When the migration velocity is
correct and the image is focused at zero subsurface
offset, the transformation to angle domain does not change the depth
of the image point, and the reflections are imaged at the same depth
for all aperture angles. In contrast, when the reflections are not
focused at zero offset, the transformation to the angle-domain maps the
events at different depths for each different angle. The variability
of the depth with the aperture angle is described by the RMO
function, which we want to measure and quantify as a function of the
perturbation in anisotropic parameters encountered along the
propagation paths.