Characterizing and suppressing a very low frequency OBC noise

Abstract

Some ocean bottom seismic records from Western Australia show very low frequency noise amplitudes that can be larger than peak-to-peak amplitudes of seismic reflections on OBC hydrophone records. When the three, orthogonal, co-located accelerometer sensors are integrated, this low frequency noise also becomes visible on the resulting velocity traces. The noise period is longer than a 5000 ms record length. Since this marine seismic noise is at a very low frequency and not generated by the seismic source, a best practice would have been additional, analogue, low cut, filtering in the field to suppress its effects on seismic records and subsequent processing. It is difficult to suppress this noise using traditional seismic processing filters without generating large truncation edge effects. Fortunately, digital recursive filters can be designed to be applied with initial condition constraints to suppress the undesired transient edge effects. As a result, the very low frequency noise can be suppressed on finite length records in the computer without truncation edge effects.