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Angle transform

Angle-domain common image gathers (ADCIGs) are decompositions of seismic images in components proportional to the reflection magnitude for various incidence angles at the reflector. Given correct velocities and migration algorithms, primaries map into flat gathers and multiples map into events with moveout.

Angle-gathers can be constructed by two classes of methods: data-space methods Mosher and Foster (2000); Prucha et al. (1999); de Bruin et al. (1990), with reflectivity described function of offset ray parameter, and image-space methods Rickett and Sava (2001); Sava and Fomel (2003); Weglein and Stolt (1999), with reflectivity described function of scattering angle. The moveout behavior of primaries and multiples are similar, irrespective of the method used to construct them.

Figure [*] shows on the left a CMP gather for a model with flat reflectors and v(z) velocity. Most of the events in the gather are multiples, and just a few of the top-most events are primaries. On the right, Figure [*] shows an angle-domain CIG for the data in the left panel. The primary events are imaged correctly and are flat, but the multiples are not imaged correctly and have strong moveout.

Angle-domain common image gathers are useful for multiple suppression for several reasons. First, events imaged with the wrong velocity show substantial moveout, which allows us to discriminate between primaries imaged with correct velocity and multiples, imaged with incorrect velocity. Second, angle-domain common image gathers describe the reflectivity at the reflection point, independent, in principle, from the actual structure for which they are computed, so they capture all 3-D propagation effects at every individual CIG.

 
synth
synth
Figure 1
Simple synthetic model. A data-space CMP (left) and a corresponding image-space CIG (right).


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sDSN
sDSN
Figure 2
Synthetic example for S/N separation in the image space: (D) data in the image domain; (P) data in the Parabolic Radon domain; (N) multiples (noise); (S) primaries (signal).


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next up previous print clean
Next: Multiple suppression Up: Sava and Guitton: Multiple Previous: Introduction
Stanford Exploration Project
7/8/2003