULTron, tested in a realistic marine environment. The swarm serves as an underwater mobile sensor network for exploration and monitoring of large areas. Different robotic units enable outlier and fault detection, verification of measurements and recognition of environmental anomalies, and relocation of the swarm throughout the environment. The motion capabilities of the robots and the reconfigurability of the swarm are exploited to collect data and verify suspected anomalies, or detect potential sensor faults among the swarm agents. The proposed methodology was tested in an experimental setup in the field in two marine testbeds: the Lagoon of Venice, Italy, and Biograd an Moru, Croatia. Achieved experimental results described in this paper validate and show the potential of the proposed approach.

AquaE-lite Hybrid-Solar-Cell Receiver-Modality for Energy-Autonomous Terrestrial and Underwater Internet-of-Things

Our goal is to develop an energy-autonomous solar cell receiver that can be integrated with a variety of smart devices to implement the Internet of Things in next-generation applications. This paper details efforts to develop such a prototype, called AquaE-lite. Owing to the capability of detecting low-intensity optical signals, 20-m and 30-m long-distance lighting and optical wireless communication with data rates of 1.6 Mbit/s and 1.2 Mbit/s have been achieved on a laboratory testbed, respectively. Moreover, field trials on an outdoor solar cell testbed and in the turbid water of a harbor by the Red Sea have been conducted. Under bright sunlight, energy autonomy and 1.2-Mbit/s optical wireless communication over a transmission distance of 15 m have been implemented, which demonstrated that AquaE-lite with an elaborate receiver circuit has excellent performance in energy harvesting and resistance to background noise. In a more challenging underwater environment, 1.2-Mbit/s signals were successfully received over a transmission distance of 2 m. It indicates that energy-autonomous AquaE-lite with large detection area has promising prospects in future underwater mobile sensor networks to significantly relieve the requirement of pointing, acquisition and tracking while resolving the energy issues.

MEDUSA: A Multi-Environment Dual-Robot for Underwater Sample Acquisition

Aerial-aquatic robots possess the unique ability of operating in both air and water. However, this capability comes with tremendous challenges, such as communication incompatibility, increased airborne mass, potentially inefficient operation in each of the environments and manufacturing difficulties. Such robots, therefore, typically have small payloads and a limited operational envelope, often making their field usage impractical. We propose a novel robotic water sampling approach that combines the robust technologies of multirotors and underwater micro-vehicles into a single integrated tool usable for field operations. The proposed solution encompasses a multirotor capable of landing and floating on the water, and a tethered mobile underwater pod that can be deployed to depths of several meters. The pod is controlled remotely in three dimensions and transmits video feed and sensor data via the floating multirotor back to the user. The `dual-robot' approach considerably simplifies robotic underwater monitoring, while also taking advantage of the fact that multirotors can travel long distances, fly over obstacles, carry payloads and manoeuvre through difficult terrain, while submersible robots are ideal for underwater sampling or manipulation. The presented system can perform challenging tasks which would otherwise require boats or submarines. The ability to collect aquatic images, samples and metrics will be invaluable for ecology and aquatic research, supporting our understanding of local climate in difficult-to-access environments [Video attachment: https://youtu.be/v4xWmEHUSM4].

TRiForm: Formation Control for Underwater Sensor Networks With Measurement Errors

The formation control of mobile underwater wireless sensor networks (MUWSNs) is difficult due to the severe errors in distance and motion measurements. To address this problem, we propose a distributed formation control scheme, TRiForm (Triangle Formation). TRiForm constructs a virtual structure that is a rigid graph formed by triangles of nodes in an MUWSN for high reliability and efficiency in formation control. Furthermore, it utilizes the anchor information to detect and to compensate for measurement errors. We have proven the correctness of the rigidity graph construction by TRiForm. We have also evaluated TRiForm in various scenarios using simulation with the measured parameters from real underwater sensor nodes. The results show that TRiForm can successfully maintain the formations of an MUWSN and control the MUWSN to reach the predefined destination under distance and motion measurement errors.

