Spectral clipping: a ProMAX module for attenuating strong monochromatic noise
David C. Henley
One of the more pervasive noises encountered on raw seismic data is that due to the inductive pickup by geophones and cables of 60 Hz signals from nearby power transmission lines. The noise often completely swamps any seismic signals detected by the affected channels and appears as continuous sinusoidal waveforms of 60 Hz, or less commonly, 120 Hz or even 180 Hz. When the frequency of such noise is known exactly, it can be removed by one of several well-known techniques, though these can affect the data in adverse ways. Presented here is an algorithm that automatically detects any strong single-frequency or narrow-band noise on seismic traces and attenuates it in a relatively harmless way. A ProMAX module has been written to apply the algorithm, and its parameters and some test results are presented.