Seismic data is used to visualize the ground. This is achieved by measuring travel times of reflections of from pressure waves traveling 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 the travel timestime values, 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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The constant ground velocity model is a single layer velocity model. It uses one single constant ground velocity. Input to the velocity model is Water water velocity, the seabed surface in time, and the ground velocity. . The Seabed data may be interpreted lines from 2D seismic (IHorizon or PolyData) or grids (StructuredPoints).
Layer Velocity model
In the Layer Velocity model, you may use seismic horizons as interval velocity boundaries. The horizons may be interpreted lines from 2D seismic (IHorizon or PolyData) or grids (StructuredPoints). You may set the interval velocity of each interval using a table. In the table you also need to set the top horizon of each interval. You also In addition you need to set the water velocity as input.
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 until it meets the next horizon, and so on.
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The velocity model will clamp the bottom velocity in the velocity cube as velocity below the cube.
Depth Conversion
The command "Velocity Model Depth Convert" can be used to depth convert data in Geocap. The command is available on a velocity model. Right click the velocity model you want to use, and select "Velocity Model Depth Convert".
The command can be used to depth convert many different datatypes in Geocap, including:
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In order for the command to succeed, make sure that the output folder can contain the input data sets. Please note that a "Generic" folder cannot hold
seismic 2D Lines data set directly. However a generic folder can hold a seismic lines foldera "Generic" folder can hold a "Seismic Data" folder, which again can hold seismic data sets.
The depth conversion command has options to store the Average velocity used to do the depth conversion of each point in the result. You may also choose to store the "instantaneous Velocity". The "Instantaneous Velocity" is computed by looking at the change of average velocity from the velocity model around this point. For seismic lines the the "Instantaneous Velocity" is the interval velocity of a single sample in the seismic. Storing and visualizing these velocities will make you able to quality control the velocity model used for the depth conversion.
If you store velocities when depth converting seismic lines, the velocity values are stored as seismic attributes to the resulting seismic lines. You may visualize the velocities with the regular "Seismic Display" command. Note that storing velocities will make the depth conversion of seismic lines slower.