Electrical Resistivity Imaging Equipment for 2-D and 3-D Applications

Electrical Resistivity Imaging (ERI) is a subset of a broader method called Electrical Imaging (EI).

Modern ERI equipement is used to automate the process of moving the 4 electrodes (2 transmitter electrodes and 2 receiver electrodes) around the surface which is very time consuming and labor intensive (expensive).

The Parts of a Elecrical Imaging System for performing resistivity, induced polarization and SP measurements:

  • resistivity/IP/SP meter contains
    • a direct current (DC) transmitter
    • a sensitive volt measuring circuit (channel)
  • Inversion modeling software (EarthImager) to compute the resistivity values in 1D, 2D or 3D.
  • a switching apparatus (the AGI SwitchBox) capable of switching the transmitter and receiver connections quickly and efficiently
  • an electrode cable with a number of electrode takeouts at a regular spacing (typically 6.25m or 20')
  • stainless steel stakes: are used to connect the electrode cable to the ground via stainless steel springs. Stainless steel is used for corrosion resistance.
  • a power source: AC/DC power supply with a gas generator or 12V deep cycle batteries

The Steps for performing a 2D Resistivy/IP/SP survey

  1. Stretch out a long tape measure (100 meter) in a straight line
  2. Install the stainless steel electrode stakes at even intervals
  3. Lay out the electrode cable and connect each takeout to each electrode stake
  4. Connect the SuperSting instrument and SwithBox to the electrode cable
  5. Perform the Contact Resistance Test as a last check that the system is connected correctly
  6. Gather the data (typically 5 min)
  7. Transfer the data to a laptop computer running Windows
  8. Process data using the AGI EarthImager 2D software
    1. Read in data
    2. Set the defaults for a surface survey
    3. Press the Start Button (takes less than a second usually)
  9. View and Print the finished result

The Steps for performing a 3D Resistivy/IP/SP survey

  1. Perform steps 1-9 of the 2D Survey outlined above and collect at least two parallel 2D survey lines.
  2. Assume that the first data scan in steps 1-9 was produced starting at the (0,0) coordinate along the X-axis
  3. Move the next 2D survey line one electrode spacing (ES) parallel to the first line and record the new starting coordinate. I.e. If the electrode spacing is 5 meter then the new location for the second line is (0,5)
  4. Repeat steps 1-9 of the 2D Survey outlined above.
  5. Repeat steps 10-12 by collecting 2 or more parallel 2D lines
  6. Process the multiple parallel 2D lines using the AGI EarthImager 3D
    1. Go to Tools -> Combine 2D Parallel Lines and save files to a new "combined" dataset
    2. Read in the "combined" dataset
    3. Set the defaults for a surface survey
    4. Press the Start Button (takes less than a minute)
  7. View and Print the finished result