An Overview of Next-Generation Underwater Target Detection and Tracking: An Integrated Underwater Architecture <s> C. GLIDERS <s> Wireless sensor networks (WSNs) research has pre-dominantly assumed the use of a portable and limited energy source, viz. batteries, to power sensors. Without energy, a sensor is essentially useless and cannot contribute to the utility of the network as a whole. Consequently, substantial research efforts have been spent on designing energy-efficient networking protocols to maximize the lifetime of WSNs. However, there are emerging WSN applications where sensors are required to operate for much longer durations (like years or even decades) after they are deployed. Examples include in-situ environmental/habitat monitoring and structural health monitoring of critical infrastructures and buildings, where batteries are hard (or impossible) to replace/recharge. Lately, an alternative to powering WSNs is being actively studied, which is to convert the ambient energy from the environment into electricity to power the sensor nodes. While renewable energy technology is not new (e.g., solar and wind) the systems in use are far too large for WSNs. Those small enough for use in wireless sensors are most likely able to provide only enough energy to power sensors sporadically and not continuously. Sensor nodes need to exploit the sporadic availability of energy to quickly sense and transmit the data. This paper surveys related research and discusses the challenges of designing networking protocols for such WSNs powered by ambient energy harvesting. <s> BIB001 </s> An Overview of Next-Generation Underwater Target Detection and Tracking: An Integrated Underwater Architecture <s> C. GLIDERS <s> Using traditional sonar arrays may be difficult and impractical in some mission-critical scenarios, because they should be mounted on or towed by a ship or a submersible. Alternatively, underwater acoustic sensor networks (UW-ASNs) offer a promising solution approach. In this paper, a target-tracking algorithm for UW-ASNs, i.e., 3-D underwater target tracking (3DUT), is presented. The objective of 3DUT is to collaboratively accomplish accurate tracking of underwater targets with minimum energy expenditure. Based on the time of arrival of the echoes from the target after transmitting acoustic pulses from the sensors, the ranges of the nodes to the target are determined, and trilateration is used to obtain the location of the target. The location and the calculated velocity of the target are then exploited to achieve tracking. To realize energy-effective target tracking, 3DUT incorporates a new target-movement-based duty-cycle mechanism. To avoid rapid depletion of the energy resources of boundary nodes due to continuous surveillance, 3DUT employs an adaptive procedure to find, designate, and activate new boundary nodes. Performance evaluation shows that 3DUT is a promising alternative to the traditional sonar-based target-tracking approaches, particularly for on-demand surveillance applications. <s> BIB002 </s> An Overview of Next-Generation Underwater Target Detection and Tracking: An Integrated Underwater Architecture <s> C. GLIDERS <s> The recently developed wave glider has the potential to be an effective unmanned platform for acoustic applications. We present the results of a variety of experiments that quantify this potential. The radiated self-noise of the autonomous platform is evaluated using an integrated passive acoustic recorder during a set of field trials off the coast of Hawaii. We present the radiated noise spectra from these trials to illustrate the dependence on hydrophone location and sea state. Using the same instrumentation, we demonstrate the ability of a modified wave glider to detect marine mammals using passive acoustic monitoring techniques. We also evaluate the performance of the wave glider operating as an active acoustic gateway, highlighting the potential of this platform to serve as a navigation reference and communications relay for scientific, industrial, and military subsea assets. To demonstrate the potential of the wave glider platform to support acoustic navigation, we assess the performance of time-of-flight range estimation and seafloor transponder localization. These tests were performed using commercial off-the-shelf acoustic positioning hardware integrated with the wave glider to illustrate that the low self-noise of the wave glider makes it possible to achieve acoustic positioning performance similar to previously reported results. Finally, we show that the glider can operate as a station-keeping surface communications gateway and provide recommendations for its use. © 2012 Wiley Periodicals, Inc. © 2012 Wiley Periodicals, Inc. <s> BIB003 </s> An Overview of Next-Generation Underwater Target Detection and Tracking: An Integrated Underwater Architecture <s> C. GLIDERS <s> This paper presents an optimal and efficient path planner using adaptive B-spline approximation mechanism for Autonomous Underwater Vehicles (AUVs) operating in turbulent, cluttered and uncertain environments. The proposed method recursively inserts midpoint knots until an approximated B-Spline curve that satisfies the accuracy criteria is achieved. The method is able to adapt the quantity