Underwater Positioning System Research Articles

An identification method of LBL underwater positioning systematic error with optimal selection criterion

Unlike the space targets such as satellites whose observation distance is about the order of 100 km, the measurement distance of long baseline (LBL) underwater positioning system is much shorter. If the noncoincidence between the multiple beacons and the target center is not considered, this systematic error will cause a little larger positioning error. Therefore, aiming at the situation that multiple beacons are installed outside the target and the distance between the beacons and the target center is significant, a multi-beacon positioning model of the LBL underwater system is constructed in this paper. Furthermore, for the sound speed systematic error and the time of arrival (TOA) systematic error in the multi-beacon LBL system positioning measurement data, three identification models of systematic error are constructed. According to the positioning process of the LBL underwater system, the expression of the optimal test statistic D is derived based on the TOA residual. Finally, the optimal selection criterion is given, and the underwater target position and systematic error can be accurately estimated. Both of the numerical simulation and the underwater positioning test show that the appropriate identification model of systematic error in the measurement data can be selected according to the optimal selection criterion, and the underwater target positioning accuracy of the LBL system can be improved.

Voronoi Diagram-based USBL Outlier Rejection for AUV Localization

USBL systems are essential for providing accurate positions of autonomous underwater vehicles (AUVs). On the other hand, the accuracy can be degraded by outliers because of the environmental conditions. A failure to address these outliers can significantly impact the reliability of underwater localization and navigation systems. This paper proposes a novel outlier rejection algorithm for AUV localization using Voronoi diagrams and query point calculation. The Voronoi diagram divides data space into Voronoi cells that center on ultra-short baseline (USBL) data, and the calculated query point determines if the corresponding USBL data is an inlier. This study conducted experiments acquiring GPS and USBL data simultaneously and optimized the algorithm empirically based on the acquired data. In addition, the proposed method was applied to a sensor fusion algorithm to verify its effectiveness, resulting in improved pose estimations. The proposed method can be applied to various sensor fusion algorithms as a preprocess and could be used for outlier rejection for other 2D-based location sensors.

A hovering micro autonomous underwater vehicle with integrated control and positioning system

Autonomous underwater vehicle (AUV) is currently the mainstream equipment for ocean exploration due to its long endurance and large operating range. However, the torpedo profile of traditional AUVs limits their maneuverability and hovering capabilities. This hinders the application and popularity of AUVs in near-seabed operations and accurate detection in small areas. This paper presents a novel disc-shaped micro AUV characterized by using a multi-core heterogeneous architecture to integrate control and positioning systems to obtain a lightweight design with complete functionality. Through the special structure and adaptive sliding mode controller, it can achieve high maneuvering navigation and stable hovering under different working conditions. A passive inverted ultra-short baseline (piUSBL) underwater positioning system is developed to provide accurate and instantaneous underwater position at low cost and power consumption. Field experiments, including special circular cruising and acoustic docking, were conducted in an open-water environment. The experimental results show that this vehicle has a depth control accuracy of 5 cm and a heading control accuracy of 3°, which well proves that this prototype can carry out accurate detection in a small range. In addition, this vehicle has a diameter of only 42 cm, a height of 23 cm, and a weight of 14 kg, making it easy to deploy and recover. To the best of our knowledge, this is the first AUV to be successfully tested in the field using a multi-core heterogeneous architecture with such small size and light weight.

FPGA-Based Real-Time Synchronous Parallel System for Underwater Acoustic Positioning and Navigation

With the development of autonomous underwater vehicles, the research of underwater acoustic positioning and navigation technology is becoming increasingly important. However, most underwater positioning systems use the traditional acoustic response synchronization method, which leads to insufficient positioning real-time performance and refresh rate. To solve this problem, this paper proposes a real-time global synchronization mechanism with high-precision atomic clocks, which can realize one positioning through one-way propagation, so that the positioning efficiency is at least doubled. To further improve the positioning accuracy, an M-sequence-based phase offset modulation method is proposed to facilitate beacon identification. Consequently, a normalized signal matching capture algorithm against Doppler effect is designed, and the positioning solution is fused with the real-time sound ray bending compensation mechanism. Based on the above content, we developed an FPGA-based real-time synchronous parallel underwater positioning and navigation (RSPUPN) system, which uses FPGA+MCU architecture to accelerate signal processing operations in a low-power and parallel way. The test results in the South China Sea show that the operating range of the system can reach 8 km, the positioning refresh rate can reach 0.2 Hz, and the relative average position error is 0.25%, confirming the effectiveness of the designed system in industrial applications.

