Geology Reference
In-Depth Information
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Figure 10.19
Three-dimensional (3D) display of a high-resolution ground
penetrating radar (GPR) data set (left) collected on a 0.1-m orthogonal
grid to locate a safe area to drill a hole through a reinforced concrete
slab. On the left, unprocessed data are presented as a 3D cube showing X
and Y image sections. In the centre, a time slice (in the Z plane) has been
selected to highlight a conduit cross-cutting the slab. The location of the
recommended drill hole is shown (right) superimposed on the data cube. No
data processing other than 3D presentation and selection of interpolation
parameters was required, and nobody was hurt in the making of the hole.
shown in Figure 10.19 are still relatively uncommon, but their use is likely
to increase.
10.3.2 Migration
Water tables and sedimentary layering appear on GPR sections as contin-
uous events (Figure 10.18), but pipes, cables, drums and UXO are usually
Figure 10.20
Geometric distortion on radar sections. In each case the con-
tinuous lines show the actual reflection paths (for near-coincident receiver
and transmitter antennas) and the dotted lines show the positions on the
B-scans where the corresponding A-scans will be plotted. Thick grey lines
show the plotted image, assuming no major velocity changes. (a) Diffrac-
tion pattern caused by a point reflector; (b) reduction in dip and lateral
displacement of a dipping bed; (c) 'bow-tie' from a tight syncline. Examples
of some of these features can be seen on the seismic section of Figure 12.8.
