Method and apparatus for testing seismic vibrators

Claim 1

A system for seismic exploration wherein a plurality of vibrator sources are employed simultaneously to generate an input signal whose frequency varies as a function of time and wherein said signal is reflected and refracted to detector stations from subsurface beds, in which said sources are tested to select for exploration those sources having substantially the same output characteristics, said system comprising: a. means for generating at a first location a system vibratory reference signal having a pattern of known phase and frequency characteristics, b. means for generating at a first vibrator source a signal representative of the output of said source, c. means for converting said system reference signal and said signal representative of the output of said source to constant amplitude such that the signal pattern of each is represented only by phase and frequency, d. means for cross-correlating said converted system reference signal with said converted signal representative of the output of said source to generate a cross-correlation function, e. means for generating with said reference signal a correlation function, and f. means for comparing the peak value of said cross-correlation function with the peak value of said correlation function to obtain the degree of accuracy of said signal representative of the output of said source, whereby the degree of accuracy of each source is utilized to select for exploration those sources whose accruracy is substantially the same.

Claim 2

A system for seismic exploration wherein a plurality of vibrator sources are employed simultaneously to generate an input signal whose frequency varies as a function of time and wherein said signal is reflected and refracted to detector stations from subsurface beds, in which said sources are tested to select for exploration those sources having substantially the same output characteristics, said system comprising: a. means for generating at a first location a system vibratory reference signal having a pattern of known phase and frequency characteristics, b. means for generating at a first vibrator source a signal representative of the output of said source, c. means for converting said system reference signal and said signal representative of the output of said source to constant amplitude such that the signal pattern of each is represented only by phase and frequency, d. means for cross-correlating said converted system reference signal with said converted signal representative of the output of said source to generate a cross-correlation function, e. means for generating with said reference signal a correlation function, and f. means for comparing the peak value of said cross-correlation function with the peak value of said correlation function to obtain the degree of accuracy of said signal representative of the output of said source, whereby the degree of accuracy of each source is utilized to select for exploration those sources whose accruracy is substantially the same.

Claim 5

A method of seismic exploration wherein a plurality of vibrator sources are employed simultaneously to generate vibratory input signals each having a characteristic which varies as a function of time and wherein said signals are reflected and refracted to detector stations from subsurface beds, in which said sources are tested for signal accuracy comprising the steps of: a. generating at a first location a system vibratory reference signal having a pattern of known phase and frequency characteristics, b. generating at a vibrator source a signal representative of the output of said source, c. cross-correlating said system reference signal with said signal representative of the output of said source to generate a cross-correlation function having a peak value representative of phase coherence, d. establishing from said reference signal a correlation function having a peak value representative of maximum coherence, e. comparing the peak value of said cross-correlation function with the peak value of said correlation function to obtain an indication of accuracy of said signal representative of source output, f. comparing the time of occurrence of the peak value of the cross-correlation function and the time of occurence of the peak value of the correlation function to obtain an indication of time alignment of said signal representative of the output of said source, and g. utilizing in exploration those sources tested having outputs whose degree of accuracy and time alignment are substantially the same.

Claim 6

A method of seismic exploration wherein a plurality of vibrator sources are employed simultaneously to generate vibratory input signals each having a characteristic which varies as a function of time and wherein said signals are reflected and refracted to detector stations from subsurface beds, in which said sources are tested for signal accuracy comprising the steps of: a. generating at a first location a system vibratory reference signal having a pattern of known phase and frequency characteristics, b. generating at a vibrator source a signal representative of the output of said source, c. cross-correlating said system reference signal with said signal representative of the output of said source to generate a cross-correlation function having a peak value representative of phase coherence, d. establishing from said reference signal a correlation function having a peak value representative of maximum coherence, e. comparing the peak value of said cross-correlation function with the peak value of said correlation function to obtain an indication of accuracy of said signal representative of source output, f. comparing the time of occurrence of the peak value of the cross-correlation function and the time of occurence of the peak value of the correlation function to obtain an indication of time alignment of said signal representative of the output of said source, and g. utilizing in exploration those sources tested having outputs whose degree of accuracy and time alignment are substantially the same.