Accession Number:

AD0733191

Title:

Multiple Frequency Studies of Sound Transmission Fluctuations in Shallow Water,

Descriptive Note:

Corporate Author:

ADMIRALTY RESEARCH LAB TEDDINGTON (ENGLAND)

Report Date:

1970-12-01

Pagination or Media Count:

21.0

Abstract:

Studies of sound propagation in the shallow waters of the Bristol Channel were carried out between 1967 and 1969, with a systematic coverage of the seasons. Acoustic signals were transmitted and monitored by fixed bottom-laid transducers, the main path lengths being 17, 23 and 137 km. Transmissions consisted of a sequence of tone pulses, varying from 0.3 to 4.5 kHz. Both symmetrical and asymmetrical patterns of modal interference were seen, and it was deduced that at 23 km the number of effective modes was proportional to frequency. Seasonal changes were not marked at 17 and 23 km, but at 137 km there was about 30 dB extra loss in the summer. The latter is thought to be mainly due to fish attenuation, with a significant contribution from summer layering effects at the lower frequencies only. Five other types of amplitude fluctuation were seen, which it is hoped to report elsewhere. Author

Subject Categories:

  • Acoustic Detection and Detectors
  • Acoustics

Distribution Statement:

APPROVED FOR PUBLIC RELEASE