Numerical solution of the fourth moment equation for acoustic intensity correlations and comparison with the mid‐ocean acoustic transmission experiment

In this paper numerical results for the solution of the fourth moment equation describing intensity fluctuations in the ocean are described. The work of previous authors who used adaptive grid methods to deal with the propagation of scalar waves through idealized random media with simple correlation functions is followed. Similar methods are applied to the analysis and prediction of the acoustic intensities measured in the mid‐ocean acoustic transmission experiment (MATE). Here extensive measurements provide the parameters needed to define the statistical ocean medium completely, using existing models for internal waves and fine structure that are well‐documented in the literature. When such models are used in the numerical solution of the fourth moment equation it is found that there are some discrepancies when comparisons are made with acoustic measurements of intensity fluctuations. However, if the fine structure model is modified in a simple way, then very good agreement is obtained with the experimental data. Most results are presented for the acoustic fluctuations of a propagating acoustic signal of fixed frequency, but some predictions for the cross correlation between two signals of different frequencies are also given.