Analysis of acoustic-energy fluctuations caused by internal waves in the Yellow Sea

This paper analyzes experimental data on internal waves and acoustic intensity fluctuations in the Yellow Sea. The temperature profile of the experimental sea area has a typical three-layered structure. Internal waves with the tidal-period, nonlinear internal waves, and high-frequency internal waves are all observed, and among these the semidiurnal internal tide and nonlinear internal waves are the more active. The acoustic-energy fluctuations of 600-900 Hz linear frequency-modulated (LFM) signals exceed 10 dB over 10km. The time-varying acoustic-energy fluctuation curve contains two periodic components on timescales of the order of hours and minutes. Data analyses and simulations show that the different periodic components of the LFM signal fluctuations are related to changes in the depth of the sound source and of the receiving array caused by tides and to changes in the acoustic-velocity profile caused by internal waves.