Illumination‐based normalization for wave‐equation depth migration

Abstract

Illumination problems caused by finite-recording aperture and lateral velocity lensing can lead to biased amplitudes in migrated seismic images. I calculate weighting functions that compensate for illumination problems in wave-equation depth migration. The methodology takes into account reflector dip as well as both shot and receiver geometries, and because it is based on wave-equation migration, it naturally models the finite-frequency effects of wave propagation. The first step in the process is to model synthetic data with the true recording geometry over a reference model. Migrating the synthetic data then produces an image whose amplitude can be compared to the reference image to produce an illumination-based weighting function. These weighting functions can be applied directly to the migrated images to mitigate the effects of poor subsurface illumination. The reference model should be as close to the true model as possible; good choices include the migrated image, or a synthetic image with a single known dip that corresponds to the expected dip of a reflector of

Illumination and Resolution Analyses on Marine Seismic Data Acquisitions by the Adjoint Wavefield Method

“…Because of "checkerboard like" and irregular illumination strength pattern observed in the computed image, additional regularization (Rickett 2003;Operto et al 2006;Guitton et al 2010) is required. The bottom panels in Fig.…”

“…These results are usually restricted to simple geometries or do not provide directional information that is crucial for target oriented imaging. Rickett (2003) developed a normalization scheme to compensate for the effect of irregular illumination. Based on a one-way wave-equation, Xie et al (2006) utilized generalized screen propagator and local plane-wave analysis methods to properly cope multiplescattering phenomena, including focusing/defocusing, diffraction and wave-interference effects but ignored reverberations between heterogeneous layers.…”

High Resolution/High Fidelity Seismic Imaging and Parameter Estimation for Geological Structure and Material Characterization

“…This demonstrated the significance of acquisition aperture correction in true-reflection imaging. For wave-equation based migration methods, the subsurface angle-domain common-image gathers (CIGs) can be obtained either by decomposing the propagated wavefield before imaging ("data-space methods") (e.g., de Bruin et al, 1990;Mosher et al, 1997;Prucha et al, 1999;Mosher and Foster, 2000;Wu and Chen, 2002;Xie and Wu, 2002;Chen et al, 2006), or by prestack imaging at zero time but not at zero offset ("image-space methods") (e.g., Rickett andSava, 2001, 2002;Biondi and Shan, 2002;Sava and Fomel, 2003;Biondi and Symes, 2004;Biondi 2007;Rosales et al, 2008). In the image-space method, the subsurface offset-domain CIGs are firstly computed and then transformed to the subsurface angle-domain CIGs.…”

“…For source-receiver migration, the subsurface offset-domain CIGs are naturally available. For shot profile migration, the subsurface offset-domain CIGs are obtained by crosscorrelating the source and receiver wavefields shifted horizontally with respect to each other extended from conventional crosscorrelation imaging condition in time (Rickett andSava, 2001, 2002). The prestack image becomes a function of the horizontal relative shift, which has the physical meaning of subsurface half offset.…”

Multi‐source least‐squares reverse time migration

“…The simplest approximation is the reciprocal of the diagonal matrix (Beydoun and Mendes, 1989;Rickett, 2003) that is applied to the image to compensate for uneven illumination. This is computationally inexpensive, but it only compensates for amplitude distortation but does not correct for aliasing artifacts or strong footprint noise.…”