Ultra-short Baseline Positioning Research Articles

A New Angle-Calibration Method for Precise Ultra-Short Baseline Underwater Positioning

Ultra-short baseline (USBL) underwater positioning systems are widely used in marine scientific research and ocean engineering. Angle misalignment is a main error that reduces the accuracy of USBL underwater positioning. The conventional angle-calibration method assumes that the transponder position obtained by USBL positioning is an errorless coefficient matrix. However, errors inevitably exist in the estimation of the transponder’s position via USBL positioning, and the precision varies at different epochs. Ignoring the error in the transponder’s position will significantly reduce the precision of the angle misalignment estimation. In this paper, a new angle-calibration method is proposed for precise USBL underwater positioning. The angle alignment model is derived by treating the transponder’s position obtained by USBL positioning as an observation, and the stochastic model is then established according to the bearing angles. Robust estimation is likewise applied to further improve the precision of the angle misalignment estimation. To verify the performance of the proposed method, a sea experiment was performed. The results show that the new method has high calibration accuracy and robustness. The estimation precision of this method is improved by 0.0457°~0.6896° in heading, 0.0125°~0.8072° in roll, and 0.0077°~0.9436° in pitch, compared with that of the conventional angle alignment method.

A differential-based method for correcting ultra-short baseline positioning results

The primary factors influencing the positional accuracy of an ultra-short baseline (USBL) system are errors in sound speed, delay, installation deviation, and the bending of sound rays. Premised on the USBL positioning model, an error contribution model including ranging error, delay error, sound speed error and array element installation deviation was constructed. In parallel, an indirect difference correction method with additional coefficients was proposed based on the geometric correlation of the error function model. Specifically, a reference beacon was deployed on the seabed, and differential correction was achieved by directly computing target coordinates, integrating them with the positional data from the reference beacon. The proposed method demonstrated efficacy in mitigating errors associated with gradual variations or pronounced geometric correlations, including discrepancies in sound speed, bending of sound rays, and deviations in the installation of array elements. The correction method was applied to the USBL positioning, and the simulation results show that the proposed method notably enhanced both accuracy and consistency in positioning, particularly in shallow water environments characterised by significant sound speed errors. The sea trial data from the R/V Dayang Yihao in the Western Pacific demonstrate that the proposed method can effectively mitigate the errors induced by sound ray bending in deep-sea environments. The mean absolute error (MAE) and standard deviation (STD) were reduced by 51.3% and 55.3%, respectively, compared with the results of the USBL direct solution.

Error Analysis on Ultra-Short Baseline Positioning System

Aiming at the problem of low accuracy of ultrashort baseline positioning system in practical applications, this paper introduces hydroacoustic channel response error and transducer distortion error, and analyses the influence of each factor on positioning accuracy in the positioning process according to the time delay estimation method. Finally, the major and minor factors are distinguished according to the influence mechanism and the degree of influence of the error factors. The results show that the ship attitude error and hydroacoustic channel error are the main factors affecting the positioning accuracy.

Guided Trajectory Filtering for Challenging Long-Range AUV Navigation

Aiming at the challenging underwater navigation of autonomous underwater vehicle (AUV), this paper develops a novel filtering method with guided trajectory. The relatively low frequency of ultra-short baseline positioning system (USBL) measurement and the noise caused by complex scenes have a significant impact on the accuracy of AUV motion estimation. Although the existing adaptive extended Kalman filter (EKF) and adaptive unscented Kalman filter (UKF) which can roughly eliminate these outliers, the filtering results of these algorithms are not smooth and have the serious degree of the jitter, and then greatly affect the local consistency and quality of topographic map seamless stitching. We exploit the relatively smooth strap-down inertial navigation system (SINS) as the guided trajectory for motion estimation, and propose a trajectory smoothness preserving filter algorithm. This system has the advantage of maintaining local gradient consistency, which not only improves the navigation accuracy, but also ensures the smoothness of the estimation system. Simulation results show that our approach has high robustness and good smoothness. The effectiveness and practicability of the method are demonstrated by real experiments in multiple deep-sea areas with an average depth of more than 1000 meters in the southwest Indian Ocean.

