tTEM 3x3 System Brand Name OR Equal.pdf

Minimum Requirements and Specifications

A towed time-domain electromagnetic tTEM system consists of a geographical position system and electronics which pulls a dual moment transmitter (a 2- by 4-m single-turn coil) and a receiver (a multi-turn 0.5- by 0.5-m coil with an effective area of 5 m2) that are separated by 9 m in an out-of-loop offset configuration. A time-varying electrical current is applied to the transmitter loop and held at a steady-state to induce a static primary magnetic field. When the transmitter current is turned off, the change in the primary magnetic field induces an electromotive force in the ground that results in decaying electrical eddy currents and secondary magnetic fields. The time derivative of the vertical component of the induced magnetic field is measured in the receiver coil. This signal contains the subsurface resistivity information and ranges over a few orders of magnitude in a very short time span. A transmitter current of 2.8 A is used for shallow depths that reflect early-moment and time data, whereas a 30 A current is used for deeper depths (40 to 70 m) that correspond to high-moment and late time data. The measured 3D maps of soil resistivity have a horizontal resolution of about 10-15 m and a vertical resolution of around 1 m near the surface to meters at maximum depth.