BUCK: ARCTIC ENVIRONMENTAL LF ACOUSTICS MEASUREMENTS, 

 MODELS AND PLANS 



Therefore, we are naturally interested in the character of explosives, 

 and especially in their source energy. The Arctic affords in two ways 

 an excellent testing ground for shot source energy. First, it is a 

 highly stable platform from which shots, projectors, and hydrophones 

 can be easily and precisely positioned and, second, at selected times 

 the noise is extremely low. In 1970 we conducted the following 

 experiment to test Weston's predictions of source energy. A low- 

 frequency projector was suspended below the ice and CW signals received 

 on hydrophones at distances of 1.2 and 2.3 nautical miles away to 

 "calibrate" the path. Then the projector was raised and an explosive 

 lowered to the same depth through an ice hole. The CW transmission 

 loss was added to the shot signal energy flux density to attain energy 

 source levels. Forty shots, ranging from 0.0012 to 126 pounds TNT 

 equivalent (measured from the bubble pulse frequency) were detonated 

 and measured with the results shown in Figure 5. Weston's predictions 

 of source energy were subtracted from the measured values at 11 

 analysis frequencies. Here all the shots were averaged at each 

 frequency but there was no observed dependence on yield. The vari- 

 ation was due more to CW signal fluctuations than differences between 

 shots. 



Somewhat typical in acoustic experiments is another measurement 

 opportunity which comes along to cloud rather than clear the issue. 

 This was an experiment in shallow, ice-covered water in the Bering 

 Sea in 1973. Over a particular propagation path at a range of 15 

 nautical miles, with a sloping bottom, we noted the repeated signature 

 from a MK61 (1.8 pounds TNT) at 60 feet (see top left of Figure 6). 

 This is the first time we had ever seen such a signature at a 

 reasonably long range, one where the multipaths were so limited that 

 the shock energy almost completely died out before the arrival of 

 the first bubble pulse which, in turn, died out before the second 



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