Discussion of the filtering method

Using a PEF to approximate the covariance matrix (equation (1)) leads to a proper filtering of the coherent noise present in the data. Nonetheless, this PEF has to estimate accurately the noise pattern. If a noise model does not exist, the PEF can be calculated from the residual of a previous inverse problem in which no attempt has been made to attenuate the noise.

The next section describes what I call the subtraction method which does not filter the noise but rather predicts it. This method has the ability to decrease the effects of signal/noise correlations.