Deployment Strategy Analysis for Underwater Geodetic Networks

Seafloor geodetic network (SGN) is the foundation for building an underwater positioning, navigation and timing (PNT) system. Traditional network deployment mainly focuses on the deployment of underwater sensor network nodes. However, for SGN, there is no surface buoy node and submarine buoy node, and the number of anchors is limited because it is quite expensive to fully cover large scale areas. To achieve wide coverage and good positioning service of each set of underwater base stations, we focus on the network design of a single set of reference stations in this paper. We propose several deployment plans for a local SGN and then analyze their service quality indicators by considering the stratification effect caused by non-uniformly distributed sound speed. To evaluate the performance of each topology of SGN, we compare their coverage range, horizontal dilution precision (HDOP) and accuracy performance of positioning tests. Based on the overall performance in our simulation, we believe that the star five-node topology is a good topology design under sufficient economic conditions.

Long-range and high-precision localization method for underwater bionic positioning system based on joint active–passive electrolocation

Active electrolocation organ of weakly electric fish act as a proximity detection system with high accuracy in recognizing object parameters such as size and shape. In contrast, some fish with passive electrolocation organ are able to detect objects at a greater range. This paper proposes a joint active–passive electrolocation algorithm for long-range and high-precision underwater localization, inspired by the active and passive electroreceptive organs of fish. The study begins by designing a large experimental platform for the underwater localization system to investigate the response of underwater objects to active and passive electric fields. Based on the response, the paper proposes separate underwater active and passive electrolocation algorithms, which are then combined to form a joint algorithm. Experimental results demonstrate that the proposed algorithm achieves high localization accuracy and long detection distance. The joint active–passive electrolocation algorithm has potential applications in submarine resource exploration, underwater robotics, and maritime military projects, while also providing new ideas for future research on long-range underwater object detection and identification based on electrolocation.

Underwater Positioning Analysis and System Establishment of the Towed Underwater Hydrophone Array System

The aim of this study is to establish an underwater towed hydrophone array detection and positioning system, which serves as a rescue device for detecting flight recorders in the event of a maritime accident. By using Time Difference of Arrival (TDOA) to calculate the azimuth of the underwater locator beacon (ULB) which is located inside the black box, the position of the flight recorder can be obtained. The underwater towed hydrophone array detection and positioning system was tested for a three-day experiment in the waters off the southwest coast of Taiwan. The azimuth of the sound source was determined by using two frequencies generated by different types of underwater locator beacons (37.5 kHz and 8.8 kHz) and post-processing. The accuracy of the positioning was achieved by controlling the depth of the underwater hydrophone array. This study can deduce the location of the underwater locator beacon through subsequent positioning analysis, which can be used by search and rescue teams in the future to improve the efficiency of the rescue process.

An Average Speed of Sound Method for Underwater Positioning Based on Time of Arrival

This article uses the distance and sound spread time of each monitoring base station in the underwater positioning system, calculates the effective sound speed of the sound wave to the base station, and proposes a TOA underwater positioning method based on the average speed. The influence of small underwater sound changes the system positioning accuracy, reducing system positioning errors. Simulation experiments show that compared with the traditional fixed sound velocity method, this method has higher positioning accuracy and lower error. The positioning effect in a long baseline underwater positioning system is less dependent on the number of monitoring base stations. The cumulative probability of positioning error within 5 m can reach 70%, and the cumulative probability of error within 10 m can reach over 95%.

Underwater Localization of AUVs in Motion Using Two-Way Travel Time Measurements With Unknown Sound Velocity

For an autonomous underwater vehicle (AUV) underwater localization system based on acoustic two-way travel time measurements, the motion of the AUV during the interrogation-reception time interval, unknown underwater sound velocity, and beacon calibration error affect the performance of the positioning solution. Ignoring these factors significantly deteriorates the performance of the localization system. This paper focuses on the localization problem of AUV in motion with an unknown sound velocity and beacon calibration error. The Cramér–Rao lower bound of the concerned localization problem is first derived as the performance bound of an unbiased estimator. Next, through multi-stage processing, we design a closed-form solution that can attain the corresponding performance bound under small measurement noise conditions. Furthermore, considering that the AUV motion velocity is typically much lower than the sound velocity in practical applications, a simpler and more efficient simplified closed-form solution is proposed, which can guarantee localization performance under the condition that the AUV motion speed is low, as well as small measurement noise. Finally, the theoretical performance and superiority of the proposed solutions were verified through numerical simulation.

