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Over the last 10 years, there has been a revolutionary change in the resistivity (and IP) surveying method.
Until the early 1990's, the resistivity method has been used as a one-dimensional (1D) tool where quantitative
modelling was confined to simple horizontal layers which are not sufficiently accurate for complex geological
environments. However due to recent developments in field equipment design, interpretation software and
microcomputer technology, two-dimensional (2D) and even three-dimensional (3D) surveys are now practical
geophysical exploration tools for environmental and engineering studies.
Over the last few years, there has been an explosive growth in the number of commercial multi-electrode
resistivity meter systems for electrical imaging surveys. A set of free lecture notes which cover a
number of practical aspects of 2D and 3D electrical imaging surveys, including field methodology and
data interpretation, may be downloaded from the Geotomo website.
The second development that has made 2D and 3D electrical imaging surveys practical tools is fast
interpretation software that can be used on commonly available Windows based microcomputers. From
the Geotomo website, you can download working demo versions of the RES2DINV and RES3DINV inversion
software. The demo versions have some limitations, but you can use them to invert most common
resistivity and IP data sets. For current RES2DINV and RES3DINV users, you can update the
software by just downloading the same files. Unlike most commercial geophysical software, updates at present are free
RES2DINV is the 2D resistivity and IP inversion software. Besides normal land surface surveys,
it also supports underwater and cross-borehole surveys. In addition to the standard Wenner (alpha,
beta, gamma), Wenner-Schlumberger, pole-pole, pole-dipole, inline dipole-dipole, equatorial
dipole-dipole arrays; it also supports non-conventional electrode arrangements. It is probably
an order of magnitude faster than some other commercially available 2D inversion software.
RES3DINV is the 3D resistivity and IP inversion software, and it is probably the first widely available
commercial software of this type. 3D surveys are more time-consuming and expensive to carry out, but
could be useful for very complex geological situations. To reduce costs to the user, RES3DINV is sold
as a combined package with RES2DINV which costs only about 25% more than the RES2DINV program alone.
(information above is taken from the Geotomo website (www.geoelectric.com) and is copyright Y.Gan 2000)
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