Limitations - Radiodetection RD1000 Operation Manual

Notice that as the pipe gets deeper, the strength of the target arch
gets weaker. This is a result of the GPR signal being absorbed as
it travels deeper into the subsurface. In all soil types eventually the
GPR signal will be completely absorbed and only the background
radio noise in the area will be detected by the GPR sensor. The
noise is seen in the image a fuzzy signal like a TV station not
properly received. To see the deepest possible targets with a GPR,
it is important to have a quiet, highly sensitive system.

4.2 Limitations

GPR is not without its limitations. GPR radio wave signals are
absorbed by the ground with some soils (clays, saline) greatly
limiting exploration depth. GPR effectiveness is thus site specific
and varies greatly from place-to-place. GPR also responds to
changes in soil type, density, water content, as well as many other
buried objects; making unique identification of the desired target
difficult. (i.e. you can not see the individual tree in the middle of the
forest).
RD1000™ Operation Manual