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The ``bispectrum" is another statistic
that is used to search for nonlinear interactions.
For a Fourier transform 
, it is
defined by
| ![\begin{displaymath}
B(\omega_1,\omega_2) \eq
\E [ F(\omega_1) F(\omega_2) \overline{F(\omega_1+\omega_2)}]\end{displaymath}](img134.gif) |
(56) |
A statistic defined analogously is the ``bispectral coherency."
In seismology, signals rarely have adequate duration
for making sensible bispectral estimates from time averages.
Stanford Exploration Project
10/21/1998