of internal knots inserted based on the specific needs of each path to conform to its respective desired smooth path and satisfy the accuracy criteria. Consequently, this method effectively minimizes the number of internal knots for any given trajectory, thus effectively improving the computation efficiency of the path fitness evaluation and hence path planning. The proposed method is integrated with a Genetic Algorithm (GA) based path planner and tested to generate an optimal trajectory for an AUV travelling through a turbulent ocean field in scenarios with uncertainty in position estimates. Simulation results show that the resulting approach is able to quickly and effectively guide the AUV to its destination with significant savings in computation time compared with B-Spline based planners with fixed numbers of internal nodes. <s> BIB004 </s> An Overview of Next-Generation Underwater Target Detection and Tracking: An Integrated Underwater Architecture <s> C. GLIDERS <s> Approximately 71% of the Earth's surface is covered by ocean, a continuous body of water that is customarily divided into several principal oceans and smaller seas. Ocean temperatures determine climate and wind patterns that affect life on land. Freshwater in lakes and rivers covers less than 1%. Its contamination seriously damages ecosystems. The Internet of Underwater Things (IoUT) is defined as a world-wide network of smart interconnected underwater objects that enables to monitor vast unexplored water areas. The purpose of this paper is to analyze how to benefit from the IoUT to learn from, exploit and preserve the natural underwater resources. In this paper, the IoUT is introduced and its main differences with respect to the Internet of Things (IoT) are outlined. Furthermore, the proposed IoUT architecture is described. Important application scenarios that illustrate the interaction of IoUT components have been proposed. Critical challenges have been identified and addressed. <s> BIB005 </s> An Overview of Next-Generation Underwater Target Detection and Tracking: An Integrated Underwater Architecture <s> C. GLIDERS <s> Underwater Wireless Sensor Networks (UWSNs) are considered as tangible, low cost solution for underwater surveillance and exploration. Existing acoustic wave-based UWSN systems fail to meet the growing demand for fast data rates required in military operations, oil/gas exploration, and oceanographic data collection. Electromagnetic (EM) wave-based communication systems, on the other hand, have great potential for providing high speed data rates in such scenarios. This paper will discuss the challenges faced in the utilization of EM waves for the design of tactical underwater surveillance systems and evaluate several EM wave-based three-dimensional (3D) UWSN architectures differing in topologies and/or operation principles on the performance of localization and target tracking. To the best of our knowledge, this is the first of its kind in the field of underwater communications where underwater surveillance techniques for EM wave-based high speed UWSNs have been investigated. Thus, this will be a major step towards achieving future high speed UWSNs. <s> BIB006 </s> An Overview of Next-Generation Underwater Target Detection and Tracking: An Integrated Underwater Architecture <s> C. GLIDERS <s> The underwater glider changes its direction to follow the preset path in the horizontal plane only by flapping its vertical rudder. Heading tracking control plays the core role in the navigation process. To deal with non-linear flow disturbance and saturation in actuator, a new hybrid heading tracking control algorithm was presented, which integrated an adaptive fuzzy incremental PID (AFIPID) and an anti-windup (AW) compensator to improve the adaptability and robustness of underwater glider's heading control. The dynamic model of an underwater glider named as Petrel-II 200 was modeled to serve as a controlled plant. The proposed heading tracking control algorithm was described in detail, where the rudder angle, a control quantum to the controlled plant were calculated to get forces and moments required for the desired glider heading. A closed loop motion control system with desired heading angle as input and actual heading angle output was put forward, which included the dynamic model of the Petrel-II 200 and the given heading tracking control algorithm. The simulations followed three typical mathematical signals and the experimental tests were carried out by taking in the dynamic parameters of the controlled plant. And the effectiveness of the proposed control algorithm was assessed and verified. <s> BIB007 </s> An Overview of Next-Generation Underwater Target Detection and Tracking: An Integrated Underwater Architecture <s> C. GLIDERS <s> Target tracking is an important application of underwater wireless sensor networks (UWSNs). Due to the energy constraint and energy imbalanced dissipation of underwater nodes, it is a challenge to maximize the energy efficiency and balance energy consumption simultaneously. In this paper, we propose an adaptive sampling algorithm for target tracking in UWSNs to address this issue. First, for maximizing the energy efficiency, we design an adaptive sampling interval adjustment (ASIA) method