This example shows two borehole seismic traces (VSP, vertical seismic profile) (VSP Gaz De France) where it is possible to compensate the shift between the traces. The example shows the autocorrelation of the traces (either trace 1 or 2 can be chosen) and the intercorrelation between the two traces.
The autocorrelation of trace 1 differs little from the autocorrelation of trace 2. This is due to the fact that the descending wave is identical from one trace to another, for those with a close delay, as the down-going wave amplitude is clearly higher than the up-going wave. The differences between the two traces, after correction for the time variation, show the presence of the up-going waves.
The intercorrelation very closely looks like the autocorrelation when the shift between traces is close. The measurement of the time delay between the traces is itself made from the measurement of the maximum position of the intercorrelation.
When the delay between the two traces is compensated, the maximum of the intercorrelation has a null delay.