An ODCIG can be transformed to another image-space volume, termed an angle-domain common-image gather (ADCIG), representing reflectivity as a function of reflection angle. Sava and Fomel (2003b) present a post-imaging, Fourier-domain transform between these spaces appropriate for conventional reflection wavefields. However, as discussed by Rosales and Rickett (2001), this transform does not hold for converted waves because Snell's Law partitions the total reflection angle into unequal source- and receiver-side reflection contributions.
Figure illustrates the generalized geometry of the forward-scattering scenario for a subsurface geologic discontinuity, , oriented at geologic dip angle, , with normal, . An upgoing planar source wavefield propagating at angle to the upward vertical has already interacted at to generate an upgoing, planar wavefield propagating at angle .
For P-P interactions, Snell's Law requires that total reflection opening
angle, , is split equally between the source- and
receiver-side reflection angles (i.e., ). For P-S
conversions, Snell's Law requires that angle is not bisected
into equal components, leaving unequal to . Hence,
additional constraint equations must be included to isolate the
receiver-side reflectivity contributions.