using a two-input-single-output fuzzy logic controller. In this method, the sampling interval is adaptively adjusted to make the actually uncertainty equal to the uncertainty threshold, which minimizes the sampling frequency and then reduces the energy consumption of information exchange. Second, for balancing the energy consumption, we develop a dynamic uncertainty threshold adjustment (DUTA) method using a single-input-single-output fuzzy logic controller. According to the residual energy of network nodes, the DUTA method dynamically adjusts the uncertainty threshold in the ASIA method, which changes the sampling frequency for avoiding premature death of nodes. Finally, the simulations show that, compared to the existing adaptive sampling algorithm, the proposed algorithm not only saves about 36% of energy but also alleviates the imbalance of energy consumption in different parts of the tracking area. <s> BIB008 </s> An Overview of Next-Generation Underwater Target Detection and Tracking: An Integrated Underwater Architecture <s> C. GLIDERS <s> Today, underwater target tracking using underwater wireless sensor networks (UWSNs) is an essential part in many military and non-military applications. Most of moving target tracking studies in UWSNs are considered in two-dimensional space. However, most practical applications require to be implemented in three-dimensional space. In this paper an adaptive method based on Kalman filter for moving target tracking in three dimensional space using UWSNs is proposed. Since, energy protection is a vital task in UWSNs; the proposed method reduces the energy consumption of the entire network by a sleep/wake plan. In this plan only 60% of the closer nodes along the path of the moving target will be waked up using a sink activation message and participate in the tracking, while the other nodes remain in sleep state. At each stage of tracking, the location of the target is estimated using a 3D underwater target tracking algorithm with the trilateration method. Subsequently, the estimations and target tracking results are inserted into the Kalman filter as measuring model to produce the final result. Performance evaluation and simulations results indicated that the proposed method improves the average location error by 45%, average estimated velocity by 86%, and average energy consumption by 33% in comparison to the trilateration method. However, computation time is increased as a result of improving tracking accuracy; and tracking accuracy is lost about 20% due to saving energy. It was shown that the proposed method has been able to adaptively achieve a trade-off between tracking accuracy and energy consumption based on real-time user requirements. Such adaption can be controlled trough the sink node based on real-time requirements. <s> BIB009 </s> An Overview of Next-Generation Underwater Target Detection and Tracking: An Integrated Underwater Architecture <s> C. GLIDERS <s> Aiming at addressing the problem caused by multipath effects in direction of arrival (DOA) estimation for underwater targets, a method based on the active detection on virtual time reversal (ADVTR) Capon algorithm is proposed. Unlike the conventional passive target estimation method ignoring the multipath effects but only considering the direct wave, the proposed method is closer to the actual situation in that the multipath signal propagation model is fully taken into account; in addition, active detection (AD) and virtual time reversal (VTR) processes are added, which use active detection to estimate channels, and virtual time reversal to realize focusing in a computer after the source-receive array (SRA) receives the reflected signal of the target. The combination of the two methods can greatly improve the energy of SRA and the precision of target direction estimation. With the popular acoustic field simulation tool Bellhop, the model proposed in this paper is verified. Compared with the conventional Capon method without time reversal, the simulation results show that the ADVTR Capon estimation method is far better, in terms of resolution and suppressing the sidelobes. It is suitable for the target DOA estimation under low signal-to-noise ratio (SNR) conditions. Further, we also show the ADVTR Capon estimation method works well in a real tank experiment. <s> BIB010 </s> An Overview of Next-Generation Underwater Target Detection and Tracking: An Integrated Underwater Architecture <s> C. GLIDERS <s> Advances in acoustic technology and instrumentation now make it possible to explore marine resources. As a significant component of ocean exploration, underwater acoustic target tracking has aroused wide attention both in military and civil fields. Due to the complexity of the marine environment, numerous techniques have been proposed to obtain better tracking performance. In this paper, we survey over 100 papers ranging from innovative papers to the state-of-the-art in this field to present underwater tracking technologies. Not only the related knowledge of acoustic tracking instrument and tracking progress is clarified in detail, but also a novel taxonomy method is proposed. In this paper, algorithms for underwater acoustic target tracking are classified based on the methods used as: (1) instrument-assisted methods; (2) mode-based methods; (3) tracking optimization methods. These algorithms are compared and analyzed in the aspect of dimensions, numbers, and maneuvering of the tracking target, which is different from other survey papers. Meanwhile, challenges, countermeasures, and lessons learned are illustrated in this paper. <s> BIB011
