The processing technique known as raypath interferometry has been successfully applied to several different sets of 3C model and field seismic data, to correct their images for the degradation caused by irregularities in the near-surface layer. We continue to refine and improve the technique. In this report, we demonstrate an alternative scheme for creating the reference wavefield, or 'pilot traces' used in the interferometry, and we demonstrate the use of the Snell Transform, a modified Radial Trace Transform, for mapping the raw seismic data into the common-raypath domain required by raypath interferometry.
For pilot trace creation from raw data gathers, we find that singular value decomposition (SVD) methods can be used as an alternate or supplement to lateral smoothing, but that this method, like lateral smoothing, works best when lateral structure and discontinuities are first reduced by 'brute force' techniques like horizon flattening and 'trim' statics.
The Snell Transform, because its sampling trajectories are more likely to map seismic data at all depths onto common raypaths, appears to lead to slightly better interferometric images, especially at shallow depths, than the Radial Trace Transform; but trial and error are needed to set parameters appropriately.
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