Processing Data Flow
107
4
4 2
∗
0
Prediction Error Filter
–3
=
0.148
0.033
0
–0.214
–0.432
–0.164
–3
Fig. 5.29 Prediction error filter
of several effects that occur at the source, transmission through the earth, and in the recording process. These effects include the source wavelet, the recording instrument filter responses, the ghosting function, the reverberation operator, and the multiple operators. Usually none of these are known explicitly. However, the trace autocorrelation function provides information such as source wavelet shape, periods of multiples and reverberations, and amplitude relationships between multiples and primaries as shown by the autocorrelogram of Fig. 5.30. A decon filter should be somewhat longer than the period of the multiple it is to attenuate. The whitening decon filter includes approximate inverses of the source wavelet, the recording instrument filter responses, the ghosting function, the reverberation operator, and the multiple operators. The prediction error or gapped decon does not usually include an inverse filter for the source wavelet. To be exact inverses, as previously noted, the filters would have to be infinitely long. The length of the gap (α) in a gapped decon filter determines the amount of wavelet shortening, or whitening, that the filter does. Many people feel that an optimum value for gap length is the time of the second zero crossing of the autocorrelogram function this parameter. See Fig. 5.30. Figure 5.31 shows the effect of deconvolution by comparing records with, and without, decon applied. Note that the reflection widths are decreased and a number of events are removed or greatly attenuated in the deconvolved record compared to the one not deconvolved. These events are likely multiple reflections.
Source Wavelet Autocorrelation Gap Second Zero-Crossing
Lag 0
Fig. 5.30 Trace autocorrelogram and information it contains
Multiple Reflection Period