WEINSTEIN: EXPLOSIVE SOUND-SOURCE STANDARDS 



to determine the bubble-pulse period, provided we have either an 

 experimentally determined data base, or a proven computational 

 procedure, which permits us to relate depth variation to source- 

 level variation in the processing bands of interest. 



EFFECT OF NOISE 



The second source of uncertainty is background noise. To deter- 

 mine propagation loss, one integrates the signal and noise over the 

 signal arrival interval and subtracts out the noise from an estimate 

 obtained by measurement prior to signal arrival. The time interval 

 between the measurement of noise, and signal plus noise, is typically 

 about one-half minute. If the noise varies over this time interval, 

 an uncertainty will be introduced in the computed propagation loss. 

 Ordinarily, by using only data with high signal-to-noise (S/N) 

 ratios, perhaps 10 dB or more, this problem is minimal. However, 

 in large-scale experiments employing many ships, thousands of shots, 

 and automated remote recording systems, the problem may be more 

 significant. If the S/N level is less than desired, quality assurance 

 techniques must be applied to extract the good data and reject the 

 poor data. 



In Figure 4, the error in propagation loss is plotted as a 

 function of S/N ratio for changes in noise level of ± 0.2, ± 0.4 or 

 ± 1.0 dB. As one would expect, the error increases as the signal-to- 

 noise ratio decreases. 



This problem was encountered in a recent experiment. The 

 following figures illustrate the staged improvement in the quality 

 of data as quality assurance procedures were applied. 



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