IP/ERT
Induced Polarisation / Electrical Resistivity Tomography
Current is injected through two electrodes and the potential measured across others. Resistivity comes from the steady-state voltage; chargeability comes from the decaying voltage after the current is switched off, which responds to disseminated sulphides and clay.
Crew
1 operator plus 2-3 crew planting and moving electrodes
Mobilisation
1-2 days: cable check, electrode prep, line clearing
Daily coverage
0.8-1.5 line-km of 2D roll-along per day
Equipment and specifications
| Transmitter | 1-5 kW, up to 1,000 V / 5 A, 0.5-2 s current pulses |
|---|---|
| Receiver | Multi-channel, 24-bit, chargeability windows through the off-time |
| Electrode cables | Multi-core takeouts at 2-10 m spacing, 400+ electrode capability |
| Electrodes | Stainless steel stakes for current; non-polarising pots for high-precision IP |
| Contact kit | Water, salt and bentonite for resistive or frozen ground |
Setup sequence
- 01
Choose the array
Dipole-dipole for lateral resolution, Wenner-Schlumberger for depth and signal, gradient for speed.
- 02
Set spacing
Electrode spacing about a third of the shallowest target size; line length 5-6x target depth.
- 03
Plant electrodes
Firm contact, watered and salted where needed; keep contact resistance under 2 kohm.
- 04
Run a contact test
Test every electrode before the sequence and replant any failures.
- 05
Acquire
Run the sequence with reciprocals; watch stacking error per measurement live.
- 06
Invert
Filter on error, then invert resistivity and chargeability with the measured topography.
Safety
Up to 1,000 V on electrodes
Warning signs at both line ends, radio clearance before energising, no electrode handling during injection.
Public or livestock on the line
Line watchers, fenced crossings, energise only on an all-clear.
Manual electrode planting
Rotate crew, correct hammer technique, gloves and eye protection.
Cable across roads and tracks
Buried or matted crossings with signage and a spotter.
Field vs lab
| Aspect | In the simulator | In the field |
|---|---|---|
| Signal-to-noise | Clean synthetic response; noise added only if you ask for it. | Cultural noise, wind and instrument drift set the usable dynamic range. |
| Electrode contact | Perfect contact assumed. | The dominant data-quality control; resistive ground can stop injection entirely. |
| Topography | Flat surface. | Real terrain must be surveyed and carried into the inversion or it creates false anomalies. |
| Coupling and EM leakage | Absent. | Cable coupling contaminates chargeability; layout discipline matters as much as the instrument. |
| Repeatability | Identical parameters return an identical curve every time. | Coupling, moisture and temperature move the response between repeats. |
Field QC checklist
- · Contact resistance under 2 kohm on every electrode before the sequence
- · Stacking error under 3% on 95% of measurements
- · Reciprocal misfit under 5% on a sampled subset