Pre-stack f-k median filtering

David G. Schieck, Robert R. Stewart

Conventional P-wave recording makes use of receiver group arrays to attenuate the low-frequency, low-velocity ground roll. Additionally, a group of N geophones increases the signal-to-noise ratio by a factor of N1/2 times that recorded on a single geophone. In the case of converted P-SV wave data, pre-stack filtering should not only reduce the amplitudes of surface waves but also improve the signal-to-noise ratio by removing unwanted random noise and noise spikes. The median filter using f-k weights removes unwanted noise glitches, attenuates the often aliased surface waves, and improves the signal-to-noise ratio. A synthetic shot gather demonstrates these features of a weighted median filter relative to the more conventional frequency-wavenumber type filters. A 2- component (vertical and radial) line shot by the University of Calgary field school is processed with both types of pre-stack filters. The f-k weighted median removes aliased noise because it is a time domain operator and not subject to frequency domain wraparound. In addition, random noise rejection is superior because the non-linear median weighted filter removes the unwanted noise but the conventional f-k filter smears within its pass band. Noise glitches in a shot record remain as the f-k filter response after conventional f-k filtering but are completely removed by a weighted median filter.