Sound field fluctuations in shallow water waveguide in the presence of nonlinear internal waves and estimation of their speed. ASIAEX experiment as a case study

Spectra of the sound field fluctuations in shallow water waveguide in the presence of nonlinear internal waves (NIW) are studied and used for solution of inverse problem: to estimate variability of speed of NIW using results of ASIAEX experiment. ASIAEX was carried out in the South China sea since April 29 until May 14, 2001, a few tens of solitary NIW with amplitude up to 100 m were registered, moving toward the beach. Sound pulses (M-sequences, frequency 224 Hz) from the source were propagating in narrowing channel (350 m–120 m, distance 30 km) toward the beach in the presence of NIW. It was shown earlier by authors that spectrum of fluctuations measured during NIW’s motion contains peaks at frequencies F depending on speed v of NIW and scales of interference beating D of waveguide modes F ∼ v/D. D depends on bathymetry and sound speed profile in a waveguide. Using measurement of peak frequencies and known values of D, and using matching procedure between modeling and experimental data, variations of v were found for set of above mentioned events of NIW passing. Results were compared with direct measurements using satellite observations. [Work was supported by RFBR under Grant No. 20-55-S52005.]