RES3DINV - 3D inversion geophysical software for resistivity and induced polarization data
In areas where the geological structures are approximately two-dimensional (2D), conventional 2D electrical imaging surveys have been successfully used. The main limitation of such surveys is probably the assumption of a 2D structure. In areas with complex structures, there is no substitute for a fully 3D survey. This program is designed to invert data collected with a rectangular grid of electrodes. The arrays supported include the pole-pole, pole-dipole, inline dipole-dipole, equatorial dipole-dipole and Wenner-Schlumberger. The RES3DINV program uses the smoothness-constrained least-squares inversion technique to produce a 3D model of the subsurface from the apparent resistivity data alone. Like RES2DINV, it is completely automatic and the user does not even have to supply a starting model. A Pentium 4 (or compatible CPU) based microcomputer with at least 512 megabytes RAM and an 80 gigabyte hard-disk is recommended. It supports parallel calculations that significantly reduces the inversion time. On a modern Pentium 4 based microcomputer, the data inversion takes less than a minute for small surveys with 100 electrodes in a flat area, to a day for extremely large surveys with 6000 electrodes in rugged terrain. Topographic effects can be modelled by using a distorted finite-element grid such that the surface of the grid matches the topography. 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.
On a modern multi-core Windows-based microcomputer, the data inversion takes from less than a minute for small surveys with 100 electrodes in a flat area to several hours for extremely large surveys with 6000 electrodes in rugged terrain. The inversion of a data set with 198 electrode positions (BLOCKS_22x9-ws.dat example data file) just takes about 17 seconds on a PC with a hex-core i7 CPU. 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 (as in many hydogeological problems), 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. To handle very large data sets, the program also supports the incomplete Gauss-Newton optimisation method. When used together with a data compression technique, it enables the inversion of very large data sets with over 20000 data points and model cells. As an example, a data set with nearly 65000 data points and 32000 model cells was inverted on a 2Ghz P4 computer in slightly less than 2 days. On a more modern 2.4 GHz Core 2 Duo computer, this takes less than 1 day.
Supports exact and approximate least-squares optimization methods
Supports smooth and sharp contrasts inversions
Supports up to 5041 electrodes and 67500 data points on computers with 1GB RAM (RES3DINVx32)
Supports more than 20000 electrodes and 100000 data points on computers with 16GB RAM (RES3DINVx64)
Supports trapezoidal survey grids
Supports surveys with electrodes at arbitrary positions (RES3DINVx64)
Supports parallel calculations on Intel (and compatible) based computers
Multi-core support with RES3DINVx32/x64, 128GB memory support with RES3DINVx64