Ground Penetrating Radar(gpr): Amarjit Ray N.c.s.udaya Sankar Reddy

GROUND PENETRATING RADAR(GPR)

Presented by

Amarjit Ray N.C.S.Udaya Sankar Reddy

DEPT OF MINING ENGG. Dr. T. Thimmaiah Institute of Technology, KGF Karnataka – 563 120 March 05th & 06th , 2009

A Paper Presentation on Ground Penetrating Radar for the SURANG-2K9 CONTENTS

 INTRODUCTION  STEP FREQUENCY GPR  OPERATING PRINCIPLES  APPLICATIONS OF GPR  ADVANTAGES OF GPR  LIMITATION OF GPR  CRUX

INTRODUCTIO N

 It is a geophysical method that uses radar pulses to image the subsurface

 GPR is a noninvasive electromagnetic geophysical technique for subsurface exploration, characterization and monitoring.

 This non-destructive method uses electromagnetic radiations in the microwave bands (UHF/VHF frequencies).

 It is a technique used to locate both metallic and nonmetallic or conductive features.

 It can be thought as subsurface imaging system, similar to SONAR used for underwater applications.

 Targets can be seen beneath reinforced concrete ,asphalt, gravel and most other common surfaces.

STEP FREQUENCY GPR(SFR)  It is a second generation GPR that overcomes the limitations of the impulse radars.

 It works on the principle of frequency sweeping signal.  It has an advantage of large penetration and higher resolution

 It operates in frequency domain, and as such a perfect coupling between transmitter- receiver is achieved without the influence of any external perturbation.

 Resolution

is controlled by the wavelength propagating electromagnetic waves in ground.

 Resolution increases with increasing frequency

of

the

BASIC OPERATING PRINCIPLES

 GPR operates by transmitting pulses of ultra high frequency radio waves into the ground.

 There are two antennas one is for transmitting and other for receiving the refracted waves.

GPR THEORY OF OPERATION



Radar pulses are generated at a surface antenna and then propagated into the ground.



When they encounter burier discontinuities a portion of the radar is reflected back to the surface and recorded again at antenna.

 When the velocities of the radar travel-time are calculated they can be converted to depth, making GPR a 3D geophysical tool.

RECORDING RADAR REFLECTION

Antennas are moved along the ground surface in transects within a grid Many reflections are recorded per second and when they are plotted in a vertical profile a 2D vertical “slice” of reflections in the ground is produced.

When many transects are collected in a grid a 3D data base is obtained

DEPTH OF PENETRATION AND RESOLUTION



The depth of penetration and the resolution of buried features is primarily controlled by the frequency of the antenna.



Depth of investigation depends upon following factors

      

Loss Mechanisms Bandwidth Dynamic range Signal to noise Range gain Stacking dispersion

GPR DATA PROCESSING Typical GPR data reflection profile have to processed as it contains unwanted noise and reflections. These are the steps involved in processing GPR data

  

Background removal Point source hyperbola tail removal Production of rendered images of processed reflections.

GPR APPLICATIONS

 GPR locates almost anything underground  GPR makes an underground pictures  It is been used for coal depth measurement  For mapping of subsurface area to perform mining activities  Locates pipes and utilities  For Sinkhole depth and location  For geology (bedrock) and geological hazards  Archaeological studies  GPR surveys can be conducted anywhere in the world.

ADVANTAGES OF GPR

The advantages of ground penetrating radar over other non-invasive geophysical techniques are



Excellent spatial resolution

 Depth information  Geophysical properties being measured  Getting through the surface layer  Nondestructive testing (NDT) of structures and pavements,

LIMITATION OF GPR

 Interpretation of radar grams is generally non-intuitive to the novice. An experienced operator develops a real feel for the radar display and what the images represent physically.

 Considerable expertise is necessary to effectively design, conduct, and interpret GPR surveys. A reasonably intelligent operator can develop this after 5-10 surveys

 The cost of GPR equipment and software is relatively high. 

Relatively high energy consumption can necessitate large cumbersome batteries for extensive surveys.

CRUX

GPR is a versatile, accurate and reliable technique that can save significant time and money for survey teams, councils, utilities and geologists.

The improvements in this technology can provide instant results which until recently, may have been difficult and/ or costly to obtain using conventional or traditionally configured systems.

 GPR is an effective locating tool, it doesn’t work in all areas. Like any tool, it has its limitations.

GPR works best in soils or medias that are non-conductive, but not so well in all soils.

 As a general rule, soils with high mineralogical clay content inhibit the performance of the GPR signal, whilst sandy or gravely soils are much more suited to the method.

Thank You……