Statistics of sound transmission loss fluctuation due to internal waves in the north of the South China Sea

The performance of ocean acoustic devices is under the influence of sound fluctuation due to internal waves in shallow water.In order to study the intensity fluctuation of sound propagation due to internal waves,an experiment was conducted in 2015 in the northern of the South China Sea,with both linear internal waves and internal solitons existed.The statistics on transmission loss from a bottom anchored transducer to a vertical line array is made to analyze the evident variety due to linear internal wave and internal solitons.The fluctuation of transmission loss due to internal solitons can reach to 11 dB which is 5 dB greater than the fluctuations due to linear internal waves.And the probability distribution of the transmission loss due to internal solitons is much wider than that due to linear internal waves.In terms of normal mode,there is obvious coupling phenomenon among normal mods due to internal waves and the intensity fluctuation of the 3 rd mode up to 20 dB is observed in this experiment.The energy fluctuations of the normal modes due to linear internal waves and internal solitons are analyzed to explain the physical mechanism of sound intensity fluctuations.