|
Detection of Metal Objects and UXO´s with
Time
Domain
Electro-Magnetics (TDEM)
The time domain electro
magnetics
(TDEM) measuring
system which is used successfully especially for detection of metal
objects and unexploded ordnances as well as prior to building measures is a worldwide
recognized, efficient and non-destructive method.
TDEM - Method and System
The
TDEM is a geophysical sounding
method. A TDEM system consists of
a transmitter receiver spool (SES), a control unit which is needed for
the signal generation and signal answer recording as well as an
integrated PC for the data acquisition and storage. At a
TDEM examination in the area grid
the vertical distribution of the electrical sub-fundamental properties
is found out at every point of sounding.
The distribution of
the reception tensions is represented within time slices
(T1-T3) which give a measure for a relative depth estimate.
Respectively near metal objects cause laterally restricted high tensions
(red anomalies), more remote metal bodies and more conductive
underground areas of middle tensions (green) and undisturbed low
conductive areas of weak tensions (blue) (Fig.1).
The signal (A) generated by the control unit in the
transmitter receiver spool (SES) produces a primary electromagnetic
field (B) which activates eddy currents in underground.
These cause one of secondary electromagnetic fields which is detected by
the SES (C) (Fig.3).
The intensity of the
secondary electromagnetic field at a time is dependent in underground
from the electrical conductivity distribution. With increasing time the
eddy currents diffuses into underground both more deeply and laterally
("smoking rings" D, E). Signals registered from the point of view of
time early therefore include surface near areas and the signals
registered later deeper areas generally.
TDEM measurements at BASF area
1 and 2
Two test fields which were
examined
with the TDEM system from the surface were laid out by the KMRD/RP on
the BASF area in Ludwigshafen in May 2000.
The three dud storage areas could be expelled beyond all doubt despite
disturbing bodies like building rubble brought in and armoured concrete
slabs - confirmation by the KMBD/ Rheinland-Pfalz - (Fig.4 and 5).
The
TDEM
system makes a complete and economical area reconnaissance possible
which permits a specific and therefore economic opening of single
suspicion points. |
