Appendix VI - The limits of magnetic detection

While much research has been carried out in the area of mine manufacturing, the basic principles of detection equipment have not much evolved since World War II. The equipment consists mainly in magnetometers that are more or less accurate and that emit a signal in the presence of metal.

Interestingly, the concept of non-metal mines has evolved over time, and in parallel with the progress in metal detectors. Back in the 1950's, mines with a non-metal casing were considered as such, whereas they are nowadays considered as metal mines because some parts in their detonator do contain metal. Manufacturing non-metal detonators (especially the firing pin) proved more problematic than manufacturing non-metal outer casings: Bakelite, plastic, wood, etc... Moreover, the use of the detector involves a specific danger: contrary to the probes which are obviously inert, the detector is «active», since the magnetometer sends out radiations. Some sophisticated mines will react to such emissions.

· The limits of common magnetic equipment: Portable metal mine-detectors were part of the equipment in all troops throughout World War II. Although the appearance of metal detectors has not changed much since 1944, their magnetometers have been improved so that they are now able to locate just a few grams of metal (including aluminium).

Traditionally, mine detectors used a constant emission and analysed the return radiation. The German detectors METEX 4.125 (FORSTER) and the American detectors AN/PSS-11 still operate the same way. Their magnetometers operate on direct current at low frequency/audio-frequency (in the case of the American AN/PSS-11) or at high frequency/radio frequency (in the case of the German METEX).

· Modem metal detection systems: Two types of improvements were recently brought about by two European firms to portable mine detectors:

One of them exploited a technology once exclusively used in «treasure hunting»: pulse emission enabled them to reach an outstanding accuracy level and therefore a great economical success. The SCHIEBEL AN/19-2 is now extensively used by the U.N. and the Swedish army, while the British, Dutch, German and American armies all have adopted it.

The other one specializes in non-destructive tests; it has developed a very sensitive device based on a double emission, both at low and high frequency: the MINEX 2FD. Unfortunately, this highly precise detector (localization between 2 and 20 cm depending on the mine) has a high price and weighs more than the average. It will therefore be used in particularly tedious cases.

· The problem of false alarms: Obviously, as the capacity of detectors to detect very small metal parts increases, so does the rate of false alarms (currently estimated at 15 for one mine). This is due to the presence in the ground of any battle field of small metal objects (shell splinters, projectiles, garbage or lost items). In Afghanistan, 1000 inoffensive objects are picked up for one single mine, against 129 in Cambodia. Obviously, only part of those objects are responsible for false alarms, but that is enough to dramatically impair the progression of mine-clearing teams. The depollution of mined areas is delayed by the impossibility to distinguish between mines and inoffensive items, thus increasing the number of victims.

This is the reason why today, only the probe will achieve the level of precision necessary to restore an inhabited area.