\righthead{Computer Assignment 3} \lefthead{GP 284}

\title{Computer Assignment 4\\Due 3 June 1994} \begin{center} Your name \end{center} \ABS{ This computer assignment explores how smoothing the velocity field affects the migrated image. In this exercise, you are going to use Promax to migrate a stacked section with an increasingly smoother velocity field. I want you to discuss the differences between the migrated images. }

I will guide you through this exercise. You should be able to answer and check off the questions as you go. Please, be aware that the important questions are the ones in the ``Match the sections'' paragraph.


  1. Login to your student account and open a window on ``robson''.
  2. Start up Promax (command: prompt% promax ).
  3. Click on the area ``class''.
  4. Make your own copy of the ``realdata'' line.
  5. Bring up the flow panel of your line.
The Promax processing flow that you will find includes a series of steps. You will use it by commenting in and out certain Promax processes. The flow is complete; you do not need to add or change processes to successfully finish this assignment. However, feel free to change the processing if you like to. Please, document carefully any changes.


You will be asked to make print outs of your sections. I suggest you use the ``grab'' command in your ``Cakefile''. After typing ``cake grab'' the mouse cursor turns into an angle; you can crop the area you want to print by dragging the mouse across the screen while keeping the left button pressed. Whenever asked to print out a section, please crop all traces.

To make a print out of a detail on your section, you use the Promax zoom tool (fourth icon from the left in the Promax screen display window) to zoom into the desired detail; then you grab the screen as described above.

Velocity fields

In this section, you will have a look at different velocity sections. The first section displays RMS-velocity. These RMS-velocities originated by stacking corresponding CDP gathers. I generated the interval velocities by converting the RMS-velocities. The other velocity sections display interval velocities versus depth and are used for the depth migration. Geophysicists routinely derive their migration velocity section in the same fashion.

Migrated sections

Now you are going to use each of the viewed velocity sections to migrate a small post-stack data set. To prepare the different migration flows, you comment in the Disk Data Input process and the Screen Display process.

Match the sections

The next questions are important. Please, argue your answers carefully (not necessarily lengthy). Please, clean up: Delete your copy of the ``realdata'' line in the line panel. If you have any questions, please see Ray. Good luck.