Signal Fluctuations in Shallow Water: BIFI 48-Hour Tests.
NAVAL UNDERWATER SYSTEMS CENTER NEW LONDON CONN NEW LONDON LAB
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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
- Physical and Dynamic Oceanography
- Acoustic Detection and Detectors