WEINSTEIN: EXPLOSIVE SOUND-SOURCE STANDARDS 



These data have been cleansed considerably, but some artifacts 

 are still present. The total number of data points which remain is 

 considerably reduced so that other criteria can be applied. 



It is known that the nulls and peaks in the source spectrum, 

 resulting from the bubble pulse , are retained in the spectrum of 

 signals at long range. Fortunately, narrow-band FFT processing was 

 a part of the automated processing procedure, so that the spectra 

 could be examined. The criteria applied was go/no-go. If the 

 signal spectrum looked like a shot, the data point was accepted; 

 if it did not, it was rejected. 



Figure 7 shows the circled points that were rejected on the 

 basis of the spectral criteria. The remaining data can now be 

 relied upon. Further investigations of noise fluctuations permitted 

 the establishment of estimated uncertainty bars in signal-to-noise 

 bins. These exceeded our goal of ±1 dB, exclusive of the uncertainty 

 in source level. 



Figure 8 shows the spectrum for signal plus noise on the left, 

 and the noise alone at the right for a 300-foot shot at a high S/N 

 ratio. Note that the signal plus noise shows pronounced scalloping 

 with strong nulls spaced at about 25 Hz, consistent with the source 

 spectrum expectation. The noise spectrum is totally different. 



Figure 9 shows similar results for a lower S/N ratio. The 

 signal-plus-noise spectrum is still good. 



Figure 10 shows the results for a contaminated sample. Note 

 that the signal-plus-noise spectrum does not show the null sequence, 

 and is quite similar to the noise spectrum. This is a case where 

 signal plus noise is dominated by a noise burst and this data point 

 is therefore rejected. 



72 



