Pressure and velocity detectors for seismic exploration

Claim 1

A seismic detection system for suppressing ghost reflections relative to primary reflections in seismic exploration wherein a primary reflection is caused by an upwardly travelling compressional wave and a ghost reflection is caused by a rarefaction wave travelling downwardly from the surface comprising: a pressure detector producing a positive output in response to upwardly travelling compressional waves and a negative output in response to downwardly travelling rarefaction waves; a velocity detector producing a positive output in response to upwardly traveling compressional waves and a positive output in response to downwardly travelling rarefaction waves; filter means for changing the frequency content of at least one of said outputs including a minimum phase deconvolution operator having a predetermined amount of white noise added to the zero lag of the auto correlation function; means for changing the gains of said outputs so that the outputs produced in response to the ghost reflections are substantially equal; means for summing the outputs of said pressure and velocity detectors, thereby substantially cancelling the outputs produced in response to ghost reflections; and means for positioning said pressure and velocity detectors in close proximity along a line of seismic exploration.