An 1120 Hz CW sound source was placed on the bottom in 60 ft of water off Fort Lauderdale, Florida. The sound from the source was monitored by a number of hydrophones placed on the bottom about 5000 ft away in the direction parallel to the shore. The received sound was observed to be unsteady, and to exhibit fluctuations of two kinds. One fluctuation had a periodicity of 3 to 4 sec, the same as that of the sea and swell in a 5 to 15 kt wind, and was accompanied by phase difference fluctuations between hydrophones. The other had a periodicity the same as that of the tides, with fades of 15 dB or more occurring at the times of low water. This tidal variation has been accounted for by both a simplified form of normal mode and by image theory in terms of the interference between the first few modes or rays responsible for the transmission.
All Science Journal Classification (ASJC) codes
- Acoustics and Ultrasonics
- Arts and Humanities (miscellaneous)