Basic Ground Penetrating Radar Theory Slide 2 GPR LIMITATIONS
Penetration depth and ability to resolve targets at depth is
strongly dependent upon the local soil properties. Highly
conductive soils can render the GPR method ineffective. There must
be a sufficient electrical contrast between the target and the host
materials Interpretation of GPR data can be subjective. The
experience of the interpreter is very important. Slide 3
Penetration depths Average penetration depths of radar signals in
high resistivity geological environment absent of low resistive
layers. Antenna (MHz) In soil (m) 25 25 40 50 20 30 100 12 20 200 8
15 500 3.5 5 1000 1.5 3 In rock (m) Slide 4 DEPTHDEPTH 0 1 2 3 4 5
6 Deep utilities must have larger diameters than shallow utilities
in order to be detected with GPR Slide 5 GPR is an electromagnetic
method that detects interfaces between subsurface materials with
differing dielectric constants. Your Easy Locator GPR system
basically consists of: An antenna, which houses a transmitter and
receiver. A monitor, which processes the received signal and
produces a graphic display of the data. The GPR technique GPR wave
propagation from transmitter (Tx) and reflection to the receiver
(Rx). The transmitter radiates repetitive short-duration
electromagnetic signals into the earth from the antenna moving
across the ground surface. Electromagnetic waves are reflected back
to the receiver by interfaces between materials with differing
dielectric constants. Slide 6 How GPR works GPR is, in principal,
similar to sonar equipment (fish finders) found in boats The
transmitter emits a train of electromagnetic impulses which
propagate through the media Reflection (i.e. scattering) occurs
where the electrical properties of subsurface materials change The
receiver picks up the back-scattered signal and displays it on a
monitor Slide 7 Time [ns] Depth [m] ? Length [m] GPR signatures
Slide 8 Data Examples & Interpretation Slide 9 CIVIL/STRUCTURAL
ENGINEERING Utilities (pipes, cables), rebar and voids. Pre-studies
for Horizontal Directional Drilling (HDD) Transportation: Roadways
and railroad tracks, ice thickness, bridge deck and bridge
fundation studies. ENVIRONMENTAL Hazardous waste mapping,
underground storage tanks (UST), Sedimentology studies, Bathymetry.
GEOTECHNICAL Stratigraphic mapping, cavities and sinkholes,
groundwater, mining hazards, fracture detection, Earth dam studies,
foundation studies, tunnel investigations. MILITARY Ordinance
detection, runway integrity, clearing of trenching routes
ARCHAEOLOGY site mapping, grave detection, artifacts GPR
APPLICATIONS Slide 10 The most important markets for radar Utility
detection Pipe and culvert inspections Concrete and NDT Road and
bridge deck investigations Geological mapping Ice, snow and glacier
Borehole radar Slide 11 The GPR performance GPR is primarily
affected by the conductivity and dielectric permittivity of the
mediums. GPR works best in resistive, sandy or gravely soil types.
Difficult, conductive types are typically composed of silts and
clays or contains salt water. Depth of investigation is limited by
signal attenuation of conductive soil but also dependent on the
antenna selected. The difference in radargram between good and bad
soil conditions Slide 12 Comparison between the SHALLOW and MID
antenna. Unknown Force MainWater Main Electrical Conduits Force
MainWater Main Electrical Conduits Unknown Shallow antenna Mid
antenna Slide 13 Interpretation: Metallic water pipes shows sharper
Sewer line is large enough to show both top/bottom reflection Note
radiuses of the signatures Trench shows Slide 14 Thank you!
