Temporal and cross-range coherence of sound traveling through shallow-water nonlinear internal wave packets

Expressions governing coherence scales of sound passing through a moving packet of nonlinear internal waves in a continental shelf environment are presented. The expressions describe the temporal coherence scale at a point, and the horizontal coherence scale in a plane transverse to the acoustic path, respectively. Factors in the expressions are the wave packet propagation speed, wave packet propagation direction, the fractional distance from the packet to the source, and the spatial scale S of packet displacement required to cause acoustic field decorrelation. The scale S is determined by the details of coupled mode propagation within the packet and the waveguide. Here, S is evaluated as a function of frequency for one environment, providing numerical values for the coherence scales of this environment. Coherence scales derived from numerical simulation of coupled mode acoustic propagation through moving wave packets substantiate the expressions.