Presented by,

Patil Abhijit SambhajiM.tech (Geoinformatics) GIS1519Bharathidasan University, Trichy-24

Subject-

Topic Name-

“Ground Penetrating Radar” (Principle and Components)

Advance Geospatial Technology

Content Introduction

What is GPR?

Brief History of GPR

Principles of GPR

* How its works

* Operating Frequency

* Resolution depend on frequency

* How Deep Can It Go?

* Hyperbola

Component of GPR

Advantages/Disadvantages

Conclusion

Introduction:- 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 underground objects. 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 GPR image

Brief History of GPR-Foundation for radar systems by Christian Hülsmeyer in 1904Gotthelf 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 other areas.

The particular invention improved the depth resolution and is still widely used today.

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 in subsurface.

Cont...

Operating Frequency 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).

dielectric constant

Hyperbola

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 radio-wave frequency

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 frequencyObject distance from transmitter Angle/cone

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 GPR1) 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 to operator.5) Power unit provide power to all GPR system to active work6) Software's RADAN GPRmax GPRslice

Advantages of GPRhigh 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

Archeological survey

Mapping Karst Features

Sinkhole surveys

Geological & Geophysical studies

Concrete inspection

Locating trenches and landfills

Forensic & security

Underground tank storage location

Conclusion

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

objects.

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 geophysical

studies.

References:-Ground penetrating radar – theory and application-Harry.M. Jol

Ground Penetrating Radar Fundamentals by Jeffrey J. Daniels

Online reference sites-

http://www.global-gpr.com/gpr-technology/how-gpr-works.html

http://www.geo-radar.pl/en/methods/georadar/working/

http://undergroundsurveying.com/technology/ground-penetrating-radar-gpr/

http://geomodel.com/methods/ground-penetrating-radar/