Acoustic normal mode propagation through a three-dimensional internal wave field

Abstract

In describing the effects of internal waves on acoustic normal modes excited by a time-harmonic point source, all previous descriptions have neglected the existence of azimuthal fluctuations in the acoustic field. This study compares this azimuthally symmetric case with the case where azimuthal fluctuations in the acoustic field are taken into account. Although azimuthal variations can enhance the randomization of interference effects so that different depth modes decorrelate more quickly in range, this enchancement is generally small. The autocorrelation functions of the depth modes approach equipartition at long ranges as in the azimuthally symmetric case, as long as each range function is interpreted as a sum of all the azimuthal modes. The mean energy flux vector 〈j〉 becomes radial at long ranges. Integral expressions for the scattering coefficients and interference terms have been derived so that these quantities can be calculated without having to perform an infinite sum.