Magnetic targets
ENVI-MAG Manual B1-13
Overview
The remanent magnetic component of a magnetized body is a function of the
orientation of the magnetic field at the time the object was cooled below 550°C.
This temperature is called the Curie Point. While the metal, of which the drum,
pipeline or sheet metal were made of, was at a temperature above the Curie Point,
the magnetic dipoles were aligned in a random fashion. As the temperature of the
metal approaches the Curie Point, these dipoles tend to align themselves in the
direction of the dominant magnetic field (usually the Earth’s) at that point in time.
In some mineral applications and most environmental applications, the remanent
component predominates. This component can have any orientation and intensity.
Therefore the resulting total-field vector can have any orientation and intensity,
which can have serious consequences on your magnetometer survey. Remember
that it is the projected vector COMP
F
, that is measured by the magnetometer.
Consider for instance the examples illustrated in the following figure (Figure B-
12). You can see that depending upon the orientation of your traverse and the
direction of magnetization of the body, you will get a completely different shape
of profile for the same body at the same depth!
Figure B-12 Effects of orientation and magnetization on anomaly shape.
Another example is shown in (Figure B-13). This simplifies the previous example
by keeping the orientation of the traverse line and the depth of the body constant,
i.e. the measuring geometry. The only parameter that is varying is the direction of
the permanent magnetization.
T
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