Energy efficiency maximization algorithm for underwater Mobile sensor networks

Modern Underwater Wireless Sensor Networks (UWSN) would provide big administrations with numerous underwater surveying and technical applications, working in the unstable submerged deep-water conditions. A huge obstacle in these networks is the lifetime limit. The submerged correspondence frameworks mostly employ acoustic communication today. Acoustic interchange communication offers longer ranges that are yet limited by three variables: restricted and subordinate data transmission, time-differing multi-way engendering and low speed of sound. In this paper, an AUV (Autonomous Underwater Vehicle)-assisted acoustic correspondence convention, specifically Energy Efficiency Maximization Algorithm (EEMA) has been proposed to minimize the energy consumption. Underwater sensor networks depend on the hub ceaseless operation, the restricted correspondence transmission capacity and the hub lifetime, which entails difficulties in the operation of USWN. The proposed system will enhance the lifetime by lessening the number of bounces amid sensor transmissions, which fundamentally lessens time utilization and lifetime. Dynamic AUV ways and dynamic gateway assignments will enhance lifetime – proficiency balance proportion in the submerged system. To decrease the system energy utilization with an acceptable conveyance proportion is recommended. The Experimental results show that the proposed methodology has improved the level of energy compared with related techniques.

Photonic methods and technologies for monitoring the ocean and atmosphere

In this paper, we review photonic methods and technologies that are promising for monitoring the ocean and atmosphere and have been implemented mainly in recent years at the Institute of Automation and Control Processes, Far Eastern Branch, Russian Academy of Sciences. We present results of lidar studies that have made it possible to understand key features of ocean – atmosphere interaction processes under continent – ocean transition conditions, which determine specific features of the atmospheric aerosol distribution, small gaseous components of the atmosphere and its optical characteristics. We consider methods and tools for combined optical and laser fluorescence monitoring of the ocean surface. Particular attention is paid to results of research on remote methods and tools for real-time laser-induced and laser fluorescence environmental monitoring of the ocean, including specialised fibre-optic probes and mobile underwater robotic systems. We present results of the development and investigation of highly sensitive, noise-proof fibre-optic hydro- and seismic/acoustic sensors for remote monitoring of the ocean and robotic systems for underwater laser protection of marine vessels, hydraulic structures and oceanographic instruments against the negative impact of biofouling.

Multi-AUV Aided Cooperative 3D-localization for Underwater Sensor Networks

Background: Effective 3D-localization in mobile underwater sensor networks is still an active research topic. Due to the sparse characteristic of underwater sensor networks, AUVs (Autonomous Underwater Vehicles) with precise positioning abilities will benefit cooperative localization. It has important significance to study accurate localization methods. Methods: In this paper, a cooperative and distributed 3D-localization algorithm for sparse underwater sensor networks is proposed. The proposed algorithm combines with the advantages of both recursive location estimation of reference nodes and the outstanding self-positioning ability of mobile AUV. Moreover, our design utilizes MMSE (Minimum Mean Squared Error) based recursive location estimation method in 2D horizontal plane projected from 3D region and then revises positions of un-localized sensor nodes through multiple measurements of Time of Arrival (ToA) with mobile AUVs. Results: Simulation results verify that the proposed cooperative 3D-localization scheme can improve performance in terms of localization coverage ratio, average localization error and localization confidence level. Conclusion: The research can improve localization accuracy and coverage ratio for whole underwater sensor networks.

A Hybrid Localization Algorithm Based on Doppler Shift and AOA for an Underwater Mobile Node

To solve the problem of low accuracy of a mobile node localization in an underwater sensor network, this article proposes a hybrid localization algorithm based on Doppler shift and angle of arrival (AOA) for the underwater mobile node (DAHL). This algorithm utilizes the Doppler frequency shift between the different signals received from the anchor node and the mobile node and the AOA measurement of the signal reflected by the mobile node to estimate the instantaneous position and velocity information of the mobile node through a two-stage algebraic method. In view of the existing measurement errors in the actual situation, the position and velocity estimation errors of the mobile node are optimized by introducing auxiliary parameters. Theoretical analysis and simulation experiments show that the DAHL method can effectively improve the localization accuracy of the mobile node. The localization accuracy of this algorithm can be close to the Cramér-Rao Lower Bound (CRLB) with the condition of small measurement errors.

