Geophysical Mapping: Method Details
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Method Name: Surface Nuclear Magnetic Resonance (SNMR)
Method Type:   Radioactivity
Assigned Problems:
+ Fractures Groundwater
+ Groundwater table Groundwater
+ Porosity / Permeability Groundwater
   '+' = Technique applicable
Principle:   Mapping of water content and pore size. Protons of hydrogen atoms in the subsurface water are excited with electromagnetic fields at Larmor frequency using large loops on the Earth's surface. The electromagnetic field of the relaxing protons is observed with the same loop.
Keywords:   Ground water exploration; hydrogeology; aquifer characterisation; porosity and hydraulic conductivity
  • Not many equipments available yet
  • High noise sensitivity, difficult to use in urban areas
  • Currently only one dimensional exploration available
Resolution:   Resolution ca. 0,5 m in near surface and ca. 5 m in far surface. Depth of investigation about 150 m
Expected Results:  
  • Measured parameter: magnetic field of proton relaxation, amplitude and decay time
  • Data analysis: various inversion schemes available
  • Interpretation: direct and quantitative water content and hydraulic conductivity
Combination with other Methods:  
  • Required additional information: resistivity structure in the investigation area
  • Related add-on information: presence of a one dimensional structure
  • Independent additional information: any other geophysical technique for general and special geological setting, borehole measurements
Operating Expense:  
  • Crew size: 1 key person, 1 assisstant (not always necessary)
  • Aquisition speed: 2-3 hours for 1 sounding
  • Processing: immediate results. Detailed results need about 2-4 hours for one sounding
  • Equipment rental costs: low
Parameters to specify:  
  • Transmitter and receiver loop diameter 10-200 m
  • Exitation with local Larmor frequency (1-3 kHz worldwide)
  • Maximum of 300 V and 300 A
  • Record as envelope of relaxation
  • Individual record length about 250 - 1'000 ms, stacking up to 128
QC Documents:  
  • On site equipment test
  • Local Larmor frequency
  • Noise level
  • Field notes (e.g., all activities, effective time schedule, present personnel)
  • Raw data: Envelope of relaxation curves
  • Amplitude and decay time of relaxation
  • Water content and relaxation time vs. depth functions
  • Interpretation
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