bubble pulse is directly proportional to the depth at which it 

 is generated. In the region of 1000 to 3000 c/s for a non- 

 directional condition, peak acoustic pressure levels of 

 about 125 db/dyne/cm2 at 1 meter have been measured. 

 This would correspond to 300 kw of acoustic power (fig. 5). 



















































^ 



^ 



^ 



X 



^ 



^'' 









































^^ 



^ 



^ 



^' 







































,/ 



^ 



X 



^ 



^ 



^* 





Underwat 

 spark (1- 



er 

 4KC/S) 

























y^ 



X 



x* 



^ 



»* 



** 



»* 



p 



a 



P 

 a 



sis 



3B 



P 



vs 



1 



dy 



- Di 



le/cm" a 

 rectivity 



t 1 r 

 Inde 



net 



er 



) 



- 10 



Log P ,, + 70. 



^ watts 







^ 



X 



y 



X 



^ 



^* 



t*^ 

















































10,000 100,000 



Total Acoustic Power in Watts 



1, 000, 000 



Figure 5. Plot of acoustic power vs. sound pressure. 



Add to this the 10 db or more that can be gained by a reflector 

 of reasonable size, and the result is a megawatt of acoustic 

 power in a beam that can be directed wherever desired. 



By combining such features as resonant discharge loops, 

 exciting resonant cavities, and operating the spark source, if 

 possible, at a depth where the bubble pulse is at the same 

 frequency as the resonators, substantial acoustic levels could 

 be obtained in the low- frequency region required for long- 

 distance echo- ranging. The underwater spark is simplicity 

 itself when compared with complex sophisticated sonars. 



17 



