**5.4 Magnetic and electrical methods**

*Magnetic techniques*, including aeromagnetic surveys to map magnetic anomalies. *An aeromagnetic survey* is a common type of geophysical survey that is performed with a magnetometer on board a plane or pulled behind it. This principle is similar to the magnetic survey conducted with a handheld magnetometer, but it allows for much larger areas of the Earth's surface to be quickly covered for regional reconnaissance. Plane typically flies in a grid-like pattern with line spacing and elevation to determine data accuracy (and cost per unit area of scan) [25].

*Electrical techniques*, including electrical resistivity tomography and induced polarization [26].

*Stimulated polarization (IP)* is a geophysical imaging technique used to determine the electric chargeability of subsurface materials, such as ores [27, 28].

Konrad Schlumberger originally discovered the effect of polarization when measuring the resistance of rocks [27, 28].

*Induced polarization* is a widely used geophysical method in mineral exploration and mine operations [27, 28].

IP scanning can be performed in both time area and frequency area mode [28].

*Introductory Chapter: Engineering Geology DOI: http://dx.doi.org/10.5772/intechopen.95991*

*Electromagnetic methods*, such as magnetotellurics, ground penetrating radar, transient/time-domain electromagnetics and SNMR [29, 30].

*Magnetotellurics (MT)* is an electromagnetic geophysical method for inferring subsurface electrical conductivity from measurements of natural and geoelectric magnetic field anisotropy at the Earth's surface. Search depth ranges from 300 meters underground by recording higher frequencies up to 10 km or deeper with sounding for prolonged periods [29, 30].

*Ground penetrating radar (GPR)* is a geophysical method that uses radar pulses to photograph the Earth's interior. It is a non-intrusive way to survey below the surface to check underground facilities such as concrete, asphalt, minerals, pipes, cables or masonry [31, 32].

*Transient electromagnetism*, is a geophysical exploration method in which electric and magnetic fields are induced by transient pulses of an electric current and the subsequent decay response is measured [33, 34].
