| Proper implementation of the image condition is necessary for recovery of accurate angle-dependent reflection coefficients from prestack reverse-time depth migration. All the current prestack image conditions can be classified as one of three types; excitation time, cross-correlation, or the ratio of the receiver to source wavefield amplitudes, but all are particular instances of source and receiver wavefield correlation. The excitation time and cross-correlation image conditions produce arbitrarily scaled images that have relatively wide images. Only the reflection coefficients estimated by normalization of a cross-correlation image by the source illumination, and those estimated by the amplitude ratio of the receiver wavefield over the source wavefield have the required dimensionless units, and the correct scale factor. |
