Research On Underwater Buried Object Detection

In some occasion which need to detect the shallow underwater buried object such as underwater archeology,mine detection,pipeline detection and so on.Due to the high backscatter noise of the seabed sediments,the detection and identification of targets covered by seabed sediments are more difficult than in-water target.Whether the buried object echo can be effectively detected and how to identify is closely related to the emission signal source,the beam incident angle,the physical characteristics of underwater interface medium,and the geometry structure of the buried object.It is necessary to study the physical acoustics principle of the wave in the process of propagation and scattering,so as to propose a more effective detection method.In addition,due to the high-frequency ultrasonic waves in the sedimentary layer has larger attenuation than in water,the signal to noise ratio(SNR)and the signal to reverberation ratio(SRR)is very low.Generally,detection of buried objects mainly use low-frequency signal sources,but low-frequency wave has a bad directivity.With the application of acoustic parameters array which has high directivity,low frequency more and more widely,This technology has great potential in the application of buried object detection.Based on the simulation and experimental study,this paper has studied the characteristics of the signal source,the acoustic scattering mechanism,the echo characteristics and signal processing method of the underwater buried object.Firstly,This paper introduces the application background and development of buried object detection,and expounds the basic principle and application of related technology.Secondly,based on the popular multi-physics simulation software COMSOL Multiphysics and finite element methods(FEM),the Helmholtz-Kirchhoff integral method and the distribution of target scattering intensity in free space are studied.In addition,for the reason of the detection effect of buried or bottoming target depends on the physical acoustic properties of the sediments and water-sediment interface in actual environment,in this paper,acoustic properties of the sedimentary layer are simulated based on Biot-Stoll porous acoustic theory,The characteristic curves of the reflection coefficient,the absorption coefficient,the velocity dispersion phenomenon and the distribution of the acoustic field in the typical underwater sediment were obtained.According to the established model above,this thesis preliminary simulate and get the echo model of time domain waveform.Then,the spectral distortion of the LFM signal,which is commonly used in the detection is studied,and the pulse compression of the traditional matched filter is improved based on the distortion characteristic.In addition,the characteristics of the parametric array are discussed,and the basic principle of array designing is put forward.Finally,after determining the attenuation,absorption and scattering model,this paper studies the array signal processing method of the buried object echo,and designs the simulation and the practical experiment to verify the feasibility of the detection and imaging.This thesis also analyzes the experimental data to verify the effectiveness of signal processing method.