■HAMILTON: TIME VARIATIONS OF SOUND SPEED OVER LONG PATHS IN THE OCEAN 



here are of the order of 0.15 feet per second. The eight-day variation 

 is about 0.4 feet per second. 



Figure 8 data are from a series of SOFAR shots across the center 

 of the Antigua hydrophone array on a NE-SW line to see if the axis sound 

 speed to each hydrophone was sensitive to small changes in the source 

 position. As shown, there is a small effect. Additional profiles would 

 have been required to determine if this was a source-position or trans- 

 mission-path effect. 



Figure 9 is a record of the seawater temperature at the sound- 

 channel axis off Eleuthera. The equivalent sound-speed variations are 

 shown at the lower right. Shown are temperature variations in excess 

 of 0.5°C corresponding to maximum sound-speed variations of five feet 

 per second although more typical sound-speed variations are on the order 

 of three feet per second. 



Figure 9 also illustrates a rough comparison of the Figure 6 data 

 for 1961, 1962, and 1963 Eleuthera hydrophone sound speeds with the 

 seawater thermistor temperature readings. Speeds from Figure 6 are 

 plotted as circles on Figure 9 with a vertical line drawn to the sea- 

 water temperature at that time. It is apparent that the correlation 

 between the two is rather poor, indicating that the sound speed at the 

 hydrophone is not the dominant factor controlling the average sound 

 speed over this 1,000-mile transmission path. 



Figure 10 is a series of sound-speed profiles in the area of 

 the Antigua shot positions illustrating the extreme variability of the 

 water masses in this area at axis depths. Two velocimeters calibrated 

 to identical readings were used in this instrument package to increase 

 the confidence that the small perturbations in the profile were real. 



19 



