Long-range And Low-frequency Bottom Reverberation Modeling Based On Normal Mode In Shallow Water

Acoustic scattering from the seafloor has been an attractive topic for many years. But for the complex interaction of sound on the bottom and the necessity of bottom reverberation prediction, many works are still not finished. In the past, bottom reverberation is generally considered to be produced due to the roughness of the water-sediment interface. But in recent years, some evidences indicated that scattering from volume inhomogeneity within the sediment could not be neglected, especially for low-frequency signal. In this paper, monostatic and bistatic models for bottom scattering are presented respectively. Seabed roughness and the volume inhomogeneity scattering are taken into account in the scattering modeling. The models established in the paper are all suitable for low frequency cases.With the analysis of sound scattering from bottom sediment, long-range and low-frequency bottom reverberation in shallow water has been modeled. Considering the complicated multipath structure of the shallow water and the computational intensity of the geometric model, a normal mode reverberation model is introduced based on the method developed by Grigorer. Monostatic and bistatic reverberation intensities have been calculated, both in horizontally stratified media and wedged channel. Relationships between the intensity and the pulse width of the transmitted signal, range of the transmitter and the receiver have been also discussed. Except for that, statistical properties of the amplitude and phase of the scattering field have been analyzed. According to the numerical analysis, similar conclusions have been obtained comparing to other models. Computer simulation shows that normal mode model is fit to treat long-range and low-frequency bottom reverberation in shallow water.