Accession Number:

AD0671509

Title:

INVESTIGATION OF LONG PERIOD NOISE AT LASA

Descriptive Note:

Technical note

Corporate Author:

MASSACHUSETTS INST OF TECH LEXINGTON LINCOLN LAB

Personal Author(s):

Report Date:

1968-06-03

Pagination or Media Count:

65.0

Abstract:

The long-period noise in the 20 to 40 second period range limits the identification level at which the surface-wave, body-wave discriminant can be applied at the Large Aperture Seismic Array LASA. Therefore, an investigation was made to determine the sources and properties of this noise. Only the long- period vertical array at LASA was considered. Both conventional and high- resolution frequency-wavenumber spectra are presented for the noise, as well as coherence results. These data show that the noise consists of two components. One component propagates across the array as fundamental-mode Rayleigh waves and is known to be caused by the action of surf on coastlines. The other component is nonpropagating and evidence is presented which indicates it is caused by the elastic loading on the ground by the earths atmosphere. This is established by correlating the power of the nonpropagating noise with the power on the microbarograph sensors at LASA. It is also shown that the signal-to-noise ratio gain obtained with maximum-likelihood processing relative to that obtained with beamforming for the long-period noise present at LASA, will not be substantial unless it can be shown that significant amounts of propagating noise power, relative to total noise power, are present. The results at LASA indicate that such large amounts of propagating noise power are rarely to be observed. Author

Subject Categories:

  • Seismology

Distribution Statement:

APPROVED FOR PUBLIC RELEASE