Investigating the reliable acoustic path properties in a global scale

Leveraging the benefits of low transmission loss and high signal-to-noise ratio, the reliable acoustic path (RAP) has been extensively employed in various underwater applications. In this study, we investigate RAP properties on a global scale. Acoustic simulations were conducted using global grids with a 0.25° × 0.25° spatial resolution, revealing that RAP range is positively correlated with ocean depth. Contrary to the prevailing belief that RAP properties are relatively unaffected by sound speed variations, our findings indicate that sound speed profiles (SSPs) play a crucial role in determining RAP properties by altering the RAP from 15 km to 50 km at a constant ocean depth of 4000 m. Additionally, the receiver angle can vary by nearly 5 km at the same source location due to SSP variations. Consequently, utilizing highly accurate SSPs can enhance the performance of underwater localization or communication systems that rely on RAP.

수중시공현장 적용을 위한 위치 획득 신호 주기와 인식 방법에 관한 연구

With the increase in the research on marine IoT in recent years, the demand for enhanced mission performance in marine construction and civil engineering is increasing. Accordingly, various equipment have been introduced in the field. However, recognizing the location of the equipment is difficult because of the underwater environmental characteristics (e.g., radiated noise and turbidity). As a result, studies have been conducted on underwater positioning methods that combine technologies such as GPS (Global Positioning System)and IMU (Inertial Measurement Unit).However, the problem of intermittent disconnection persists due to radiated noise and turbidity generated in offshore construction environments. To solve this problem, we proposed the method of using a KF(Kalman Filter) in underwater construction environments. To verify the proposed method, we conducted an experiment on land at the speed used in offshore construction. In the experiment, the signal acquisition cycle was varied, and the usable cycle in the field was checked. The experimental results demonstrated the applicability of the proposed underwater positioning system.

Underwater Positioning System Based on Drifting Buoys and Acoustic Modems

GNSS (Global Navigation Satellite System) positioning is not available underwater due to the very short range of electromagnetic waves in the sea water medium. In this article a LBL (Long Base Line) acoustic repeater system of the GNSS positioning is presented. The system is hyperbolic, i.e., based on time differences and it does not need very accurate atomic clocks to synchronize repeaters. The system architecture and system calculations that demonstrate the feasibility of the solution are presented. The system uses four buoys that sequentially transmit their position and the time of the instant of transmission, for which they are equipped with GNSS receivers and acoustic modems. The buoys can be fixed or even drifting, but they are inexpensive devices, which pose no hazard to navigation and can be easily and quickly deployed for a specific underwater mission. The multilateration algorithm used in the receiver is presented. To simplify the algorithm, the depth of the receiver, measured by a depth sensor, is used. Results are presented for the position error of an underwater vehicle due to its displacement during the transmission frame of the four buoys.

Performance Comparison of ToA and TDOA Based Tracking In Underwater Multipath Environments Using Bernoulli Filter

Abstract Underwater localization and tracking is a challenging problem and Time-of-Arrival and Time-Difference-of-Arrival approaches are commonly used. However, the performance difference between these approaches is not well understood or analysed adequately. There are some analytical studies for terrestrial applications with the assumption that the signal arrival times are not correlated. However, this assumption is not valid for underwater propagation. To present the distinct nature of the problem under the water, a high-fidelity simulation is required. In this study, Time-of-Arrival and Time-Difference-of-Arrival approaches are compared using a ray tracing based propagation model. Moreover, basic methods to mitigate the multipath propagation problem are also implemented for Bernoulli filters. Since the Bernoulli filter is a joint detection and tracking filter, the detection performance is also analysed. Comparisons are done for all combinations of filter and measurement approaches. The results can help to design underwater localization systems better suited to the needs.

