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



Figure 11 is a series of SOFAR signals before and after a missile 

 test as recorded at Bermuda. Shown are the scheduled detonation time, 

 the detonation depth, the difference in the propagation speed from the 

 average for the SOFAR timing tick marked, and the spread in range re- 

 sulting from this timing tick. These SOFAR signals do not have the 

 sharp, clean SOFAR cutoff of those fired over a flat bottom. Presumably, 

 forward scatter from the rough mid-Atlantic Ridge topography degrades 

 the cutoff for these signals. 



Note that there is no variation in sound speed for the range of 

 detonation depths shown. Actually, this is what you would expect for 

 a SOFAR charge position east of Antigua. The average speed there at 

 the sound-channel axis is of the order of 4875 feet per second. At 

 Bermuda it's about 4890. So the axis is pinching down. This insensi- 

 tivity of average axis sound speed to detonation depth was very conve- 

 nient because the manufacturer making the SOFAR charges could never 

 meet a depth spec on the SOFAR charge. We thought depth variations 

 might cause speed variations and therefore wrote a 3 percent depth 

 specification. The manufacturer could never meet it, but, as it 

 turned out, it did not matter. 



Summarizing the conclusions, 1) the sound channel axis speed was 

 not stable; we couldn't predict it, and 2) neither the sound speed at 

 the source nor the sound speed at the receiver seemed to control the 

 average speed variation over these long transmission paths. The speed 

 variations were apparently caused by what was happening in the water 

 masses between the source and the receiver. 



23 