Calibration for Installation Errors of Ultra-short Baseline Based on Direction Cosine

In marine surveying and mapping, Ultra-short baseline (USBL) positioning system can provide accurate location information. So the USBL is the important guarantee of other marine jobs. However, under the influence of a complex marine environment, system errors, and acoustic curves, ultra-short baselines are subject to installation errors when installed, and the positioning accuracy can be seriously disturbed. To this end, this paper uses the direction cosine method to calibrate installation errors. To further improve positioning accuracy, this new method also consider the sound line correction. This method uses an equal gradient soundtracking algorithm to correct sound bending errors, constructs the error equation based on the transformation relationship between different coordinate systems by the direction cosine method, and linearizes the transformation parameters between the coordinate systems. The above two steps complete the calibration of installation errors of the USBL. The simulation results show that the underwater target position distribution calibrated by this method has a large convergence. The deviations from the data in all directions are concentrated around the zero point and approximately conform to a Gaussian distribution. The results indicate that the algorithm greatly improves the results of ultra-short baseline positioning and significantly increases the accuracy of underwater target positioning.

The COSMUS expedition: seafloor images and acoustic bathymetric data from the PS124 expedition to the southern Weddell Sea, Antarctica

Abstract. Between 3 February and 30 March 2021 the research icebreaker RV Polarstern conducted an extensive multidisciplinary research expedition across the southern Weddell Sea, Antarctica. During the Continental Shelf Multidisciplinary Flux Study (COSMUS) expedition (designated research expedition PS124), the Ocean Floor Observation and Bathymetry System (OFOBS) was deployed 20 times to collect high-resolution seafloor image and acoustic data with a 26-megapixel resolution camera, HD (high-definition) video camera, forward-facing acoustic camera and multibeam side-scan system from heights of between 1.5 and 4.5 m above the seafloor. To localise the collected data, the OFOBS was equipped with a Posidonia transponder for ultra-short baseline position triangulation, an inertial navigation system (INS) and a seafloor-tracking dynamic velocity logger (DVL). The 20 deployments were made across contrasting areas of the Weddell Sea, Filchner Trough, Filchner Sill and Filchner Shelf. Here, we present the full image dataset collected from across the various deployments as well as raw side-scan data and derived high-resolution bathymetric maps produced from these acoustic data after the cruise. All images are available from https://doi.org/10.1594/PANGAEA.936205 (Purser et al., 2021d) and https://doi.org/10.1594/PANGAEA.932827 (Purser et al., 2021a). Acoustic data for all deployments are also available from PANGAEA, with the raw side-scan data available at https://doi.org/10.1594/PANGAEA.939322 (Hehemann et al., 2021b) and forward-facing acoustic camera data at https://doi.org/10.1594/PANGAEA.939341 (Purser et al., 2021c). Seafloor topographic maps derived from the side-scan data are available at https://doi.org/10.1594/PANGAEA.939087 (Hehemann et al., 2021a).

Passive Inverted Ultra-Short Baseline Positioning for a Disc-Shaped Autonomous Underwater Vehicle: Design and Field Experiments

Underwater positioning is critical to autonomous underwater vehicles (AUVs) for navigation and geo-referencing. The rapid attenuation of the electromagnetic wave in the underwater environment prevents the use of traditional positioning methods such as the Global Positioning System, whereupon acoustic methods like ultra-short baseline (USBL) positioning systems play an important role in AUV navigation. However, the high cost and complexity of classical USBL systems have stifled the democratization of these technologies, which leads to a new method called passive inverted ultra-short baseline (piUSBL) positioning. In a typical piUSBL system, a single beacon is placed at a reference point, periodically broadcasting a positioning signal. A passive USBL receiver, time-synchronized to the beacon, is mounted on an AUV to get one-way travel-time (OWTT) slant range and azimuth estimates. The passive nature of the receiver means the system is inexpensive, low-power, and lightweight. Particularly, the omnidirectional broadcasted signals offer a feasible solution for concurrent multi-AUV navigation. This letter demonstrates a full-stack design and development of a piUSBL positioning system, and presents evaluations of the accuracy and reliability of the system through a series of experiments. More significantly, a successful sea trial of a disc-shaped AUV outfitted with our piUSBL was conducted in the South China Sea.

