Picking sea bottom reflections

Figure shows a zero-offset section recorded in a marine survey. Each trace was recorded by a hydrophone below the sea surface, with an air-gun above it. On the section, the first flat event is the direct arrival of down-going waves from sources to receivers. The picked traveltimes are superposed on the event. Because the event is isolated, and noises and wavelet distortions are small, the curve that indicates the picked traveltimes follows the event quite well. The second event is the primary reflection from the sea bottom. The event bends upwards at the left end. The curve indicating the picked traveltimes is with the event at most locations. However, at those locations where strong, spiky noises appear, the algorithm fails to pick the correct traveltimes. The algorithm is sensitive to spiky noise because adding a large-amplitude spike to a wavelet considerably changes the phase property of the wavelet.

 

zospick
Figure 5 Picked traveltimes for the direct arrival and the primary sea bottom reflection. The picks of the primary see bottom reflection are attracted to large spiky additive noises of unknown origin.