Natural Field Electromagnetics
The most advanced natural-source electromagnetic method is Magnetotellurics (MT). Its energy sources are naturally occurring electromagnetic variations generated by global lightning activity (audio-magnetotelluric range, AMT) and by solar–magnetospheric interactions (MT range).
Controlled Source Electromagnetics
Controlled-source electromagnetic (CSEM) methods can overcome some types of artificial and natural electromagnetic interference by using a man-made transmitter instead of relying solely on natural signals.
The Transient Electromagnetic (TEM), also known as Time-Domain Electromagnetic (TDEM), method is based on measuring the subsurface response to a sudden change in an externally applied electromagnetic field.
