Multiple attenuation in VSP multiple imaging and primary imaging

Imaging of downgoing first-order free-surface multiples (ghosts) with VSP data can provide a subsurface image with wider coverage, better vertical resolution, and higher-fold than conventional imaging of VSP primary reflections. A problem with VSP downgoing first-order multiple (ghost) imaging is the interference from downgoing high-order multiples, similar to the interference from multiples when CDP primaries are migrated. A solution to this problem is to attenuate the high-order multiples prior to imaging the first-order multiples (ghosts). A prediction and then subtraction strategy can be employed to attenuate the high-order multiples. A model-based prediction method is used to predict the high-order multiples, and then a multichannel matching filter is employed to subtract the modeled multiples. After these two steps a first-order multiple (ghost) imaging condition can be applied to the data, and the blurring due to high-order multiples will be diminished.