f VSP Noise suppression through spectral equalisation

Spectral equalisation or spectral balancing is the suppression of seismic noise through power-spectral processing only, the phase spectra remaining unchanged. Tufekcic et al (1981) demonstrated a multichannel scheme in which the power spectra were spatially smoothed, over a large number of traces. Coppens and Mari (1984) showed that selectively weighting the power spectrum over the useful frequency band also gave good results. Both these schemes target the distortion introduced by surface-seismic ground roll. Ground roll is usually characterised by high-amplitude narrow-band spectral interference. That is, the noise is non-Gaussian. Since the character of VSP noise is very of ten non- Gaussian, it would seem that spectral equalisation should solve some of the noise problems experienced in the borehole environment.