To introduce the theory of the Earth's magnetic field and understand how this theory can be applied to maritime archaeology. This topic covers magnetic instrumentation, survey procedures, data processing and interpretation, with particular attention towards mapping the underwater cultural resource. For an object to alter the Earth's magnetic field, it must be constructed of a ferromagnetic material. When referring to the Earth's magnetic field, it is best to refer to it within seven components. The seven field relations are shown in the figure.
Inclination is the angle the earth's magnetic field makes with the horizontal.
The earth can be thought of as having an electromagnet within it. However, the actual magnetic field of the earth is much more complicated than this, so that many irregularities are evident when magnetic data are plotted on a map. In addition, the north and south magnetic poles of the earth are known to continually be shifting. It is local variations within the magnetic field in which we are most interested. These could be caused by several features such as wrecks, buried petroleum, water, and other tanks and drums, voids within the shallow subsurface, such as caves and tunnels, and local rock variations, such as plutons and buried basalt flows.