Ground-Penetrating Radar Uses pulses of radio waves to image the subsurface (typically 25 - 1000MHz) http://upload.wikimedia.org/wikipedia/commons/8/8a/Electromagnetic-Spectrum.png

GPR uses Radio Waves to Image the Subsurface Smart Systems Made Simple GPR uses Radio Waves to Image the Subsurface The Noggin uses advanced impulse radar sensing technology. Radio waves are generated and detected by the Noggin. The buried targets are identified by the signals they reflect back to the surface and which are detected by the sensitive Noggin receiver electronics. All Sensors & Software products are certified to meet regulatory standards around the world. See the FCC label or the CE mark on the labels and serial number plates. Is the Noggin the universal answer. No! Some soils strongly absord radio signals and exploration depth is limited. Just think about how well you cell phone or car radio work in underground garages or tunnels. Again, don’t get too involved in this discussionb at this point but we need to have the response ready if some one asks. The point we want to get across is that the physics of radio waves limits exploration depth – not the product!. And no one can not increase power indefinitely. First the regulators will catch you out and second the power supply becomes prohibitively large and unwieldy. This simple animation shows how an “inverted V” (hyperbola in space time) is created when traversing over a pipe. The apex of V is the point of closest approach to the target. Moving to the top of the inverted V defines the location of the target. Depth of the target is measured at the top of V. The standard depth calibration gives useful depth estimates. More accurate depths are obtained by using the target fitting feature built into the DVL software right on the unit. Survey Mode – Reflection Survey Sensors & Software Inc.

GPR and Seismic Reflection Displaying GPR data (left) is analogous to a reflection seismic section (right) Figures 8.13 and 4.48 in Burger, Sheehan, and Jones, 2006

EM Wave Properties Characteristics of radar waves Velocity -- v Attenuation --  Reflection coefficient -- R Are controlled by the electrical properties of the soil: Dielectric Permittivity -- K Conductivity -- 𝞂

V = c /(𝝻 K)1/2 ~ c/√K Radar Velocity In a vacuum: velocity is the speed of light ( c ) In materials: Relative dielectric permittivity ( K ) Relative magnetic permeability(𝝻) Normally 1 for geological materials V = c /(𝝻 K)1/2 ~ c/√K

Radar Attenuation 𝜶 = 1.7 x 103 𝞂 / √K Radar attenuation controls how quickly the radar energy is absorbed by the medium High attenuation results in poor soil or rock penetration Attenuation is proportional to conductivity and inversely proportional to dielectric permittivity at 100 MHz 𝜶 = 1.7 x 103 𝞂 / √K

Common Material Electrical Properties @ 100 MHz Velocity Conductivity Attenuation Material K v 𝞂 a (m/ns) (mS/m) (dB/m) Air 1 0.3 0 0 Distilled Water 80 0.033 0.01 2x10-3 Fresh Water 80 0.033 0.5 0.1 Sea Water 80 0.01 3x103 103 Dry Sand 3-5 0.15 0.01 0.01 Saturated Sand 20-30 0.06 0.01-1 0.03-0.3 Limestone 4-8 0.12 0.5-2 0.4-1 Shales 5-15 0.09 1-100 1-100 Silts 5-30 0.07 1-100 1-100 Clays 5-40 0.08 2-1000 1-300 Granite 4-6 0.13 0.01-1 0.01-1 Dry Salt 5-6 0.13 0.01-1 0.01-1 Ice 3-4 0.16 0.01 0.01 Metal 1000000 ~0 ∞ ∞

GPR Limitations Does not work well in presence of high surface conductivity (e.g. wet clays or conductive fluids) because of high attenuation. The high attenuation prevents radar waves from penetrate into these materials GPR does work well in regions of ice, snow, dry sandy soil, or over concrete.

