HVA or Horizontal Velocity Analysis is another module to pick and update the velocity along a particular horizon. To work with a HVA stack imaging module, one should have a known horizon in place otherwise the user should pick the horizon(s) on the input stack or Reference stack inline/cross line.
Module name HVA Stack Imaging
Prior to the HVA Stack Imaging, we should have a reference stack. This stack can be read by using "Read seismic traces" module or add Stack Imaging module in the workflow and create a stack. Use the Stack inline as a reference stack to the HVA Stack Imaging module input data.
An example workflow of HVA Stack Imaging is as shown below.
As far as the Horizontal semblance inline is concerned, the user should look for the parameters in Horizontal analysis. For picking the horizon, the user should pay attention to the Manual picking params and adjust the parameters for a better picking response.
How to pick the horizons & velocities:
•To activate the Vista items, the user should click on the Location map and choose "Selected bin" from the 
control item. Now click anywhere on the location map to display the vista items.
•Next choose a horizon to be picked (in case there are no horizons were available or not imported). To adjust the manual picking parameters, we should go to "Manual picking params" and adjust the parameters.
•Start picking the horizon on the Reference stack inline. Once the picking is done, the user should click the middle mouse button inside the "Reference stack inline" to commit the changes.
•A new horizon displayed on the Reference stack inline. In the Horizontal semblance inline window, the user should pick the velocities and click the middle mouse button to commit the changes to get the new velocity horizon.
In the above image, we can see the purple picks on the Reference stack inline section. These are the user picked points. On the right hand side, we observe the semblance on Horizontal semblance inline window where the velocity semblance is displayed in horizontal direction. Velocity is plotted on Y-axis & trace/CDP on the X-axis. Once the user finished picking the horizon on the Reference stack inline, click the middle mouse button so that these picks will become an horizon. Click on show properties icon 
and go to Vista item properties. check/uncheck the vista items to see various options.
After the horizon picking is done, we need to pick the velocities on the Horizontal semblance inline window. In that window, we see a horizontal (aqua blue) line which is the vertical velocity projection displayed horizontally. Now we need to pick the velocities on this window as per the semblance as shown below. Once the picking is done, we need to click the middle mouse button to make it as a horizon (as shown below)
Now we can execute the HVA Stack Imaging module to generate the Output stack inline. In the below images, we are comparing the Reference stack inline against the Output stack inline after the horizontal velocity analysis. We can see the improvement on the encircled areas.
