Using yule-walker-autoin.sci

The difference between this program and the previous example in section 6.10.1.1 is that the input must be an autocorrelation instead of a seismic signal. We use the BSU program bxcr to compute an autocorrelation data set in BSEGY format. Using the same data as above, we issue the following commands from an xterm within the directory with the data set of interest.


bxcr twav.seg twav.seg 0.0 0.5 0.1
bstk bxcrtwav.seg


The first command cross correlates the data set twav.seg with itself (ie. an autocorrelation). The gate is 0 to 0.5 seconds, for a maximum correlation lag of 0.1 seconds. This is followed by a stacking or averaging of all the autocorrelations into a single signal with program bstk. This averaged autocorrelation is then replicated so that the input and output BSEGY files have the same number of traces. In generating a spectrum, it does not matter which one of the traces from file bstkbxcr.seg we use. They are all the same. In Figure 48 we again use trace 30, but could have used any other equally well.

Figure 48: (C). Autocorrelation and stack of autocorrelations (see text). Scilab program yule-walker-autoin.sci to compute the spectrum. (A) Picking a length of the autocorrelation (nlag=112 in blue box), (B) All pole spectrum, (D) same spectrum on log scale.
Image FigureW

In both of these examples of Yule-Walker spectra, the Scilab programs are computing amplitude spectra (not power spectra). The square root is taken of the power spectrum before plotting.

pm 2010-07-22