Fluctuations in sound transmission through sound speed profiles that are periodic in range and geotime

Acoustic propagation through sound speed profiles (SSPs) that are periodic in range and geotime is studied using the parabolic equationmodel and the WKB/adiabatic model. Fluctuations are shown to be significantly reduced when acoustic propagation is through a periodic range-dependent SSP, compared to a range-independent SSP. For a fixed source-receiver range, the number of tidal wavelengths contained within the range is an important factor that determines the fluctuations. The relationship of this factor to the direction of transmission relative to the tidal direction is presented. A useful criterion for predicting the extent of fluctuations under different environments has been developed by examining the range integral of the horizontal wave number for each mode.