cross correlation function (CCF)
A cross correlation(CCF) or autocorrelation is the mathematically derived correlation between two variables, functions or signals at different points in time.
This correlation can be done by multiplying both signals and then integrating the result. If the result, expressed in the correlation coefficient, is zero, the two signals have no relationship; they are uncorrelated or orthogonal.
Cross-correlation may involve finding a repeating signal pattern hidden in the noise.