Obtaining a good seismic image under a gas cloud can be a considerable challenge. The gas cloud can cause strong lateral variations in the P-wave velocities, leading to severe ray bending and scattering, and it can cause high absorption and high transmission losses. Lunskoye Field, in shallow waters offshore Sakhalin (a Russian island north of Japan), is one of those fields suffering from imaging problems due to gas above the reservoir, close to the seafloor. As shown in Figure 1, the field is elongated in the N-S direction. A time migration of a 3D streamer survey, acquired in 1996,...

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