Seismic data is used to visualize the Earth's sub surface. This is achieved by measuring travel times of reflections from pressure waves propagating through the ground. Seismic data and interpretations of seismic data will therefore often have z values in travel time, not depth. In order to get a depth value for a travel time value, we need to do a depth conversion. A depth conversion combines the velocity of the pressure wave with the travel time to get a depth value.
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When going from top to bottom , the layer velocity model will initially use the water velocity as interval velocity until it meets the top horizon. From the top horizon it will use the top horizon velocity as interval velocity until it meets the next horizon, continuing this pairwise matching of successive horizons for the rest of the horizonsseismic data.
During depth conversion the interval velocities are used to calculate an average velocity.
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In order to generate an average velocity, the velocity model will run Dix formula on the RMS velocity to generate interval velocities. An average velocity is computed from the interval velocities.
Note that the Search search radius should be big large enough so that all points where you need a velocity will have RMS points within the search radius. However if the search radius is set too big, the velocity computation for a point will include too many RMS points, and the calculation may be slow. The recommended radius will depend on the density of the RMS velocity dataset.
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