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

Jian Li,Qi Gu,Ying Chen,Haocai Huang,Guiqing Sun

doi:10.3390/s18103586

Abstract

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.

Highlights

The ultra-short baseline positioning system (USBL) is based on the installation of an ultra-short baseline array on a ship bottom and a transponder mounted on an underwater target
To verify the validity of the empirical orthogonal function (EOF), the measured velocity distribution samples were compared to the samples inversion by EOF
Due to equipment failures and environmental factors, there was an error in the measured sound speed profiles

Summary

Introduction

The ultra-short baseline positioning system (USBL) is based on the installation of an ultra-short baseline array on a ship bottom and a transponder mounted on an underwater target. The transmitter emits an acoustic signal, and the underwater target receives the transmitted acoustic signal and sends back an answer signal. The USBL calculates the azimuth and distance [1] of the target using the time-delay difference or phase difference between each receiving hydrophone [2], and calculates the position coordinates of the underwater target. The ultra-short baseline positioning system (USBL) is generally used for underwater positioning in shallow sea area [1]. Due to the complexity of the actual marine environment, the accuracy of an ultra-short baseline positioning system is limited mainly due to the existence of the ranging error, phase difference error, transmission and reception delay estimation error, and acoustic noise in the communication.

Objectives

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Results

Conclusion