When solving a whole range of historical and search tasks, special equipment is used, which has been developed for decades by geophysicists. Magnetometers are successfully used not only in the search for large metal objects, such as armored vehicles or aircraft of the Great Patriotic War, humanitarian demining, but are also used when working on the territory of historical and archaeological monuments, as one of the methods of non-destructive search and control.

Depending on the goals and objectives, different types of magnetometers, gradiometers or deep metal detectors are used. The main thing is to understand what tasks need to be solved, what and where to look for and with what device, then the issues of “monetary resources and attracting qualified specialists” will be secondary… For example, magnetometric mapping, relatively labor-intensive and long-term, should not always be carried out.

A little theory. Magnetometers for field work are divided by types into “ferrosonde”, “proton” or “quantum on the principle of optical pumping” …

1. “Ferrosonde magnetometers-gradiometers”, for example, Frster Group products (such as OGF or Ferex) or devices from Ebinger, Vallon, CST, etc.). They show only ferroalloys (iron) at a depth of up to 5 meters. They are quite sensitive and simple to work with, but they are lame with visualization, but they are operational. The boundary of the object is shown confidently and accurately, but in practice it is worse with the depth and mass of the metal (approximately like with “pulse sensors”, but only on iron, it is sometimes even more difficult to work). A relatively large weight can also be attributed to the disadvantages. There are also serious devices (MG-400) with prompt display of a map of the magnetic field gradient on the screen (and the possibility of subsequent processing in special programs with normal mapping) — this is already a cross between ferrosondes and other types of professional magnetometers.

2. “Protons” (old Soviet MMP-203/MMP-203M or MINIMAGs of different generations based on the POS-1 Overhauser effect). These are professional devices for searching for mineral deposits. The devices are quite sensitive — that’s why they are designed for magnetometric shooting, and not “looking for pieces of iron”. For search tasks, it is possible to use, but in fact, as a detector for large accumulations of iron — check the dugout for the sapper dumping of dangerous objects, a funnel for the presence of an aircraft/motor, find a tank in a pond/river. With a certain experience, it will show both the amount of iron and the depth of the object can be estimated. To try to use it simply as a deep-sea (such as a “ferrosonde” or “frame”) on a large area, conducting detailed magnetic photography — labor-intensive, long, with the application of knowledge and programs-but accurately and scientifically. Proton sensors are quite applicable when working on reservoirs — you can shoot for large anomalies if you run/drive/swim/fly, shooting points after 2-5 meters. Anomalies relative to the background of 300 nTl (and higher) above the search object at a depth of 3-4 meters are normal objects for work. One of the disadvantages is that two devices are needed for area shooting (one is preferably with GPS, if there is no desire to split and link profiles) + knowledge and programs for processing and building maps + unsatisfactory work near power lines, transformer stations, railways and other magnetic field exciters. Recently, small UAVs with protons have appeared (the area is much faster to fly, and the accuracy is almost comparable to ground-based pedestrian photography.
3. “Quantum with optical pumping” (on the Zeeman effect)

3. “Quantum with optical pumping” (on the Zeeman effect).

Modern magnetometers from the companies Geometrics, Scintrex, GEM Systems. Similar in purpose to the previous ones, but much more sensitive (by two orders of magnitude) and therefore more expensive. Interference from external objects, such as power lines, does not affect the readings and a second device for shooting variations is not required. They are usually used for professional geophysical work on mineral deposits. However, this type of magnetometers is used by American sappers when clearing mines. The high cost allows you to supplement the device with operational visualization as well.