A computer code to calculate the effect of internal waves on acoustic propagation

The signal received by a hydrophone in the ocean many kilometers from a steady sound source fluctuates dramatically due to variations of the speed of sound in sea-water. A computer code that simulates the passage of acoustic CW signals through an ocean with internal waves is written. The code generates a sound-speed field from an internal-wave spectrum that has been derived from oceanographic measurements. The acoustic propagation is achieved through the use of the parabolic-equation approximation. The code is limited fundamentally to acoustic frequencies above approximately 10 Hz, and by practical computer-time constraints to frequencies below approximately 400 Hz. The code allows the calculation of the amplitude and phase of the full acoustic field as a function of depth and range at any desired time.