Wave theory analysis for pulse propagated near sound channel axis in deep water

The conventional ocean acoustic tomography have analyzed by the ray theory. The rays propagating near the SOFAR (SOund Fixing and Ranging) axis have the slowest wave speed and tend to be over-lapped with each other, so that they become a pulse with large amplitude. But it is difficult to use the last pulse for the final analysis, because it could not be discriminated separately in time domain. In this paper, the last pulse propagating near the axis is analyzed in the time domain by the wave theory. First, the variations of the amplitude of the last pulse are obtained as a function of the propagation range. As a result, it is shown that the last pulse is built by a few waves propagating within the SOFAR channel. Next, the propagation depth range of the waves that contribute to the last pulse is determined by the comparison of the peak amplitude variation obtained by the parabolic equation method and those filtered mode pulse. Lastly, the pattern of the peak amplitude of the last pulse is shown. The vertical distributions may be measured by a vertical hydrophone array. It is thought that these results are greatly useful to the future analysis of the ocean acoustic tomography