EM%20Spectrum

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EMSpectrum
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EM WaveTheory
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EM WaveTheory

• Simplifications
• Conductors
• sgtgtwe
• Dielectrics
• sltltwe

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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

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EMSpectrum

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

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Monitoring Remediation GPR
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Monitoring Remediation GPR
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GPR
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GPRAntennas

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

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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

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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.

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GPR Fluvial Catalog
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GPRGlacial Catalog
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GPR Aeolian Catalog
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GPRMarine Catalog
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GPR Catalog, Summary
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Gasoline Spill at OGI
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OGI Test Tank
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OGI Line E6 hours 0-48

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

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OGI Line E6 Hours 48-95

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

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OGI Line E6 Hours 108-158

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

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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.

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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)?

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DaveC at Coeur dAlene
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Borehole GPR in a boat
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CDA GPR - profile
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CDA GPR - Interp
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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