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NanoTEM A Very Fast Turn-Off TEM System

Publisher –
Zonge, 2011.

[pdf]  ENV_Nano

Summary

This document presents results of Zonge NanoTEM® surveys for three different environmental problems requiring the location of: aluminum dross contamination, underground storage tanks (USTs), and abandoned well casings in a previous oil drilling area. Results are excellent in all three examples and were confirmed upon digging. Targets easily stand out against the background material.

Lastly, results from a demonstration project using planted targets at the Idaho National Engineering Laboratory (I.N.E.L.) Cold Test Pit demonstrate the effectiveness of the NanoTEM system as a deep sounding metal detector.

Background
The Zonge-manufactured NanoTEM® system is a high-speed, early-time TEM instrument that offers both metal detection capabilities and resistivity sounding data collection. NanoTEM has been used to map perched aquifers, clay lenses, landfills, USTs, abandoned wells, and dumps, as well as geologic and structural features.

One limitation of traditional transient electromagnetic sounding methods is the long turn-off times of the transmitted signals which prevents use of the method for shallow soundings and highly-resistive areas. To obtain very shallow information, the transmitted signal must go to zero very rapidly, without “ringing” or oscillations of either the electronics or the wire loops themselves.  Zonge NanoTEM transmitters overcome this limitation by completing the current-flow turn-off into a 20 meter loop in about 1.5 microseconds. 

This rapid turn-off, and the high speed analog-to-digital conversion in the GDP receiver, allow data collection at depths less than 2 meters and in areas with electrical resistivities in excess of 20,000 ohm-meters.

The receiver records the decay curve as 31 windows (or time gates) from approximately 1.5 microseconds to about 3 milliseconds after transmitter turn-off. Because of the flexibility of changing transmitter and receiver loop sizes, NanoTEM can be used for a variety of different targets. Surveys have been performed using forty meter (40 m by 40 m) transmitter loops with five meter (5 m by 5 m) receiver loops to collect resistivity soundings in highly resistive ground. The same system has also been used with a ten meter (10 m by 10 m) transmitter loop with one meter (1 m by 1 m) receiver loops to locate small metallic objects.