Page 182 - Acquisition and Processing of Marine Seismic Data

3. NOISE IN MARINE SEISMICS 173

noise, strum and tug noise, etc. Fig. 3.2A shows powerline harmonic noise interference (E)
first 48 traces of a noise record and its mean appeared at 50 Hz and its multiples and high-
amplitude spectrum. Low frequency (less than frequency random noise amplitudes between
approximately 10 Hz) swell noise amplitudes 140 and 180 Hz) and tug noise from tail buoy
(S) are dominant on the record. When the record (T) become visible on the data and on the ampli-
is filtered with a 14-Hz low-cut filter to remove tude spectrum (Fig. 3.2C).
the swell noise (Fig. 3.2B), the linear operational As the noise record indicates, seismic data con-
noise from vessel’s propeller (O) at approxi- tain different types of noise generally interfering
mately a 20-Hz frequency dominates. Finally, with the reflections in the time domain. Some of
if we again filter the record with a 24-Hz low- them are masked by relatively higher amplitudes
cut filter to remove the operational noise, other of othernoise components.For instance, whenthe
high frequency noise components (such as swell noise is removed from the record, the noise

FIG. 3.2 (A) A noise record and its filtered versions with (B) 14 Hz and (C) 24 Hz high-pass filter. Their mean amplitude
spectra are given in the upper panel. S, swell noise; O, operational noise; E, powerline harmonic noise; T, tug noise from
tail buoy.