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.

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.