Mobil Oil Corporation

Paul G Griffith

Thomas E Shirley

Andrew F Linville, Jr

The output of a local oscillator is applied to an external signal to produce a feedback error signal. The feedback error signal is utilized in adjusting the phase, frequency and amplitudes parameters of the local reference sine-cosine quadrature components which comprise the output of the local oscillator signal. Adjusting the parameters modifies the output of the local oscillator. The modified output of the local oscillator is applied to the external signal to continuously modify the feedback error signal, which in turn, continuously modifies the output of the local oscillator until the frequency and phase of the local oscillator signal is locked to that of the external signal.

Method and apparatus for locking the frequency and phase of a local

Method and apparatus for removing sinusoidal noise from seismic traces comprised of a seismic data component and a sinusoidal noise component. Seismic traces acquired by conventional seismic exploration of a subsurface formation are utilized to produce a frequency domain amplitude spectrum of the traces. The amplitude spectrum is analyzed to determine a line frequency equivalent to the sinusoidal noise frequency to be removed. A filter order N (number of filter weights) is selected and the exact autocorrelation function of the selected sinusoidal frequency is determined for lags 0, 1, . . . , N-1. An autocorrelation matrix is produced utilizing the determined autocorrelation values and predictive deconvolution techniques are applied to the autocorrelation matrix to produce a convolutional filter which will remove sinusoidal noise at the determined frequency while leaving other frequencies minimally attenuated. The sinusoidal noise is then removed from the seismic data by convolving the acquired seismic traces with the filter.

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Dallas, TX, United States of America

Paul G Griffith