E2-SCRP: An Energy Efficient Secure Cluster-based Routing Protocol for 3D Underwater Acoustic MANET (UWMANET)

In the current years, Underwater Mobile Ad hoc Network (UWMANET) has emerged as an enthusiastic field for supporting disaster prevention applications (Climate and Weather Observation, Earthquakes in Ocean (Tsunamis), underwater level navigation and tracking). In UWMANET, conventional data transmission methods have certain drawbacks such as high energy consumption, packet loss rate and end-to-end delay. Nowadays, mobile node i.e. Autonomous Underwater Vehicle (AUV) is widely used for data collection from underwater sensors, which act as a relay between sensor node and surface sink. Security is a significant issue in UWMANET, which is required for secure communications. In this paper, Energy Efficient Secure Cluster based Routing Protocol called E2-SCRP is presented in 3D UWMANET environment. The qu-Vanstone based Elliptic Curve Cryptography (qV-ECC) based short-term public key generation scheme is proposed for sensor node authentication. To reduce energy consumption, layer based clustering algorithm is proposed using Type-2 Fuzzy Logic System (T2fls) where Trust value, Distance between neighbors, Relative mobility and Node buffer size for cluster head (CH) election are considered. Next step is to execute two different security schemes based on Event Management. For event occurred clusters, Ciphertext Stealing Technique (CST) is used to resolve the ciphertext expansion problem. For normal data transmission, Lightweight Digital Watermarking (LDW) with Firefly algorithm is proposed. Optimal route for data transmission is executed by Pigeons Swarm Optimization (PiSO) and the forward to sink node via Adjacent AUV. Experiments conducted using NS3 (3.26) and the performance is evaluated for several metrics include packet delivery ratio, energy consumption, end-to-end delay, security strength, and throughput.

On the detachment from the ground of the walking locomotor’s foot of the mobile underwater robot

On the detachment from the ground of the walking locomotor’s foot of the mobile underwater robot

Tuning the demodulation frequency based on a normalized trajectory model for mobile underwater acoustic communications

AbstractWe have developed a demodulator for low data rate, asynchronous frame, and narrow bandwidth underwater acoustic communication. We aim at operation under harsh conditions, ie, low signal‐to‐noise ratio, and across long distances. In this paper, we pay a special attention to the efficiency of mobility support. Mobility results into the Doppler effect, which, for a demodulator, makes the carrier frequency drift arbitrarily during attempts to decode frames. The chances of success are better when the demodulator can tune into the drifted carrier frequency. This can be achieved by trying a range of possible drifted carriers. We introduce the novel idea of normalized trajectory. Each normalized trajectory produces a unique Doppler shift pattern that can be applied to tune into a drifted carrier. We demonstrate that this improvement is theoretically sound. From a practical point of view, the search space is potentially reduced. The actual gain in performance is application‐specific and depends on the actual sets of trajectory parameters that are considered. We introduce the concept of normalized trajectory, discuss its integration into the demodulator, and review the performance of the new design.

Research of Mobile Underwater Acoustic Communication of M-Ary Combining FDM and Piecewise-LFM

Aiming at the countering doppler shift, a mobile underwater acoustic communication scheme of M-ary via FDM-PLFM is proposed. The cross-correlation between piecewise linear frequency modulation(PLFM) and traditional LFM signal is analyzed based on the cross-correlation function. Combining with frequency division multiplexing(FDM), the spectrum utilization of traditional underwater acoustic LFM communication scheme is improved. With the underwater acoustic LFM communication scheme, the new scheme does not require the doppler frequency shift compensation at the low doppler shift. The simulation results show that the present scheme has lower bit error rate than that for the traditional underwater acoustic M-ary LFM communication method under higher data rate conditions.

Doppler scale estimation for varied speed mobile frequency-hopped binary frequency-shift keying underwater acoustic communication.

An optimized Doppler scale factor estimation method based on wavelet de-noising is proposed in this paper to improve the performance of frequency-hopped binary frequency-shift keying mobile underwater acoustic communication. The method is with regard to the Doppler scale factors of multiple symbols as a whole and focuses on the continuous variation overall trends, rather than the association between two adjacent symbols. The proposed method was demonstrated in a shallow water experiment conducted in November 2018 at Songhua River in Heilongjiang, China. Experimental data collected showed a bit error rate less than 10-4 with a data rate of 65.41 bps at a moving speed of 2.0-6.2 m/s over the horizontal range of 0.68-1.6 km.

