Frequency domain
AEM — Airborne Electromagnetics
Helicopter and fixed-wing conductivity mapping at survey scale
Frequency band
300 Hz - 200 kHz
Depth range
20 - 400 m
Resolution
Moderate (tens of metres)
Source
Towed transmitter loop
Typical cost
High per day, low per line-km
Survey speed
Very fast - hundreds of line-km per day
Best terrain
Any, including inaccessible and forested ground
Domain
Frequency domain
Overview
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.
How the physics works
The ratio of flight height to skin depth - the induction number - controls whether the response is dominated by the quadrature (resistive limit) or in-phase (inductive limit) component. Multi-frequency systems sample several depths at once.
Where it is used
- Regional mineral exploration and conductor targeting
- Groundwater and salinity mapping
- Geological mapping under cover
- Environmental baseline and tailings monitoring