Simulation study of depth characteristics of optimum frequency for acoustic propagation in shallow water based on normal mode model

  Objectives  The difference between the sea bottom and sea surface boundary conditions cause the uneven distribution of sound field energy, and the optimum frequency of acoustic propagation in shallow water also varies greatly in depth. In order to optimize the underwater acoustic communication and sonar detection,

  Methods  the normal mode method was used for the study on the depth characteristics of optimum frequency for acoustic propagation in shallow water, and the change law of optimum frequency was studied through the change of seawater depth, sea-bottom parameters, sea surface roughness and sound speed profiles while the sound source was located at middle depth and other places.

  Results  The results show that while the sound source is located near middle depth, there is an area where the optimum frequency would remain the same when the receiver depth changes, and the thickness of this area is about half of the depth of seawater when the depth of the seawater changes, which has little relationship with the sea-bottom parameters and the sea surface roughness.

  Conclusions  It is concluded that there is a trapezoidal area in shallow water, where the optimum frequency stays the same while the relative location between the sound source and the receiver changes. The discovery of this phenomenon is helpful to the development of underwater acoustic communication technology and submarine stealth performance.