Page 360 - Acquisition and Processing of Marine Seismic Data

6.8 SHAPING FILTERS 351

FIG. 6.36 Burg deconvolution results of a minimum phase synthetic seismogram for different operator lengths.
(A) Reflectivity series, (B) minimum phase synthetic seismogram, and its Burg deconvolution results for (C) n ¼ 20 ms,
(D) n ¼ 40 ms, (E) n ¼ 80 ms and (F) n ¼ 100 ms operator lengths. Corresponding amplitude spectra and autocorrelograms
are given in the top and bottom panels, respectively.

the methodology can also be used successfully if distribution is more suitable to a delayed spike
the output of the deconvolution is any desired like (0, 1, 0). Therefore, mixed or maximum
wavelet shape. In that case, the process is termed phase wavelets can be converted into delayed
wavelet shaping and generally is applied in spikes instead of zero phase spikes. Fig. 6.39
three forms: shows an example application of Wiener decon-
volution to a mixed phase wavelet. Because the
i. Converting a mixed or maximum phase
wavelet is not minimum phase, deconvolution
wavelet into a delayed spike
converting the wavelet into a 0-ms delayed spike
ii. Converting the minimum phase wavelet
fails. In this example, the deconvolution applica-
into a zero phase wavelet (dephasing)
tion to convert an 8-ms delayed spike produces
iii. Removal of the source signature from the
the optimum result.
data (designature)
In general, the wavelet embedded in the seis-
If the input wavelet is not minimum phase, it mic data is minimum phase except the Vibroseis
cannot be converted into a zero-delayed spike data from land surveys and watergun data from
by spiking deconvolution. For instance, the marine seismics. Although they are not physi-
wavelet w(t) ¼ ( 1, 2) considered in deconvolu- cally realizable since they are not causal, zero
tion with inverse filtering cannot be converted to phase wavelets have two major advantages over
a zero-delay spike of (1, 0, 0) since its energy minimum phase wavelets: