Papers Published

1. Okaya, David A. and Karageorgi, Eleni and McEvilly, Thomas V. and Malin, Peter E., Removing vibrator-induced correlation artifacts by filtering in frequency-uncorrelated time space, Geophysics, vol. 57 no. 7 (1992), pp. 916 - 926 [1.1443304] .
   (last updated on 2007/04/09)

   Abstract:
   Vibrator-to-ground coupling can produce resonance-induced energy that propagates with the primary sweep and produces serious artifacts in the correlated seismogram due to the frequency structure of this offending energy. For sweeps linearly increasing in frequency, the resulting artifact is observed (uncorrelated) to increase in frequency at a linear rate differing from the original sweep. Upon crosscorrelation with the pilot sweep, the artifact-producing energy becomes distributed over an extended range of time, while the normal reflected sweep is compressed, by design, into a narrow correlation wavelet. The resulting traces thus exhibit strong amplitudes that increase monotonically in dominant frequency. Display of individual uncorrelated seismograms using a Fourier frequency-uncorrelated time (F-T) transformation reveals the relationship between the primary sweep and the induced artifact. 'Surgical' filtering in this new F-T space provides for a first-order removal of both the artifact and the energy in sweep harmonics as induced by the strong first arrivals. Two-dimensional (2-D) spectral filtering of the modulus of the (complex) 2-D transform of the F-T data provides better rejection of the unwanted energy. Application of this trace-by-trace filtering process of a badly contaminated crustal-scale multichannel CDP profile in the southern San Joaquin Valley, California, reveals significant reflections from the middle and lower crust that were obscured in the unfiltered profile.

   Keywords:
   Acoustic Generators--Effects;Data Processing--Data Reduction and Analysis;Signal Filtering and Prediction;Mathematical Transformations--Fourier Transforms;Signal Interference--Suppression;