Spectrum of sound intensity fluctuations due to mode coupling in the presence of moving nonlinear internal waves and bottom parameters estimation

Temporal fluctuations of intensity of sound pulses (300±30 Hz) are studied in the presence of nonlinear internal waves (NIW) moving at the some angle with direction of an acoustic track providing mode coupling. In the episode of Shallow Water 2006 experiment, considered in the work, angle between wave front of NIW and source-receiver direction is about 10 degrees. It was shown that there is main maximum in the spectrum measured at fixed depth ~8 cph and set of smaller peaks ( ~15 cph, ~25 cph, and ~35 cph) in accordance with the theory proposed by authors earlier. Besides, there is maximum in the spectrum of total intensity (summarized over depth or over all hydrophones of vertical line array) at the frequency ~15 cph. In authors opinion, the last one is determined by coupling of propagating modes (excited by the source) having maximal difference in modal attenuation coefficients (in given case modes 2 and 4). Role of horizontal refraction is small. Using the spectrum speed of NIW and bottom attenuation coefficient (in our case ~0.2 dB/wavelength) are determined. Mentioned parameters are in a good agreement with estimations obtained by other methods. [Work was supported by BSF.]