18 RD1000™ Operation Manual
Figure 3.10: matching a
target line
Indicator Arch
Idealized representation of a typical pipe-like target response
observed on the GPR image. The width of the arch is controlled by
soil type setting. The soil type setting is changed using the Arch
buttons. Increasing the soil type makes the indicator arch wider
while decreasing the soil type makes it narrower.
3.4.2 Soil Type
To obtain an accurate depth axis and depth estimations of targets
in the GPR image, a Soil Type Calibration must be performed. Soil
Type Calibration can be done 3 ways:
Matching the shape of a target arch,
Using a target at a known depth, or,
Using the moisture level of the soil.
Matching a Target Arch
Targets like pipes, cables, buried artefacts, tree roots and rocks
generate arch-shaped responses on the GPR image.
Arches occur because GPR energy does not travel into the ground
as a pencil-thin beam but more like a 3D cone. Reflections can
appear on the record even though the object is not directly below
the GPR sensor. Thus, the GPR sensor “sees” the pipe before and
after going over top of it and forms an arch-shaped response on
the image.
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