Research On Geoacoustics Signal Detection Technology Based On Optical Fiber Sensor Of High Sensitivity

The acoustic energy generated by the underwater target in the shallow sea will be converted to seismic waves because of its interaction with the sea seabed.Due to the conversion between the seabed shear wave and the compression wave,a kind of seismic surface wave will propagate on the surface of the seabed losslessly similar to the cylindrical wave,which can be used to locate the underwater target if it is captured by a high sensitivity seismic geoacoustic sensor.Geoacoustic sensor system designed according to this principle can make up for the defect of the traditional hydrophone in the aspect such as insufficient low frequency signal detection capability and high layout cost.Due to the attenuation of the sea floor,signal to noise ratio of seismic wave signal is relatively high,which enable it to provide reliable raw data for underwater target recognition.Because the research of geoacoustic detection is still in its infancy,there are still many problems in geoacoustic detection system,which prevent it from being put into application.To determine the type of seismic wave to be detected,select reasonable layout position of the system and find logical locating method,this paper mainly completes the following work:1.A fast field model of shallow marine Pekeris waveguide with elastic seabed is built to study the submarine energy distribution.Confirmed the seismic surface wave is the only form of seismic wave which can be transmitted at the bottom of the sea losslessly.In this condition,the classification and the specific vibration forms of the surface seismic wave are studied.The conclusion that the energy of the sea surface seismic wave decreases with the increase of depth is demonstrated.Provide a theoretical basis for the selection of detection object and embedded position of the geoacoustic detection system.2.Design and test the interference fiber optic vector s ensor which can be used in geoacoustic detection.The test results show that the frequency response of the sensor in 20~200Hz frequency is flat.Sensitivity is up to 56 d B(0d B=1rad/g).Low frequency phase noise can be-107dB@100Hz(4.5?rad/ Hz).3.According to the geoacoustic vertical signal of the signal owns higher signal to noise ratio and better correlation characteristics than the traditional acoustic vertical signal,A vector positioning method based on seismic vector signal and its theoretical simulation is proposed.4.The validity of the method is verified by experiments on land and lake.Positioning accuracy is better than 5 degrees in 30 meters scopes.Through the comparison experiment of the signal,the theory of this paper is proved and the advantage of the signal to noise ratio of the geoacoustic signal is confirmed.