User's Manual

2150GR Ground Penetrating Radar
054-140 - Rev. 2
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o For equal propagation speed, depth and type of target, the hyperbola will be wider
for geometrically larger targets (for examples for wider diameter pipes).
When interpreting the maps, it is a good idea to remember that the width of a hyperbola does
not just depend on the geometrical size and shape of the target.
Below, two maps featuring echoes of an irregular interface between two layers with
different dielectric properties (asphalt) and six pipes situated perpendicularly to the direction
of investigation.
Maps showing traces of an interface and pipes perpendicular to the direction of investigation
As can be seen in the map above, the echo of a target doesn’t simply consist of a single dark
band, it consists of alternate dark and light bands. These derive from the signal minimums
and maximums reflected back from the target (in fact, the black and white bands represented
in the figure correspond to maximum and minimum signal amplitude respectively).
A hyperbolic echo can be used to convert the ordinate of the map from time (nanoseconds =
ns) to depth (meters= m). To do this, the hyperbola traced in ns ordinates is compared with a
family of hyperbolas traced with ordinates in meters, obtained from that in ns ordinates with
various values of v
m
. The best v
m
approximation to the real value is that with the most
similar aperture to that of the one traced in time ordinate. Once v
m
has been identified, the
depth of the target corresponding to the hyperbolic section can be found.
There are no definitive criteria for interpreting diagrams and often you have to depend on
experience. In any case, it is best to collect the largest possible amount of information for an
interfaces
: Top
surface of
the pipes