Page 298 - Acquisition and Processing of Marine Seismic Data

5.7 TRACE EDIT 289

FIG. 5.51 (A) Two filtered successive shots in which the first six and last three channels are dead. (B) Same shots after
removing the amplitudes of dead channels. The red and blue boxes correspond to close-ups from the very first and last channels
of the shot, indicated by I and II before the trace kill, respectively.

over the channels of each shot gather, as is the may be the gun control unit or communication/
case in Fig. 5.52A. Although it is also possible triggering issues between the gun controller and
to remove them with a surgical mute triggering system, and the recording unit. All
(Section 5.8), it will take too much time when traces of the missed shots are killed completely
the number of spikes is excessive and it may from the dataset; if not, these traces corrupt
be much more practical to use trace kill. the stack section after stacking and reduce the
Fig. 5.52B shows the spiky shot after the trace kill S/N ratio of the final seismic section.
in which six traces containing extremely high- Fig. 5.53A shows a number of successive shots
amplitude spike noise are edited and killed. with a missed shot (shot number 113) containing
In marine seismic acquisition, a precise tim- only noise, and the shots after removing the
ing for firing the source and starting the record- traces of shot 113 by trace kill are shown in
ing is necessary. In the case of timing issues, the Fig. 5.53B.
seismic recorder may be triggered and recording Triggering problems not only create missed
starts although the gun array is not fired. In shots, but may also constitute static time shifts
these cases, the recorded data contains only in shot gathers if a triggering delay occurs
noise and is termed a missed shot. The problem between the recording unit and the gun