ABSTRACT
Magnetic surveys are primarily used to detect ferrous metals, iron, and steel. The earth’s magnetic field (geomagnetic field) has the shape of a bar magnet and exhibits an intensity that ranges from 70,000 gammas (γ) [nanoteslas (nT)] at the polar regions to 25,000 γ at the equator. The field is shifted some 11° from the earth’s rotation, which causes a deviation from true north, resulting in a point referred to as magnetic north. Where local variations in magnetic materials occur, anomalies within the total magnetic field of 1-5000 γ may result.
