An environmental-acoustics model for sound propagation in a geostrophic flow

A model for an ocean region experiencing geostrophic motion is considered. Under suitable simplifying assumptions and boundary conditions, equations of motion are solved for the density and pressure. Next, temperature is found by means of a state equation. Then, the pressure and temperature are used to determine the sound-speed structure induced by the presence of the current. The sound speed is found to depend upon both the magnitude of the current and one's position in the current. For a bottom-mounted source and receiver in the current direction, the model is used to investigate ray geometry, travel time, spreading loss, and the total acoustic field at the receiver. It is shown that the phase and amplitude of the received signal are significantly affected by variations in the current. Further, the dependence of sound speed on current is shown to be important so that these two quantities should not be considered separately as has been done in the past.