Effects of Medium Fluctuations on Underwater Acoustic Transmissions in a Shallow Water Area
time (duration of individual experiments and season of the year)
space (source location, source and receiver depth)
center frequency of transmission (1 to 6 kHz)
Fluctuations are observed both in amplitude, frequency and phase (delay) of a signal. As a combined measure of fluctuations we used spreading functions and their widths in frequency and time. We also measured transmission loss and transmission loss time variations over the duration of individual experiments (30 minutes). The results showed small spreading in time. Three different classes of frequency spreading ranging from less than 50 mHz to more than 1 Hz were observed. Sea surface roughness has been identified as one source of fluctuations. Mean transmission loss is found to be rather high and seems to be more dependent on bottom properties than on range.
KeywordsInternal Wave Transmission Loss Sound Field Small Spreading Shallow Water Area
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- 1.C. Garrett and W. Munk, “Internal Waves in the Ocean”, for “Annual Review of Fluid Mechanics”, (1979).Google Scholar
- 3.Y. J. F. Desaubies, “Acousitc Fluctuations in the Ocean”, for the “Congress on Caviation and Inhomogeneities in Underwater Acoustics”, Göttingen (1979).Google Scholar
- 4.S. M. Flatte, “Sound Transmission through a Fluctuating Ocean”, Cambridge University Press, Cambridge (1979).Google Scholar
- 10.K. A. Søstrand, “Measurements of Coherence and Stability of Underwater Acoustic Transmissions”, in “Proc. of Nato Advanced Study Institute on Signal Processing”, Enschede (1968).Google Scholar
- 11.R. Laval, “Sound Propagation Effects on Signal Processing”, in “Proc. of Nato Advanced Study Institute on Signal Processing”, Loughborough (1972).Google Scholar
- 12.D. Costa and E. Hug, “An Estimate of the Scattering Function of an Undersea Channel”, Alta Frequenza 45:245 (1976).Google Scholar
- 13.E. Sevaldsen, “Variability of Acoustic Transmissions in a Shallow Water Area”, (Saclant Report in press, March 1980).Google Scholar