Acoustic dispersion in a deep ocean channel

Abstract

Acoustic dispersion in a deep ocean channel is characterized by the dependence of sound propagation speed on signal frequency along the axial propagation path. A model normal‐mode solution of the wave equation is employed to compute the acoustic field for sinusoidal signals as a function of both axial range and frequency. A virtual propagation time is defined which reflects the range‐dependent phase of the acoustic field. When signals of different frequency are transmitted, the remotely observed frequency ratio (for a given range rate) will fluctuate about the true frequency ratio of the transmitted signals. The magnitude of the fluctuation is directly proportional to the true frequency ratio. A measure of the spectral dispersion is defined as the difference between the observed and true frequency ratios. The dependence of this measure on range and signal frequencies (for a given frequency ratio) is determined to be relatively insignificant. It is concluded that acoustic dispersion in a deep ocean channel is microscopic in its measure, but it can be significant for applications involving the phase correlation of broadband (or spectrally separated) signals over long time intervals.