Multi-body modelling and analysis of the motion platform for underwater acoustic dynamic communication

With the development of marine science, the dynamic underwater acoustic network composed of many underwater and surface nodes has become an active research field of information science. The network in this study mainly involves the underwater gliders integrating underwater acoustic transducers and the wave glider carrying an ultra-short baseline positioning system. The attitude change of the underwater glider during zigzag profiling changes the beam pointing of the underwater acoustic transducer, which may lead to communication failure in the network. To deal with this problem, a motion platform for integrating an underwater acoustic transducer is proposed to be installed on the underwater glider. This work first integrates an underwater glider and a wave glider into a multi-body model by taking underwater acoustic signals as the media to illustrate the kinematics of the proposed motion platform. According to screw theory, the motion platform needs at least two rotational degrees of freedom to follow the ultra-short baseline positioning system. According to the bend of the sound ray, the motion angles of the motion platform are modified, and the motion platform controller is designed. The simulation results show that the controller can keep the underwater acoustic transducer tracking and pointing to the ultra-short baseline positioning system during communication when the underwater glider and wave glider move freely.

An USBL/DR Integrated Underwater Localization Algorithm Considering Variations of Measurement Noise Covariance

Ultrashort baseline (USBL) positioning system is an important part of the integrated navigation for underwater vehicles. The single USBL positioning system has problems such as reduced accuracy of azimuth measurement due to target motion and large impact of small angular variations, especially in the region where the target is close to the conical boundary, that is, the low-elevation region. To improve the positioning accuracy of the USBL-based integrated navigation system, a tightly coupled USBL/Dead Reckoning (DR) integrated localization algorithm that considers the time varying characteristics of the measurement noise was proposed, and the filtering model of the algorithm was designed. The algorithm exploits the mechanism of the azimuth measurement covariance variation of the USBL system, constructs an adaptive measurement noise estimator for the USBL system, and applies it to the integration filtering of USBL/DR data. A nonlinear extended Kalman filtering (EKF) model was used to fuse the USBL positioning and dead reckoning trajectories. A number of simulation tests with different elevation angle settings were performed to compare the performance of the proposed algorithm with that of a conventional EKF for underwater localization. The test results reveal that the proposed algorithm can effectively reduce the positioning error caused by the change in the relative azimuth of the acoustic signal owing the motion of the mother ship and the motion of the underwater vehicle.

Accurate two-step filtering for AUV navigation in large deep-sea environment

Underwater navigation is a challenging topic in the field of underwater exploration. Accurate and effective underwater navigation is necessary in applications such as 3D seafloor topography scanning, cable laying, deep-sea resource survey and wreck salvage. However, underwater navigation becomes difficult due to the variability and complexity of underwater environment. In the deep-sea environment, the ultra-short baseline positioning system (USBL) is very unstable, and the flying abnormal points and signal loss often occur. To solve these problems, this paper proposes a two-step filtering scheme combined with doppler velocity log (DVL). The first step is to construct a rough Monte Carlo particle filter (MPF) model for the autonomous underwater vehicle (AUV) position, and then select candidate particles with the strategy of minimizing the local backward dead reckoning (DR) errors. In the second step, the results of the first step are further smoothed and optimized using the weighted extended Kalman filter (WEKF). Finally, the robustness and practicability of the proposed method are verified by the multiple data obtained from several sea trials in the South-West Indian Ocean. The results also show that the integrated navigation framework is superior to single navigation method and other traditional filtering methods. The best balance between accuracy and computational cost is achieved.

