The applicability of principal component analysis to the separation of multiple plane-wave signals

It is shown that principal component analysis (eigenvector-eigenvalue decomposition of array spectral matrices) can be used for the approximate separation of superposed plane-wave signals only if at least one of the following conditions is satisfied: 1. (a) The signals are grossly unequal in amplitude. 2. (b) The directions and the velocities of the various signals are such that if the array is beamed at a given signal the other signals do not fall on prominent sidelobes of the array response. Application of the method for such cases is demonstrated on composited long-period seismograms using recordings from the D ring and center element of ASA.