Geoacoustic inversion in shallow water by matching vertical particle velocity

Bottom acoustic parameters are significant for the research of sound propagation properties and corresponding applications in ocean waveguides. The propagation properties and the normal-mode structure of vertical particle velocity in the ocean environment with a thermocline in shallow water are studied for the experiment conducted in the Yellow Sea in summer. It is shown that vertical particle velocity has higher energy at most depth except for near-bottom depth when the source and the receiver are both under the thermocline. Moreover, high-order modes contribute more to vertical particle velocity and vertical-particle-velocity-based Matched-Field-Processing (MFP) inversion method can acquire higher sensitivity to bottom parameters in comparison with sound pressure. The influences of the bottom absorption coefficient on the vertical-particle-velocity-based MFP inversion method are studied, it is shown that the accurate sound speed, density and water depth can be obtained only when the bottom absorption coefficient is set around the real value during the MFP procedure. By using the vertical particle velocity signals acquired by the vector hydrophones during the experiment and searching the sound speed, density and water depth under different bottom absorption coefficient, the stable inversion results are acquired. The transmission losses of the sound pressure at different ranges are used to invert the bottom absorption coefficient. The transmission losses of sound pressure calculated by using the inverted bottom parameters are in consistent with the measured results acquired by the pressure hydrophones in the experiment.