Spectrum of sound intensity fluctuations in shallow water due to mode coupling in the presence of moving internal soliton and estimation of its velocity

In the paper results of experiment ASIAEX 2001 are considered. Episodes are analysed when soliton-like nonlinear internal wave (NIW) moves approximately along acoustic track: from the source to receiver, located at the distance ~ 30 km from each other. The depth of the ocean changes from ~ 350 m near the source up to ~ 120 m near the receiver (Vertical Line Array). The source, placed near the bottom, transmitted pulses (M-sequences) with the frequency 224 Hz. It is shown that there are "predominating" frequencies in the spectrum of intensity fluctuations measured during ~ 6 hours of NIW motion from the source to receiver. Numerical modelling on the base of authors theory (Grigorev et al, JASA, v.140(5), 3980-3994, 2016) shows that peak frequencies correspond to the most strongly interacting pairs of modes: in given case pairs 2-3, 3-4. Due to narrowing channel velocity V of soliton should decrease; note that the corresponding change of the predominating frequency as a function of range (or time) was observed while soliton was moving. It is shown that if we take speed V as the fitting parameter then it is possible to estimate V of real soliton and its variation using comparison of experimental data and results of modelling. The corresponding procedure for episode where the comparison with direct measurement of velocity was done, gives values of V changing from 1.8 to 0.8 m/s, what is in a good agreement with experimental data.