Accession Number : AD0763360

Title :   Signal Fluctuations in Shallow Water: BIFI 48-Hour Tests.

Descriptive Note : Research rept.,

Corporate Author : NAVAL UNDERWATER SYSTEMS CENTER NEW LONDON CONN NEW LONDON LAB

Personal Author(s) : Kanabis,William G.

Report Date : 10 MAY 1973

Pagination or Media Count : 63

Abstract : Short- and long-term fluctuation studies were made in the 37-kyd Block Island-Fishers Island (BIFI) Shallow Water Acoustic Range at a frequency of 1700 Hz. It is shown in this report that time smear analysis may be used to predict the extent of short-term signal fluctuation by taking into account the energy content of the 'front' and the 'tail' of the received signal. This method is then applied to an actual received signal with good results. Long-term fluctuation, such as that caused by tide, is considered in terms of normal mode theory and the results of the time smear analysis are used to provide an estimate of the relative strengths of the modes. When applied to the BIFI range, the estimate predicts that tidal effects will cause negligible fluctuations in the received signal because of the absence of other than the fundamental modes - a prediction that has been verified by experiment. At shorter ranges, interactions of several modes cause relatively large fluctuations in the signal as water depth changes during the tidal cycle. Measurements of frequency smear over the BIFI range are also described. The nonuniformity of the smearing of energy into the sidebands that is apparent in the measurements is explained. (Author)

Descriptors :   (*UNDERWATER SOUND, SHALLOW WATER), SOUND TRANSMISSION, ULTRALOW FREQUENCY, TIDES, WIND, ATTENUATION

Subject Categories : Physical and Dynamic Oceanography
      Acoustic Detection and Detectors
      Acoustics

Distribution Statement : APPROVED FOR PUBLIC RELEASE