CHRISTIAN: THE ACOUSTIC OUTPUT OF EXPLOSIVE CHARGES 



charge weight, W, and stand-off range, R. The Gaspin and Shuler model 

 as it stands is a rather crude one and we need new data to remove some 

 of its limitations. Nevertheless, in my opinion, the model provides 

 the best source level estimates that are available, and it has been 

 widely used. 



Varying Charge Depth. In many experiments it is easier to control 

 the weight of the explosive charge than to control its depth. This is 

 especially true for acoustic research experiments, where free-fall 

 charges are often dropped from moving ships or planes, and detonation 

 depths depend on hydrostatic pressure devices or lengths of fuze. The 

 SUS Mk-61 sound signal is such a charge. In Figure 10 are shown the 

 Gaspin and Shuler (1971) theoretical spectra for 1.8 pounds of TNT — 

 the Mk-61 loading — detonated at three depths, 700, 800, and 900 

 feet. These three curves indicate the range of source levels one 

 might encounter with the Mk-61 SUS set at a nominal 800-foot burst 

 depth. Although detonation depths might vary by only a few feet for 

 charges drawn from the same lot, the MILSPEC standards are so written 

 that mechanisms with variations of almost ± 100 feet about the nominal 

 800-foot depth might come within acceptable limits and be included in 

 stock. The alternate shaded and unshaded frequency bands are the 

 popular 1/3-octave bands. What these kinds of depth variations mean 

 in terms of source level uncertainty is shown in Figure 11. The 

 ordinate of Figure 11, AE, shows the dB error introduced when actual 

 detonation depth deviates from the ideal 800-foot value. At high 

 frequencies, where the 1/3-octave band encompasses a number of bubble 

 harmonics, the errors fall within 1 dB of the norm. But down at low 

 frequencies, where the measurement band width is narrow relative to 

 the spectrum oscillation pattern, the errors are ± 3 dB. So much for 

 the hope of predicting source levels to within 1 dB, unless the actual 

 detonation depth is taken into account. Recent efforts along this 

 line will be discussed by Dr. Weinstein. 



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