Researches On Acoustic Signal Fluctuation Caused By Shallow Water Internal Waves

Sound wave is the most effective kind of wave which can propagate long distance under the water in the ocean. The horizontal variations in sound speed and bottom plays an important role on the sound propagation in shallow water. The existence of shallow water internal waves is the main reason for the horizontal variations in sound speed. Ocean internal wave is a kind of gravity wave generated in the ocean, especially when the stratification is strong and steady. Researches about underwater sound propagation when the internal waves exist will be very important for both the civilian use and the military use. The information of the sound propagation fluctuation can also be used to monitor the internal waves.The thesis is composed mainly of four parts. In the first part, two numerical computing model of sound propagation are discussed and a new method is presented to improve the speed of the normal mode sound propagation model. In the second part, the data obtained from the SSIAEX2001 experiment is analyzed and the double internal solitary waves are found, In the third part, the relation between internal waves and acoustical signal fluctuation is analyzed. The wave numbers, group speed and coupling features of normal mode are analyzed to classify the effect of internal tides ,internal solitary waves and the linear internal waves. In the last part, three methods are presented to monitor the shallow water internal waves.