### ASA 124th Meeting New Orleans 1992 October

## 3aAO2. Characteristics of near-surface, low-frequency sound speeds.

**John Cartmill
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*Planning Systems, Inc., Slidell, LA 70458
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**Ming-Yang Su
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*Naval Res. Lab. Detachment, SSC, MS 39529-5004
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The bubble size density for radius of 34 to 1200 (mu)m in near-surface
ocean from depths of 0.25 m down to 7.00 m were measured by an acoustic
resonator array during a 1992 field experiment in the Northeast Pacific. The
void fractions were computed by integrating those bubble densities. The
low-frequency (less than 1 kHz) sound speed, averaged over 3.5 s, is then
estimated from the void fraction based on a theoretical computation. A set of
more than 50 time series of the low-frequency sound speed, each of about 12 min
in length, were then subjected to several statistical analyses. The statistical
characteristics include (a) the probability density which provides, in turn,
the mean and standard deviation, skewness and kurtosis, (b) Gaussian
distribution fit, and (c) autocorrelation coefficient. The mean sound-speed
deficit from the nominal sound speed of 1500 m/s and the corresponding standard
deviation (in the order of 100 m/s) are at least 10 times larger than expected
earlier. Large zero-crossing times of the autocorrelation on the order of 100 s
for depth <1 m are also found for wind speed between 10 and 15 m/s. The
autocorrelation analysis further indicates the evidence of coupling between the
fluctuation in the bubble density and the prevailing dominant wave train. [Work
supported by ONR Acoustical Reverberation SRP.]