Acoustical monitoring of ocean environment at the very shallow area

Very small scale reciprocal sound propagation experiment has carried out since 2006 in Hashirimizu Port, Tokyo Bay. The distance between the transducers is 110 m and the average depth of the area is about 6 m. M- sequence phase modulated signal was sent each other with the duration of 30 s in reciprocally. The peak tracking of the biggest peak of the demodulated signal included travel time from at least two paths. The calculated results from FDTD method indicated that the peak shape varied according to the environmental changes of the propagation area, especially by the tidal changes. Tracking of the two bigger peaks comparing with the previous status had relatively reasonable results especially the second arrival peak. The firs peak tracking still include the travel time of the several paths and more accurate tracking will be required to monitor the temperature or current from the reciprocal sound propagation.