Modeling and dynamic analysis of a mobile underwater turbine system for harvesting Marine Hydrokinetic Energy

We present the modeling and dynamic analysis of a Mobile Underwater Turbine System, a novel integration of Autonomous Underwater Vehicles and Hydrokinetic Turbines, for harvesting Marine Hydrokinetic Energy from the Gulf Stream. The Gulf Stream, an ocean current that flows off the coast of North Carolina, is a source of hydrokinetic energy. However, the meandering nature of the Gulf Stream makes it challenging to harvest the full energy potential of the stream using fixed turbine systems. One possible solution for increasing the amount of energy that can be extracted from the Gulf Stream involves using a mobile underwater energy harvester system that can follow the meandering stream so as to remain in regions of maximum energy potential. The framework for the conceptual design, and studies focusing on the feasibility of such a system, have been presented previously in (Divi, 2017). The focus of this paper is a mathematical model of the system which has been developed to analyze the dynamics of such a system, along with parametric studies utilizing this model to come up with a system with an optimized set of design parameters. A 6-DOF analytical model of the system is developed to gain an understanding of the system's dynamic behavior and stability. A bead-based tether model is further developed to analyze the behavior of the system when it is anchored and harvesting energy. A study regarding the effects of tether parameters such as the number of tether elements, the spring constant, and the damping coefficient of the tether on the tether behavior and computation time required for analysis, is put forth to help determine an optimal set of tether parameters. In addition, a set of system parameters such as turbine diameter, hull diameter, L/D ratio of the hull and ballast tank size, are analyzed to see how they affect the net energy produced and the maximum distance travelled by the system. Finally, three modes of power transfer to the shore are considered, and an optimization algorithm is presented and used to find the best set of parameters suited for maximum energy transfer for each mode.

Field testing of underwater acoustic communication using Doppler-resilient orthogonal signal division multiplexing in coastal area of Suruga Bay

Mobile underwater acoustic (UWA) communication is still challenging, since the mobile UWA channel is characterized by severe delay and Doppler spreads. In this paper, we describe a field test of Doppler-resilient orthogonal signal division multiplexing (D-OSDM)—a signal modulation technique designed to address delay and Doppler spreads efficiently. The experiment was performed in a coastal area of Suruga Bay, which has typical shallow-water sound speed profiles with delay and Doppler spreads of 5–25 ms and 1–8 Hz, respectively. The results indicated that UWA communication using D-OSDM is an effective communication tool that can provide reliable data transfer even in a mobile UWA channel with delay and Doppler spreads.

Enhancing coverage and connectivity using energy prediction method in underwater acoustic WSN

In a mobile underwater acoustic wireless sensor networks (MUAWSN), one of the most important challenging issues is coverage and connectivity during data transmission. It is very difficult to access and cover the monitoring region due to less coverage in underwater environments. Various algorithms, strategies and mechanisms have been proposed by researchers around the world to solve these problems. A new approach is implemented in mobile underwater acoustic wireless sensor networks to enhance maximum coverage and connectivity of the cluster networks. In our proposed work, random cluster deployment of sensors in MUAWSN is used. The coverage hole problem is realistic in the MUAWSN due to node damage or active node count goes below the threshold limit. An energy prediction algorithm is proposed using Markov Chain Monte Carlo (MCMC) process which enhances the maximum coverage and connectivity during data transmission by analyzing the sample value of known parameter in water surface. The topology gets altered due to water mobility caused by several factors such as waves, winds, currents and network coverage and connectivity performance. In addition, to improve hop-by-hop dynamic address based (HH-DAB) Routing Protocol predicting energy consumption is re-framed as modified hop-by-hop dynamic address based (modified HH-DAB) Routing Protocol in which the random mobility of the node get stretched in 2-D space which leads to maximum coverage and connectivity in 3-D. Theoretical analysis and experimental simulation results are evaluated based on performance metrics such as residual energy consumption (REC), packet delivery ratio (PDR), network coverage ratio (NCR) and Network Lifetime. The results shows that the proposed Modified HH-DAB system has maximum residual energy consumption of 14.28%, maximum increase in packet delivery ratio of 50%, maximum increase in network coverage ratio of 50% and maximum increase in network lifetime of 50%. The results are encouraging and our proposed method is found to be more efficient than the HH-DAB protocol. The proposed protocols of modified HH-DAB mechanism improves coverage, connectivity and network lifetime.

A Two-Stage Localization Scheme with Partition Handling for Data Tagging in Underwater Acoustic Sensor Networks.

