Geoscience Reference
In-Depth Information
INPUT
OUTPUT
Signal
Generator
Transmit
Antenna
Receive
Antenna
Processor
and Recorder
Ground
(a) Input/output of a GPR system
Trace
amplitude
Direct arrival
Traces at different locations
Direct Arrivals
Reflection
Reflections
Recorder
Transmitter
electronics
Receiver
electronics
Electronics
and recorder
Transmit-receive
antenna box
Tow vehicle
Transmit
antenna
Receive
antenna
(b) Fixed mode equipment,
and GPR trace
(c) Moving mode equipment,
and GPR record
fIGURe 7.5
Operational components of a GPR system: (a) input/output components; (b) operation in fixed-
offset mode, showing a single trace output; and (c) operation in moving mode, whereby a series of traces are
recorded at different positions along the surface, producing a time-distance cross section over the earth.
of the electronics are contained in one box. In some cases, the electronics may be mounted on top of
the antennas, making for a compact system but decreasing the operational flexibility of the system.
GPR systems are digitally controlled, and data are usually recorded digitally for postsurvey
processing and display. The digital control and display part of a GPR system generally consist of
a microprocessor, memory, and a mass storage medium to store the field measurements. A small
microcomputer and standard operating system are often utilized to control the measurement pro-
cess, store the data, and serve as a user interface. Data may be filtered in the field to remove noise, or
the raw data may be recorded and the data processed for noise removal at a later time. Field filtering
for noise removal may consist of electronic filtering and digital filtering prior to recording the data
on the mass data storage medium. Field filtering should normally be minimized except in those
cases where the data are to be interpreted immediately after recording.
7.3.2 a
n t e n n a s
The most important components of a GPR system are transmit and receive antennas. The purpose of
a transmit antenna is to launch an electromagnetic wave into the ground; the purpose of the receive
