Ocean Bottom Stations provide wide-azimuth multi-component data with great advantages for exploration, reservoir characterization, and identification of drilling hazards. However, due to the high cost of deploying OBS nodes, large receiver intervals are used. In practice, poor illumination due to sparse receivers is a major problem. This problem is particularly, but not exclusively, associated with gaps in the coverage of shallow targets, and is greatly exasperated if some OBS nodes fail. The same problem affects both sparse OBS nodes and ocean bottom cables in the cross-line direction. Fortunately there is an effective solution. The first step in our method is the separation of seabed hydrophone and geophone data to upgoing and downgoing waves. Downgoing waves just above the seabed contain only multiples, or ghost reflections. Nevertheless, we image the ghosts, pretending that the data were acquired with a certain equivalent geometry recorded above the sea surface. This alternate surface is the top of a virtual water layer whose thickness is twice the sea depth. We applied this method to OBS data recorded in the North Sea and generated better images from the downgoing ghosts than the images produced conventionally from the primary upgoing waves.


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