Abstract
For transmission paths between a fixed acoustic source at 527‐m depth near Eleuthera and a fixed receiver at 1723 m near Bermuda, G. E. Stanford [J. Acoust. Soc. Am. 55, 968–977 (1974)] has shown that the spectrum of fluctuations in acoustic intensity is nearly flat up to 3 cycles/h and drops off as 1/f3 above this frequency. For comparison with internal gravity wave disturbances of the sound velocity profile, we have analyzed amplitude fluctuations of transmissions from floats deployed as part of the 1973 series of Mid‐Ocean Dynamics Experiments (MODE). These floats carrying 30‐W input, 270‐Hz sound sources pulsed for 1.67 sec at 3‐min intervals were released to drift near 28°N,70°W at a depth of approximately 1500 m. The transmissions were received by fixed hydrophones (MILS system), located on the sound channel axis on the slopes of Eleuthera and Grand Turk. We find a spectrum similar to that of Stanford except that the 1/f3 characteristic begins at 1 cycle/h. For each experiment this rolloff frequency coincides approximately with the Brunt–Väisälä frequency at the turning points of those SOFAR paths with minimum excursion from the axis.
Published Version
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