The detection method of wrecked plane's black box based on SCOUT+ ultra short baseline positioning system

The black box of wrecked aircraft, as the witness of air disaster, need to be salvaged quickly. In the ocean environment of twenty meters deepth, we search to locate the aircraft black box based on SCOUT+ ultra-short baseline positioning system (USBL). The black box simulator is located in 20 m water depth ocean environment. The positioning accuracy reaches 6.35 m, and the angle positioning accuracy reaches 2.78°. After eliminating the fixed error of installation, the angle positioning accuracy reaches 0.40°. In general, the SCOUT+ detecting accuracy of the black box reaches the expected requirement and meet real needs.

An Ultra-Short Baseline Underwater Positioning System with Kalman Filtering.

The ultra-short baseline underwater positioning is one of the most widely applied methods in underwater positioning and navigation due to its simplicity, efficiency, low cost, and accuracy. However, there exists environmental noise, which has negative impacts on the positioning accuracy during the ultra-short baseline (USBL) positioning process, which results in a large positioning error. The positioning result may lead to wrong decision-making in the latter processing. So, it is necessary to consider the error sources, and take effective measurements to minimize the negative impact of the noise. In our work, we propose a USBL positioning system with Kalman filtering to improve the positioning accuracy. In this system, we first explore a new kind of element array to accurately capture the acoustic signals from the object. We then organically combine the Kalman filters with the array elements to filter the acoustic signals, using the minimum mean-square error rule to obtain accurate acoustic signals. We got the high-precision phase difference information based on the non-equidistant quaternary original array and the phase difference acquisition mechanism. Finally, on account of the obtained accurate phase difference information and position calculation, we determined the coordinates of the underwater target. Comprehensive evaluation results demonstrate that our proposed USBL positioning method based on the Kalman filter algorithm can effectively enhance the positioning accuracy.

A Calibration Method of USBL Installation Error Based on Attitude Determination

The Ultra-short baseline (USBL) positioning system has important application in the positioning of underwater vehicles. The installation error angle of the USBL positioning system has an important influence on the positioning accuracy of USBL system. The traditional calibration methods have limited estimation accuracy for installation error angles and have high route requirements. To solve the above problems, a calibration method of installation error angle based on attitude determination is proposed in this paper. When strapdown inertial navigation system (SINS) and USBL are fixed together in the application process, the installation error angle of USBL is fixed and unchanged. Then the calibration of installation error angle can be accomplished with the idea of attitude determination. The vector observation model based on the installation error angle matrix is established first. Observation vectors are obtained by the relative position of transponders in the USBL coordinate frame. The reference vector is calculated by position of transponder, position and attitude of SINS and lever arm between SINS and USBL. By constructing the observation vectors and the reference vectors, the proposed method can calibrate the installation error angle of SINS and USBL in real time. The advantages of the proposed method are that it has no specific requirements for the calibration route and can calibrate the installation error angle in real time with high accuracy. In order to verify the performance of the proposed algorithm, simulation experiment and field experiment are carried out in this paper. The results of simulation experiment and field experiment show that the proposed method can give the estimated installation error angle of USBL in real time, and the estimated result is the best among several methods. The proposed method can not only achieve the calibration of the installation error angle in circular trajectory, but also in straight trajectory.

A Novel and Robust Calibration Method for the Underwater Transponder Position

This article addresses the transponder position calibration problem for the ultrashort baseline (USBL) system. Calibration is an important technique for the positioning of the USBL and the calibration of the installation error. The estimation error of the transponder position is greatly affected by the slant distance error in the traditional method. Furthermore, the calibration accuracy depends heavily on the slant distance error and it has poor robustness in the presence of outliers. Thus, a robust calibration model combining slant distance and bearings is developed, which overcomes the disadvantage of poor robustness of the traditional method. The transponder position can be estimated in real time by the adaptive fault-tolerant Kalman filter designed in this article. Some experiments are carried out to prove the superiority of the proposed algorithm. The USBL positioning accuracy is also improved with the novel calibration method.

