Physics
Purpose
Demonstrate the fundamental physical principles governing the airborne FDEM experiment.
Most of the physics related to airborne FDEM is available in Maxwell I: Fundamentals and Maxwell III: FDEM. Because an airborne FDEM system uses small coils as the transmitter and receiver, geophysicists have developed some representative physical models. Readers are supposed to be familiar with the following concepts.
A circuit model for EM induction
Sphere excited by a magnetic dipole
Magnetic dipole in a whole space
Magnetic dipole above a half space
The basic physics of airborne FDEM is illustrated by the animation below. Click through the radio buttons to see how an airborne FDEM system senses a buried conductive object.
Two typical earth models are of particular interest in airborne EM: the 1D layered earth model and the sphere-in-halfspace model. Here we illustrate the basic physics involved in airborne FDEM with a small horizontal loop source (a vertical magnetic dipole) over a three-layer earth model. The receiver is another horizontal loop coil measuring the magnetic field. Both loops are at the same altitude 20 metres above the surface and are separated by 10 metres. Click through the radio buttons to explore the problem.
