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Introduction to Ground Penetrating Radar Bryan S. Haley.

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Introduction to Ground Penetrating Radar Bryan S. Haley
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Page 1: Introduction to Ground Penetrating Radar Bryan S. Haley.

Introduction to Ground Penetrating Radar

Bryan S. Haley

Page 2: Introduction to Ground Penetrating Radar Bryan S. Haley.

Introduction

Page 3: Introduction to Ground Penetrating Radar Bryan S. Haley.

History• 1920s: rudimentary GPR, applications such as

ice thickness• Air radar used in WWII for aircraft, Radio

Detection and Ranging (RADAR) acronym• 1950s,60s: ice thickness, geological applications• 1972: NASA Apollo 17 on moon, carrying GPR • 1980s: engineering applications, concrete

assessment, void detection, land mine detection

Page 4: Introduction to Ground Penetrating Radar Bryan S. Haley.

History of GPR in Archaeology

1970s and 1980s• Chaco Canyon,

Cyprus, Ceren, Japan• Analysis of raw profile

data from plotters

Page 5: Introduction to Ground Penetrating Radar Bryan S. Haley.

History of GPR in Archaeology1990s and 2000s

• Computers more powerful and affordable

• Onboard storage• Time slice maps, 3D

modeling, rendering, etc.

Page 6: Introduction to Ground Penetrating Radar Bryan S. Haley.

How Does It Work?

Page 7: Introduction to Ground Penetrating Radar Bryan S. Haley.

How Does It Work?

Trace Profile

Page 8: Introduction to Ground Penetrating Radar Bryan S. Haley.

Relative Dielectric Permittivity (RDP)RDP( ) = (c / V)2

• Ranges from 1 (air) to 81 (water).

• Related primarily to water content of materials.

• Higher ε values mean less radar penetration (more attenuation).

• Strength of reflection is controlled by RDP contrast between the two materials.

• A reflection can occur in dielectric contrasts as small as 1.

ε

c: speed of light in a vacuum (3 X 108 m/s)

V: velocity of radar wave through the material

Page 9: Introduction to Ground Penetrating Radar Bryan S. Haley.

Conductivity (σ)• High σ inhibits radar penetration (more attenuation).• Increases with moisture content, and salinity.• So highly conductive soils (ie. clays) are not as ideal for

GPR investigation as soils with low σ (such as dry sand).

Magnetic Permeability (μ)• High μ inhibits radar penetration (more attenuation).

• Most soils have relatively low μ.

Other Properties

Page 10: Introduction to Ground Penetrating Radar Bryan S. Haley.

Conductivity and RDP for Common Materials

Page 11: Introduction to Ground Penetrating Radar Bryan S. Haley.

Strength of ReflectionReflection Strength = √ε2 - √ε1 / √ε2 + √ε1

ε1: RDP of first material

ε1: RDP of second material

Page 12: Introduction to Ground Penetrating Radar Bryan S. Haley.

Strength of Reflection

Reflection coefficient for 2 layer case. From GSSI SIR System-2000 Training Notes 1999.

Page 13: Introduction to Ground Penetrating Radar Bryan S. Haley.

Anomaly Shape

Simulations From GPRSIM 2D Forward Modeling Software

Page 14: Introduction to Ground Penetrating Radar Bryan S. Haley.

Antennas

• Identified by center frequency in MHz

• Higher frequency = greater vertical resolution

• Lower frequency = greater penetration depth

• Typical penetration depths

100Mhz 4-25m

300Mhz 1-10m

400Mhz .5-4m

500Mhz .5-3.5m

900Mhz 0-1m

Page 15: Introduction to Ground Penetrating Radar Bryan S. Haley.

Vertical Resolution

Tm = c / (4f √ε)

Tm: minimum thickness resolved.

c: speed of light in a vacuum (3 X 108 m/s).

f: center frequency of antenna.

ε: RDP.

Example: For 400 Mhz antenna and RDP of 10, the minimum thickness is about 6 cm.

Antennas

Page 16: Introduction to Ground Penetrating Radar Bryan S. Haley.

AntennasHorizontal Resolution

A = λ / 4 + D / √ (ε + 1)

• A = long dimension radius of footprint.• λ = center frequency wavelength of antenna.• D = depth.

• ε = RDP.

Example: For 400 Mhz antenna, a depth of 50 cm, and a RDP of 10, A is about 21 cm. Therefore the footprint is approximately 42 cm on the front to back axis and 28 cm on the side to side axis.

Page 17: Introduction to Ground Penetrating Radar Bryan S. Haley.

Antennas

Simplified antenna patterns.

Page 18: Introduction to Ground Penetrating Radar Bryan S. Haley.

Setup: Gaining

No Gain 5 Gain Points

Page 19: Introduction to Ground Penetrating Radar Bryan S. Haley.

Other Setup Parameters• Samples per scan (512)• Scans per time (16 to 64 / sec)• Bit depth of data (8 bit or 16 bit)

Page 20: Introduction to Ground Penetrating Radar Bryan S. Haley.

Determining Position

User Marks• Marks inserted manually

with trigger at fixed interval.Survey wheel

• Calibrated so that distance is determine based on number of revolutions.

GPS• Location determined by

GPS and synched with GPR based on time.

Page 21: Introduction to Ground Penetrating Radar Bryan S. Haley.

• Must record file name, X value, and Y start and finish

• Very important for GPR since software is flexible

• Basic instrument settings

Field Notes

Page 22: Introduction to Ground Penetrating Radar Bryan S. Haley.

Depth (Velocity) Estimation• Estimate from RDP.• Shoot to target of known depth.• Hyperbola fitting (geometric scaling).• Common Mid Point (CMP) testing.

