WEINSTEIN: EXPLOSIVE SOUND-SOURCE STANDARDS 



The central plot of Figure 5 shows the propagation- loss data. 

 The ambient- noise levels which were received concurrent with the 

 shots are plotted in the upper part of Figure 5 at the ranges of 

 the shot. The resulting S/N ratio for each data point is shown in 

 the lower set of data. S/N ratios as low as -10 dB had been 

 accepted at this stage. Note that the background noise shows a 

 large increase and that the propagation loss follows this change. 

 Also note that the S/N ratio is poor over this entire region. What 

 is happening is simply that following the noise measurement a noise 

 burst coincidentally occurs at the approximate time that the SUS 

 signal was expected, which is read as signal plus noise, so that, 

 in effect, a noise fluctuation is mistaken for signal and an 

 erroneous propagation loss is computed. 



It is important to note that the processing system was fully 



automated. In a large experiment, the product of the number of hydro- 



6 

 phones, shots and frequency bands of interest is of the order of 10 . 



Automation is essential to handle this quantity of data. The care 

 and subjective experience which the scientist can apply when process- 

 ing data by hand have to be converted to definitive algorithms for 

 the computer to make a decision. This is not an easy task, particu- 

 larly for those qualitative factors which the scientist does not 

 verbalize but applies by gut feeling. If a 10-dB S/N ratio require- 

 ment were applied to this data set, nothing would be left. 



Based on the preceding curves, we therefore decided to reject 

 all data for which S/N was less than -3 dB , and plotted the remaining 

 data with different symbols for S/N of -3 to dB, to +3 dB, and 

 greater than +3 dB. The result is shown in Figure 5. Data rejected 

 for poor S/N are shown along the bottom at the appropriate range. 



70 



