In this paper, the results of experiments concerning the fluctuations of internal waves on the thermocline and the fluctuations of acoustic amplitudes at different ranges in typical shallow water are presented. Record...In this paper, the results of experiments concerning the fluctuations of internal waves on the thermocline and the fluctuations of acoustic amplitudes at different ranges in typical shallow water are presented. Recorded time is 48.96 h. Thickness of the thermocline is about 2 m-4 m. The deviation of temperature recorded at a fixed depth is 10℃-15℃. The vertical displacement of isotherm curves is about 5 m-6 m, which is mainly dominated by the lowest model. The measured spectrums of vertical displacement have obvious spectral packet within the range of 0.05 cpm (20 min) and 0. 143 cpm (7 min) besides the diurnal and semidiurnal tide frequency bands. Spectrum attenuation coefficients are between -1.5 and -1.7. Numerical calculation shows that phase velocity and group velocity of internal waves are equal to 0.329 m/s at lower frequencies. And with the increasing of frequency, the group velocity differs from phase velocity at about 0.03 cpm (33.33 min) and drops more quickly. The measured fluctuation of acoustic amplitude is about 8 dB-10 dB. With the increasing of range, the fluctuation trends to be faster and acoustic signals are declining. Spectrum attenuation coefficients are between -1.45 and -2.0. At last, PE method is used to simulate the acoustic amplitude fluctuation, in which internal waves are the important element.展开更多
文摘In this paper, the results of experiments concerning the fluctuations of internal waves on the thermocline and the fluctuations of acoustic amplitudes at different ranges in typical shallow water are presented. Recorded time is 48.96 h. Thickness of the thermocline is about 2 m-4 m. The deviation of temperature recorded at a fixed depth is 10℃-15℃. The vertical displacement of isotherm curves is about 5 m-6 m, which is mainly dominated by the lowest model. The measured spectrums of vertical displacement have obvious spectral packet within the range of 0.05 cpm (20 min) and 0. 143 cpm (7 min) besides the diurnal and semidiurnal tide frequency bands. Spectrum attenuation coefficients are between -1.5 and -1.7. Numerical calculation shows that phase velocity and group velocity of internal waves are equal to 0.329 m/s at lower frequencies. And with the increasing of frequency, the group velocity differs from phase velocity at about 0.03 cpm (33.33 min) and drops more quickly. The measured fluctuation of acoustic amplitude is about 8 dB-10 dB. With the increasing of range, the fluctuation trends to be faster and acoustic signals are declining. Spectrum attenuation coefficients are between -1.45 and -2.0. At last, PE method is used to simulate the acoustic amplitude fluctuation, in which internal waves are the important element.