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Hardware

• GSSI– SIR 2000– SIR 3000

• Sensors and Software– Noggin

• Mala

• Others

Page 24: Introduction to Ground Penetrating Radar Bryan S. Haley.

Processing Steps Radargram Processing

• Background removal• Box car filter• Band pass filter• Migration• Hilbert Transform• Topographic Correction• Antenna tilt correction

Page 25: Introduction to Ground Penetrating Radar Bryan S. Haley.

Processing Steps Create Info File

• Contains file name, X value, and Y start and finish.

Reverse Files• Align zig-zagged lines.

Set Navigation• Specify survey wheel,

user marks, GPS.• Fix marks if there are

errors.

Page 26: Introduction to Ground Penetrating Radar Bryan S. Haley.

Processing StepsSlice / Resample

• Set # of slices, thickness.• Radargrams resampled to

constant number per distance unit.

• Data collected from each radargram.

• Time slice values computed for each radargram are merged with the navigation.

• XYZ file created for each slice.

0.25 0.0625 12720.25 0.3125 15410.25 0.5625 12820.25 0.8125 17720.25 1.0625 16150.25 1.3125 13870.25 1.5625 1680

Page 27: Introduction to Ground Penetrating Radar Bryan S. Haley.

Processing StepsGridding

• Specify cell size, search radius.• Interpolate the XYZ files already created.

0.25 0.0625 12720.25 0.3125 15410.25 0.5625 12820.25 0.8125 17720.25 1.0625 16150.25 1.3125 13870.25 1.5625 1680

Page 28: Introduction to Ground Penetrating Radar Bryan S. Haley.

Time Slices• Processing: low pass, high pass, etc.• Set color scheme• Set data range• Set transforms

Page 29: Introduction to Ground Penetrating Radar Bryan S. Haley.

3D Data Cubes

Page 30: Introduction to Ground Penetrating Radar Bryan S. Haley.

Isosurface Rendering

Page 31: Introduction to Ground Penetrating Radar Bryan S. Haley.

Animations

Page 32: Introduction to Ground Penetrating Radar Bryan S. Haley.

Support Software

• Surfer

• ArcView / ArcGIS

Page 33: Introduction to Ground Penetrating Radar Bryan S. Haley.

Interpretation•Anomaly Shape / Size / Orientation

•Strength / Amplitude

•Context

•Multiple Instrument Response

•Data from other projects•Historic Documents•Aerial Photos•Lore•Etc.•Ground Truthing

Page 34: Introduction to Ground Penetrating Radar Bryan S. Haley.

Results

Page 35: Introduction to Ground Penetrating Radar Bryan S. Haley.

For More Reading…

• Conyers and Goodman 1997

• Conyers 2004

• Heimmer and Devore 1995

• Bevan 1998

• Clark 1995

• Gaffney and Gater 2003

• Johnson 2006

Page 36: Introduction to Ground Penetrating Radar Bryan S. Haley.

Part II: Case Studies

Bryan S. Haley

Page 37: Introduction to Ground Penetrating Radar Bryan S. Haley.

Sapelo Island Shell Rings (Georgia)

Page 38: Introduction to Ground Penetrating Radar Bryan S. Haley.

Sapelo Island

Reconstruction

Page 39: Introduction to Ground Penetrating Radar Bryan S. Haley.

Sapelo Island

Early sketch map. Modern topo map.

Page 40: Introduction to Ground Penetrating Radar Bryan S. Haley.

Sapelo Island

Page 41: Introduction to Ground Penetrating Radar Bryan S. Haley.

Sapelo Island

Page 42: Introduction to Ground Penetrating Radar Bryan S. Haley.

St. Michael’s Cemetery (Pensacola FL)

Page 43: Introduction to Ground Penetrating Radar Bryan S. Haley.

St. Michael’s Cemetery

Page 44: Introduction to Ground Penetrating Radar Bryan S. Haley.

St. Michael’s Cemetery

Page 45: Introduction to Ground Penetrating Radar Bryan S. Haley.

St. Michael’s Cemetery

Page 46: Introduction to Ground Penetrating Radar Bryan S. Haley.

St. Michael’s Cemetery

Page 47: Introduction to Ground Penetrating Radar Bryan S. Haley.

Memorial Cemetery (St. Genevieve Missouri)

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Memorial Cemetery

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Memorial Cemetery

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Memorial Cemetery

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Belle Alliance (Louisiana)

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Belle Alliance

Page 53: Introduction to Ground Penetrating Radar Bryan S. Haley.

Belle Alliance

Page 54: Introduction to Ground Penetrating Radar Bryan S. Haley.

Belle Alliance

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Jackson Barracks (New Orleans)

Page 56: Introduction to Ground Penetrating Radar Bryan S. Haley.

Jackson Barracks

Possible Burial

Page 57: Introduction to Ground Penetrating Radar Bryan S. Haley.

Jackson Barracks

Possible Burials

Page 58: Introduction to Ground Penetrating Radar Bryan S. Haley.

Jackson Barracks

Interpretation

Page 59: Introduction to Ground Penetrating Radar Bryan S. Haley.

Hollywood (NW Mississippi)

1923 Sketch Map of Mounds

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Hollywood

Page 61: Introduction to Ground Penetrating Radar Bryan S. Haley.

Hollywood

Excavated Structures

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Hollywood

Page 63: Introduction to Ground Penetrating Radar Bryan S. Haley.

Cahal Pech (Belize)

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Cahal Pech

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Cahal Pech

Page 66: Introduction to Ground Penetrating Radar Bryan S. Haley.

Cahal Pech

Excavated Structure


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