Reflections are caused by Contrasts in Dielectric Permittivity Incident Reflected K1 K2 Transmitted K1- K2 R = K1+ K2

Reflection Strength depends on the Contrast of Materials Smart Systems Made Simple Reflection Strength depends on the Contrast of Materials Material 1 K1 Material 2 K2 Reflectivity Air 1 Dry Soil 5 -38% Wet Soil 25 Rock 6 -5% 34% Water 80 57% Ice 3 -67% Permafrost -34% Soil 12 Metal 1000000 -99% Sensors & Software Inc.

Resolution and Depth Smallest resolvable layer is assumed to be of thickness ( λ/4 ) where ( V = f λ ) higher frequencies have higher resolution; however, they have small penetration depths lower frequencies have lower resolution; however, they have large penetration depths

GPR for Subsurface Imaging Antenna Center Frequency 500 MHz 1000 MHz Freq. (MHz) Wave length (m) 12.5 12 25 6 50 3 100 1.5 250 0.6 500 0.3 1000 0.15 Typical Application Glaciology Geology Utility Locating 250 MHz Archaeology Forensics Roads Concrete Sensors & Software Inc.

GPR for Subsurface Imaging Frequency 12.5 25 50 100 200 Lower Frequency = longer wavelength = deeper penetration = less resolution Higher Frequency = shorter wavelength = less penetration = more resolution Sensors & Software Inc.

GPR for Subsurface Imaging Frequency vs. Depth Frequency (MHz) Depth (m) Depth (ft) 12.5 50+ 165+ 25 30 100 50 10 33 5 16 200 2 6 500 1 3 1000 0.5 1.5 Values are based on practical experience. Should only be used as a quick guide. Sensors & Software Inc.

Data Acquisition Data is collected by moving a transmitter and a receiver antenna over the area continuously broadcasting and receiving radar waves. The antenna are usually separated by a fixed distance and moved together. Figure 8.15 in Burger, Sheehan, and Jones, 2006

GPR for Subsurface Imaging Antenna Center Frequency 500 MHz 1000 MHz Freq. (MHz) Wave length (m) 12.5 12 25 6 50 3 100 1.5 250 0.6 500 0.3 1000 0.15 Typical Application Glaciology Geology Utility Locating 250 MHz Archaeology Forensics Roads Concrete Sensors & Software Inc.

pulseEKKO PRO SmartCart with Antennas GPR for Subsurface Imaging pulseEKKO PRO SmartCart with Antennas Sensors & Software Inc.

GPR for Subsurface Imaging SmartChariot Sensors & Software Inc.

Applications Historic cemetery in Alabama (yellow arrows are strong reflectors, red arrows are weak reflectors, and blue lines are bedrock interfaces http://upload.wikimedia.org/wikipedia/commons/9/9c/LINE21.jpg

Diffraction Hyperbola Radar waves go out in all directions so the strongest reflections may not be directly below the radar antennas Figures 8.21 and 8.19 in Burger, Sheehan, and Jones, 2006

Utility SmartCart Training Sensors & Software Inc.

Utility SmartCart Training Sensors & Software Inc.

Utility SmartCart Training Sensors & Software Inc.

Utility SmartCart Training Sensors & Software Inc.

Utility SmartCart Training Sensors & Software Inc.

Utility SmartCart Training Sensors & Software Inc.

Utility SmartCart Training Sensors & Software Inc.

Velocity Calibration Method: Hyperbola Matching GPR for Subsurface Imaging Velocity Calibration Method: Hyperbola Matching Velocity and depth can be extracted by matching the shape of a hyperbola in the data with an adjustable on-screen overlay of a hyperbola Sensors & Software Inc.

Water Table Reflection

Water Table One of the strongest reflecting horizons – large dielectric permittivity contrast K= 5 to K = 25

Polar Applications

Planetary Applications SHARAD (SHAllow RADar) aboard the Mars Reconnaissance Orbiter Spacecraft 15 – 25 MHz Hres = 0.3 - 3 km Vres = 10 - 15 m http://www.nasa.gov/mission_pages/MRO/multimedia/1334-0-gram.html