Underwater Positioning Based on an Artificial Lateral Line and a Generalized Regression Neural Network

Taking advantage of the lateral line organ, fish can navigate, feed, and avoid predators and obstacles by sensing surrounding flow fields. The lateral line organ provides an important reference for the development of new underwater detection technology. Inspired by the lateral line organ, in this paper, for the sake of localizing the target dipole source in three-dimensional underwater space, an artificial lateral line consisting of nine underwater pressure sensors forming a cross-shaped sensor array is applied. Combined with the method of gener- alized regression neural network, which is suitable for solving nonlinear pattern recognition problems, a corresponding experimental platform has been built to sample data for training the neural network from a 12 cm by 12 cm by 24 cm cuboid space. The experimental results indicate that the cross-shaped artificial lateral line can localize the target dipole source two body-lengths away. The well- performing perceptual distance is below 13 cm away from the sensing array. Moreover, decreasing the data sampling interval and in- creasing the number of sensors utilized can help improve the positioning accuracy.

Hardware pre-processing for data of SBL underwater positioning system

The synchro double pulse signal mode is freuqently used in Short Base Line (SBL)underwater positioning system so as to obtain the information of both distance and depth of a target simultaneously. Howerer, this signal mode also brings about ranging indistinctness resulting in a shorter positioning distance much less than that limited by the period of the synchro signal. This paper presents a hardware distance-gate data acquiring scheme. It puts the original data sent to the computer in order of ' direct first pulse- depth information pulse (or first pulse reflected by water surface )…' to guarantee the effective positioning distance of the system. It has the advantage of reducing the processing time of the computer thus ensuring the realtime functioning of the system. A figure of the orbit of an underwater moving target measured in practice is attached to the end of the paper.

Virtual Reality Simulation of Fuzzy-logic Control during Underwater Dynamic Positioning

In this paper, graphical-user-interface （GUI） software for simulation and fuzzy-logic control of a remotely operated vehicle （ROV） using MATLABTM GUI Designing Environment is proposed. The proposed ROV＇s GUI platform allows the controller such as fuzzy-logic control systems design to be compared with other controllers such as proportional-integral-derivative （PID） and sliding-mode controller （SMC） systematically and interactively. External disturbance such as sea current can he added to improve the modelling in actual underwater environment. The simulated results showed the position responses of the fuzzy-logic control exhibit reasonable performance under the sea current disturbance.

An improved positioning model of deep-seafloor datum point at large incidence angle

The inhomogeneous sound speed in seawater causes refraction of sound waves,and the elimination of the refraction effect is essential to the accuracy of underwater acoustic positioning.The raytracing method is an indispensable tool for effectively handling problems.However,this method has a conflict between localization accuracy and computational quantity.The equivalent sound speed profile(ESSP)method uses a simple sound speed profile(SSP)instead of the actual complex SSP,which can improve positioning precision but with residual error.The residual error is especially non-negligible in deep water and at large beam incidence angles.By analyzing the residual error of the ESSP method through a simulation,an empirical formula of error is presented.The data collected in the sailing circle mode(large incidence angle)of the South China Sea are used for verification.The experiments show that compared to the ESSP method,the improved algorithm has higher positioning precision and is more efficient than the ray-tracing method.

Robust SLAM localization method based on improved variational Bayesian filtering

Aimed at the problem that the state estimation in the measurement update of the simultaneous localization and mapping(SLAM)method is incorrect or even not convergent because of the non-Gaussian measurement noise,outliers,or unknown and time-varying noise statistical characteristics,a robust SLAM method based on the improved variational Bayesian adaptive Kalman filtering(IVBAKF)is proposed.First,the measurement noise covariance is estimated using the variable Bayesian adaptive filtering algorithm.Then,the estimated covariance matrix is robustly processed through the weight function constructed in the form of a reweighted average.Finally,the system updates are iterated multiple times to further gradually correct the state estimation error.Furthermore,to observe features at different depths,a feature measurement model containing depth parameters is constructed.Experimental results show that when the measurement noise does not obey the Gaussian distribution and there are outliers in the measurement information,compared with the variational Bayesian adaptive SLAM method,the positioning accuracy of the proposed method is improved by 17.23%,20.46%,and 17.76%,which has better applicability and robustness to environmental disturbance.

Solution to Long-Range Continuous and Precise Positioning in Deep Ocean for Autonomous Underwater Vehicles Using Acoustic Range Estimation and Inertial Sensor Measurements

Although advances in research into autonomous underwater vehicles(AUVs)have been made to extend their working depth and endurance,underwater experiments and missions remain to be restricted by the positioning performance of AUVs.With the Global Navigation Satellite System(GNSS)precluded due to the rapid attenuation of radio signals in underwater environments,acoustic positioning methods serve as an effective substitution.A long-range continuous and precise positioning solution for AUVs in deep ocean is proposed in this study,relying on acoustic signals from beacons at the same depth and aided by onboard inertial sensors.A signal system is investigated to provide time of arrival(TOA)estimation in a resolution of milliseconds.Without pre-knowledge or local measurement of the accurate sound speed,an AUV is enabled to continuously locate its horizontal position based on rough ranges estimated by an iterative least square(ILS)based algorithm.For better accuracy and robustness,range deviations are compensated with a reference point of known position and outliers in the trajectory are eliminated by an implementation of the extended Kalman filter(EKF)coupled with the state-acceptance filter.The solution is evaluated in simulation experiments with environmental information measured on the spot,providing an average position error from ground truth below 10 m with a standard deviation below 5 m.

Analysis and implementation of cross sync period underwater acoustical positioning techniques for underwater targets

The sampling rate of an underwater acoustical synchronous positioning system for the track of an underwater target will be decreasing during the process of positioning while the target moves away, resulting in the reduction of raw data and insufficient use of the processing ability of the positioning system. For a long time, this problem has remained unsolved, and it is even pushed forward recently because of the rapid development of modern electronic tech- niques. Based on the thorough study and investigation of the problem, we developed a new synchronous positioning technique called 'Cross Sync Period' underwater acoustical positioning. It can increase the sampling rate of an underwater acoustical positioning system for the track of an underwater target at long range significantly Besides, a new algorithm specially designed for the detection of the propagation time delay of the positioning signals called 'Mod-ulo Algorithm' was also developed, which makes the implementation of the 'cross sync period'underwater acoustical positioning technique easier and more efficient. These techniques have been successfully applied in a real positioning system. The system can position 5 underwater targets at the maximum range of 6 km simultaneously without any ambiguity of target distances with the working period of 0.4 s. The 'cross sync period' underwater acoustical positioning technique applied in the system was performed in lake and searun tests, and satisfactory re-sults were obtained.