Method and System
In contrary to the conventional passive magnetic techniques TDEM is an active method transmitting a controlled-source electromagnetic field into the underground. Interference from external noise sources are thereby largely diminished, thus TDEM-surveys can be applied also in difficult terrain like urban sites, industrial and military areas.
Furthermore the measurements are nearly independent from the subsurface electrical conductivity corresponding to low influence of geological and anthropological layering.
The TDEM-instrumentation consists of a transmitter unit which generates a duty cycle unipolar rectangular current within a transmitter coil on the surface. By means of the abrupt current shut-off an electromagnetic force is created, whereby during the shut-off time a subsurface current system („smoke rings“) is
diffusing towards increasing depths. In the presence of a metal object a secondary eddy current is induced exhibiting a secondary magnetic field.
The timely change of this magnetic field is recorded by two receiver coils during the transmitter shut-off time. The decay curves are dependent on electrical conductivity, magnetic susceptibility, size, shape and depth of the metal objects. They are significant enhanced as compared to the non-metallic bearing underground.
Based on the focused field radiation and the close meshed data acquisition a TDEM survey enables a highly accurate lateral location of the detected metal objects. The resolution ability is compared to magnetics extremely good.
Distribution of the receiver signal represented within time slices (T)
Principle of TDEM
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/Rheinland Pfalz 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 KMRD/ Rheinland-Pfalz
The TDEM system makes a complete and economical area reconnaissance possible which permits a specific and therefore economic opening of single suspicion points.
TDEM measurements at BASF area 2 of the Kampfmittelräumdienstes Rheinland Pfalz
TDEM measurements at BASF area 1 of the Kampfmittelräumdienstes Rheinland-Pfalz
Economically, non-invasive and flexibly applicabler
Detection of bomb duds up to a depth of approx. 8m and area top edge, depending on capability of TDEM system and object dimensions
Low influence of surface near disturbing bodies (building rubble, conductive upper floor, armoured concrete slabs, lines, fences etc.) and which denying conventional measurement procedures in areas in these also usably
Our team has more than 18 years of experience in the area of detection of metal objects and unexploded ordnaces by using TDEM method in Germany.
So we have experience of more than 1,500 projects in Germany since 1998.