Fluctuating Acoustic Refraction in the Deep Water of the Caribbean Sea

Abstract

The velocity of sound in the Caribbean was measured with high sensitivity and data-sampling rate, using the automatic NBS type of velocimeter. At four latitudes between 16° N and 13° N, a meter moving at 2 knots at a depth of 800 m was read 4 times per second. A statistical analysis was made in terms of the deviation in sound velocity from a moving average over 10 m of path length, which eliminated the influence of depth variation. Over the four latitudes, rms deviations were between 0.05 and 0.08 msec−1. All of the normalized autocorrelation coefficients showed the same shape as a function of space interval. The first null, a measure of “patch size,” was generally around 1.2 m. North of Bonaire Island, the sound velocity was monitored at depths between 300 and 1200 m, with a stationarily suspended set of 3 velocimeters. They were sampled simultaneously, one every 9 sec, and a similar moving average technique was used in analysis. The best evidence available for the underwater current indicates that the averaging length varied from 10–20 m. The rms deviations were from 0.05 to 0.12 msec−1 for depths greater than 500 m. The spacings between the meters were 9, 12, and 21 m, and there was no discernible crosscorrelation of the sound-velocity deviations. By careful comparison with similar but differently observed results for deep Atlantic Ocean water, it is quite clear that the inhomogeneity of the Caribbean is generally smaller and finer grained. [Hudson Laboratories of Columbia University Informal Documentation No. 42. Work supported by the U. S. Office of Naval Research.]