Taking steps toward generating angle-domain common-image gathers

Faranak Mahmoudian, Gary F. Margrave, P. F. Daley

The amplitude of the output of any true-amplitude migration can be used to estimate the angular-dependant reflectivity. However, explicit information regarding the reflection angle will be missing after a standard true-amplitude migration. In an amplitude-versusangle (AVA) study, the explicit relation of the reflectivity function to the reflection angle is needed. This motivates us to work toward having the reflectivity function in the angledomain from migrated data.

This short note summarizes the steps that we will investigate towards generating angle-domain common-image gathers (ADCIGs). Two approaches to generate ADCIGs are considered. In the first method, a shot-domain common-image gather (SDCIG), generated from true-amplitude common-shot Kirchhoff migration (Bleistein et al., 2001) is converted to the ADCIG; a postmigration mapping from surface-domain (shotcoordinate) to angle-domain. Based on the a priori knowledge of opening angle the calculated reflectivity function is placed in an angle bin. In standard common-shot migration and migrating nshot the reflectivity function for each subsurface point is stored in a vector of size nz*nshot (nz: number of depth samples). In this method the reflectivity function will be stored in an nbin*nz array where the nbin is number of angle bins. In the second approach, a 2.5D version of common-opening angle migration discussed in Bleistein and Gray (2002) for constant velocity is presented.