Passive Acoustic Signal Processing at Low Frequency With a 3-D Acoustic Vector Sensor Hosted on a Buoyancy Glider

This article deals with the detection of low-frequency noise sources and the estimation of their direction of arrivals using an acoustic vector sensor hosted on a buoyancy Slocum glider. The sensor used is a 3-D directional hydrophone capable of acquiring both the acoustic pressure and the components of the particle velocity vector. This article presents experimental results with data collected at sea and describes the signal processing chain, including detection, direction of arrival, and clustering. The vehicle is equipped with a modem and is supported by an ultrashort baseline (USBL) located on a mother ship or gateway to achieve the navigational accuracy required for correct target localization. The surface vessel localizes the glider via the USBL and then transmits position fixes, which are used by the underwater vehicle to reset the drift error of its navigation filter. The results discussed in this article demonstrate two important achievements, i.e., an underwater glider can produce accurate bearing estimates on a target and the feasibility of the integration of an acoustic modem and a USBL positioning system on a glider. The results obtained open up the possibility of using multiple autonomous sensorized gliders integrated in intelligent surveillance robotic networks.

Adaptive Robust Unscented Kalman Filter for AUV Acoustic Navigation.

Autonomous underwater vehicle (AUV) acoustic navigation is challenged by unknown system noise and gross errors in the acoustic observations caused by the complex marine environment. Since the classical unscented Kalman filter (UKF) algorithm cannot control the dynamic model biases and resist the influence of gross errors, an adaptive robust UKF based on the Sage-Husa filter and the robust estimation technique is proposed for AUV acoustic navigation. The proposed algorithm compensates the system noise by adopting the Sage-Husa noise estimation technique in an online manner under the condition that the system noise matrices are kept as positive or semi positive. In order to control the influence of gross errors in the acoustic observations, the equivalent gain matrix is constructed to improve the robustness of the adaptive UKF for AUV acoustic navigation based on Huber’s equivalent weight function. The effectiveness of the algorithm is verified by the simulated long baseline positioning experiment of the AUV, as well as the real marine experimental data of the ultrashort baseline positioning of an underwater towed body. The results demonstrate that the adaptive UKF can estimate the system noise through the time-varying noise estimator and avoid the problem of negative definite of the system noise variance matrix. The proposed adaptive robust UKF based on the Sage-Husa filter can further reduce the influence of gross errors while adjusting the system noise, and significantly improve the accuracy and stability of AUV acoustic navigation.

An Ultra-Short Baseline Positioning Model Based on Rotating Array & Reusing Elements and Its Error Analysis

The USBL (Ultra-Short Base Line) positioning system is widely used in underwater acoustic positioning systems due to its small size and ease of use. The traditional USBL positioning system is based on ‘slant range and azimuth’. The positioning error is an increasing function with the increase in distance and the positioning accuracy depends on the ranging accuracy of the underwater target. This method is not suitable for long-distance underwater positioning operations. This paper proposes a USBL positioning calculation model based on depth information for ‘rotating array and reusing elements’. This method does not need to measure the distance between the USBL acoustic array and target, so it can completely eliminate the influence of long-distance ranging errors in USBL positioning. The theoretical analysis and simulation experiments show that the new USBL positioning model based on ‘rotating array and reusing elements’ can completely eliminate the influence of the wavelength error and spacing error of underwater acoustic signals on the positioning accuracy of USBL. The positioning accuracy can be improved by approximately 90%, and the horizontal positioning error within a positioning distance of 1000 m is less than 1.2 m. The positioning method has high precision performance in the long distance, and provides a new idea for the engineering design of a USBL underwater positioning system.

