The heart of the near-surface correction technique known as raypath interferometry is the transform (and its inverse) used to move standard field seismic data from the conventional X/T domain to a raypath-oriented domain, and back to the X/T domain. We have extensively tested two different transforms for this purpose; the Radial Trace Transform, a simple point-to-point mapping, and the Tau-P Transform, an integral transform. We show here that, while either transform can be used on 2D seismic data, for the 3D case, geometrical considerations favour the Tau-P Transform, since the current Radial Trace algorithm does not properly handle seismic survey geometry. The Tau-P Transform is not without problems, however, the most serious being the massive storage required for transforms whose parameters are chosen to properly preserve the lateral resolution of the input data. We illustrate the issues here using the 1995 Blackfoot 3D 3C data set and show images of the successful application of raypath interferometry to both the PP (vertical) and PS (radial) components of this data set.
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