Tracking bandpass filter for conditioning vibrator accelerometer waveform

In a system for imparting vibratory seismic energy to the earth, the combination which comprises:

• a. means for generating a first digital signal,
• b. a digital to analog converter responsive to said first digital signal to provide a first analog electrical signal for controlling the motion of a hydraulic vibrator,
• c. means for generating a second analog electrical signal representative of the motion of said hydraulic vibrator,
• d. a signal conditioning means including a tracking bandpass filter responsive to said second analog electrical signal to provide a modified signal, and
• e. comparator means responsive to said modified signal and to said means for generating a first digital signal for providing an error signal whereby said first digital signal is modified.

A method of controlling the operation of a variable frequency vibratory seismic source comprising the steps of:

• a. controlling a tracking bandpass filter to maintain the peak of its amplitude response near the desired instantaneous frequency of said source,
• b. providing a signal representative of the motion of said source,
• c. applying said signal to said tracking bandpass filter.
• d. comparing the phase of the signal produced by said tracking bandpass filter with the phase of a reference signal to provide an error signal, and
• e. controlling the movement of said source by utilizing said error signal.

A vibratory seismic source comprising:

• a. a pad for imparting elastic waves to the underlying earth material,
• b. hydraulic piston means for applying reciprocating forces to said pad,
• c. sensor means for providing a first electrical signal representative of the motion of said pad,
• d. means for generating a second electrical signal representative of the desired motion of said pad,
• e. tracking bandpass filter means responsive to said first electrical signal, the frequency response of said tracking bandpass filter means being variable to maintain a local amplitude response peak at the instantaneous frequency of said second electrical signal;
• and
• f. phase comparator means responsive to said second electrical signal and to the signal produced by said tracking bandpass filter means to generate an error signal for controlling the operation of said hydraulic piston means.

A vibratory seismic source comprising:

• a. a hydraulically operated vibrator means,
• b. means for generating a first digital signal,
• c. a digital to analog converter responsive to said first digital signal to provide a first analog electrical signal for controlling the motion of said hydraulically operated vibrator means,
• d. means for generating a second analog electrical signal representative of the motion of said hydraulically operated vibrator means,
• e. signal conditioning means including a tracking bandpass filter responsive to said second analog electrical signal to provide a modified signal, and
• f. comparator means responsive to said modified signal and to said means for generating a first digital signal for providing an error signal whereby said first digital signal is modified.