Page 190 - Acquisition and Processing of Marine Seismic Data

3.4 SWELL NOISE 181

FIG. 3.10 Swell noise is formed by (A) wind-driven sea surface waves, and (B) turbulence effect of dynamic pressure fluc-
tuations along the streamer. Their formation mechanisms are schematically illustrated in the upper panels.

a vertical high-amplitude noise band exactly at surface. However, the frequency band of the
the recording channels where the streamer recorded data is strongly dependent on the
bends. As the vessel proceeds along the line, streamer tow depth because of the ghost signal
the channels with the swell noise band move interference producing notches in the amplitude
gradually to the far offsets. spectrum (Section 2.5.1.2). The lower the tow
It is possible to reduce swell noise amplitudes depth, the wider the frequency band, and hence
by selecting suitable acquisition parameters. For the higher the resolution, although this will
instance, tow depth of the streamer can signifi- induce higher swell noise in the data. Therefore,
cantly affect the swell noise level in the data, high-resolution seismic surveys are exposed
because a deeper tow ensures acquisition in a more swell noise interference because of shal-
quieter environment, since wind-driven swell lower streamer tow depths. In order to avoid
noise activity is much stronger close to the turbulence effect of hydrostatic pressure