1. Tom Wilson, Department of Geology and Geography Environmental and Exploration Geophysics II tom.h.wilson tom.wilson@mail.wvu.edu Department of Geology and Geography West Virginia University Morgantown, WV Radar Methods – General Overview

2. Tom Wilson, Department of Geology and Geography Brown (2004)

3. Tom Wilson, Department of Geology and Geography Sheriff (1996) Neidell (1990)

4. Tom Wilson, Department of Geology and Geography Neidell (1990)

5. Tom Wilson, Department of Geology and Geography Brown (2004)

6. Tom Wilson, Department of Geology and Geography Sheriff (1996)

7. Tom Wilson, Department of Geology and Geography The radar band is loosely taken to extend from approximately 0.1cm to 100cm. The microwave region is often used for surface imaging from airborne or satellite platform.

8. Tom Wilson, Department of Geology and Geography Radar image of the earth’s surface at 5.4cm or 5.6 GHz. Seneca Rocks

9. Tom Wilson, Department of Geology and Geography 25MHz = 12m wavelength (40ns) 50MHz = 6m (20ns) 100MHz = 3m (10ns) 1GHz = 0.3m (1ns) Times in nanoseconds represent the time it takes light to travel through 1 wavelength in a vacuum. Ground penetrating radar (GPR) systems often operate in the tens of MHz to GHz region of the spectrum.

10. Tom Wilson, Department of Geology and Geography Visual wavelength image Shuttle Imaging Radar - SIR A ~ 25cm Sabins, 1996

11. Tom Wilson, Department of Geology and Geography Sabins, 1996

12. Tom Wilson, Department of Geology and Geography GPR mono-static and bi-static transmitter-receiver configurations. Note similarity to coincident source-receiver and offset source receiver configurations discussed in the context of seismic methods Daniels, J., 1989 & Sensors and Software Ground Surveys

13. Tom Wilson, Department of Geology and Geography Spectral and temporal characteristics of the GPR wavelet. Sensors & Software Inc. - Ekko Updates Does this sound familiar!

14. Tom Wilson, Department of Geology and Geography As with seismic data, reflection arrival times are 2-way times and depth equals ½ the two-way time x average velocity. Velocity in air is approximately equal to the velocity of light in a vacuum: c. c = 3 x 10 8 m/sec = 9.84 x 10 8 f/s or approximately 1 foot per nanosecond. 1 nanosecond is 10 -9th seconds. This also corresponds to or 0.3 m/nanosecond Thinking in terms of two-way times, it takes 2ns to travel 1 ft.

15. Tom Wilson, Department of Geology and Geography In general the velocity of the radar wave is defined as where c is the velocity of light in a vacuum (or air), and  r is the electric permitivity of the material through which the radar wave travels. Examples of  r (see Daniels) are 81 for water 6 for unsaturated sand 20 for saturated sand The presence of water has a significant effect on velocity. Valid only when electrical conductivity is small

16. Tom Wilson, Department of Geology and Geography c ~ 1ft/ns in air v ~ 1/2 to 1/3rd ft/ns in unsaturated sand v ~ 1/3rd to 1/5th ft/ns in saturated sand Typical velocities  is proportional to conductivity  - materials of relatively high conductivity have slower velocity than less conductive materials.

17. Tom Wilson, Department of Geology and Geography In our discussions of seismic we recognized absorption as an important process affecting the ability of the seismic wave to penetrate beneath the earth’s surface. High attenuation coefficient  produces rapid decay of seismic wave amplitude with distance traveled (r). The same process controls the ability of electromagnetic waves to penetrate beneath the earth’s surface. The expression controlling attenuation is a function of several quantities, the most important of which are conductivity and permitivity.

18. Tom Wilson, Department of Geology and Geography Attenuation of electromagnetic waves is controlled by the propagation factor which has real and imaginary parts. The real part  (the attenuation coefficient) illustrates the influence of permitivity and conductivity on absorption. Note in this equation that increases of  translate into increased attenuation. Also note that increases of angular frequency (  =2  f) will increase attenuation.

19. Tom Wilson, Department of Geology and Geography The display of radar waves shows considerable similarity to that of seismic data

20. Tom Wilson, Department of Geology and Geography Diffraction events are commonly produced by heterogeneity in the electrical properties of subsurface materials

21. Tom Wilson, Department of Geology and Geography The diffraction response can be used - as you would have guessed – to determine velocity.