Gliders have the capability to stay in the ocean for long periods with less energy consumption as compared to other two UUVs. Gliders have undulating trajectory as they propel through water using a buoyancy engine. They are not as fast as other UUVs therefore are difficult to control due to lack of power force systems. A recently developed wave glider BIB003 has the potential to become an important part of acoustic applications as it is mobile and could coordinate with the other ocean devices accordingly. Also, it could reduce energy costs for long durable missions. A novel hybrid heading tracking control algorithm to advance the flexibility and robustness of heading control of underwater glider is presented in BIB007 . Heading tracking control considers all the present and future information about the target area by reflecting the planned behavior during a mission BIB004 . Peter-II 200 was used to model the controller and an adaptive fuzzy incremental PID (AFIPID) along with an antiwindup (AW) compensator was considered in this algorithm. The results showed that with AFIPID and AW compensator, desired heading can be maintained even in harsh underwater environment. Due to the self-adaptation of parameters controlled by AFI system, the cost for testing underwater glider in the ocean can be reduced. A summary of all the schemes described in this section is given in Table 2 . In a nutshell, due to autonomy and the active power propelled system of AUVs, they are the best suited UUVs for underwater target tracking (see Table 1 ). AUVs are used to classify targets (either hidden in the depths, rocks or locate at the sea surface) due to having capability of reaching the depths of the oceans. But AUVs have the battery charging issues, which need to be considered while proposing a novel next-generation target detection and tracking scheme. Also, energy consumption is a critical issue in underwater sensor networks; therefore, integration of different novel technologies is required to solve this issue for oceanic environment. Here, we briefly discuss the existing solutions in literature for the issues of underwater energy consumption. Ambient energy harvesting joined with supercapacitors is an up-and-coming technology to remove the necessity of using batteries and entrust only harvested energy for operational purposes BIB001 . Solar energy is the promising energy harvesting technique for terrestrial networks. It can be employed in IoUT with solar-powered AUVs. Solar-powered AUVs need to operate on the sea surface for battery charging via solar energy input. Other energy harvesting techniques for IoUT can be piezoelectric energy harvesting and ocean thermal energy BIB005 . Energy consumption is a critical issue in target tracking that can be resolved by implementing energy-efficient algorithms for target tracking. An adaptive sampling algorithm for target tracking is proposed in BIB008 that considers two-input-single-output fuzzy logic controller. The algorithm maximizes the energy efficiency by designing an adaptive sampling interval adjustment (ASIA) method and balances the energy consumption by developing a dynamic uncertainty threshold adjustment (DUTA) method. The authors prove 36% of energy saving in different tracking areas through simulation results. A 3D underwater target tracking (3DUT) algorithm BIB002 is proposed to minimize energy consumption by incorporating a target-movement-based duty-cycle mechanism. The approach is an efficient alternate for sonar-based target tracking algorithms. Another adaptive method based on Kalman filter to minimize energy consumption in 3D underwater environment for target tracking is proposed in BIB009 . The method uses sleep/wake plan to track the mobile target with the trilateration method. The results show reduction in energy consumption by 33% and improvement in location error by 45%. An active detection on virtual time reversal (ADVTR) method is proposed in BIB010 to consider AD for channel estimation and VTR for focusing when the source-receive array (SRA) receives the reflected signal of target. Bellhop simulator was used to verify improvement in the energy of SRA and accuracy of estimating target. All these energy-efficient protocols have been proposed with some specific designed purposes to show improvement in the overall system. None of the schemes discussed above have been considered all the aspect of target detection and tracking algorithms. The target tracking using underwater sensor networks has been gaining great attention due to low cost, medium level precision and complexity, rapid deployment, self-organized nature, real-time monitoring, and wide-range distribution BIB006 , BIB011 . Therefore, we consider underwater sensor networks as a viable solution in the nextgeneration target detection and tracking integrated scheme. The integration helps resolving different issues that will be explained in Section IV.