Kirchhoff ZO Radar Migration Lab

OBJECTIVE: Migrate ZO radar data from Canada with a MATLAB script. Determine how migration section is affected by accuracy of migration velocity, sampling interval, obliquity factor and aperture width. Determine best velocity profile by migration focusing analysis.

PROCEDURE:

• Load into your working directory MATLAB scripts for diffraction stack migration (post1.m), (agc.m), Ricker wavelet generator (ricker.m), plotter (plotit.m, Kirchhoff migration routine (migrate1.m), anti-aliased Kirchhoff migration routine (AntiAliasedMig.m), and crosscorrelation (xcorr1.m). Load the canada_radar.mat data. Unfortunately, the server at INSCC corrupts the radar data during download, but INSCC tells me they are working to solve this problem. William has a memory stick with this data set. Please get it from him, or he can make you a CD. Name each file by their names given above.
• In MATLAB, type "post1" to generate and migrate the ZO radar data. Data are in 2-way travel time so this is why c is halved in the program. Why?
• Examine the migrate1.m code and convince yourself that it honors the Kirchhoff migration algorithm.
• Migration Velocity Errors: Introduce velocity errors (typical errors no greater than 10 percent) into the migration velocity "c" in "migrate1.m" and execute "post1.m" again.
• What are the effects of migration velocity error on estimates of depth and reflector shape?
• Migration operator aliase: try the anti-aliased migration function (comment the sentence calling function "migrate1" and uncomment the sentence calling function "AntiAliasedMig") and compare the migrated sections from these two migration functions. Try different aperture widths with these two migration functions and compare the results.
• Aperture Width: Just before calling "migrate1.m" reset the migration aperture variable to "app=5" , which means that the trace aperture for migration is just 10 traces rather than the full data set of traces. Now type post1.m to get the migration section.
  1. Is lateral resolution reduced with decreased trace aperture? Explain.
  2. Migration Focusing Velocity Analysis. Use MFVA to determine velocity as a function of depth for different sections of the data.
  3. In practice a depth aperture limit should be imposed, otherwise known as dip limited migration. As an example, if the dip limitation is 45⁰, then this means that , where X=xg-x and Z is depth of trial image point. Implement this condition in the code and comment on results for different dip limitation. o
  4. The data set is about 5 times wider than the piece migrated. If you have time you might try migrating different portions of the entire large data set.