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Research on the Space-time Correlation Characteristics of Vector Noise Field in Boundary Conditions

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Tutor: YangDeSen
School: Harbin Engineering University
Course: Underwater Acoustics
Keywords: Vector hydrophone,Vector noise field,Ocean ambient noise model,correlation funct
Type: Master's thesis
Year:  2010
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It is difficult to avoid the effect of boundary condition in the use of vector hydrophones and their array. Hydrophone can receive underwater ambient noise in the meantime of receiving signals. In order to further improve the detection gain of vector hydrophones¡¯array and to provide basis for the design of sonar, it is need urgently to study the correlation structure of the vector noise field in boundary condition.Acoustic reflection and transmission of different boundary conditions was firstly discussed in this paper. On this basis, the vector hydrophone¡¯s directivity by the plane baffle was studied and some theoretical simulation was conducted. Then,¡°absolute hard¡±and¡°absolute soft¡±boundary conditions were added to the three-dimensional spherical isotropic noise field. Various space-time correlation functions based on the acoustic pressure, vibration velocity and sound intensity were derived. Later, baffle boundary condition is added to the sea surface noise field model. A variety of coherence functions were theoretically derived in the following different conditions: the baffle is horizontal and vertical; the vector hydrophone array is horizontal and vertical. In this model, the spatial coherence characteristic of the vector noise field is discussed in the external and internal of the composite baffle system. The result show that some influence on the vector hydrophone¡¯s directivity and the correlation structure of vector noise filed is caused by receiving frequency, installation distance, reflection value and other factors, and the influence of boundary can not be ignored. Correlation radius and other parameters can be provided to guide the design of vector hydrophone¡¯s array by analyzing the specific application environment, and greater detection gain can be obtained.Finally, the pool experiment of vector hydrophone¡¯s directivity in boundary condition verified the related theories. It is showed that the boundary¡¯s influence on the correlation structure of vector noise filed can not be ignored by handling underwater ambient noise of the Songhua Lake. The actual ambient noise field is so particularly complex that it need to be studied more in-depth.
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