bxcr twav.seg twav.seg 0.0 0.5 0.1
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.
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.