Applications
B1-12 ENVI-MAG Manual
Figure B-11 Total field response for different target distance
and mass (after Benson et al., 1982).
The above information should give you a feel for the amplitude of the anomaly
to expect in typical environmental applications. But it can be slightly misleading.
These values are for the magnetic intensity that is induced in the material by the
Earth’s magnetic field. Unfortunately all man-made metallic objects carry with
them a magnetic memory of their orientation when they were created.
Unfortunately, this can lead to complications.
Induced and Remanent magnetism
The local disturbance caused by a buried drum, a pipeline or a sheet can be
represented as a vector. The disturbance can also be further decomposed into
two components: an induced and a permanent (or remanent) component. The
ability of a ferrous object to be magnetized is termed its susceptibility. The
intensity of the induced magnetization is directly related to the ambient field by
the susceptibility, and is therefore the induced part of the disturbance.
Susceptibilities are measured in cgs units.
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