since a streamer depth of 8m produces a notch at 94 Hz, which is normally outside the frequency band of interest. However, when the streamer depth is changed to, for instance, 25m, this ghost notch occurs at 30 Hz, which is in the middle of the useful seismic spectrum. Terefore, there is a strong need for effective and accurate ways to remove the ghosts from data acquired using a deep towed streamer. Since different vendors prefer to use different streamer configurations and some vendors measure particle velocities in addition to pressure, the deghosting algorithms used will also differ. Tere has also been a significant research


effort aimed at increasing understanding of ghost effects in seismic data and especially at developing robust and effective deghosting algorithms. Te example shown in Figure 5.62 probably demonstrates this time evolution rather than differences in processing skills between various vendors. It is, however, interesting to notice major differences especially for the deeper data when it comes to image quality (Figure 5.63).


5.9.4 The Answer is Hiding in the Waves


Tere is no doubt – the marine seismic industry has changed significantly over the last decade. Today more and more marine seismic streamers are towed at between 20 and 40m. Tis is a


Figure 5.63: Comparison of 8m (left) and 60m (right) streamer depth for the low frequency response (0-1-3-4 Hz bandpass filter has been applied). A stronger and more continuous response is observed for the deep-towed streamer data.


huge change, and has proved to be the beginning of a new era in marine seismic. As technology is improving, new efficient ways of towing both source arrays and streamers will be found. Te oil industry is facing severe changes in the years to come, and cost savings and other challenges might slow down the broadband revolution. Despite this, there is a huge reward waiting for the organisations that are capable of understanding and exploiting information that is still hidden in the waves. One thing is sure: geophysics rocks, and the waves will


continue to propagate. We just need to understand how and why.


231


Lundin


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