EM Spectrum

1
EMSpectrum
2
EM WaveTheory
3
EM WaveTheory

• Simplifications
• Conductors
• sgtgtwe
• Dielectrics
• sltltwe

4
Conductors and Dielectrics

• Skin depth
• SQRT (2/wms)
• Wave speed
• SQRT (2w/ms)
• Wavelength
• 2p SQRT (2/wms)
• Note - ms are together

• Skin depth
• 2 SQRT (e/m) / s
• Wave speed
• 1 / SQRT (me)
• Wavelength
• 2p / w SQRT (me)
• Note - e appears here

5
EMSpectrum

• GPR frequencies
• Lowest 80 MHz
• sees deepest 30m
• but poor rez.
• Highest 1200 MHz
• Shallow 10 cm
• High rez

6
Monitoring Remediation GPR
7
Monitoring Remediation GPR
8
GPR
9
GPRAntennas

• 
  100 Mhz
• 
  (lair 300 cm)
• 
  200MHz
• 
  ( 150 cm)
• 
  500 Mhz
• 
  ( 60 cm)
• 
  900 Mhz
• 
  ( 33 cm)

10
Dielectric constant, K

• permittivity e K eo
  
  where
  eo 1/36p x 10-9 sec/ohm-m
• K 1 air V 30 cm/ns
• 4 gasoline 15
• 6 dry sand 12.25
• 20 wet sand 6.7
• 81 water 3.33

11
(No Transcript)
12
GPR Catalog

• Summary of GPR signatures found by the
  Netherlands Institute of Applied Geoscience
• R.A. van Overmeeren, 1998, Radar facies of
  unconsolidated sediments in The Netherlands a
  radar stratigraphy method for hydrogeology,
  Journal of Applied Geoscience, v. 40, p.1-18.

13
GPR Fluvial Catalog
14
GPRGlacial Catalog
15
GPR Aeolian Catalog
16
GPRMarine Catalog
17
GPR Catalog, Summary
18
Gasoline Spill at OGI
19
OGI Test Tank
20
OGI Line E6 hours 0-48

• Pre-spill
• 12 hrs
• 24 hrs
• 36 hrs
• 48 hrs

21
OGI Line E6 Hours 48-95

• 48 hrs
• 60 hrs
• 72 hrs
• 84 hrs
• 96 hrs

22
OGI Line E6 Hours 108-158

• 108 hrs
• 120 hrs
• 132 hrs
• 144 hrs
• 158 hrs

23
Things to notice

• Gasoline spreads in fingers, maybe reflecting
  microtextures in the sand.
• The fingers wax (and wane?) as heads build up at
  the source. They pulse outward.
• (Not shown) A repeat survey done the following
  spring showed bright spots (gas pockets)
  scattered at different depths.

24
Problem Why bright spots?

• Jeff Daniels and his students at Ohio State have
  studied many LNAPL spills in the Midwest. They
  find that GPR reflections are almost always dim
  or absent over gasoline spills.
• Why was my result (in Oregon) different from his
  (in Illinois, Indiana, and Ohio)?

25
(No Transcript)
26
(No Transcript)
27
DaveC at Coeur dAlene
28
Borehole GPR in a boat
29
CDA GPR - profile
30
CDA GPR - Interp
31
GPR Characteristics

• 80-1200 MHz
• Uses true EM reflections
• Textures, petro-chemicals, UXO...
• High rez (10 cm)
• Fast ( km/hr)
• Can work near cultural noise

• Maximum depth penetration lt30m
• Cant penetrate conductive ground (gt30 mS/m)
• clays
• brackish porewaters
• Realistic sections