1. Ground Penetrating Radar
Kenton Mick

2. What is Ground Penetrating Radar?
GPR is a technique used to locate objects or interfaces buried beneath the Earth’s surface.
Typically operate with
Frequency: MHz
Tx Waveform: Impulse Time Domain
Rx: Sampling Receiver
As component price decreases, Dynamic Range is improving through FM-CW and stepped frequency modulation.

3. Antenna Location Collocated Bi-Static Typical in most applications
Uses the reflection from the buried object
Bi-Static
One antenna must be buried beneath the surface
Uses forward scattering from the buried object
Application: Borehole Tomographic Radar Imaging

4. Problems Clutter Efficiently coupling the energy into the ground
Signals that are unrelated to the target scattering characteristics but occur in the same sample time window and have similar spectral characteristics.
Can be from breakthrough between Tx and Rx or multiple reflections between the antenna and the ground.
Typically the severity of the effects decreases with penetration depth
Efficiently coupling the energy into the ground
Reflections caused from the reflections from the air to the ground
Penetration Depth

5. Typical Applications Archaeological Investigations
Borehole Inspections
Detection of Buried Mines
Forensic Investigations
Planetary Exploration
Road Condition Survey

6. Archaeological Example
Archaeological site in the city of Pompeii, Roman Empire
Covered in volcanic deposit from eruption
Used a Noggin Plus system with 250 MHz
Time window of 100 ns
Max depth of 5 meters of volcanic deposit
There data only went 2 meters

7. Road Survey Example
Difference in moisture levels between the asphalt and the ground below causes landslides to occur
Experiment took place in Limiti di Greccio, Italy
Had two analysis methods
Amplitude Attenuation on return signal
Change in frequency between transmit and received signal
The frequency used varied between 3 frequencies
1 GHz
600 MHz
1.6 GHz

8. Analysis Center Frequency analysis in terms of Resolution and Depth
Time window in terms of Depth
Sampling Interval in terms of center frequency

9. Center Frequency with respect to Resolution
Spatial Resolution places a lower bound on the center frequency
Assuming a center frequency to bandwidth ratio of 1
So as frequency decreases, the spatial resolution increases

10. Center Frequency with respect to Depth
The penetration depth places an upper bound on the frequency
Assuming the target dimension is as close in size to a Fresnel zone in order for the return signal arrive coherently

11. Time Window
The time window is the amount of time it take for the signal to return from the farthest penetration depth.

12. Selecting Sampling Interval
Selecting the time interval at which samples will be taken on the return signal’s waveform must abide by the Nyquist Sampling Criteria.
Typically an antenna for GPR will radiate a frequency (+/-) 50% the center frequency
For this reason the sampling rate should consider the highest frequency component at least 1.5 times the center frequency.

13. Results Pompeii Max_frequency = 725 MHz to see 5 meters down
Min_frequency = 50 MHz to be able to spatially resolve to 0.5 meters
Time Window = ns
Sampling Interval of 3.33 ns
Assuming K = and velocity = [m/ns]

14. Results Limiti di Greccio, Italy 1 GHz Antenna 1,600 MHz Antenna
Max_frequency = 3 GHz to get 1 meter of depth
Min_frequency = 1 GHz to get 0.03 meter spatial resolution
Sampling Interval = ns for 1 GHz
1,600 MHz Antenna
Min_frequency = 1,600 MHz to get meter spatial resolution
Sampling Interval of ns
600 MHz Antenna
Min_frequency = 600 MHz to get 0.05 meter spatial resolution
Sampling Interval = ns
Assuming
K = 6.25
Velocity = 0.12 [m/ns]

15. Q25 GPR Available through US Radar Inc
Center Frequency of 250 MHz or 270 MHz
Sampling Interval of 10 ps to 6.4 ns
Will it work for the two applications?
Pompeii
Yes, the center frequency of Q25 falls within the range and the sampling interval needed is met.
Limiti di Greccio, Italy
Yes but no, the center frequency of 250 MHz will give the required depth but not the resolution needed.

16. Resources
D. J. Daniels, Ground Penetrating Radar, 2nd ed. Stevenage: IET,
A. P. Annan, “Ground Penetrating Radar Workshop Notes,” Ground Penetrating Radar Workshop Notes. Sensors and Software Inc, Ontario, Canada, 1992.
F. Benedetto and C. Schettini, “Evaluation of Geotechnical Stability of Road using GPR ,” IEEE, rep., 2011.
P. M. Barone, E. Pettinelli, T. Bellomo, and C. Scarpati, “Applications of GPR to archaeology and geology: the example of the regio III in Pompeii (Naples, Italy),” rep.

17. Resources
J. K. Russell and M. V. Stasiuk, “Characterization of volcanic deposits with ground-penetrating radar,” eoas.ubc.ca, 27-Dec [Online]. Available: eoas.ubc.ca/~krussell/epapers/bv_rs97.pdf. [Accessed: 28-Apr-2018].
R. Evans, M. Frost, and R. Morrow, “Assessing the influence of moisture on the dielectric properties of asphalt,” rep.