Magnetometers

A magnetometer is a passive instrument that measures changes in the Earth’s magnetic field. In ocean exploration, it can be used to survey cultural heritage sites such as ship and aircraft wrecks and to characterize geological features on the seafloor.

A magnetometer is a device used to measure the magnetic field, particularly with respect to its magnetic strength and orientation. A popular example of a magnetometer would be the compass, which is used to measure the direction of an ambient magnetic field (i.e. in this case, the earth’s magnetic field). Other magnetometers measure magnetic dipole moments; a magnetic dipole is the limit of either a closed loop of electric current or a pair of poles, since the size of the source is reduced to zero while keeping the magnetic moment - the magnetic field’s magnetic strength and orientation - constant. Think of the ferromagnet, a type of magnetic material that is used to  record the effect of this magnetic dipole on the induced current in a coil.

A magnetometer can work in different ways. Take for instance, a compass. Now we know that the compass’s needle aligns itself with the north of the earth’s magnetic field when it’s at rest. In other words, the sum of the forces acting upon it is zero and the weight of the compass’s own gravity cancels out the earth’s magnetic force acting upon it. This simple example explains how this property of magnetism lets other magnetometers work. Electronic compasses can similarly help indicate which direction is the magnetic north using phenomena such as the Hall effect, magneto induction, or magnetoresistance.