Study On Acoustic Scattering Characteristics Of Shallow Water Targets

The scattering echo detection of underwater target is very important for the development of underwater acoustics,and the active detection of target,as the only effective detection method of underwater silent target,has more irreplaceable value.The analysis of target characteristics comes from the measurement of target echo in free field,which means to identify the target through the time-domain waveform and frequency-domain characteristics of target echo.However,in shallow water waveguide,the scattered sound field of the target becomes extremely complex due to the existence of boundary,so the echo information of the target cannot be obtained accurately.In this paper,the scattering characteristics of targets in shallow water waveguides are studied by analyzing the flux characteristics of scattered sound field.The angular density of horizontal energy flux is the physical meaning of the vertical average intensity of sound field,and the vertical average intensity is the mean square sound pressure level of sound field in the vertical direction.The scattered sound power of underwater targets can be calculated by using the mean square sound pressure level,Therefore,vertical averaging in shallow water waveguide can improve the measurement accuracy,simplify the measurement steps and improve the measurement efficiency.This paper studies the sound field scattered by targets in shallow water waveguides from three aspects: theoretical analysis,simulation and experiment.Firstly,according to the research theory of free field target scattering,the characteristics of spherical and cylindrical simple targets are analyzed,and the shape function of the target is determined,which can be used to identify the target;Then,using the normal wave expansion method,taking a rigid sphere as an example,the scattered sound field under the conditions of absolute hard,absolute soft and liquid seabed is simulated,and the influence of various parameters on the scattered sound field is analyzed by the control variable method;Finally,the simulation data are processed by using the analysis of scattered sound field flux characteristics,and the law of target sound scattering in shallow water waveguide and the relationship with free field are obtained.The regularity,effectiveness and practicability of the analysis of scattered sound field flux characteristics are verified by experiments.The results show that the scattering sound field of the target in the free field is completely different from that in the shallow water waveguide,and the scattering sound field of the target in the waveguide is very complex due to the existence of normal wave interference;Using the vertical average intensity can eliminate the normal wave interference of the target scattered sound field in the waveguide,make the sound field uniform,and obtain the same scattered sound power as the free field;The fluctuation of the incident sound field in the waveguide can affect the frequency characteristics of the target scattering in the waveguide,and then cause the fluctuation of the measurement results.In this paper,a vertical sound field analysis method is proposed to measure the scattered sound field of targets in shallow water,which is of great significance for underwater acoustic measurement based on active detection.