Introduction:
Currently, three types of magnetometers and gradiometers are most often used to
detect buried munitions:

Fluxgate Magnetometers
A fluxgate magnetometer measures the magnitude and direction of the magnetic
field. They are inexpensive, reliable, rugged, and have low energy consumption.
Fluxgate magnetometers have long been a standard tool of EOD teams and are best
used for rapid investigation by foot. For a quick, inexpensive field survey of a site
containing ferrous munitions they are hard to beat. Fluxgate magnetometers can
detect single "munition-size" items (for purposes of this discussion, a cylindrical object varying in size from a beer can to a large loaf of bread) to a depth of 2 to 3 meters.
However, they also are sensitive to small fragments and do not always discriminate
well between small, shallow fragments and deeper, larger intact munitions. Most
fluxgate magnetometers provide analog, rather than digital, output that makes it
difficult to apply computer enhancement techniques.

Proton Precession Magnetometers
The proton precession magnetometer is based on the principle that magnetic fields
can be inferred by measuring the movement of protons in a liquid such as water,
kerosene or other hydrocarbon. When these protons are polarized and subjected to
an ambient magnetic field, the frequency of precession will deviate from their natural
frequency in proportion to the strength of the ambient field. This type of magnetometer is more sensitive than a fluxgate magnetometer. However, it is
especially susceptible to noise from nearby power sources. Also, the quality of the
data collected by a proton precession magnetometer is dependent upon the time
spent collecting each data sample. As a result, they are slower to use than fluxgate
magnetometers. Proton precession magnetometers can typically detect single
"munition size" items to a depth of 2 or 3 meters.

Optically Pumped Atomic Magnetometers
Optically Pumped Atomic Magnetometers (also called atomic magnetometers or
cesium vapor magnetometers) operate similarly to proton precession magnetometers except that the proton is replaced by an atom of a specific gas vapor, such as cesium or potassium. However atomic magnetometers are more sensitive and have faster
sampling rates than proton precession magnetometers. Atomic magnetometers can
typically detect single "munition size" items to a depth of 2 or 3 meters. Although
atomic magnetometers are more expensive to purchase than the other two types of
magnetometers their high sensitivity, speed of operation and high quality digital signal output make them a good choice for situations where data fusion or digital
post-processing is desired.