Localization By Single Vector Hydrophone Based On Array Invariant

As a novel underwater acoustic sensor, the vector hydrophone arises at the late 20th century. Because of its good spatial gain in the low frequency and very low frequency band,vector hydrophones have been used to solve the problem of large volume of some sonar equipments. In addition, it can measure the sound pressure and the three orthogonal components of the particle velocity simultaneously and colocatedly, which can provide more comprehensive information for further underwater acoustic signal processing and inspire new thoughts and methods in solving undersea problems. At present, there is an increasingly urgent need for vector hydrophones in many underwater acoustic research areas because of the weaker and weaker noise radiated by the target of interest and the long range detection requirement. And it greatly prompts the rapid development of the vector hydrophone technology and the acoustic vector signal processing technology.Because of its good concealment, the passive location technology has a very good prospect in the military field. And it has been concerned and taken attention by underwater acoustic scholars in the world for many years. At present, there are a lot of mature positioning technology, such as three-sensor array, matched filed processing (MFP), target moving analysis (TMA), and waveguide invariant. However, those passive location methods have many problems: lack of understanding of the acoustic propagation in the shallow water,dependent too much on marine environmental parameters, and only adapted to the specific sound field situation. So the passive localization technology still needs to be improved. In recent years, with the deepening of the understanding of the acoustic propagation in shallow water, the passive localization method based on the array invariant has been successfully applied. And the method has no more requirements and dependence on the marine environment parameters. As a small size array, vector hydrophone can extract the pitch angle of normal mode and describe the multimode propagation and single mode dispersion of shallow water waveguide. So vector hydrophone has the feasibility of target passive location based on array invariant. In this paper, combing single vector hydrophone with array invariant,the method of passive localization by single vector hydrophone based on array invariant is presented.Firstly, it is derived from normal mode theory of the acoustic field in the ocean waveguide. By solving the equation of Helmholtz, the pressure can be expressed using normal mode. And the concrete expressions of phase velocity and group velocity are derived under ideal conditions that the top surface is absolutely soft and the bottom is absolutely hard. Then,based on normal mode theory, utilizing phase velocity and group velocity of normal mode, the expression of array invariant is derived. In the end, combining frequency dispersion characteristics of the acoustic pressure component and the vibration velocity component of the vector field, the basic principle of the passive localization by the single vector hydrophone based on the array invariant is studied, and the specific implementation steps of the single the passive localization by the single vector hydrophone based on the array invariant are introduced in detail.Secondly, according to the basic principle of location by the single vector hydrophone based on the array invariant, the positioning simulation of the single vector hydrophone in the shallow water waveguide is carried out. The method of location by single vector hydrophone based on array invariant is verified by simulation. The ocean parameters, such as the sound profile, the parameters of sea floor, and the sea depth etc, are changed to study how the ocean parameters affect the estimate results. The results show that the dependence on the marine environmental parameters of the method is relatively weak. Finally, the influence of the error of sound pressure amplitude and amplitude of vibration velocity on the positioning method is analyzed.Lastly, utilizing the data of the sea trial, which took place in October of 2012 in SouthChina Sea, the method of localization by single vector hydrophone based on array invariant is feasible.