next up previous print clean
Next: Discussion Up: Diffraction-focusing WEMVA example Previous: Delineation of rough salt

Imaging of GPR data

The next example concerns a zero-offset GPR dataset over a lava flow region. In this situation, diffraction focusing is the only option available for migration velocity analysis. The data depicted in LAVAdata show many diffractions spread over the entire dataset. A few obvious ones are at x=22 ft, t=27 ns, at x=28 ft, t=22 ns, and at x=35 ft, t=23 ns.

 
LAVAdata
LAVAdata
Figure 46
Zero-offset GPR data used for focusing migration velocity analysis.
view burn build edit restore

I follow the same procedure for migration velocity analysis as the one described for the preceding example. LAVAimag(a) shows the initial image obtained by migration with a constant velocity of 0.2 ft/ns, and LAVAimag(b) shows the final image obtained after velocity update. We can notice that the image has been vertically compressed, since the velocity update indicated a faster velocity, and most of the diffractions have been collapsed.

 
LAVAimag
LAVAimag
Figure 47
Zero-offset migrated images for the data in LAVAdata using the initial velocity (a) and the updated velocity (b).
[*] view burn build edit restore

LAVAyoom and LAVAzoom are detailed views of the initial and final images and slownesses at various locations of interest. LAVAyoom shows collapsed diffractions in the left part of the image. We can also observe features with better continuity in the updated image than in the original image, for example at x=20-24 ft and z=2 ft in LAVAyoom(a,c). Likewise, LAVAzoom shows a better focused image than in the original, for example at x=34 ft and z=1.8 ft in LAVAzoom(a,c).

 
LAVAyoom
LAVAyoom
Figure 48
Detail of the images depicted in LAVAimag. Migration with the initial velocity (a), updated slowness model (b) and migration with the updated slowness (c). The window corresponds to x=20-24 ft and z=2 ft.
[*] view burn build edit restore

 
LAVAzoom
LAVAzoom
Figure 49
Detail of the images depicted in LAVAimag. Migration with the initial velocity (a), updated slowness model (b) and migration with the updated slowness (c). The window corresponds to x=34 ft and z=1.8 ft
[*] view burn build edit restore


next up previous print clean
Next: Discussion Up: Diffraction-focusing WEMVA example Previous: Delineation of rough salt
Stanford Exploration Project
11/4/2004