## A STUDY OF THE ELIMINATION OF THE INFINITE POLE IN THE POLE-DIPOLE ELECTRICAL RESISTIVITY ARRAY

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##### Date

2016-02-16##### Author

Liang, Xiao

##### Type

Thesis##### Degree Level

Masters##### Abstract

The pole-dipole (PD) electrical resistivity array is used as part of a geophysical technique,
which can be used in exploration for mineral, geothermal and hydrological resources. Furthermore, it can be used in archaeological investigations. The PD array is useful in obtaining
large depths of investigation, but the array requires one pole to be planted at a greater distance from the other electrodes. Placing the infinite pole is time consuming and costly, especially in rough terrains. It can also be a liability in populated areas. Previous data inversion software assumes the infinite pole to be planted at infinity. Therefore, the field data
collected has to mimic the assumptions of the inversion software.
Some recent inversion programs use all 4-electrode positions for data inversion. In this case, is a good approximation of infinity for the infinite pole still necessary? Is the depth of investigation still the same or relevant with a non-infinite, infinite pole? Is the resolution of the cross-sections retained?
To answer the above questions a Generalized Electrode Array (GEA) 1 dimensional (1D) inversion program is used. Different sets of field data were collected with non-infinite pole
(NIP) PD arrays; these arrays are set up as PD arrays with an infinite pole planted relatively close to or on the survey lines itself. A COMSOL finite element model were modelled with
varying infinite pole distances to identify the distance required for the retention of the depth of investigation and resolution of the PD array.
Modelling from GEA shows the NIP distances do not affect the 1D inversion accuracy of the resistivity nor the layer thickness. The field data indicates that it is necessary to have
an infinite pole, but the distance to the infinite pole can be substantially less than 10 times the array length, which is the usual rule of thumb for infinite pole placement. With 3 dimensional (3D) COMSOL modelling results, it indicates a minimum pole distance to be 2.5-array length to retain the depth of investigation and precision of the inverted sections of the PD
array.

##### Degree

Master of Science (M.Sc.)##### Department

Geological Sciences##### Program

Geology##### Supervisor

Merriam, Jim##### Committee

Butler, Samuel##### Copyright Date

December 2015##### Subject

Pole Dipole, resistivity array, Resistivity field surveys, Electrical resistivity