Magnetometer
A Magnetometer measures the Earth's magnetic field. Earth's magnetism varies from place
to place. Differences in the Earth's magnetic field (the magnetosphere) can be caused by a couple things.
Magnetometers are used in geophysical surveys to find deposits of iron because they can measure the magnetic pull of iron. A Magnetometer can also be used by satellites like GOES to measure both the magnitude and direction[?] of the earth’s magnetic field.
Magnetometers are very sensitive, and can give an indication of possible auroral activity before one can even see the light from the aurora.