TEM is not suitable on resistive ground, e.g. above 600 ohm-m approx. as little induction will be seen even in the early channels, and if metallic structures are nearby, the induction in these features will dominate the response with noisy data.
@Andrew EM systems respond better to conductors. In this case the depth to the conductive layer and the conductivity of that layer will be determined quite accurately, but the resistivity of the resistive layer will be less well-defined.
@@karhukivi Thank you sir. Could you please expand on this in laymans? I would like others, (hopefully future students) to understand this. I worked at the ISOR in Iceland around 200 ish...my main issue was scientists writing 1 vs 7 in the field book...and GPS... also...meeting each other was hard...to connect the wires...at the end ....
@@victorblaer Yes, TEM transmitter loops can get very large and trying to join up the four sides of a large square loop of wire can get tricky. The video is very comprehensive and has all the basics. In layman's language, the TEM loop is like a large metal detector and a large primary current is sent in pulses which induce currents to flow in the ground. The receiver detects these secondary induced currents in the ground as they decay between each transmitter pulse, a bit like radar. The decaying secondary pulses can be converted to give a depth section of how electrical conductivity (we use the inverse "resistivity") varies with depth. If the ground is very conductive, the secondary currents are very strong but they don't penetrate very far down. If the ground is resistive, the currents are weak but they diffuse rapidly downwards and the information is poor. So, depending on the geological conditions, there is usually a happy medium where the method works well and gives good information to a significant depth. The ideal is when you are looking for a conductive layer in otherwise resistive layers, that is when the method really works best. Hope that helps, there is probably better material online, but the video is very good.
TEM is not suitable on resistive ground, e.g. above 600 ohm-m approx. as little induction will be seen even in the early channels, and if metallic structures are nearby, the induction in these features will dominate the response with noisy data.
@Andrew EM systems respond better to conductors. In this case the depth to the conductive layer and the conductivity of that layer will be determined quite accurately, but the resistivity of the resistive layer will be less well-defined.
@@karhukivi Thank you sir. Could you please expand on this in laymans? I would like others, (hopefully future students) to understand this.
I worked at the ISOR in Iceland around 200 ish...my main issue was scientists writing 1 vs 7 in the field book...and GPS... also...meeting each other was hard...to connect the wires...at the end ....
@@victorblaer Yes, TEM transmitter loops can get very large and trying to join up the four sides of a large square loop of wire can get tricky. The video is very comprehensive and has all the basics.
In layman's language, the TEM loop is like a large metal detector and a large primary current is sent in pulses which induce currents to flow in the ground. The receiver detects these secondary induced currents in the ground as they decay between each transmitter pulse, a bit like radar.
The decaying secondary pulses can be converted to give a depth section of how electrical conductivity (we use the inverse "resistivity") varies with depth.
If the ground is very conductive, the secondary currents are very strong but they don't penetrate very far down. If the ground is resistive, the currents are weak but they diffuse rapidly downwards and the information is poor.
So, depending on the geological conditions, there is usually a happy medium where the method works well and gives good information to a significant depth. The ideal is when you are looking for a conductive layer in otherwise resistive layers, that is when the method really works best. Hope that helps, there is probably better material online, but the video is very good.