Deep 2D & 3D IP / Resistivity & Broadband Magneto-Tellurics
For acquisition of Pole-Dipole, Bipole-Dipole or Dipole-Dipole Induced Polarization / Resistivity data, multiple spreads of receiver dipoles are installed along the survey line. Each spread usually comprised of 4 Ex-dipoles, or 3 Ex- and 1 Ey-dipole which is connected to a gDAS24 acquisition unit. A transmitter pole, bipole or dipole source is stepped through the receiver array such that data is acquired simultaneously on all of the Rx-dipoles to provide maximal n-levels for both leading and trailing Tx-Rx geometries. Stimulation via the transmitter pole, bipole or dipole source while acquiring data on 2 or more survey lines provides a degree of 3-dimensionality to the array, apt for full 3D inversion modelling.
The IP receiver array provides an EMAP-style or (sparse) Tensor array for Broadband Magneto-Telluric data acquisition for modelling of impedance estimates up to several kilometers depths and beyond.
Tensor IP / Resistivity & Broadband Tensor Magneto-Tellurics
Vector and Tensor Induced Polarization / Resistivity surveying provides broad mapping of IP and Resistivity distributions. The methodology is designed to maximise coverage rates whilst maintaining a minimum sample density for detection of the target of interest. This is achieved through measurement of the electric field resulting from a grounded current source (transmitter bipole) at discrete locations, often on a grid pattern, using orthogonal pairs of receiver dipoles. Acquisition of the vector electric field (in-phase-quadrature / primary-secondary) with a single transmitter source at each station, comprised of orthogonal E-field dipoles, provides a Vector result, whilst acquisition from two or more differently oriented or located
transmitter dipoles may provide a Tensor solution for the apparent resistivity and IP transfer functions in which these parameters may be defined for all possible source field orientations provided the primary current density (and electric field) vectors are adequately non-parallel. 3D forward modelling suggests that typical maximum depths of investigation for Vector parameters may range up to 1000m according to the transmitter-receiver separation (around 2.5-3km or more), though these assumptions must be tempered by several limitations, the most important of which is related to the resistivity contrast between host and target.
Other ground geophysical methods and consulting
SouthernRock Geophysical also provides the following survey techniques;
Transient Electromagnetics (TEM), Moving-In-loop, Coincident-loop, Fixed-loop, 3-component downhole EM
Controlled Source Audio Magneto-Tellurics (CSAMT)
Ground Magnetics and Gradiometry (Proton Precession, Overhauser, Potassium & Cesium vapour sensors)
Gravity (digital gravimeter, CS-3M)
SouthernRock retains a number of consulting contracts with junior companies or other clients who do not maintain in-house geophysical expertise. These services may include quality control for contracted or in-house data acquisition, review of historic data or survey planning.