Focus on sound intensity, particle velocity, complex sound intensity and waveguide impedance, the formation mechanism of interference structures in range-frequency domain for the above four kinds of physical quantities in Pekeris waveguides is analyzed based on Nor- mal Mode Theory. Also, a sea-trial with broadband radiated source is conducted to verify the analysis results. Both the simulation results and the analysis of sea-trial data indicate that, in range-frequency domain, the four kinds of physical quantities will exhibit a stable interfer- ence structure which can be expressed with waveguide invariant /3. Among these quantities, the coherent components of complex sound intensity can better reflect the interference char- acteristics of the waveguide. Finally, a multi-scale linear filter is introduced to deal with the sea-trial LOFAR （Low Frequency Analysis Recording） spectrum, the processing results show that the proposed filter can effectively enhance the interference characteristics in images, and conductively detect and extract striations＇ information from interference structures in LOFAR spectrum.
The signal to noise ratio （SNR） of seismic waves is usually very low after long distance transmission. For this condition, to improve the bearing estimation capability in the low SNR, a frequency domain polarization weighted ESPRIT method using a single vector device is proposed. The frequency domain polari- zation parameters extracted from the signals are used to design the weighted function which is applied to the received signals. The bearing angle and the target frequency are estimated through ESPRIT using the weighted signals. The simulation and experiment results show that the presented method can obtain accurate estimation values under the low SNR with little prior information.
