In comparing one wave-form with another, the correlation of two digital traces (i.e. wave-forms that have been digitized) which are similar but not the same, with one being delayed in time with respect to the other. The operator slides one trace past the other in small time steps (called delays or lags) and at each step the elements of the traces are multiplied together, term by term, and the products added. The maximum value (almost equal to unity) of this cross-correlation is obtained when the two traces are in closest alignment with each other. A value of -1 means the wave-forms are identically matched but opposite in phase; a value approaching zero indicates low degrees of similarity. The method is extremely useful for detecting wave-forms swamped by noise and, in particular, in the analysis of Vibroseis records. See also auto-correlation.
Subjects: Earth Sciences and Geography.