A theoretical and experimental study of the behaviour of a parametric array in a random medium

The fluctuations of a parametric signal in a random medium have been investigated. A theoretical expression for the mean square amplitude and phase fluctuations has been derived, by using the small perturbation method. A simplified version of the theoretical model, which predicts the axial amplitude fluctuations of the difference frequency signal, was computerized. Laboratory experiments were carried out in a heated tank in which the fluctuations of a parametric signal and a linearly generated signal were compared. A similar experiment was also carried out in an estuary. The experimental results obtained were consistent with the theoretical estimates.