EXTRACTION OF A DIRECTIONAL SIGNAL FROM ISOTROPIC NOISE OF THE SAME SPEED ADVANCED ARRAY RESEARCH.

Abstract : A theoretical comparison is made between Wiener multichannel filtering and beamsteer processing for arrays of long-period vertical seismometers. A 7- and a 19-element array are considered. Both are arranged on a hexagonal grid with 20-km spacing between elements. The S/N ratio improvement is calculated for the range of 0 to 0.25 Hz. The signal is a Rayleigh wave propagating in a specific direction at 3 km/sec. The noise consists of an isotropic component, also propagating at 3 km/sec, and of a small amount of random energy. The vertical displacements of both noise components and of the signal have white power-density spectra. The principal result is that MCF processing in this particular situation is significantly better than beamsteering only below 0.05 Hz, where neither processor approaches a square root of (N) S/N ration improvement. At higher frequencies, the improvement provided by either processor oscillates about the square root of (N) level as a function of frequency. The maxima and minima in the S/N ratio curves are easily interpretable in terms of the aliasing properties of the arrays. (Author)