More details about Rayfract® software

WET Wavepath Eikonal Traveltime tomography models multiple signal propagation paths contributing to one first break, based on the Fresnel volume approach. Conventional ray tracing tomography is limited to the modelling of just one ray per first break. Also, our Eikonal solver (Lecomte, Gjoystdal et al. Geophysical Prospecting May 2000) used for traveltime field computation explicitly models diffraction besides refraction and transmission of acoustic waves. As a consequence the velocity anomaly imaging capability is enhanced with our WET tomographic inversion compared to conventional ray tomography.

Our Smooth inversion tomographic method is based on physically realistic modeling of first break propagation, for P-wave and S-wave surveys. We forward model refraction, transmission and diffraction (Lecomte, 2000) and back-project traveltime residuals along wave paths, also known as Fresnel volumes (Watanabe, 1999) instead of conventional rays. This increases the numerical robustness of the inversion. A smooth minimum-structure and artefact-free 1D starting model is determined automatically directly from the seismic traveltime data, by horizontally averaging DeltatV (Wiechert-Herglotz) method 1D velocity-depth profiles along the seismic line. The starting model is then refined with 2D WET Wavepath Eikonal Traveltime inversion (Schuster, 1993). We use an adapted SIRT algorithm for velocity update of grid cells, when back-projecting traveltime residuals along wavepaths (Schuster, 1993) and (Watanabe, 1999).

Rayfract® supports any surface based 2D recording geometry, including roll-along seismic reflection lines. Up to 500 shots may be imported into the same 2D profile database. These shots may be recorded with just one or with multiple overlapping receiver spreads. 10 or more shots per receiver spread are recommended. The spacing of adjacent receivers may vary along the same user-defined receiver spread type. We support from 12 up to 360 channels per receiver spread. 24 or more channels are recommended. Supports many input data formats. Import shots interactively, our with our .HDR batch import.

Review our
SAGEEP 2010 manual (PowerPoint version, function key help). Allows bidirectional frequency filtering of traces, with single-pole or Chebyshev-Butterworth filter. Pick first breaks interactively for each trace, or use our polyline picker, combined with automatic picking. Pick shear wave first breaks in Trace|Shot point gather, for shot pairs with same shot position but reversed trace polarity. Check your picks for reciprocal traveltime errors in Trace|Offset gather display. Shift picks for all traces of same shot with trigger delay correction.

We support the conventional, layer-based refraction seismic Plus-Minus method (J.G. Hagedoorn 1959) and the Wavefront method (E. Brueckl 1987 and Glyn M. Jones and D.B. Jovanovich 1985). Our Wavefront method uses a laterally varying XY receiver separation, and is an optimized version of the GRM Generalized Reciprocal Method (Palmer 1980 and 1981). Map traveltimes to refractors interactively or semi-automatically.

WET inversion does not require mapping traveltimes to refractors. We allow plotting of 1.5D refractors obtained with layer-based methods on 2D WET tomograms. Supports Smooth inversion of borehole surveys with constant-velocity starting model, for crosshole, zero-offset VSP, walkaway VSP, reverse VSP and uphole refraction surveys. Uses multiple CPU cores, for fast parallel forward modeling of traveltimes and back-projection of residuals along wave paths (Fresnel volumes), with SIRT algorithm.

Shots positioned at the bottom of deep holes located on the 2D seismic profile, i.e., "uphole" shots, may be recorded with the same receiver spread layouts as surface-based shots. First breaks picked for these uphole shots are used to constrain the WET tomography. Convert walkaway VSP surveys into uphole refraction surveys with our software and then use the resulting GeoTomCG .3DD with simulated uphole shots to constrain surface-based WET tomography. Or process uphole shots from two or more boreholes into one common, surface-based receiver/hydrophone spread as a reverse VSP survey and horizontal borehole survey, without surface-based refraction shots.

The software handles extreme topography and allows computation of velocity vs. two-way time for reflection processing, i.e., for static corrections. Golden Software Surfer is required for automatic imaging and plotting of XTV and WET tomography output. You may download a free demo from http://www.goldensoftware.com. This is print-disabled, and edited tomogram plots can't be saved. But otherwise this works fine, for on-the-fly automatic creation of tomogram plots with our software, from computed Surfer .GRD velocity grid files.

Generate pseudo-3D fence diagrams with Golden Software Voxler. You can import Surfer .GRD grids VELOITXY.GRD generated with our software, into Voxler.

For further details, please check our .pdf reference chapters "System limitations", "Seismic and header data import" etc. You are welcome to send us a test profile for free interpretation.

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