Reinforcement Learning for Autonomous Underwater Vehicles via Data-Informed Domain Randomization

Autonomous Underwater Vehicles (AUVs) or underwater vehicle-manipulator systems often have large model uncertainties from degenerated or damaged thrusters, varying payloads, disturbances from currents, etc. Other constraints, such as input dead zones and saturations, make the feedback controllers difficult to tune online. Model-free Reinforcement Learning (RL) has been applied to control AUVs, but most results were validated through numerical simulations. The trained controllers often perform unsatisfactorily on real AUVs; this is because the distributions of the AUV dynamics in numerical simulations and those of real AUVs are mismatched. This paper presents a model-free RL via Data-informed Domain Randomization (DDR) for controlling AUVs, where the mismatches between the trajectory data from numerical simulations and the real AUV were minimized by adjusting the parameters in the simulated AUVs. The DDR strategy extends the existing adaptive domain randomization technique by aggregating an input network to learn mappings between control signals across domains, enabling the controller to adapt to sudden changes in dynamics. The proposed RL via DDR was tested on the problems of AUV pose regulation through extensive numerical simulations and experiments in a lab tank with an underwater positioning system. These results have demonstrated the effectiveness of RL-DDR for transferring trained controllers to AUVs with different dynamics.

Survey on Low-Cost Underwater Sensor Networks: From Niche Applications to Everyday Use

Traditionally, underwater acoustic modems and positioning systems were developed for military and Oil & Gas industries, that require deep water deployments and extremely reliable systems, focusing on high power expensive systems and leaving the use of low-cost devices only attractive for academic studies. Conversely, recent developments of low-cost unmanned vehicles, such as remotely operated vehicles (ROVs) and autonomous underwater vehicles (AUVs), suitable for shallow water coastal missions, and the need of sensors network deployments for measuring water quality and studying the effect of climate change in coastal areas, called to the need of low-cost and low-power acoustic modems and positioning systems that are gaining more and more momentum to date. The use of these devices can enable a wide set of applications, often based on low-cost AUV swarm formations, where an acoustic link between the vehicles is required to coordinate the mission, perform the maneuvers, and maintain the formation along the time. Moreover, they can make environmental wireless sensor deployment cost effective by substituting wired systems. Underwater positioning systems, usually used in large-scale operations, can be finally applied to small-scale application thanks to the reduction in costs, at the price of a lower transmission and positioning range and precision. While in open-sea application this performance reduction is a huge limitation, in river, lagoon, port and lake deployments this is not an issue, given that the extremely shallow water and the presence of many obstacles would deteriorate the acoustic signal anyway, not allowing long range transmissions even with expensive and sophisticated acoustic devices. In this paper, we review the recent developments of low-cost and low-power acoustic communication and positioning systems, both analyzing University prototypes and new commercial devices available in the market, identifying advantages and limitations of these devices, and we describe potential new applications that can be enabled by these systems.

A Wireless Autonomous Real-Time Underwater Acoustic Positioning System.

Recent acoustic telemetry positioning systems are able to reconstruct the positions and trajectories of organisms at a scale of a few centimeters to a few meters. However, they present several logistical constraints including receiver maintenance, calibration procedures and limited access to real-time data. We present here a novel, easy-to-deploy, energy self-sufficient underwater positioning system based on the time difference of arrival (TDOA) algorithm and the Global System for Mobile (GSM) communication technology, capable of locating tagged marine organisms in real time. We provide an illustration of the application of this system with empirical examples using continuous and coded tags in fish and benthic invertebrates. In situ experimental tests of the operational system demonstrated similar performances to currently available acoustic positioning systems, with a global positioning error of 7.13 ± 5.80 m (mean ± SD) and one-third of the pings can be localized within 278 m of the farthest buoy. Despite some required improvements, this prototype is designed to be autonomous and can be deployed from the surface in various environments (rivers, lakes, and oceans). It was proven to be useful to monitor a wide variety of species (benthic and pelagic) in real time. Its real-time property can be used to rapidly detect system failure, optimize deployment design, or for ecological or conservation applications.

