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The concept of **autocorrelation** and spectra is
easily generalized to
**crosscorrelation**
and **cross-spectra**.
Consider two *Z*-transforms *X*(*Z*) and *Y*(*Z*).
The cross-spectrum *C*(*Z*) is defined by

| |
(48) |

The crosscorrelation function is the coefficients *c*_{k}.
If some particular coefficient *c*_{k} in *C*(*Z*)
is greater than any of the others,
then it is said that the waveform *x*_{t} most resembles the waveform *y*_{t}
if either *x*_{t} or *y*_{t}
is delayed *k* time units with respect to the other.

** Next:** Matched filtering
** Up:** CORRELATION AND SPECTRA
** Previous:** Spectral transfer function
Stanford Exploration Project

10/21/1998