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Right-clicking on a Seismic Line or a Seismic Brick Cube and selecting "Seismic Trace Attributes..." pops up the following dialog:
Dip and Coherence dialog
The Dip and Coherence process estimate the surface normal G=[Gx,Gy,Gt] at each sample in the seismic from an image analysis of the samples in a window around the sample in question.
If there happen to be a minima or maxima at the sample; this surface normal will point in the same direction as the normal to the interpreted horizon going trough the sample.
From the surface normal: the following are calculated:
InlDip=Gx/Gt
CrlDip=Gy/Gt
Estimate surface normal ├ G┴⇀=[Gx,Gy,Gt ] directly from seismic for every seismic sample.
The Coherence attribute is a byproduct of the dip telling us how reliable the InlDip and CrlDip estimates are: 0 <= Coherence <=1, where 1: absolute certain.
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