== Squared coherency spectrum == which expresses the amplitude spectrum in dimensionless units. ...
The cross spectrum Fxy(f) of fx(t) and fy(t) is the forward Fourier Transformof the cross correlation function Rxy(T). The cross spectrum is in generalcomplex. The cross spectrum can also be obtained from the individual Fourier spectra Fx(f) and Fy(f)Fxy(f)=F'