- Copyright © 2008 Society of Exploration Geophysicists
Seismic exploration is widely used to locate geologic formations for hydrocarbon accumulations. In a typical marine seismic survey, one or more marine seismic streamers are towed behind a survey vessel. As the streamers are towed, acoustic signals, commonly referred to as “shots,” are produced by the seismic source. These travel down through the water column into strata beneath the water bottom surface, where they are reflected from the various geologic formations and travel back to the sea surface. One well-known marine seismic problem is that these upgoing waves are then reflected with inverted polarity at the sea surface because of the air/water interface. Hence, the sensors in the seismic streamer cable record not only the desired wavefield (i.e., the upgoing wave-reflected signal from various subterranean geologic formations), but also their reflections from the sea surface (the downgoing wave). The undesired downgoing reflected signal is known as the “receiver ghost.” Depending on the incidence angle of the upgoing wavefield and depth of the streamer cable, the interference between the upgoing and downgoing wavefields creates nulls or notches in the recorded spectrum. As illustrated in Figure 1, these notches reduce the useful bandwidth of the spectrum especially at increasing streamer depths.