Quantitative Non-Destructive Testing (NDT) of Submerged Civil Concrete Structures Using Remotely Operated Robotic Drones

Periodic inspection is of paramount importance to assess structural integrity and safety. Conventional concrete inspection procedures ranging from rebound hammer, to state-of-the-art ground penetrating radar and ultrasonic tomography focus on superstructures. Often, the part of the structure underwater, is subject to significant levels of corrosion. Today, qualitative visual inspection of the submerged surface can be performed by diving teams, wherein internal defects often go undetected. Furthermore, divers are limited to shallow depths and face several risks, especially when visibility is poor and operating in confined spaces. Presently, there are few commercially available quantitative NDT techniques for submerged structures. This paper presents an alternate solution to inspection of submerged concrete structures — using lightweight remotely operated vehicles (ROV) manufactured by Planys Technologies to perform concrete NDT underwater. Rebound hammer and ultrasonic pulse velocity techniques, although elementary, have been redesigned for use on a submersible drone. Several challenges were addressed including long-range communication and data acquisition, marinizing transducers and pulser-receivers, obtaining measurements in water currents and over deformed surfaces. Planys’ ROVs carry payloads including high-definition cameras, lasers, sonar, and underwater positioning systems to improve data-acquisition quality and location tagging of defects. Key results from experimental studies in a laboratory on canonical specimens are presented. Furthermore, the technology has been successfully tested in a port — details of the structure, operational arrangement and sample results from the field trial are also presented. Following calibration procedures, ROV based underwater concrete NDT was used to acquire data from the structure in grids and subsequently, identify zones of potential non-homogeneity. Numerous challenges, including interpretation of the time traces obtained, and correlation of results to structural integrity and to structures above water, are discussed in the paper. This work will be of interest to asset owners in marine, water management and power generation industries.

An Underwater Positioning System for UUVs Based on LiDAR Camera and Inertial Measurement Unit.

Underwater positioning presents a challenging issue, because of the rapid attenuation of electronic magnetic waves, the disturbances and uncertainties in the environment. Conventional methods usually employed acoustic devices to localize Unmanned Underwater Vehicles (UUVs), which suffer from a slow refresh rate, low resolution, and are susceptible to the environmental noise. In addition, the complex terrain can also degrade the accuracy of the acoustic navigation systems. The applications of underwater positioning methods based on visual sensors are prevented by difficulties of acquiring the depth maps due to the sparse features, the changing illumination condition, and the scattering phenomenon. In the paper, a novel visual-based underwater positioning system is proposed based on a Light Detection and Ranging (LiDAR) camera and an inertial measurement unit. The LiDAR camera, benefiting from the laser scanning techniques, could simultaneously generate the associated depth maps. The inertial sensor would offer information about its altitudes. Through the fusion of the data from multiple sensors, the positions of the UUVs can be predicted. After that, the Bundle Adjustment (BA) method is used to recalculate the rotation matrix and the translation vector to improve the accuracy. The experiments are carried out in a tank to illustrate the effects and accuracy of the investigated method, in which the ultra-wideband (UWB) positioning system is used to provide reference trajectories. It is concluded that the developed positioning system is able to estimate the trajectory of UUVs accurately, whilst being stable and robust.

Research on Towed Linear Array Shape Measurement Method Based on Biorthogonal Signal

Systematic error and random error are main factors affecting the positioning of biorthogonal signal underwater positioning system. Based on the operation theory of USBL, this paper quantitatively analyzes a theoretical analysis and simulation calculations on influence of different error sources on the positioning accuracy and qualitatively analyzes the effectiveness of the towed linear array shape measurement method based on biorthogonal signal through practical experiments. By comparing the measurement effect after correction by using the measurement array with the measurement effect based on the linear array, the effectiveness of the method is verified.

Adaptive location correction and path re-planning based on error estimation method in underwater sensor networks

Due to the accuracy limitation of the underwater positioning system and the interference of the external environment, the actual trajectory of the autonomous underwater vehicle (AUV) will deviate from the predetermined path during the underwater mission, which cannot guarantee the mission completion and safety. To reduce navigation errors, this paper introduces forward-looking sonar (FLS) and proposes a path correction scheme based on error estimation of underwater sensor networks: Derive the position and attitude of the AUV by processing FLS images to obtain the relative orientation between the robot and the target; combine the node information in the time-varying navigation map to calculate the error with the planned path; then fused with the a priori error of the underwater sensor network to build the error system model; completion of path re-planning based on the improved Bionic Neural Wave Network (BNWN) algorithm and time-varying navigation map; adjust the weight parameters during the iteration to make the drift error converge and finally complete the correction of the path. Simulation experiments prove that the path planned in this scheme can neutralize the drift errors from the algorithm level, and the AUV can complete the capture of dynamic and static targets with a small error when tracking this path.