Estimation of parameters of moving nonlinear internal waves using spectrogram of sound intensity fluctuations due to mode coupling

Abstract

In this paper, results of experiment ASIAEX in the South China sea are considered. Episodes are analyzed when soliton-like nonlinear internal wave moves during ∼6 h approximately along acoustic track ∼30 km; from the source to receiver, where depths of the sea is ∼350 and ∼120 m correspondingly. The source, placed near the bottom, transmitted pulses (M-sequences) with the frequency 224 Hz. Spectrogram of intensity fluctuations calculated on the base of theory of authors [Grigorev et al., J. Ascout. Soc. Am.140(5), 3980–3994 (2016)] shows that peak frequencies in spectrogram correspond to the most strongly coupling pairs of modes: in given case 2-3, 3-4. Due to narrowing channel velocity V of moving soliton should decrease; note that the corresponding change of the predominating frequency as a function of position of soliton (or time) was observed. It is shown that temporal dependence of soliton’s speed can be the fitting parameter to estimate this dependence using comparison of experimental data and results of modeling. The corresponding procedure gives values of V changing from 1.8 to 0.8 m/s, what is in a good agreement with satellite data, obtained for the same event. [Work was supported by RFBR, Grant 20-55-S52005.]