Page 11 - FOERSTER_Detection_Geophysics_en

DIFFERENT DEPTHS

The right detector for the object and its depth is evaluated by the metal detector. Acoustic and opti-
cal alerts provide an accurate prospect of the object’s
Contaminated sites and unexploded ordnance can position and allow for precise localization. The detec-
usually be assigned typical depths. As a rule, mines are tion range is affected by the transmitting power, the
located close to the surface. Over the course of time, shape of the antenna, and ground conditions, as well
however, these can be covered over through environ- as the type and volume of metal in the target object.
mental effects. The same applies to unexploded cluster Depending on the desired emitted signals, the devices
munitions and relics from ground battles. Mortar and employ either pulse or sinusoidal (continuous wave)
artillery grenades are usually found in deeper zones, technology.
and – depending on their size – bombs dropped from
airplanes mostly below that. But later events such as For items at greater depths, large loops based on
flooding and soil deposition can increase the depth of pulse technology are the most suitable. Systems car-

any of these things. ried by hand or moved by vehicles have a typical ran-
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ge of 3-4 m maximum depth. For things up to 7-8 m
Archaeological artifacts can be found at even greater deep, passive magnetometers that can sound out fer-
depths. Magnetic measuring techniques typically detect romagnetic material are better. In general, the objects
anomalies in the upper to middle soil layers, depending are detected using an analysis of the Earth‘s normally

on the magnitude of the magnetic contrast between the homogenous magnetic field; ferromagnetic bodies
different material zones. Detection systems contribute cause a distortion of the magnetic field. It is this dis-

greatly to the localization effort, as the position of an turbance that is recorded, evaluated and displayed. As
article is displayed directly and unambiguously by the with the metal detector, beeps and lights alert the user
detection signal - which is then visualized using appro- where the thing lies. Recording systems make it pos-
priate software. sible to display magnetic anomalies across large areas,
and, with the use of appropriate algorithms, to cal-
In the field of near-surface detection, active metal de- culate detailed object lists that provide information

tectors based on the electromagnetic induction method about the position, size, depth and orientation of the
(EMI) have proven valuable and effective. The elec- items in question.
tromagnetic fields emitted by the device induce eddy

currents in the metal parts of buried mines / ammu-
nition; this generates a secondary field, which in turn