Let us consider a simple model of seismic traces recorded
by an N-channel seismic array:

X_{i}(f)=U_{i}(f)+S_{i}(f),

(1)

where X_{i}(f) is the Fourier component of the trace i for
frequency f, U_{i}(f) is signal from the source we want
to locate, and S_{i}(f) is the unwanted (interfering) signal.
An important assumption is
that signals from different sources are uncorrelated with
one another, but signals from the same source at different traces
are well-correlated.