GROUND PENETRATING RADAR 4/28/2017 Xstrata Alloys GROUND PENETRATING RADAR A Basic Overview to RAdio Detection And Ranging 2010-09-27 GPR Training Notes

HOW GPR WORKS ANATOMY OF A RADAR RECORD GPR DETECTION CAPABILITIES ELECTRICAL PROPERTIES OF MATERIALS GPR PENETRATION DIELECTRIC CONSTANTS OF COMMON MATERIALS REFLECTION STRENGTH GPR DEPTH OF INVESTIGATION GPR APPLICATIONS CONCLUSION

4/28/2017 HOW GPR WORKS Theory The unit transmits a short pulse of radio signal, and measure the time it takes for the reflection to return. The distance is one-half the product of the round trip time and the speed of the signal. The receiver does not detect the return while the signal is being transmitted. Through the use of a device called a duplexer, the radar switches between transmitting and receiving at a predetermined rate. minimum range is calculated by measuring the length of the pulse multiplied by the speed of light, A similar effect imposes a maximum range as well These two effects tend to be at odds with each other, and it is not easy to combine both good short range and good long range in a single radar. The Typical System is a low power GPR system that transmits electromagnetic energy in the frequency range of 16 MHz to 2600 MHz (2.6GHz) into the subsurface. The total power transmitted is only a few milliwatts; less than that of cellular telephones. GPR Training Notes

HOW GPR WORKS Practice SIR-3000 console transmits signal via cable to antenna Antenna radiates a cone of energy Energy is reflected off of “interfaces” Antenna receives reflected signal and transmits to console

ANATOMY OF A RADAR RECORD 4/28/2017 ANATOMY OF A RADAR RECORD Surface Reflection from interface Time/Depth Very important: Note the TIME – DEPTH ambiguity Horizontal axis is the antenna position on the surface GPR Training Notes

GPR DETECTION CAPABILITIES 4/28/2017 GPR DETECTION CAPABILITIES DEPTH OF PENETRATION Highly dependent on subsurface conductivity (to be discussed later) Maximum depth: ± 30 meters (this is in ideal soil conditions) 400Mhz antenna : ± 4m (this is the antenna we have to use for hard rock) SIZE OF OBJECTS DETECTABLE Smallest in soil: Wire mesh (millimeters) Largest in soil: Geological features (hundreds of meters) Smallest in hard rock: Wire mesh (: A few cm) Largest in hard rock: Geological features (tens of meters) GPR Training Notes

ELECTRICAL PROPERTIES OF MATERIALS 4/28/2017 ELECTRICAL PROPERTIES OF MATERIALS ELECTRICAL CONDUCTIVITY Siemens/meter (S/m) The ability of a material to conduct electric current The reciprocal is resistivity (high conductivity = low resistivity) The value is primarily controlled by water content and/or clay content Higher conductivity makes radar signal penetration difficult Resistivity < S/m are VERY difficult GPR conditions DIELECTRIC CONSTANT Dimensionless measure of the capacity of a material to store a charge; The value ranges from 1 to 81 (AIR = 1, WATER = 81) The value is primarily controlled by water content; Dielectric constant differences at boundaries cause reflections in the radar data; The strength of reflections is controlled by the contrast in the dielectric constants of the two adjacent materials. GPR Training Notes

GPR PENETRATION 300 MHz antenna depth in feet depth in feet 4/28/2017 GPR PENETRATION 300 MHz antenna depth in feet depth in feet Electrical conductivity in mmhos/m terrain conductivity in mmhos/m GPR Training Notes

DIELECTRIC CONSTANTS OF COMMON MATERIALS 4/28/2017 DIELECTRIC CONSTANTS OF COMMON MATERIALS AIR 1 SNOW 1-2 PVC 3 ASPHALT 3-5 FRESHWATER ICE 4 CONCRETE 4-11 (5) ROCK GRANITE 4-7 SANDSTONE 6 SHALE 5-15 LIMESTONE 4-8 BASALT 8-9 SOILS AND SEDIMENTS 4-30 FRESH AND SALTWATER 81 GPR Training Notes

EFFECT OF WATER ON DIELECTRIC CONSTANT 4/28/2017 EFFECT OF WATER ON DIELECTRIC CONSTANT % Water Content Dielectric Constant GPR Training Notes

REFLECTION STRENGTH The strength of a reflection is dependent on the difference in dielectric between the host & the target? Simply put … If the dielectric contrast between the two rocks is too small, you will not reflect enough energy to see the target ` Reflected waves Transmitted waves

GPR DEPTH OF INVESTIGATION 4/28/2017 GPR DEPTH OF INVESTIGATION DECREASES AS: Conductivity of the rock increases Water Content Increases (especially if salts are present) Clay Content Increases Scattering Increases (if the feature is not parallel to the hanging wall) GPR user has no control over these factors INCREASES AS: Antenna Frequency Decreases (but this decreases resolution/sensitivity) GPR user has control over these factors. These factors not only change from day to day but from area to area. The ability to interpret a radar plot is as much an art as a science. GPR Training Notes

NORMAL INVESTIGATION DEPTHS OF GSSI ANTENNAS 4/28/2017 NORMAL INVESTIGATION DEPTHS OF GSSI ANTENNAS Frequency (MHz) Typical applications Depth (m) 16 – 80 Geologic 5 - 30+ 100 Geologic, 4 - 25 Environmental 400 Geotechnical, Utility detection, 1 - 4 Archaeology 900 Concrete NDT, Soils, 0 - 1 Archaeology, Bridges 1500 Concrete NDT 0 - .5 GPR Training Notes

GPR APPLICATIONS UTILITY DETECTION & NDT 4/28/2017 GPR APPLICATIONS UTILITY DETECTION & NDT Utilities (pipes, cables), rebar and voids GPR Training Notes

GPR APPLICATIONS TRANSPORTATION ENGINEERING 4/28/2017 GPR APPLICATIONS TRANSPORTATION ENGINEERING Transportation: roadways and railroad tracks Ice thickness GPR Training Notes

GPR APPLICATIONS ENVIRONMENTAL Hazardous waste mapping 4/28/2017 GPR APPLICATIONS ENVIRONMENTAL Hazardous waste mapping Storage tank detection GPR Training Notes

GPR APPLICATIONS MILITARY ARCHAEOLOGY Ordnance detection 4/28/2017 GPR APPLICATIONS MILITARY Ordnance detection Runway integrity ARCHAEOLOGY GPR Training Notes

GPR APPLICATIONS MINING SAFETY 4/28/2017 GPR APPLICATIONS MINING SAFETY Imaging of hanging wall for fractures & faults Identification of ramps and sills GPR Training Notes

CONCLUSION Radar requires an exposed surface to operate. Radar detects change in electrical conductivity Radar is one dimensional. Many readings and computations are required to return an image (2D or 3D) It takes a skilled operator and a skilled analyst to get meaningful results. You need to have a good idea of what you are looking for before you start. With an increase in frequency we get better resolution but worse penetration. Water and clays absorb the radar pulse and weaken return. Radar is one of the many powerful new tools available.