CHRISTIAN: THE ACOUSTIC OUTPUT OF EXPLOSIVE CHARGES 



In the lower set of curves, where the close-in measurement was at a 

 935-foot standoff, the near-field and far-field curves are nearly 

 coincident. This might suggest that perhaps 300 yards is a reasonable 

 "reference range" for a 50-pound charge at 15,000 foot depth. 



The quality of these few exploratory data is too poor, and the 

 extent of them too limited, to give the kind of information on source 

 level that we need. But they do show that we must re-examine the 

 subject of reference ranges. This is not an academic question, I 

 am convinced that the methods of extrapolating and interpolating 

 among different sets of measurements contributes some of the vari- 

 ation found in reported source levels. And that the choice of 

 reference range is important to the third and last of our desirable 

 source attributes: predictability to within 1 dB in 1/3-octave bands. 



FACTORS IN SOURCE LEVEL DETERMINATION 



As noted earlier, we must still look primarily to empirical, 

 rather than theoretical, methods of determining source levels. Even 

 if we had an infinite, homogeneous ocean in which to work, source 

 level determination would not be easy, because so many factors enter 

 into the acquisition of the right number. The following list shows 

 the major factors in more-or-less decreasing order of importance: 



• CHARGE CHARACTERISTICS 



Weight 



- Depth 



Explosive Composition 



- Configuration 



• MEASUREMENT RANGE (discussed above) 



• RECORDING EQUIPMENT CHARACTERISTICS 



• PROCESSING METHODS 



43 



