next up previous print clean
Next: Sensitivity of the estimation Up: Biondi and Tisserant: 3-D Previous: Examples of 3-D ADCIGs

Angle-Domain Common Image Gathers and velocity

Migration Velocity Analysis (MVA) is one of the most important applications of ADCIGs, and the main focus of this paper. MVA from ADCIGs computed using wavefield-continuation migration is conceptually analogous to MVA from conventional offset-domain CIGs obtained by Kirchhoff migration. The ADCIGs are analyzed for departure from flatness, usually by applying some kind of Residual Moveout (RMO) analysis. The RMO analysis provides measurements of depth errors that are first transformed into traveltime perturbations and finally inverted into velocity perturbations by a ray-based tomographic inversion. This process is repeated several times in order to converge to a satisfactory result.

In this section we analyze the kinematic properties of 3-D ADCIGs when the migration velocity is not correct. First, we qualitatively analyze the sensitivity of the estimation of the angles $(\gamma,\phi)$to velocity errors. Second, we develop a quantitative relationship between depth errors in ADCIGs and traveltime perturbations caused by velocity errors. Third, we present a 3-D RMO function for measuring the depth errors in ADCIGs. Finally, we compare the imaging-point shifts predicted by our results with the actual images produced from a synthetic data set migrated with the wrong velocity.