Knowledge about the geographic coordinates of underwater sensor nodes is of primary importance for many applications and protocols of under water sensor networks (UWSNs) thus making localization of sensor nodes a crucial part of underwater network design. In case of mobile underwater sensor network, location estimation becomes challenging not only due to the need for periodic tracking of nodes, but also due to network partitioning caused by the pseudo-random mobility of nodes. Our proposed technique accomplishes the task of localization in two stages: (1) relative localization of sensor nodes with respect to a reference node at regular intervals during sensing operation. (2) Offline absolute localization of sensor nodes using absolute coordinates of the reference node and relative locations estimated during stage 1. As our protocol deals with mobile underwater sensor networks that may introduce network partitioning, we also propose a partition handling routine to deal with network partitions to achieve high localization coverage. The major design goal of our work is to maximize localization coverage while keeping communication overhead minimum, thus achieving better energy efficiency. Major contributions of this paper are: (1) Two energy efficient relative localization techniques, and (2) A partition handling strategy that ensures localization of partitioned nodes.

Learning Environmental Field Exploration with Computationally Constrained Underwater Robots: Gaussian Processes Meet Stochastic Optimal Control.

Autonomous exploration of environmental fields is one of the most promising tasks to be performed by fleets of mobile underwater robots. The goal is to maximize the information gain during the exploration process by integrating an information-metric into the path-planning and control step. Therefore, the system maintains an internal belief representation of the environmental field which incorporates previously collected measurements from the real field. In contrast to surface robots, mobile underwater systems are forced to run all computations on-board due to the limited communication bandwidth in underwater domains. Thus, reducing the computational cost of field exploration algorithms constitutes a key challenge for in-field implementations on micro underwater robot teams. In this work, we present a computationally efficient exploration algorithm which utilizes field belief models based on Gaussian Processes, such as Gaussian Markov random fields or Kalman regression, to enable field estimation with constant computational cost over time. We extend the belief models by the use of weighted shape functions to directly incorporate spatially continuous field observations. The developed belief models function as information-theoretic value functions to enable path planning through stochastic optimal control with path integrals. We demonstrate the efficiency of our exploration algorithm in a series of simulations including the case of a stationary spatio-temporal field.

A Dynamic Surface Gateway Placement Scheme for Mobile Underwater Networks.

Deployment of surface-level gateways holds potential as an effective method to alleviate high-propagation delays and high-error probability in an underwater wireless sensor network (UWSN). This promise comes from reducing distances to underwater nodes and using radio waves to forward information to a control station. In an UWSN, a dynamic energy efficient surface-level gateway deployment is required to cope with the mobility of underwater nodes while considering the remote and three-dimensional nature of marine space. In general, deployment problems are usually modeled as an optimization problem to satisfy multiple constraints given a set of parameters. One previously published static deployment optimization framework makes assumptions about network workload, routing, medium access control performance, and node mobility. However, in real underwater environments, all these parameters are dynamic. Therefore, the accuracy of performance estimates calculated through static UWSN deployment optimization framework tends to be limited by nature. This paper presents the Prediction-Assisted Dynamic Surface Gateway Placement (PADP) algorithm to maximize the coverage and minimize the average end-to-end delay of a mobile underwater sensor network over a specified period. PADP implements the Interacting Multiple Model (IMM) tracking scheme to predict the positions of sensor nodes. The deployment is determined based on both current and predicted positions of sensor nodes, which enables better coverage and shorter end-to-end delay. PADP uses a branch-and-cut approach to solve the optimization problem efficiently, and employs a disjoint-set data structure to ensure connectivity. Simulation results illustrate that PADP significantly outperforms a static gateway deployment scheme.

ProLo: Localization via Projection for Three-Dimensional Mobile Underwater Sensor Networks.

We study the problem of three-dimensional localization of the underwater mobile sensor networks using only range measurements without GPS devices. This problem is challenging because sensor nodes often drift with unknown water currents. Consequently, the moving direction and speed of a sensor node cannot be predicted. Moreover, the motion devices of the sensor nodes are not accurate in underwater environments. Therefore, we propose an adaptive localization scheme, ProLo, taking these uncertainties into consideration. This scheme applies the rigidity theory and maintains a virtual rigid structure through projection. We have proved the correctness of this three-dimensional localization scheme and also validated it using simulation. The results demonstrate that ProLo is promising for real mobile underwater sensor networks with various noises and errors.