Counterevasion Studies - the Effects of Noise, Dissimilarity, and Prefiltering on Cepstrum Analysis
Semi-annual technical rept. no. 5, (pt. B), 1 May-31 Oct 1975
TEXAS INSTRUMENTS INC DALLAS EQUIPMENT GROUP
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The effects of the noise, the dissimilarity, and the prefiltering on the detection of the P-pP delay time and the successful decomposition of the mixed P- and -pP wave by employing the cepstrum analysis are studied here. These effects have been investigated by extracting the direct P-phases and the surface reflected pP-phases from several presumed underground explosions in eastern Kazakh, and remixing them at various time delays with the addition of various levels of the realistic seismic noise. The quality of the cepstrum analyzed results as a function of the signal-to-noise ratio, the delay time, and the dissimilarity between the P-phase and the pP-phase have been obtained for a number of such events. In general, it is found that the cepstrum analysis can detect the P-pP delay time as short as 0.4 second and successfully recover the P- and the pP-phases for the signal-to-noise ratio down to about 12 dB. When the similarity coefficient between the P- and the pP-phases is less than 1.0, the detection of the P-pP delay time becomes not so obvious as it is when they are identical. The dissimilarity between the P-Phase and the pP-phase will affect the detection of the P-pP delay time more seriously than the noise in the cepstrum analysis.