Reciprocal Sound Propagation Experiment and Analysis at Hashirimizu Port

摘要

A fundamental experiment for one of the environmental monitoring using reciprocal sound propagation was promoted at very shallow water area of Hashirimizu port over against Tokyo bay. Sound propagation systems with 80 kHz transducer were placed at the opposed pier with the distance of 120 m. Sound arrival time were monitored using M-sequence phase modulated signals so that accurate arrival time could be detected in noisy environment. Arrival time changes through the experimental period about 2 weeks almost followed the changes of water temperature. But in some conditions such as low tide and high temperature gradient in depth direction, arrival time was later than expected. Ray tracing calculation by Bellhop program reveal that all rays from the transducer bend toward down because of the sound speed profile changes. It turns out that the travel pass changes, which caused lost of the direct pass from the sound source, depend on the ocean environmental changes especially in temperature and tide. It also has have potentials to get wide area ocean environment by using reflected waves..