Tidal Effect in Small-Scale Sound Propagation Experiment

A sound propagation experiment in very shallow water was conducted at Hashirimizu port in 2009. We transmitted 5 kHz sinusoidal waves with $M$-sequence modulation. As a result, we found that the travel time concentrated in two time frames. When comparing the travel time with the tide level, the trav...

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Bibliographic Details
Published inJapanese Journal of Applied Physics Vol. 51; no. 7; pp. 07GG08 - 07GG08-7
Main Authors Kamimura, Seiji, Ogasawara, Hanako, Mori, Kazuyoshi, Nakamura, Toshiaki
Format Journal Article
LanguageEnglish
Published The Japan Society of Applied Physics 01.07.2012
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Summary:A sound propagation experiment in very shallow water was conducted at Hashirimizu port in 2009. We transmitted 5 kHz sinusoidal waves with $M$-sequence modulation. As a result, we found that the travel time concentrated in two time frames. When comparing the travel time with the tide level, the travel time was dependent on the tide level. In terms of the wave patterns, most of the wave patterns have two peaks. As the tide level changed, the biggest peak switched within two peaks. To discuss this, numerical simulation by finite difference time domain (FDTD) method was carried out. The result agreed with the experimental result. Finally, we changed the material of the quay wall in the FDTD simulation and concluded that the first peak is a multireflected combination wave and the effect of its reflected wave at a quay wall has superiority in the second peak.
Bibliography:Map of experimental site, Hashirimizu port. The circles and star indicate the location of the transducers and ADCP, respectively. Vertical sectional view of the device arrangement in water. The depth of bathymetry is adjusted to the depth at full tide. Block diagram of the underwater sound transceiver system. This system consists of two parts, a transmission part and a reception part. (a) Example of wave patterns observed by the sound propagation experiment. There is a transient noise near 0.02 ms. (b) Wave pattern after demodulation. Travel time and normalized amplitude of correlation value during the analysis period, where the travel time is represented by the white line and the correlation is represented by the background color. There are two time frames. Sound speed and water temperature during analysis period. The sound speed is calculated by using the water temperature data. Comparison between travel time and tide level from 07:00 to 22:30 on 11/5. The solid line and the dotted line represent the travel time and the tide level, respectively. Travel time and correlation value from 07:00 to 22:30 on 11/5. Most of the wave patterns have two peaks. Typical examples of wave patterns after demodulation at 19:20, 19:40, and 20:00 on 2009/11/5. The correlation values change with time. Calculation model for sound propagation in the FDTD method. This figure is not to scale. Wave pattern after demodulation and phase calculated by FDTD method. The travel times become almost the same in the column figure. Comparison of travel time with tide level in the experiment and FDTD method. Wave patterns after propagation of 5 m. The tide level is 1.0 m. The calculation conditions are changed.
ISSN:0021-4922
1347-4065
DOI:10.1143/JJAP.51.07GG08