Geophysical Services & Advance Technologies Co.Ltd.

Brosures

RESISTIVITY IMAGING

Recent developments of the resistivity method have improved the resolution and quality of the data interpretation, providing a continuous 2-D model of resistivity along the section lines known as electrical imaging. The data processing procedures for the imaging method are more complicated and the rate of data aquisition is slower, making it most useful for investigating areas of complicated ground conditions. Resistivity imaging is particularly suitable for engineering sites where a detailed understanding of complex subsurface structure is important. Typically a series of 25 or 50 electrodes are placed in a line at set spacings, and connected to a computer controlled resistivity meter using a multicore cable. A special switching unit takes a series of constant separation traverses along the array with increasing electrode spacing.
The results of the resistivity imaging survey are displayed on site as an apparent resistivity pseudosection, presented as either a black and white or colour coded contour section. The pseudosection gives an indication of subsurface geology, but is still strongly effected by the electrode geometry. Advanced processing of the sectional data using specialist inversion software removes the effects of electrode geometry, to provide an accurate 2-D resistivity section. Our geophysicists use the standard resistivity depth probes and resistivity imaging profiles to produce a detailed geological interpretation of the site in an easy to understand engineering compatible format.

X2IPI Tool box for 2D DC and DC-IP measurements

X2IPI allows to perform 5 main tasks with data of multielectrode measuruments:

To prepare and to modify protocols files [*.seq or *.org] files needed for multielectrode measurements with SYSCAL® or SAS4000/SAS1000 equipments
prepare protocol file for the next types of array:

Pole-Dipole (forward and reverse)
Half Wenner
Wenner alpha
Wenner beta
Wenner-Schlumberger
Dipole-dipole
Modifying electrodes unit spacing
Removing a faulty electrode
Removing measurement lines
Preparing a ;Roll along” [*.seq, *.up, *.dwn] files
Changing the numbers of the MULTINODE® used in a [*seq] file, i.e. the hard reference numbers of the electrodes
To work with field data files from SYSCAL® or SAS4000/SAS1000 equipments and in Res2dInv format:
visualization of data,
trim outlier measurements,
merge data files,
remove a faulty electrode,
input topography;
To remove "geological noise" linked to near-surface inhomogeneities;
To prepare input files with the convenient formats for interpretation softwares (including new general format for Res2dInv);
To work with results of 2D inversion by Res2dInv.

Specifications:
Sensor,Weight;Size 1 x 10-7 SI Two Lithium CR2430,9KHz,80 Hours Typical Four Digit LCD,-20oC to 50oC,50mm Coil 6 Ounce(0.180 Kg),4x2.5x1"(100x65x25mm)

2-D Modeling: RES2DINV, 2-D Resistivity & IP Inversion Software

For Windows 95/98/2000/NT

Two-dimensional (2D) electrical imaging surveys are now widely used to map areas of moderately complex geology where conventional 1D resistivity sounding and profiling techniques are inadequate. The results from such surveys are usually plotted in the form of a pseudosection (Figure 1a) which gives an approximate but distorted picture of the subsurface geology.
The RES2DINV program uses the smoothness-constrained least-squares method inversion technique to produce a 2D model of the subsurface from the apparent resistivity data alone. It is completely automatic and the user does not even have to supply a starting model. This program has been optimised for the inversion of large data sets. The use of available memory is optimised so as to reduce the computer time by minimising disk swapping. On a Pentium based microcomputer, the inversion of a single pseudosection is usually completed within minutes. Four different techniques for topographic modelling are available in this program. Together with the free 2D forward modeling program RES2DMOD, it forms a complete 2D resistivity forward modeling and inversion package.

The program will automatically choose the optimum inversion parameters for a particular data set. However, the parameters which affects the inversion process can be modified by the user. Three different variations of the least-squares method are provided; a very fast quasi-Newton method, a slower but more accurate Gauss-Newton method, and a moderately fast hybrid technique which incorporates the advantages of the quasi-Newton and Gauss-Newton methods. The smoothing filter can be adjusted to emphasize resistivity variations in the vertical or horizontal directions. Two different variations of the smoothness constrained least-squares method are provided; one optimised for areas where the subsurface resistivity varies in a smooth manner (such as chemical plumes), and another optimised for areas with sharp boundaries (such as massive ore bodies). A robust data inversion option is also available to reduce the effect of noisy data points. Resistivity information from borehole and other sources can also be included to constrain the inversion process.

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