Sound Amplitude Fluctuations Due to Internal Tides.
Abstract
Large amplitude and phase fluctuations in underwater acoustic wave fields occur and are primarily due to the temporal and spatial variability of the water and its boundaries. The amplitude part of this phenomenon is investigated by obtaining simultaneously, time and space series of environmental and acoustic data from sensor arrays fixed in space, in shallow coastal water off California. The signal output from an ultrasonic source, mounted on a tripod three meters above the bottom, is monitored continuously by a hydrophone 150 meters away. The source radiates CW pulses at the repetition rate of one pulse per three seconds at 30 kHz. Time series of temperature from a vertical thermistor array, surface wave height, and the two horizontal components of water motion from an EM current meter are obtained. A sampling interval of three seconds was used. In continental shelf areas, the tidal force is frequently the principal driving mechanism giving rise to internal fluid oscillations of tidal period. Herein, the effect of 'internal tides' upon acoustic wave propagation is examined. A low pass numerical filter was used to reject all nontidal, high-frequency components from each of the time series. Vertical, time-dependent, sound-speed profiles were determined at hourly intervals. A ray optics technique is employed to clarify the interaction mechanism and good agreement is obtained between theoretical and experimental results. (Author)
Document Details
- Document Type
- Technical Report
- Publication Date
- May 01, 1978
- Accession Number
- ADA054609
Entities
People
- P. A. Barakos