22. Tom Wilson, Department of Geology and Geography Remember the ray path geometry for the diffraction event? For coincident source and receiver acquisition *

23. Tom Wilson, Department of Geology and Geography *

25. Average Velocity = 1/2 the reciprocal of the slope

26. Tom Wilson, Department of Geology and Geography Sensors & Software Inc. - Ekko Updates Note that the 0.2 m/ns velocities in the sand dune complex is pretty high compared to the above.

27. Tom Wilson, Department of Geology and Geography The characteristics of a common midpoint gather from a GPR data set look very similar to those from a seismic CMP gather. Reflection hyperbola Direct “air- wave” arrival Direct arrival through surface medium Smith and Jol, 1995

28. Tom Wilson, Department of Geology and Geography Thinning layer response and resolution considerations. Daniels, J., 1989

29. Tom Wilson, Department of Geology and Geography Horizontal Resolution: The Fresnel Zone

30. Tom Wilson, Department of Geology and Geography The Fresnel Zone Radius R f An approximation

31. Tom Wilson, Department of Geology and Geography Topographic variations must also be compensated for. Daniels, J., 1989

32. Tom Wilson, Department of Geology and Geography West Pearl Queen Field Area

33. Tom Wilson, Department of Geology and Geography Surface along the GPR line shown below was very irregular so that apparent structure in the section below is often the result of relief across features in the surface sand dune complex.

34. Tom Wilson, Department of Geology and Geography GPR data is often collected by pulling the GPR unit across the surface. Subsurface scans are made at regular intervals, but since the unit is often pulled at varying speeds across the surface, the records are adjusted to portray constant spacing between records. This process s referred to as rubbersheeting. Daniels, J., 1989

35. Tom Wilson, Department of Geology and Geography Smith and Jol, 1995, AG

36. Tom Wilson, Department of Geology and Geography Smith and Jol, 1995, AG

37. Tom Wilson, Department of Geology and Geography Increased frequency and bandwidth reduce the dominant period and duration of the wavelet

38. Tom Wilson, Department of Geology and Geography Comparison of the 25MHz and 100 MHz records Smith and Jol, 1995, AG

39. Tom Wilson, Department of Geology and Geography Smith and Jol, 1995, AG We also expect to see decreased depth of penetration (i.e. increased attenuation) for higher frequency wavelets and components of the GPR signal.

40. Tom Wilson, Department of Geology and Geography Sensors & Software Inc. - Ekko Updates

41. Tom Wilson, Department of Geology and Geography In the acquisition of GPR data one must worry about overhead reflections. Daniels, J., 1989

42. Tom Wilson, Department of Geology and Geography …. and tree branches! Daniels, J., 1989

43. Tom Wilson, Department of Geology and Geography GPR unit Sensors & Software Inc. – Smart Cart Visit http://www.sensoft.ca/

44. Tom Wilson, Department of Geology and Geography Sensors & Software Inc. – Salt Water Infiltration

45. Tom Wilson, Department of Geology and Geography Pulse EKKO bistatic

46. Tom Wilson, Department of Geology and Geography Sensors and Software - Locating underground storage tanks

47. Tom Wilson, Department of Geology and Geography Sensors and Software - Locating unexploded ordnance

48. Tom Wilson, Department of Geology and Geography Sensors and Software - forensic applications

49. Tom Wilson, Department of Geology and Geography Time slice map from 3D data volume of radar data. This is a surface of equal travel time. Disruptions in the reflection pattern are associated with the waste pit. Green et al., 1999, LE

50. Tom Wilson, Department of Geology and Geography Bright red areas define the location of the landfill; the orange objects represent gravel bodies. The brownish-pink lobes are high reflectivity objects of unknown origin. The view at bottom profiles the underside of the landfill and gravel bodies. Green et al., 1999, LE

51. Tom Wilson, Department of Geology and Geography Sensors and Software - Avalanche Assessment

52. Tom Wilson, Department of Geology and Geography Sensors & Software Inc. – Glaciers, Ice and Snow

53. Tom Wilson, Department of Geology and Geography http://www.sciencedaily.com/releases/2008/04/080420114718.htm http://www.nasa.gov/mission_pages/MRO/multimedia/phillips-20080515.html

54. Tom Wilson, Department of Geology and Geography Sensors & Software Inc. – Plastic and metal pipes

55. Tom Wilson, Department of Geology and Geography Sensors & Software Inc. - Ekko Updates