Geology Reference
In-Depth Information
Figure 10.14
Radar system with air-launched horn antennas being used to
monitor railway trackbed ballast.
be done in the field. In some early systems the CRU functions could be
performed by any suitable laptop PC loaded with appropriate software, but
this placed the user at the mercy of operating-system upgrades. Moreover,
few laptops can survive being rained on.
10.2.2 Survey types
In most GPR surveys, the antenna separation is kept constant. This is
common-offset profiling
(Figure 10.15a). The alternative is to vary the
distances of the two antennas from a fixed mid-point to obtain multi-fold
Common Mid-Point
(
CMP
) coverage (Figure 10.15b). CMP surveys allow
velocities to be calculated from the variations in reflection time with offset
but are slow, and therefore relatively rare, in GPR (as discussed in Section
Figure 10.15
(a) Fixed or constant offset profiling. (b) Common mid-point
sounding.
