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A Presentationon

Ground Penetrating Radar(GPR)

Presented By:Ajay Kumar Sah

069/MSI/602

2/16/2014

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What is RADAR?

RAdio Detection And RangingOriginally called Radio Direction Finding

(R.D.F.) in England.Electronic equipment that detects the

presence of objects by using reflected electromagnetic energy

Transmits a wave into atmosphere and measures the return power

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How does RADAR work?

Operating Principle of RADAR - Bats use to find their path during their flight.

Emits ultrasonic sounds in a certain frequency (120KHz) and hear the echoes of these sounds.

Echoes make them enable to locate and avoid the object in their path

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How does RADAR work?

Pulse of microwave energy is sent out , dish focuses energy into beam

Beam travels through atmosphere If the beam hits an object, them some of the energy is reflected

back to RADAR Return power is measured Data processed to a visual display

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Ground Penetrating RADAR (GPR)High resolution electromagnetic technique that is

designed primarily to investigate the shallow subsurface of the earth, building materials, and roads and bridges.

GPR is a time-dependent geophysical technique that can provide a 3-D pseudo image of the subsurface, including the fourth dimension of color

Can also provide accurate depth estimates for many common subsurface objects.

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GPR Principle An EM pulse is sent through

an antenna, penetrating into the surveyed material

A portion of the energy is reflected back to the antenna when an interface between materials of dissimilar dielectric constants is encountered

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GPR Principle The reflected signal has

information on: how quickly the signal

traveled how much was

attenuated

These quantities depend on spatial configuration and materials

The thickness of a layer is given by:

where di is the thickness of layer i, ti the total travel time through that layer, C is the speed of light and εr,i the dielectric constant of the layer

ir

ii

Ctd

,2

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GPR Principle The amount of reflected

energy at an interface is governed by:

where ρ1,2 is the reflection coefficient and εr1 and εr2 are the dielectric constants

Typical Dielectric Constants

Material Dielectric Constant

Air 1Water 81Concrete 6-12HMA 4-7Ice 1.5Metals ∞

21

212,1

rr

rr

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Instrumentation

The typical instrumentation for GPR includes the following: Antenna Control Unit Display device Storage device

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Applications

Geological and hydro-geological investigations including mapping of bedrock topography, water levels, solution features, glacial structures, soils and aggregates.

Engineering investigations to evaluate dams, sea walls, tunnels, pavements, roadbeds, railway embankments, piles, bridge decks, river scour, buildings and monuments.

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ApplicationsLocation and evaluation of buried structures

including utilities, foundations, reinforcing bars, cavities, tombs, archaeological artifacts, and animal burrows.

Site investigations: location of buried engineering structures and underground storage tanks.

Subsurface mapping for cables, pipes and other buried structures prior to trench-less operations.

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Applications

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Advantages

Rapid ground coverage- Antenna towed either by hand or from a vehicle.

High-resolution coverage of the survey area, detecting even small objects.

On-site interpretation possible due to instant graphic display.

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LimitationsData acquisition may be slow over difficult terrain.Depth of penetration is limited in materials with

high electrical conductivities, clays.Energy may be reflected and recorded from

aboveground features, walls, canopies, unless antennae are well shielded.

Artifacts in the near surface may scatter the transmitted energy and complicate the received signal and/or reduce depth of penetration.

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References• D. J. Daniels, Ground Penetrating Radar, 2nd Ed. IEE

Radar Sonar Navigation and Avionics Series, London: IEE Books, July 2004.

• Cardimona, S., Webb, J., Lippincot T., 2000, Ground Penetrating Radar, Geophysics 2000, Dec 11- 15th, St Louis, Missouri.

• Introduction to radar systems, Merrill L. Skolnik, Third Edition.

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Thank You !

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