What is GPR?
Brief History of GPR
Principles of GPR
* How its works
* Operating Frequency
* Resolution depend on frequency
* How Deep Can It Go?
Component of GPR
Today, the advance space technology almost reached on extraterrestrial
(Mars) planet and deep ocean exploration also possible to human using
submarine technologies like sonar, scuba diving etc.
But sill today human have no proper answer what are actually below us?
Using direct investigation like bore wells and mining's can provide information
regarding to underground objects with some depth limitations. But using
electromagnetic waves we can get some 100s of meter information regarding
Ground Penetrating Radar (GPR) is one of those techniques which used
radar waves to exploration of underground surface. It can be helpful to many
mapping application with some extent of depth.
What is GPR?
Ground penetrating radar (GPR) is now a well-accepted geophysical
technique. It is a high resolution electromagnetic technique that is designed
primarily to investigate underground surface.
GPR has been developed over the past thirty years for shallow, high
resolution investigations of the subsurface. GPR is a time-dependent
geophysical technique that can provide a 3-D pseudo image of the subsurface,
including the fourth dimension of color, and can also provide accurate depth
estimates for many common subsurface objects. GPR can provide precise
information concerning the nature of buried objects. It produces a continuous
cross-sectional profile or record of subsurface features, without drilling,
probing, or digging.
3D GPR image
Continuous cross sectional
Brief History of GPR-
Foundation for radar systems by Christian Hülsmeyer in 1904
Gotthelf Leimbach and Heinrich Löwy applied for a patent to use radar
technology to locate buried objects with radar technology in 1910
A glacier's depth was measured using ground penetrating radar in 1929
by W. Stern
Military applications began driving research in 1970s
Commercial applications began in 1985
GPR is becoming the new tool in archaeological remote sensing & many
The particular invention improved the depth resolution and is still widely
Principles of GPR
How it works ?
Ground Penetrating Radar (GPR) uses the same fundamental physical principles
as conventional radar. It uses radio waves to map structure and features buries in the
ground /man-made structures. The pulses always propagates in a shape of a cone.
The radar technique principally detect back-scattered energy from a target.
GPR uses a high frequency radio signal that is transmitted by the antenna and
travels downward until it hits an object that has different electrical properties from
the surrounding medium then its get scattered from the object and receive by the
receiver antenna and stored on digital media. The computer measures the time taken
for a pulse to travel from the target which indicates its depth and location. The
reflected signals are interpreted by the system and displayed on the unit's LCD panel
in the form of cross-sectional profile .
If the wave hits a buried object, then part of the waves energy is
reflected back to the surface, while part of its energy continues to travel
downward. The wave that is reflected back to the surface is captured by a
receive antenna, and recorded on a digital storage device for later
interpretation. The GPR method measures the travel time of
electromagnetic impulses in subsurface materials.
Antenna is able to detect and measure the depth of reflecting discontinuities
There is an optimum choice of frequency of operation to achieve
best performance in terms of depth and ability to see details in the
target structure. This choice is between 1 and 5000 MHz. Generally low
frequencies are used for deep probing (>50 m) and high frequencies are
used for shallow probing (<50 m).
The initial frequency estimation formula:
X-specify a desire spatial resolution
K - relative permittivity (dielectric constant) of most material
Resolution (depend on Frequency)
Low frequencies (a few MHz) give good depth penetration, but low
resolution ( more than 50 m).
High frequencies (about a GHz) can resolve cm-sized objects, but
penetrate only a meter or less in many materials ( less than 50 m).
In archaeology, resolution is generally more important than depth, so
high frequencies are commonly used.
In geologic survey, depth is generally more important than resolution,
so low frequency are used to survey.
How Deep Can It Go?
For applications requiring higher
resolution, such as locating conduits in
concrete, a higher frequency GPR system
(1,000 MHz) is used. This will give high
resolution detail for down to approximately
24 inches in depth. Applications which
require deeper penetration in ground soil
requires a lower frequency (12.5 MHz to 500
MHz). Depending on the subsurface material
the depth range can be from a few inches to
thousands of feet (as indicated in the chart).
The GPR image shows buried objects in a hyperbolic shape; the top
of the hyperbola represents the exact location of buried object. It is
a well known fact that GPR images are obtained by using a single
Regular radar image interpreters decide the exact location and
depth of targets depending on a direct distance measurement from
the top of the hyperbola
How create Hyperbola ?
Intensity of frequency
Object distance from transmitter
3D GPR Images
Multiple lines of data systematically collected over
an area may be used to construct three-dimensional
or tomographic images. Data may be presented as three-
dimensional blocks, or as horizontal or vertical slices.
Components of GPR
1) Transmitter Antenna
The GPR transmitter produces the short duration high-power RF pulses
of energy that are radiated into ground by the antenna.
2) Receiver Antenna
The GPR receiver receive reflected/backscattered RF pulses of energy
from the object which are located in beneath the ground.
As a general rule, the frequency of the antenna determines the depth
of penetration and the resolution – the higher the frequency the better the
resolution but at the expense of the depth of penetration.
3) The Control unit
The Control unit is the brain center for the GPR system and is
responsible for coordinating the operation of the subordinate components.
It has ability to control all functions of GPR and it is one of the main junction
of data flow.
4) Display unit
Display continuous cross sectional profile or record of subsurface features
5) Power unit
provide power to all GPR system to active work
Advantages of GPR
high speed recording (8km/hr)
Able to detect voids and trenches
Able to determine depths and lengths of targets
Colors also improve data quality
Easy to handle
Changeable frequency (1 mhz 5 ghz)
Real time display unit represent cross sectional profile
Used in lot of applications
Disadvantages of GPR
Higher frequencies do not penetrate as far as lower frequencies
(penetration is limited )
Doesn't work well in clay
Terrain must be flat and even
Interpretation of radargrams is generally complex
Cellular telephones, two-way radios, television, and radio and
microwave transmitters may cause noise on GPR record
Highly expensive survey method
Brief overview of Application of GPR
To find out underground utilities
Mapping Groundwater Table
Mapping Karst Features
Geological & Geophysical studies
Locating trenches and landfills
Forensic & security
Underground tank storage location
GPR has been developed into a sophisticated technique that can
provide detailed images of the near surface. GPR is a time-dependent
geophysical technique that can provide a 3-D pseudo image of the
subsurface, including the fourth dimension of color. It can also provide
accurate information of depth estimation for many common subsurface
In the field of Earth science, it used to study bedrock, soils,
groundwater, and ice depth estimation. GPR is an excellent tool for
mapping underground surface of the earth in recent geological and
Ground penetrating radar – theory and application-Harry.M. Jol
Ground Penetrating Radar Fundamentals by Jeffrey J. Daniels
Online reference sites-