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



Again, this is a Sanborn recorder with log-audio recording. The verti- 

 cal scale for each of the records covers 50 dB. Shown at the bottom 

 is a one-second interval. Direct signals are marked with a D, 

 surface reflections with an S. Rise times for these signals are 

 less than 0.01 seconds. The two pulses following D and S are sub- 

 bottom echoes. 



In Figure 5 are shown the results of the first year's program. 

 Primarily shown here are results for two phones at Bermuda and three 

 at Eleuthera. The error bars indicate the full spread of the sound- 

 speed data. There are two immediate conclusions. Obviously, the sound- 

 channel axial speed was not constant. There are times when the speed 

 remains constant for a month or two, but it can also change by 2 feet 

 per second within a month. The second conclusion concerned the cause 

 of the sound-speed variations. The month-to-month variations on the 

 Bermuda and Eleuthera phones do not correlate. The inference there- 

 fore is that the cause of the speed variations is not a phenomenon at 

 the source. Note also that speed variations at the two Bermuda phones 

 track very nicely. Although these phones are about ten miles apart, 

 the line between the "SOFAR Station bottom hydrophone" and the "BOA 

 Spd" (Broad Ocean Area suspended) hydrophone continues directly to the 

 Antigua hydrophone area. And so we inferred that whatever is causing 

 the variations in the average sound-channel speed between Antigua and 

 Bermuda is not some small-scale effect in the area of the receiving 

 hydrophones . 



For the three Eleuthera phones, the transmission paths to each of 

 the individual phones are not identical, and the speed variations, 

 although similar, don't track as accurately as those at Bermuda. 



In Figure 6 are the SCAVE results for 2.5 years. At the top are 

 three additional transmission paths. Ascension and Fernando de Noranha 



14 



