AEM
Airborne Electromagnetics
A transmitter loop slung beneath an aircraft induces currents in the ground and a receiver measures the secondary field in parts per million. It is the fastest way to map conductivity over large exploration areas.
Crew
Pilot, system operator, ground data QC geophysicist
Mobilisation
3-5 days: ferry, bird rigging, calibration flights, permits
Daily coverage
200-400 line-km per flying day
Equipment and specifications
| Platform | Helicopter with 30-40 m tow, or fixed-wing with towed bird |
|---|---|
| Transmitter | Multi-turn loop, 300 Hz - 200 kHz (frequency domain) or 25-30 Hz base (time domain) |
| Receiver | Three-component induction coils, in-phase and quadrature at each frequency |
| Altimetry | Radar plus laser altimeter, 0.1 m resolution |
| Navigation | Differential GNSS, 1-2 m along-line positioning |
Setup sequence
- 01
Plan the flight
Line spacing 2-4x target width, flown across strike, with tie lines every 10 lines.
- 02
Calibrate
High-altitude zero and calibration-coil checks at the start and end of every flight.
- 03
Hold terrain clearance
Nominal 30-40 m bird height; log every departure for later levelling.
- 04
Monitor drift
Watch the zero level in real time; return to a repeat line if drift exceeds spec.
- 05
Level and grid
Apply calibration, remove drift, level to tie lines, then grid each channel.
Safety
Low-level flight
Terrain clearance minima, obstacle survey, daylight VFR only.
Sling load and bird
Rigging checks, hook-up drill, exclusion zone under the aircraft.
Fatigue
Duty-time limits for pilot and operator, mandatory rest between sorties.
Fuel handling
Bonding, spill kit and no-smoking zone at the fuel cache.
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. |
| Flight height | A fixed number you set once. | Varies continuously with terrain; the single biggest amplitude control. |
| System drift | None. | Thermal drift needs high-altitude zeros every 30-60 minutes. |
| Culture | Absent. | Powerlines, fences and pipelines produce anomalies larger than the target. |
| Repeatability | Identical parameters return an identical curve every time. | Coupling, moisture and temperature move the response between repeats. |
Field QC checklist
- · High-altitude zero drift within the system specification per flight
- · Line separation within 20% of nominal for 95% of the block
- · Tie-line misfit under 2 ppm after levelling