The Total Field Array

Since 2009, AGI has been recommending suggest using the Total Field Array for scanning the subsurface using the Electrical Resistivity Imaging Method (ERI).

The simple premise is that we want to define the total potential field for every transmitter current injection source position. To do this we will need to combine two array types: The Dipole-Dipole Array and the StrongGradient Array.

The Strong Gradient Array

The StrongGradient Array is a subset of the Gradient Array where we impose the same relationship as in the Schlumberger, namely the MN receiver dipole size has to be 1/10th the size of the AB transmitter dipole. If we were to use the Gradient Array there is a concern that the signal levels become too small to measure accurately compared to the noise. In other words the snr (signal to noise ratio) is small. By imposing the >= 1/10th restriction we guarantee that the receiver measurement at the center of the transmitter dipole (i.e. AB) is measureable.

Expanding Dipole-Dipole Array

The Expanding Dipole-Dipole Array is a version of the Dipole-Dipole Array where the receiver dipole (MN) increases with increasing distance from the transmitter dipole (AB). Since the potential field signal strength decreases with the inverse square law, the signal at the furthest dipoles (i.e. n=7 and n=8) can become indestinguishable from the noise (again think: snr). Increaseing those two dipoles makes sure that the deeper data is collected.

Both the StrongGradient Array and the Expanding Dipole-Dipole Arrays can be found in the AGI EarthImager 2D CommandCreator tool for automatically creating the array measuring scripts for the SuperSting.