Monochromatic filter for seismic signals - generates cancellation signal equal in amplitude and phase to interference

摘要

An electronic filter removes approximately sinusoidal parasitic or interference waveforms from signals received by geophones during seismic exploration. The filter mechanism is based on the use of a second signal having the same frequency and amplitude as that of the interference, this signal being used to cancel the unwanted one. The phase and amplitude of the two signals are compared providing control signals correcting any dissimilarity. A third reference signal enables the basis of further phase correction to be derived from its comparison with the residual waveform. Analysis of phase and amplitude relationships is obtained by manipulation of pulse trains having frequencies which are multiples of the interference.