GPR uses high frequency pulsed electromagnetic (EM) waves
(typically from 10 MHz to 1,000 MHz) to acquire subsurface information.
Energy is propagated downward into the ground and is reflected
back to the surface from boundaries at which there are EM property
contrasts (Annan, 1992, Daniels, 1989). GPR equipment utilized
for the measurement of subsurface conditions normally consists
of a transmitter and receiver antenna, a radar control unit,
and suitable data storage and/or display devices. A circuit within
the radar control unit generates trigger pulses that are sent
simultaneously to the transmitter and receiver electronics. The
transmitter electronics produce output pulses that are radiated
into the ground from the transmitting antenna, and the receiver
is turned on to wait for radar energy that is transmitted into
the subsurface. When the transmitted radar energy encounters
and abrupt change in the EM properties (primarily the relative
dielectric permittivity) of the subsurface, a portion of the
energy is reflected back to the radar antenna and the remaining
energy is transmitted downward to deeper material. The reflected
EM energy is detected by the receive antenna, and these signals
are sent to the control unit for amplification. As the antenna(s)
are moved along a survey line, a series of scans are collected
at discrete points along the line. These scans positioned side
by side to form a display profile of the subsurface.
