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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.

the measuring function between the remote-control boat and other reference equipment to survey the accuracy of our proposed method. The results confirmed the accuracy of position, sounding, and temperature measurements made by the boat in practical use. Next, we measured water temperature profiles in Hashirimizu port using the remote-control boat system. According to the temperature data, unexpected changes of water temperature were found at different locations and times, caused, we believe, by variations in the air temperature accompanying weather conditions. Finally, we calculated the sound ray trace using actual sea temperature data and confirmed the available path for sound propagation in very shallow water. Classification: 音波伝搬，海洋構造，その他 (観測，計測等)Keyword

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