Sound Propagation through Random Currents Using Parabolic Approximations

摘要

The influence of random, horizontal, depth-dependent ocean currents in the parabolic approximation is studied. The current is taken to have a depth-dependent mean, upon which is superimposed a small fluctuating component. Emphasis is placed on received acoustic intensity. Recently derived parabolic equations including currents are examined using asymptotic and numerical methods. Expressions are derived for the mean and standard deviation of intensity. The fluctuating current component is taken as having an exponential-cosine autocorrelation function with depth, although other functions could be used. Formulas obtained are sufficiently general to permit many types of depth-dependent sound speeds and bottom interface models. Current fluctuation effects on acoustic intensity moments are illustrated for the specific case of an isospeed channel with a perfectly hard bottom. The acoustic consequences of changes in physical parameters directly related to current fluctuations, such as its standard deviation and correlation length, are discussed. Also exhibited are changes in random current effects on intensity that result from changes in noncurrent related parameters, such as acoustic frequency and channel depth. Keywords: Underwater sound transmission, Reprints, Parabolic approximations. (kr)