A misalignment angle error calibration method of underwater acoustic array in strapdown inertial navigation system/ultrashort baseline integrated navigation system based on single transponder mode.

The angle misalignment error of a USBL (Ultrashort Baseline) acoustic array is one of the major error sources of the strapdown inertial navigation system/USBL positioning system, which will directly affect the positioning accuracy of the USBL positioning system. For the traditional calibration method cannot accurately estimate the angle misalignment error due to its strict trajectory requirements in the field experiment and the high-precision layout of the transceiver array elements, a new method for estimating the angle misalignment error of a USBL acoustic array based on single transponder and dual-vector reconstruction is studied in this paper. The precondition of USBL misalignment calibration is to locate the underwater transponder accurately. In this paper, the single transponder segmentation iterative long baseline method is used to locate the underwater target transponder. The dual-vector reconstruction method is studied to control the estimation accuracy of USBL misalignment error calibration based on the traditional single transponder method, which provides a theoretical basis for the determination of the iteration times to the USBL angle misalignment error estimation module. The underwater experiment results show that the positioning error could be reduced to less than 1 m after the angle misalignment error compensation. The underwater transponder positioning and the angle misalignment error estimation of USBL could be accomplished in a circle sailing. It is a new method with good performance of high estimation accuracy, simple operation, and easy realization.

Optimal Design of Beacon Array for Long Baseline Positioning System Used in Manned Deep-Sea Submersibles

Ultrashort baseline positioning systems are used to localize manned deep-sea submersibles. A long baseline positioning system is a significant supplement to an ultrashort baseline positioning system and provides more precise positioning. The long baseline beacon array design applied is a primary factor affecting the accuracy of long baseline positioning. However, beacon array designs have mainly been studied in autonomous underwater vehicles (AUVs). Because the characteristics and dive tasks between AUVs and manned deep-sea submersibles are different, the simple beacon array formations used in AUVs cannot be directly used in manned deep-sea submersibles. To the best of our knowledge, this study is the first to present the optimal design of a beacon array for a long baseline positioning system used in manned deep-sea submersibles. In this paper, based on the characteristics of a manned deep-sea submersible, the seven basic principles used for the optimal design of a long baseline beacon array are presented. First, the dive tasks of a JIAOLONG manned deep-sea submersible are analyzed, including the relationship between the dive survey lines, and the depth and distance of each line. Second, we explore the minimum beacon number to cover the dive site and its vicinity. Third, we adjust the beacon position based on the seven optimal design principles. The beacon array is designed to satisfy manned deep-sea submersible dive requirements during the JIAOLONG Test Applications Voyage 2013. A sea trial demonstrates that the long baseline positioning results are reliable if at least three beacons are not blocked, and the accuracy of the long baseline positioning system is better than that of an ultrashort baseline.

A Combined Ray Tracing Method for Improving the Precision of the USBL Positioning System in Smart Ocean.

The ultra-short baseline positioning system (USBL) has the advantages of flexible application and easy installation, and it plays an extremely important role in the underwater positioning and communication. The error of the USBL in underwater positioning is mainly caused by a ranging error due to ray tracing, a phase difference error of the USBL, and acoustic noise in the underwater communication. Most of these errors are related to the changes in the sound speed during its propagation through the ocean. Therefore, when using the USBL for underwater detection, it is necessary to correct the sound speed profile in the detection area and optimize the ray tracing. Taking into account the actual conditions, this paper aims at correcting the model of underwater sound speed propagation and improving the tracking method of sound lines when the marine environment in the shallow sea area changes. This paper proposes a combined ray tracing method that can adaptively determine whether to use the constant sound speed ray tracing method or the equal gradient ray tracing method. The theoretical analysis and simulation results show that the proposed method can effectively reduce the error of slant distance in USBL compared with the traditional acoustic tracking method and the constant sound speed ray tracing method. The proposed sound ray correction algorithm solves the contradiction between the number of iterations and the reduction of positioning error and has engineering application value.